| 72. | Thomas B. R. Robertson, Rose C. Bannister, Topaz A. A. Cartlidge, Thimo Hugger, Sebastien Breham, Klaus Zick, Frank Engelke, Sam Thompson, Giuseppe Pileio: A dual-core NMR system for field-cycling singlet assisted diffusion NMR. In: Frontiers in Chemistry, vol. 11, 2023, ISSN: 2296-2646. (Type: Journal Article | Abstract | Links)@article{10.3389/fchem.2023.1229586,Long-lived singlet spin order offers the possibility to extend the spin memory by more than an order of magnitude. This enhancement can be used, among other applications, to assist NMR diffusion experiments in porous media where the extended lifetime of singlet spin order can be used to gain information about structural features of the medium as well as the dynamics of the imbibed phase. Other than offering the possibility to explore longer diffusion times of the order of many minutes that, for example, gives unprecedented access to tortuosity in structures with interconnected pores, singlet order has the important advantage to be immune to the internal field gradients generated by magnetic susceptibility inhomogeneities. These inhomogeneities, however, are responsible for very short T2 decay constants in high magnetic field and this precludes access to the singlet order in the first instance. To overcome this difficulty and take advantage of singlet order in diffusion experiments in porous media, we have here developed a dual-core system with radiofrequency and 3-axis pulsed field gradients facilities in low magnetic field, for preparation and manipulation of singlet order and a probe, in high magnetic field, for polarisation and detection. The system operates in field-cycling and can be used for a variety of NMR experiments including diffusion tensor imaging (both singlet assisted and not). In this paper we present and discuss the new hardware and its calibration, and demonstrate its capabilities through a variety of examples. |
| 71. | Giulia Melchiorre, Francesco Giustiniano, Sundeep Rathore, Giuseppe Pileio: Singlet-assisted diffusion-NMR (SAD-NMR): extending the scope of diffusion tensor imaging via singlet NMR. In: Frontiers in Chemistry, vol. 11, 2023, ISSN: 2296-2646. (Type: Journal Article | Abstract | Links)@article{10.3389/fchem.2023.1224336,In this study, long-lived nuclear singlet order methods are combined with diffusion tensor imaging with the purpose of characterizing the full diffusion tensor of molecules diffusing freely in large pores of up to a millimeter in size. Such sizes are out of reach in conventional diffusion tensor imaging because of the limitations imposed by the relaxation decay constant of the longitudinal magnetization. A singlet-assisted diffusion tensor imaging methodology able to circumvent such limitations is discussed, and the new possibilities that it offers are demonstrated through simulation and experiments on plastic phantoms containing cylindrical channels of 1 mm in diameter. |
| 70. | Topaz A. A. Cartlidge, Thomas B. R. Robertson, Marcel Utz, Giuseppe Pileio: Theory and Simulation Framework for the Relaxation of Nuclear Spin Order in Porous Media. In: The Journal of Physical Chemistry B, vol. 126, no. 34, pp. 6536-6546, 2022, (PMID: 35976731). (Type: Journal Article | Links)@article{aaa, |
| 69. | Giulia Melchiorre, Ciara Nelder, Lynda J Brown, Jean-Nicolas Dumez, Giuseppe Pileio: Single-scan measurements of nuclear spin singlet order decay rates. In: Phys. Chem. Chem. Phys., pp. -, 2021. (Type: Journal Article | Abstract | Links)@article{D1CP00807B,Measurements of singlet spin order decay rates are time consuming due to the long-lived nature of this form of order and the typical pseudo-2D mode of acquisition. Additionally, this acquisition modality is not ideal for experiments run on hyperpolarized order because of the single-shot nature of hyperpolarization techniques. We present a methodology based on spatial encoding that not only significantly reduces the duration of these experiments but also confers compatibility using spin hyperpolarization techniques. The method condenses in a single shot the variable delay array used to measure decay rates in conventional pseudo-2D relaxation experiments. This results in a substantial time saving factor and, more importantly, makes the experiment compatible with hyperpolarization techniques since only a single hyperpolarized sample is required. Furthermore, the presented method, besides offering savings on time and costs, avoids reproducibility concerns associated with repetition in the hyperpolarization procedure. The method accelerates the measurement and characterization of singlet order decay times, and, when coupled with hyperpolarization techniques, can facilitate the quest for systems with very long decay times. |
| 68. | Aliki Moysiadi, Francesco Giustiniano, Andrew M R Hall, Topaz A A Cartlidge, Lynda J Brown, Giuseppe Pileio: Nuclear Spin Relaxation of Longitudinal and Singlet Order in Liquid-CO2 Solutions. In: Frontiers in Chemistry, vol. 9, pp. 243, 2021, ISSN: 2296-2646. (Type: Journal Article | Links)@article{10.3389/fchem.2021.668044, |
| 67. | K. A. Williams, S. A. Ruiz, C. Petroselli, N. Walker, D. M. McKay Fletcher, G. Pileio, T. Roose: Physical Characterisation of Chia Mucilage Polymeric Gel and its Implications on Rhizosphere Science - Integrating Imaging, MRI, and Modelling to Gain Insights into Plant and Microbial Amended Soils. In: Soil Biology and Biochemistry, pp. 108404, 2021, ISSN: 0038-0717. (Type: Journal Article | Abstract | Links)@article{WILLIAMS2021108404,Root-secreted mucilage and microbially produced extracellular polymeric substances (EPS) modify soil physical and biogeochemical processes. Most studies infer the effects of these polymeric substances from soil bulk behaviour rather than investigating the pore scale. This investigation quantified the isolated physical behaviour of mucilage in a simplified pore-scale setup. We placed drops of mucilage of different concentrations between two flat surfaces to form liquid bridges and monitored their drying using optical imaging and magnetic resonance imaging (MRI). We used our observations to validate a polymer-based multi-phase model that characterises the gel-water-air interactions. In the experiments, while pure water liquid bridges rupture, the mucilage buckled under drying, but maintained connection between the surfaces. MRI showed more water was lost from the central region in the middle of the two plates. In the model, mucilage gel accumulated near the boundaries where surface adhesion occurs. The modelled accumulation times overlapped with monitored bridge buckling for the different concentrations, showing the model can predict the observed transition at which the mixture no longer behaves like a pure liquid. Results suggest that the earlier phase transitions observed for higher mucilage concentrations show a potential mechanism for the greater drought tolerance for plant roots and increase the soil water holding capacity. Furthermore, we discuss potential applications of our model for describing the impacts that microbial biofilms may have on soil structure along with impacts of soil fauna on soil physical functions. |
| 66. | Giuseppe Pileio: Chapter 7 Manipulating Spin Order by J-synchronised Echo Schemes. In: Long-lived Nuclear Spin Order: Theory and Applications, pp. 136-150, The Royal Society of Chemistry, 2020, ISBN: 978-1-78801-568-4. (Type: Book Section | Abstract | Links)@incollection{10.1039/9781788019972-00136,This chapter discusses the use of J-synchronised spin echo schemes with the purpose to manipulate singlet order and their ability to interconvert transverse and singlet order in a very selective manner. The combination of J-synchronised spin echo schemes with pulsed field gradient is also discussed in the context of spatial localisation of singlet order. Examples of the use of these pulsed schemes in conjunction with dissolution dynamic nuclear polarisation and para-hydrogen induced polarisation are discussed and experimental evidence reported. |
| 65. | Giuseppe Pileio: Chapter 3 Relaxation Theory of Long-lived Spin Order. In: Long-lived Nuclear Spin Order: Theory and Applications, pp. 64-91, The Royal Society of Chemistry, 2020, ISBN: 978-1-78801-568-4. (Type: Book Section | Abstract | Links)@incollection{10.1039/9781788019972-00064,This chapter discusses several relaxation mechanisms that contribute to the relaxation decay rate of singlet and longitudinal order. In a systematic approach I use the Redfield theory to obtain analytical equations for these contributions. The mechanisms that occur in isolated two-spin-1/2 pairs are discussed first and apply to cases where the singlet pair is the only spin system in the molecule. When other spins are present, other mechanisms may arise and some of these are discussed below. Finally, coherent leakage mechanisms that contribute to singlet but not to longitudinal order relaxation decay rates are introduced and discussed. |
| 64. | Monique Tourell, Giuseppe Pileio: Chapter 15 Singlet-assisted Diffusion NMR. In: Long-lived Nuclear Spin Order: Theory and Applications, pp. 280-301, The Royal Society of Chemistry, 2020, ISBN: 978-1-78801-568-4. (Type: Book Section | Abstract | Links)@incollection{10.1039/9781788019972-00280,The incorporation of long-lived singlet states into diffusion-NMR experiments allows the translational motion of molecules to be observed over many minutes. This is a significant improvement of the observation times available in traditional NMR techniques, and allows for measurements of large macromolecules with slow diffusion coefficients and restricted diffusion in macroporous systems. This chapter introduces the methodology for singlet-assisted diffusion-NMR (SAD-NMR), a method that uses nearly-equivalent spin-1/2 pairs to store spatially encoded magnetization in long-lived singlet states for up to ten minutes. The potential for this method to characterize the morphological properties of macroporous media is demonstrated, and future “real-world” applications are discussed. |
| 63. | Allan M Torres, Giuseppe Pileio, William S Price: Chapter 16 Q-space Singlet NMR. In: Long-lived Nuclear Spin Order: Theory and Applications, pp. 302-319, The Royal Society of Chemistry, 2020, ISBN: 978-1-78801-568-4. (Type: Book Section | Abstract | Links)@incollection{10.1039/9781788019972-00302,Long-lived singlet spin states can be used to characterise the structures of microscopic pores in a liquid environment using NMR q-space diffusion imaging. The longer lifetimes of singlet states compared to conventional NMR spin coherences allow the extension of the measurements to larger pores. Two different pulsed gradient NMR q-space diffusion methods for singlet states can be utilised depending on the type of probe molecule and the dimension of the porous system. The first method, which incorporates a spin-locking pulse, is specifically designed for molecules with two spins that are weakly coupled, while the second method, that includes a series of spin-echo trains, is intended for molecules with nearly equivalent spins that are strongly coupled. These advances involving singlet states have allowed the investigation of macroscopic pores (e.g., capillaries and rectangular pores) with dimensions up to 2 mm to be studied by q-space NMR. This chapter covers the theory of q-space diffusion imaging using singlet states together with recent experimental examples from the literature. |
| 62. | Andrew M R Hall, Topaz A A Cartlidge, Giuseppe Pileio: A temperature-controlled sample shuttle for field-cycling NMR. In: Journal of Magnetic Resonance, pp. 106778, 2020, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{HALL2020106778,We present a design for a temperature-controlled sample shuttle for use in NMR measurements at variable magnetic field strength. Accurate temperature control was achieved using a mixture of water-ethylene glycol as a heat transfer fluid, reducing temperature gradients across the sample to <0.05 °C and minimising convection. Using the sample shuttle, we show how the longitudinal (T1) and singlet order (TS) relaxation time constants were measured for two molecules capable of supporting long-lived states, with new record lifetimes observed at low field and above ambient temperatures. |
| 61. | S J Elliott, C Bengs, L J Brown, J T Hill-Cousins, D J O'Leary, G Pileio, M H Levitt: Nuclear singlet relaxation by scalar relaxation of the second kind in the slow-fluctuation regime. In: The Journal of Chemical Physics, vol. 150, no. 6, pp. 064315, 2019. (Type: Journal Article | Links)@article{doi:10.1063/1.5074199, |
| 60. | Kirill F Sheberstov, Alexey S Kiryutin, Christian Bengs, Joe Hill-Cousins, Lynda J Brown, Richard Brown, Giuseppe Pileio, Malcolm H Levitt, Alexandra V Yurkovskaya, Konstantin L Ivanov: Excitation of singlet-triplet coherences in pairs of nearly-equivalent spins. In: Phys. Chem. Chem. Phys., pp. -, 2019. (Type: Journal Article | Abstract | Links)@article{C9CP00451C,We present approaches for an efficient excitation of singlet-triplet coherences in pairs of nearly-equivalent spins. Standard Nuclear Magnetic Resonance (NMR) pulse sequences do not excite these coherences at all or with very low efficiency. The single quantum singlet-triplet coherences, here termed the outer singlet-triplet coherences, correspond to lines of low intensity in the NMR spectrum of a strongly-coupled spin pair (they are sometimes referred to as “forbidden transitions”), whereas the zero-quantum coherences, here termed the inner singlet-triplet coherences, do not have a direct spectral manifestation. In the present study, we investigated singlet-triplet coherences in a pair of nearly-equivalent carbon spins of the 13C-isotopomer of a specially designed naphthalene derivative with optimized relaxation properties. We propose and compare several techniques to drive the singlet-triplet coherence in strongly coupled spin pairs. First, we study different methods for efficient excitation of the outer singlet-triplet coherences. The achieved conversion efficiency of magnetization to the coherences of interest is close to the theoretically allowed maximum. Second, we propose methods to convert the outer coherences into the inner singlet-triplet coherence. The inner singlet-triplet coherence is insensitive to field inhomogeneity and can be long-lived. By probing this coherence, we perform a very precise measurement of the spin-spin J-couplings. A remarkable property of this coherence is that it can be preserved even in absence of a spin-locking radiofrequency field. Consequently, it is possible to shuttle the sample between different magnetic fields preserving the coherence. This allows one to study the field dependence of the relaxation time, T_IST, of the inner singlet-triplet coherence by performing field-cycling experiments. We observed dramatic changes of the ratio T_IST/T_1 from about 1 (in strong fields) up to 2.4 (in weak fields), which is the evidence of a significant influence of the chemical shift anisotropy on relaxation. We have detected a remarkably long lifetime of the inner singlet-triplet coherence of about 200 s at the magnetic field of 5 mT |
| 59. | Dmitry Shishmarev, Alan J Wright, Tiago B Rodrigues, Giuseppe Pileio, Gabriele Stevanato, Kevin M Brindle, Philip W Kuchel: Sub-minute kinetics of human red cell fumarase: 1H spin-echo NMR spectroscopy and 13C rapid-dissolution dynamic nuclear polarization. In: NMR in Biomedicine, vol. 31, no. 3, pp. e3870–n/a, 2018, ISSN: 1099-1492, (e3870 NBM-17-0125.R2). (Type: Journal Article | Abstract | Links)@article{NBM:NBM3870,Fumarate is an important probe of metabolism in hyperpolarized magnetic resonance imaging and spectroscopy. It is used to detect the release of fumarase in cancer tissues, which is associated with necrosis and drug treatment. Nevertheless, there are limited reports describing the detailed kinetic studies of this enzyme in various cells and tissues. Thus, we aimed to evaluate the sub-minute kinetics of human red blood cell fumarase using nuclear magnetic resonance (NMR) spectroscopy, and to provide a quantitative description of the enzyme that is relevant to the use of fumarate as a probe of cell rupture. The fumarase reaction was studied using time courses of 1H spin-echo and 13C-NMR spectra. 1H-NMR experiments showed that the fumarase reaction in hemolysates is sufficiently rapid to make its kinetics amenable to study in a period of approximately 3 min, a timescale characteristic of hyperpolarized 13C-NMR spectroscopy. The rapid-dissolution dynamic nuclear polarization (RD-DNP) technique was used to hyperpolarize [1,4-13C]fumarate, which was injected into concentrated hemolysates. The kinetic data were analyzed using recently developed FmRα analysis and modeling of the enzymatic reaction using Michaelis–Menten equations. In RD-DNP experiments, the decline in the 13C-NMR signal from fumarate, and the concurrent rise and fall of that from malate, were captured with high spectral resolution and signal-to-noise ratio, which allowed the robust quantification of fumarase kinetics. The kinetic parameters obtained indicate the potential contribution of hemolysis to the overall rate of the fumarase reaction when 13C-NMR RD-DNP is used to detect necrosis in animal models of implanted tumors. The analytical procedures developed will be applicable to studies of other rapid enzymatic reactions using conventional and hyperpolarized substrate NMR spectroscopy. |
| 58. | Monique C Tourell, Ionut-Alexandru Pop, Lynda J Brown, Richard C D Brown, Giuseppe Pileio: Singlet-assisted diffusion-NMR (SAD-NMR): redefining the limits when measuring tortuosity in porous media. In: Phys. Chem. Chem. Phys., vol. 20, pp. 13705-13713, 2018. (Type: Journal Article | Abstract | Links)@article{C8CP00145F,Long-lived singlet order is exploited in diffusion NMR experiments to successfully measure the tortuosity of randomly packed spheres with diameters ranging from 500 to 1000 [small mu ]m. The pore spaces in such packings have characteristic length scales well beyond the length scale limit set by spin relaxation in conventional NMR-diffusion experiments. Diffusion times of up to 240 s were used to obtain the restricted diffusion coefficient as a function of diffusion time in the long-time diffusion regime. Experimental results were validated with numerical simulations and data from X-ray micro-computed tomography. |
| 57. | Correlative Visualization of Root Mucilage Degradation Using X-ray CT and MRI. In: Frontiers in Environmental Science, vol. 6, pp. 32, 2018, ISSN: 2296-665X. (Type: Journal Article | Abstract | Links)@article{10.3389/fenvs.2018.00032,Root exudates are a crucial component of the rhizosphere. Often, they take a form of a gel exuded by the plant roots and are thought to influence the soil aggregation, root penetration into soil, soil nutrient availability, immobilization of toxic cations and microbial activity amongst other things. In addition, the capacity of exudates to store water makes the plants potentially less susceptive to drought. Major components of root exudates are high molecular weight organic compounds consisting of predominantly polysaccharides and proteins, which makes it challenging to visualize using current rhizosphere visualization techniques, such as X-ray computed tomography (CT). In this contribution, we use correlative X-ray CT (resolution ~20 m) in combination with Magnetic Resonance Imaging (MRI, resolution ~120 m) to set up groundwork to enable in situ visualization of mucilage in soil. This multimodal approach is necessary because mucilage density closely matches that of water. We use chia seeds as mucilage analogue, because it has been found to have a similar consistency to root mucilage. Moreover, to understand mucilage development in time, a series of samples made by chia seeds placed in different porous media were prepared. Structurally and chemically, mucilage breaks down towards a water-like substance over a course of two weeks. Depending on its relative concentration, these changes were found to be less dominant when seeds were mixed in porous media. Having set up the groundwork for correlative imaging of chia seeds in water and an artificial soil (Nafion and sand/beads) this enables us to expand this imaging to deal with plant root exudates under natural conditions. |
| 56. | Giuseppe Pileio, Sylwia Ostrowska: Accessing the long-time limit in diffusion NMR: The case of singlet
assisted diffusive diffraction q-space. In: JOURNAL OF MAGNETIC RESONANCE, vol. 285, pp. 1-7, 2017, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000418312800001,The latest developments in the field of long-lived spin states are merged with pulsed-field gradient techniques to extend the diffusion time beyond what is currently achievable in standard q-space diffusive diffraction studies. The method uses nearly-equivalent spin-1/2 pairs that let diffusion times of the order of many minutes to be measured allowing access to the long-time limit in cavities of macroscopic size (millimeters). A pulse sequence suitable to exploit this regime has been developed and validated with the use of numerical simulations and experiments. (C) 2017 The Authors. Published by Elsevier Inc. |
| 55. | Gabriele Stevanato, James Eills, Christian Bengs, Giuseppe Pileio: A pulse sequence for singlet to heteronuclear magnetization transfer:
S2hM. In: JOURNAL OF MAGNETIC RESONANCE, vol. 277, pp. 169-178, 2017, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000399861500022,We have recently demonstrated, in the context of para-hydrogen induced polarization (PHIP), the conversion of hyperpolarized proton singlet order into heteronuclear magnetisation can be efficiently achieved via a new sequence named S2hM (Singlet to heteronuclear Magnetisation). In this paper we give a detailed theoretical description, supported by an experimental illustration, of S2hM. Theory and experiments on thermally polarized samples demonstrate the proposed method is robust to frequency offset mismatches and radiofrequency field inhomogeneities. The simple implementation, optimisation and the high conversion efficiency, under various regimes of magnetic equivalence, makes S2hM an excellent candidate for a widespread use, particularly within the PHIP arena. (C) 2017 The Authors. Published by Elsevier Inc. |
| 54. | Lynda J Brown, Giuseppe Pileio, Malcolm H Levitt, Richard C D Brown: Synthesis of carbon-13 labeled oxalates exhibiting extended nuclear
singlet state lifetimes. In: JOURNAL OF LABELLED COMPOUNDS & RADIOPHARMACEUTICALS, vol. 60, no. 2, pp. 135-139, 2017, ISSN: 0362-4803. (Type: Journal Article | Abstract | Links)@article{ISI:000397024800006,Unsymmetrical perdeuterated doubly C-13 labelled oxalates exhibit extended lifetimes in the nuclear singlet state. Synthesis of 1,2 C-13(2) oxalates from commercially available precursors is described, facilitating preparation of unsymmetrical oxalates in a controlled manner. |
| 53. | Giuseppe Pileio: Singlet NMR methodology in two-spin-1/2 systems. In: PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY, vol. 98-99, pp. 1-19, 2017, ISSN: 0079-6565. (Type: Journal Article | Abstract | Links)@article{ISI:000396958200001,This paper discusses methodology developed over the past 12 years in order to access and manipulate singlet order in systems comprising two coupled spin-112 nuclei in liquid-state nuclear magnetic resonance. Pulse sequences that are valid for different regimes are discussed, and fully analytical proofs are given using different spin dynamics techniques that include product operator methods, the single transition operator formalism, and average Hamiltonian theory. Methods used to filter singlet order from byproducts of pulse sequences are also listed and discussed analytically. The theoretical maximum amplitudes of the transformations achieved by these techniques are reported, together with the results of numerical simulations performed using custom-built simulation code. (C) 2016 Elsevier B.V. All rights reserved. |
| 52. | James Eills, Gabriele Stevanato, Christian Bengs, Stefan Gloggler, Stuart J Elliott, Javier Alonso-Valdesueiro, Giuseppe Pileio, Malcolm H Levitt: Singlet order conversion and parahydrogen-induced hyperpolarization of
C-13 nuclei in near-equivalent spin systems. In: JOURNAL OF MAGNETIC RESONANCE, vol. 274, pp. 163-172, 2017, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000393446000020,We have demonstrated two radiofrequency pulse methods which convert the nuclear singlet order of proton spin pairs into the magnetisation of nearby C-13 nuclei. These irradiation schemes work well in the near-equivalence regime of the three-spin system, which applies when the difference in the two H-1-C-13 couplings is much smaller than the H-1-H-1 coupling. We use pulse sequences to generate thermally polarized singlet states in a reproducible manner, and study the singlet-to-magnetisation transfer step. Preliminary results demonstrate a parahydrogen-enhanced C-13 polarization level of at least 9%, providing a signal enhancement factor of more than 9000, using 50% enriched parahydrogen. (C) 2016 Elsevier Inc. All rights reserved. |
| 51. | G Pileio: Nuclear Singlet Spin States. In: Lindon, John C; Tranter, George E; Koppenaal, David W (Ed.): Encyclopedia of Spectroscopy and Spectrometry (Third Edition), pp. 456 - 462, Academic Press, Oxford, 2017, ISBN: 978-0-12-803224-4. (Type: Book Section | Abstract | Links)@incollection{PILEIO2017456,Isolated pairs of spin-1/2 nuclei can be prepared in a singlet state configuration that is immune to intrapair dipole–dipole relaxation, often the main source for the longitudinal magnetization decay constant T1. Because of this property singlet states can hold polarization for much longer than T1. In given circumstances, singlet states may be partially immune to other relaxation mechanisms thus offering spectacularly slow decay times. This article presents the most relevant theory beyond these phenomena, the methodology introduced to prepare these states and the current and potential applications of singlet states. |
| 50. | Francesca Piana, David H Case, Susana M Ramalhete, Giuseppe Pileio, Marco Facciotti, Graeme M Day, Yaroslav Z Khimyak, Jesus Angulo, Richard C D Brown, Philip A Gale: Substituent interference on supramolecular assembly in urea gelators:
synthesis, structure prediction and NMR. In: SOFT MATTER, vol. 12, no. 17, pp. 4034-4043, 2016, ISSN: 1744-683X. (Type: Journal Article | Abstract | Links)@article{ISI:000374974000021,Eighteen N-aryl-N'-alkyl urea gelators were synthesised in order to understand the effect of head substituents on gelation performance. Minimum gelation concentration values obtained from gel formation studies were used to rank the compounds and revealed the remarkable performance of 4-methoxyphenyl urea gelator 15 in comparison to 4-nitrophenyl analogue 14, which could not be simply ascribed to substituent effects on the hydrogen bonding capabilities of the urea protons. Crystal structure prediction calculations indicated alternative low energy hydrogen bonding arrangements between the nitro group and urea protons in gelator 14, which were supported experimentally by NMR spectroscopy. As a consequence, it was possible to relate the observed differences to interference of the head substituents with the urea tape motif, disrupting the order of supramolecular packing. The combination of unbiased structure prediction calculations with NMR is proposed as a powerful approach to investigate the supramolecular arrangement in gel fibres and help understand the relationships between molecular structure and gel formation. |
| 49. | Joseph T Hill-Cousins, Ionut-Alexandru Pop, Giuseppe Pileio, Gabriele Stevanato, Paer Hakansson, Soumya S Roy, Malcolm H Levitt, Lynda J Brown, Richard C D Brown: Synthesis of an Isotopically Labeled Naphthalene Derivative That
Supports a Long-Lived Nuclear Singlet State. In: ORGANIC LETTERS, vol. 17, no. 9, pp. 2150-2153, 2015, ISSN: 1523-7060. (Type: Journal Article | Abstract | Links)@article{ISI:000354004400029,The synthesis of an octa-alkoxy substituted isotopically labeled naphthalene derivative, shown to have excellent properties in singlet NMR experiments, is described. This highly substituted naphthalene system, which incorporates an adjacent C-13 spin pair, is readily accessed from a commercially available C-13(2)-labeled building block via sequential thermal alkynyl- and arylcyclobutenone rearrangements. The synthetic route incorporates a simple desymmetrization approach leading to a small difference in the chemical shifts of the C-13 spin pair, a design constraint crucial for accessing nuclear singlet order. |
| 48. | Gabriele Stevanato, Joseph T Hill-Cousins, Paer Hakansson, Soumya Singha Roy, Lynda J Brown, Richard C D Brown, Giuseppe Pileio, Malcolm H Levitt: A Nuclear Singlet Lifetime of More than One Hour in Room-Temperature
Solution. In: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, vol. 54, no. 12, pp. 3740-3743, 2015, ISSN: 1433-7851. (Type: Journal Article | Abstract | Links)@article{ISI:000351178300036,Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are supremely important techniques with numerous applications in almost all branches of science. However, until recently, NMR methodology was limited by the time constant T-1 for the decay of nuclear spin magnetization through contact with the thermal molecular environment. Long-lived states, which are correlated quantum states of multiple nuclei, have decay time constants that may exceed T-1 by large factors. Here we demonstrate a nuclear long-lived state comprising two C-13 nuclei with a lifetime exceeding one hour in room-temperature solution, which is around 50 times longer than T-1. This behavior is well-predicted by a combination of quantum theory, molecular dynamics, and quantum chemistry. Such ultra-long-lived states are expected to be useful for the transport and application of nuclear hyperpolarization, which leads to NMR and MRI signals enhanced by up to five orders of magnitude. |
| 47. | Giuseppe Pileio, Jean-Nicolas Dumez, Ionut-Alexandru Pop, Joseph T Hill-Cousins, Richard C D Brown: Real-space imaging of macroscopic diffusion and slow flow by singlet
tagging MRI. In: JOURNAL OF MAGNETIC RESONANCE, vol. 252, pp. 130-134, 2015, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000352757200015,Magnetic resonance imaging can be used to study motional processes such as flow and diffusion, but the accessible timescales are limited by longitudinal relaxation. The spatially selective conversion from magnetization to long-lived singlet order in designer molecules makes it possible to tag a region of interest for an extended period of time, of the order of several minutes. Here we exploit this concept of ``singlet tagging'' to monitor diffusion over a macroscopic scale as well as very slow flow. (C) 2015 The Authors. Published by Elsevier Inc. |
| 46. | Jean-Nicolas Dumez, Paer Hakansson, Salvatore Mamone, Benno Meier, Gabriele Stevanato, Joseph T Hill-Cousins, Soumya Singha Roy, Richard C D Brown, Giuseppe Pileio, Malcolm H Levitt: Theory of long-lived nuclear spin states in methyl groups and
quantum-rotor induced polarisation. In: JOURNAL OF CHEMICAL PHYSICS, vol. 142, no. 4, 2015, ISSN: 0021-9606. (Type: Journal Article | Abstract | Links)@article{ISI:000349018100035,Long-lived nuclear spin states have a relaxation time much longer than the longitudinal relaxation time T-1. Long-lived states extend significantly the time scales that may be probed with magnetic resonance, with possible applications to transport and binding studies, and to hyperpolarised imaging. Rapidly rotating methyl groups in solution may support a long-lived state, consisting of a population imbalance between states of different spin exchange symmetries. Here, we expand the formalism for describing the behaviour of long-lived nuclear spin states in methyl groups, with special attention to the hyperpolarisation effects observed in (CH3)-C-13 groups upon rapidly converting a material with low-barrier methyl rotation from the cryogenic solid state to a room-temperature solution [M. Icker and S. Berger, J. Magn. Reson. 219, 1 (2012)]. We analyse the relaxation properties of methyl long-lived states using semi-classical relaxation theory. Numerical simulations are supplemented with a spherical-tensor analysis, which captures the essential properties of methyl long-lived states. (C) 2015 AIP Publishing LLC. |
| 45. | Soumya Singha Roy, Jean-Nicolas Dumez, Gabriele Stevanato, Benno Meier, Joseph T Hill-Cousins, Richard C D Brown, Giuseppe Pileio, Malcolm H Levitt: Enhancement of quantum rotor NMR signals by frequency-selective pulses. In: JOURNAL OF MAGNETIC RESONANCE, vol. 250, pp. 25-28, 2015, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000349578200004,Quantum-rotor-induced polarisation (QRIP) enhancement is exhibited by substances which contain freely rotating methyl groups in the solid state, provided that the methyl groups contain a C-13 nucleus. Strong signal enhancements are observed in solution NMR when the material is first equilibrated at cryogenic temperatures, then rapidly dissolved with a warm solvent and transferred into an NMR magnet. QRIP leads to strongly-enhanced C-13 NMR signals, but relatively weak enhancements of the H-1 signals. We show that the H-1 signals suffer from a partial cancellation of degenerate contributions, which may be corrected by applying a frequency-selective pi pulse to the inner peaks of the C-13 multiplet prior to H-1 observation. (C) 2014 Elsevier Inc. All rights reserved. |
| 44. | Gabriele Stevanato, Soumya Singha Roy, Joe Hill-Cousins, Ilya Kuprov, Lynda J Brown, Richard C D Brown, Giuseppe Pileio, Malcolm H Levitt: Long-lived nuclear spin states far from magnetic equivalence. In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, vol. 17, no. 8, pp. 5913-5922, 2015, ISSN: 1463-9076. (Type: Journal Article | Abstract | Links)@article{ISI:000349697200045,Clusters of coupled nuclear spins may form long-lived nuclear spin states, which interact weakly with the environment, compared to ordinary nuclear magnetization. All experimental demonstrations of long-lived states have so far involved spin systems which are close to the condition of magnetic equivalence, in which the network of spin-spin couplings is conserved under all pair exchanges of symmetry-related nuclei. We show that the four-spin system of trans-[2,3-C-13(2)]-but-2-enedioate exhibits a long-lived nuclear spin state, even though this spin system is very far from magnetic equivalence. The 4-spin long-lived state is accessed by slightly asymmetric chemical substitutions of the centrosymmetric molecular core. The long-lived state is a consequence of the locally centrosymmetric molecular geometry for the trans isomer, and is absent for the cis isomer. A general group theoretical description of long-lived states is presented. It is shown that the symmetries of coherent and incoherent interactions are both important for the existence of long-lived states. |
| 43. | Francesca Piana, Marco Facciotti, Giuseppe Pileio, Jennifer R Hiscock, Wim Van Rossom, Richard C D Brown, Philip A Gale: Organophosphorus chemical warfare agent simulant DMMP promotes
structural reinforcement of urea-based chiral supramolecular gels. In: RSC ADVANCES, vol. 5, no. 16, pp. 12287-12292, 2015, ISSN: 2046-2069. (Type: Journal Article | Abstract | Links)@article{ISI:000348985400075,Six urea-based supramolecular gels have been obtained in situ by mixing either (R)-(+/-)-1-(1-naphthyl)ethyl isocyanate or (+/-)-1-(1-naphthyl) ethyl isocyanate with various amines. This allowed a comparative study on the effects of chirality on the response of the molecular gels to the presence of the neutral organophosphate guest dimethyl methylphosphonate (DMMP). The inversion test results show that the absence of enantiomeric purity causes marked instability of the gel network in the presence of the guest. DSC and rheology measurements reveal the promotion of a structural reinforcement of the gels when 0.01 mL of DMMP interacts with the enantiomerically pure systems. This effect was investigated by means of electrostatic potential surface calculations and P-31-H-1 NMR spectroscopy. |
| 42. | Jean-Nicolas Dumez, Joseph T Hill-Cousins, Richard C D Brown, Giuseppe Pileio: Long-lived localization in magnetic resonance imaging. In: JOURNAL OF MAGNETIC RESONANCE, vol. 246, pp. 27-30, 2014, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000342120500005,The longitudinal nuclear relaxation time, T-1, sets a stringent limit on the range of information that can be obtained from magnetic resonance imaging (MRI) experiments. Long-lived nuclear spin states provide a possibility to extend the timescale over which information can be encoded in magnetic resonance. We introduce a strategy to localize an ensemble of molecules for a significantly extended duration (similar to 30 times longer than T-1 in this example), using a spatially selective conversion between magnetization and long-lived singlet order. An application to tagging and transport is proposed. (C) 2014 Elsevier Inc. All rights reserved. |
| 41. | Benno Meier, Jean-Nicolas Dumez, Gabriele Stevanato, Joseph T Hill-Cousins, Soumya Singha Roy, Paer Hakansson, Salvatore Mamone, Richard C D Brown, Giuseppe Pileio, Malcolm H Levitt: Long-Lived Nuclear Spin States in Methyl Groups and
Quantum-Rotor-Induced Polarization. In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 135, no. 50, pp. 18746-18749, 2013, ISSN: 0002-7863. (Type: Journal Article | Abstract | Links)@article{ISI:000328865100011,Substances containing rapidly rotating methyl groups may exhibit long-lived states (LLSs) in solution, with relaxation times substantially longer than the conventional spin-lattice relaxation time T-1. The states become long-lived through rapid internal rotation of the CH3 group, which imposes an approximate symmetry on the fluctuating nuclear spin interactions. In the case of very low CH3 rotational barriers, a hyperpolarized LLS is populated by thermal equilibration at liquid helium temperature. Following dissolution, cross-relaxation of the hyperpolarized LLS, induced by heteronuclear dipolar couplings, generates strongly enhanced antiphase NMR signals. This mechanism explains the NMR signal enhancements observed for C-13-gamma-picoline (Icker, M.; Berger, S. J. Magn. Reson. 2012, 219, 1-3). |
| 40. | Irene Marco-Rius, Michael C D Tayler, Mikko I Kettunen, Timothy J Larkin, Kerstin N Timm, Eva M Serrao, Tiago B Rodrigues, Giuseppe Pileio, Jan Henrik Ardenkjaer-Larsen, Malcolm H Levitt, Kevin M Brindle: Hyperpolarized singlet lifetimes of pyruvate in human blood and in the
mouse. In: NMR IN BIOMEDICINE, vol. 26, no. 12, pp. 1696-1704, 2013, ISSN: 0952-3480. (Type: Journal Article | Abstract | Links)@article{ISI:000327157400009,Hyperpolarized NMR is a promising technique for non-invasive imaging of tissue metabolism in vivo. However, the pathways that can be studied are limited by the fast T-1 decay of the nuclear spin order. In metabolites containing pairs of coupled nuclear spins-1/2, the spin order may be maintained by exploiting the non-magnetic singlet (spin-0) state of the pair. This may allow preservation of the hyperpolarization in vivo during transport to tissues of interest, such as tumors, or to detect slower metabolic reactions. We show here that in human blood and in a mouse in vivo at millitesla fields the C-13 singlet lifetime of [1,2-C-13(2)]pyruvate was significantly longer than the C-13 T-1, although it was shorter than the T-1 at field strengths of several tesla. We also examine the singlet-derived NMR spectrum observed for hyperpolarized [1,2-C-13(2)]lactate, originating from the metabolism of [1,2-C-13(2)]pyruvate. (c) 2013 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd. |
| 39. | Luke J Edwards, D V Savostyanov, A A Nevzorov, M Concistre, G Pileio, Ilya Kuprov: Grid-free powder averages: On the applications of the Fokker-Planck
equation to solid state NMR. In: JOURNAL OF MAGNETIC RESONANCE, vol. 235, pp. 121-129, 2013, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000324846900016,We demonstrate that Fokker-Planck equations in which spatial coordinates are treated on the same conceptual level as spin coordinates yield a convenient formalism for treating magic angle spinning NMR experiments. In particular, time dependence disappears from the background Hamiltonian (sample spinning is treated as an interaction), spherical quadrature grids are avoided completely (coordinate distributions are a part of the formalism) and relaxation theory with any linear diffusion operator is easily adopted from the Stochastic Liouville Equation theory. The proposed formalism contains Floquet theory as a special case. The elimination of the spherical averaging grid comes at the cost of increased matrix dimensions, but we show that this can be mitigated by the use of state space restriction and tensor train techniques. It is also demonstrated that low correlation order basis sets apparently give accurate answers in powder-averaged MAS simulations, meaning that polynomially scaling simulation algorithms do exist for a large class of solid state NMR experiments. (c) 2013 Elsevier Inc. All rights reserved. |
| 38. | M Concistre, S Mamone, M Denning, G Pileio, X Lei, Y Li, M Carravetta, N J Turro, M H Levitt: Anisotropic nuclear spin interactions in H2O@C-60 determined by
solid-state NMR. In: PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL
AND ENGINEERING SCIENCES, vol. 371, no. 1998, 2013, ISSN: 1364-503X. (Type: Journal Article | Abstract | Links)@article{ISI:000329926300008,We report a solid-state NMR study of the anisotropic nuclear spin interactions in H2O@C-60 at room temperature. We find evidence of significant dipole-dipole interactions between the water protons, and also a proton chemical shift anisotropy (CSA) interaction. The principal axes of these interaction tensors are found to be perpendicular. The magnitude of the CSA is too large to be explained by a model in which the water molecules are partially aligned with respect to an external axis. The evidence indicates that the observed CSA is caused by a distortion of the geometry or electronic structure of the fullerene cages, in response to the presence of the endohedral water. |
| 37. | N N Kuzma, P Hakansson, M Pourfathi, R K Ghosh, H Kara, S J Kadlecek, G Pileio, M H Levitt, R R Rizi: Lineshape-based polarimetry of dynamically-polarized (N2O)-N-15 in
solid-state mixtures. In: JOURNAL OF MAGNETIC RESONANCE, vol. 234, pp. 90-94, 2013, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000323085800011,Dynamic nuclear polarization (DNP) of (N2O)-N-15, known for its long-lived singlet-state order at low magnetic field, is demonstrated in organic solvent/trityl mixtures at similar to 1.5 K and 5 T. Both N-15 polarization and intermolecular dipolar broadening are strongly affected by the sample's thermal history, indicating spontaneous formation of N2O clusters. In situ N-15 NMR reveals four distinct powder-pattern spectra, attributed to the chemical-shift anisotropy (CSA) tensors of the two N-15 nuclei, further split by the intramolecular dipolar coupling between their magnetic moments. N-15 polarization is estimated by fitting the free-induction decay (FID) signals to the analytical model of four single-quantum transitions. This analysis implies (10.2 +/- 2.2)% polarization after 37 h of DNP, and provides a direct, instantaneous probe of the absolute N-15 polarization, without a need for time-consuming referencing to a thermal-equilibrium NMR signal. (C) 2013 Elsevier Inc. All rights reserved. |
| 36. | Giuseppe Pileio, Sean Bowen, Christoffer Laustsen, Michael C D Tayler, Joseph T Hill-Cousins, Lynda J Brown, Richard C D Brown, Jan H Ardenkjaer-Larsen, Malcolm H Levitt: Recycling and Imaging of Nuclear Singlet Hyperpolarization. In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 135, no. 13, pp. 5084-5088, 2013, ISSN: 0002-7863. (Type: Journal Article | Abstract | Links)@article{ISI:000317259300038,The strong enhancement of NMR signals achieved by hyperpolarization decays, at best, with a time constant of a few minutes. Here, we show that a combination of long-lived singlet states, molecular design, magnetic field cycling, and specific radiofrequency pulse sequences allows repeated observation of the same batch of polarized nuclei over a period of 30 min and more. We report a recycling protocol in which the enhanced nuclear polarization achieved by dissolution-DNP is observed with full intensity and then returned to singlet order. MRI experiments may be run on a portion of the available spin polarization, while the remaining is preserved and made available for a later use. An analogy is drawn with a ``spin bank'' or ``resealable container'' in which highly polarized spin order may be deposited and retrieved. |
| 35. | Giuseppe Pileio, Joseph T Hill-Cousins, Sam Mitchell, Ilya Kuprov, Lynda J Brown, Richard C D Brown, Malcolm H Levitt: Long-Lived Nuclear Singlet Order in Near-Equivalent C-13 Spin Pairs. In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 134, no. 42, pp. 17494-17497, 2012, ISSN: 0002-7863. (Type: Journal Article | Abstract | Links)@article{ISI:000310103800042,Molecules that support C-13 singlet states with lifetimes of over 10 min in solution have been designed and synthesized. The C-13(2) spin pairs in the asymmetric alkyne derivatives are close to magnetic equivalence, so the C-13 long-lived singlet states are stable in high magnetic field and do not require maintenance by a radiofrequency spin-locking field. We suggest a model of singlet relaxation by fluctuating chemical shift anisotropy tensors combined with leakage associated with slightly broken magnetic equivalence. Theoretical estimates of singlet relaxation rates are compared with experimental values. Relaxation due to antisymmetric shielding tensor components is significant. |
| 34. | Christoffer Laustsen, Giuseppe Pileio, Michael C D Tayler, Lynda J Brown, Richard C D Brown, Malcolm H Levitt, Jan H Ardenkjaer-Larsen: Hyperpolarized singlet NMR on a small animal imaging system. In: MAGNETIC RESONANCE IN MEDICINE, vol. 68, no. 4, pp. 1262-1265, 2012, ISSN: 0740-3194. (Type: Journal Article | Abstract | Links)@article{ISI:000309203500029,Nuclear spin hyperpolarization makes a significant advance toward overcoming the sensitivity limitations of in vivo magnetic resonance imaging, particularly in the case of low-gamma nuclei. The sensitivity may be improved further by storing the hyperpolarization in slowly relaxing singlet populations of spin-1/2 pairs. Here, we report hyperpolarized 13C spin order transferred into and retrieved from singlet spin order using a small animal magnetic resonance imaging scanner. For spins in sites with very similar chemical shifts, singlet spin order is sustained in high magnetic field without requiring strong radiofrequency irradiation. The demonstration of robust singlet-to-magnetization conversion, and vice versa, on a small animal scanner, is promising for future in vivo and clinical deployments. Magn Reson Med, 2012. (c) 2012 Wiley Periodicals, Inc. |
| 33. | Michael C D Tayler, Irene Marco-Rius, Mikko I Kettunen, Kevin M Brindle, Malcolm H Levitt, Giuseppe Pileio: Direct Enhancement of Nuclear Singlet Order by Dynamic Nuclear
Polarization. In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 134, no. 18, pp. 7668-7671, 2012, ISSN: 0002-7863. (Type: Journal Article | Abstract | Links)@article{ISI:000303696200024,Hyperpolarized singlet order is available immediately after dissolution DNP, avoiding need for additional preparation steps. We demonstrate this procedure on a sample of [1,2-C-13(2)]pyruvic acid. |
| 32. | Jiri Bocan, Giuseppe Pileio, Malcolm H Levitt: Sensitivity enhancement and low-field spin relaxation in singlet NMR. In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, vol. 14, no. 46, pp. 16032-16040, 2012, ISSN: 1463-9076. (Type: Journal Article | Abstract | Links)@article{ISI:000310740000011,The singlet states of nuclear spin-1/2 pairs often display extended lifetimes that can be an order of magnitude longer than conventional relaxation times. We show that, in favourable circumstances, acquisition of the NMR signal during an extended multiple spin-echo train, followed by suitable data processing, enhances the signal-to-noise ratio of singlet NMR by up to an order of magnitude. The achievable enhancement depends on the transverse relaxation time constant, the magnetic field inhomogeneity, and the acceptable degradation in digital spectral resolution. We use the combination of singlet NMR and multiple spin-echo data acquisition to study the low-field nuclear relaxation processes of N-15-labelled nitrous oxide ((N2O)-N-15) in solution. A general relaxation theory for coupled 2-spin-1/2 systems in low magnetic field is developed. Experimental trajectories of the nuclear spin observables are compared with theoretical expressions, including dipole-dipole and spin-rotation relaxation mechanisms. The estimated values of the spin-rotation tensors are compared with previous estimations from NMR and molecular beam electric resonance. |
| 31. | G Pileio: Singlet state relaxation via scalar coupling of the second kind. In: JOURNAL OF CHEMICAL PHYSICS, vol. 135, no. 17, 2011, ISSN: 0021-9606. (Type: Journal Article | Abstract | Links)@article{ISI:000296733300017,The contribution of scalar coupling relaxation of the second kind on the relaxation behaviour of nuclear spin singlet states has been derived. The analytical equation found for the relaxation rate constant of singlet state has been compared to the equation for the relaxation of longitudinal magnetization in order to find the conditions for which the singlet state remains long-lived even in the presence of this scalar relaxation mechanism. These results are relevant when the singlet state is formed in molecules with more than two interacting spins. (C) 2011 American Institute of Physics. |
| 30. | R K Ghosh, S J Kadlecek, J H Ardenkjaer-Larsen, B M Pullinger, G Pileio, M H Levitt, N N Kuzma, R R Rizi: Measurements of the Persistent Singlet State of N(2)O in Blood and Other
Solvents-Potential as a Magnetic Tracer. In: MAGNETIC RESONANCE IN MEDICINE, vol. 66, no. 4, pp. 1177-1180, 2011, ISSN: 0740-3194. (Type: Journal Article | Abstract | Links)@article{ISI:000295356500029,The development of hyperpolarized tracers has been limited by short nuclear polarization lifetimes. The dominant relaxation mechanism for many hyperpolarized agents in solution arises from intramolecular nuclear dipole-dipole coupling modulated by molecular motion. It has been previously demonstrated that nuclear spin relaxation due to this mechanism can be removed by storing the nuclear polarization in long-lived, singlet-like states. In the case of N(2)O, storing the polarization of the nitrogen nuclei has been shown to substantially increase the polarization lifetime. The feasibility of utilizing N(2)O as a tracer is investigated by measuring the singlet-state lifetime of the N(2)O when dissolved in a variety of solvents including whole blood. Comparison of the singlet lifetime to longitudinal relaxation and between protonated and deuterated solvents is consistent with the dominance of spin-rotation relaxation, except in the case of blood. Magn Reson Med 66:1177-1180, 2011. (C) 2011 Wiley-Liss, Inc. |
| 29. | G Pileio: Singlet state relaxation via intermolecular dipolar coupling. In: JOURNAL OF CHEMICAL PHYSICS, vol. 134, no. 21, 2011, ISSN: 0021-9606. (Type: Journal Article | Abstract | Links)@article{ISI:000291402700029,The intermolecular contribution to the relaxation of singlet states has been derived on the basis of a translational-rotational diffusion model that describes molecules as impenetrable spheres which translate and rotate in an isotropic low-viscosity medium. The equations for the relaxation rate constants obtained are discussed and the dependence on physical parameters is exploited. Theoretical predictions are compared with experiments when the intermolecular relaxation is due to both protons and deuterons present in the sample. An agreement between experiments and theory of +/-4% was obtained when the physical parameters are estimated from first-principles calculation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3596379] |
| 28. | Giuseppe Pileio, Marina Carravetta, Malcolm H Levitt: Storage of nuclear magnetization as long-lived singlet order in low
magnetic field. In: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF
AMERICA, vol. 107, no. 40, pp. 17135-17139, 2010, ISSN: 0027-8424. (Type: Journal Article | Abstract | Links)@article{ISI:000282512000018,Hyperpolarized nuclear states provide NMR signals enhanced by many orders of magnitude, with numerous potential applications to analytical NMR, in vivo NMR, and NMR imaging. However, the lifetime of hyperpolarized magnetization is normally limited by the relaxation time constant T(1), which lies in the range of milliseconds to minutes, apart from in exceptional cases. In many cases, the lifetime of the hyperpolarized state may be enhanced by converting the magnetization into nuclear singlet order, where it is protected against many common relaxation mechanisms. However, all current methods for converting magnetization into singlet order require the use of a high-field, high-homogeneity NMR magnet, which is incompatible with most hyperpolarization procedures. We demonstrate a new method for converting magnetization into singlet order and back again. The new technique is suitable for magnetically inequivalent spin-pair systems in weak and inhomogeneous magnetic fields, and is compatible with known hyperpolarization technology. The method involves audio-frequency pulsed irradiation at the low-field nuclear Larmor frequency, employing coupling-synchronized trains of 180 degrees pulses to induce singlet-triplet transitions. The echo trains are used as building blocks for a pulse sequence called M2S that transforms longitudinal magnetization into long-lived singlet order. The time-reverse of the pulse sequence, called S2M, converts singlet order back into longitudinal magnetization. The method is demonstrated on a solution of (15)N-labeled nitrous oxide. The magnetization is stored in low magnetic field for over 30 min, even though the T(1) is less than 3 min under the same conditions. |
| 27. | Salvatore Mamone, Giuseppe Pileio, Malcolm H Levitt: Orientational Sampling Schemes Based on Four Dimensional Polytopes. In: SYMMETRY-BASEL, vol. 2, no. 3, pp. 1423-1449, 2010, ISSN: 2073-8994. (Type: Journal Article | Abstract | Links)@article{ISI:000208831900009,The vertices of regular four-dimensional polytopes are used to generate sets of uniformly distributed three-dimensional rotations, which are provided as tables of Euler angles. The spherical moments of these orientational sampling schemes are treated using group theory. The orientational sampling sets may be used in the numerical computation of solid-state nuclear magnetic resonance spectra, and in spherical tensor analysis procedures. |
| 26. | Giuseppe Pileio: Relaxation theory of nuclear singlet states in two spin-1/2 systems. In: PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY, vol. 56, no. 3, pp. 217-231, 2010, ISSN: 0079-6565. (Type: Journal Article | Links)@article{ISI:000276340100001, |
| 25. | James W Emsley, Philippe Lesot, Anne Lesage, Giuseppina De Luca, Denis Merlet, Giuseppe Pileio: The conformation and orientational order of a 1,2-disubstituted ethane
nematogenic molecule (I22) in liquid crystalline and isotropic phases
studied by NMR spectroscopy. In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, vol. 12, no. 12, pp. 2895-2914, 2010, ISSN: 1463-9076. (Type: Journal Article | Abstract | Links)@article{ISI:000275385700013,The structure, conformation and orientational order of the mesogen I22 have been studied by proton, carbon-13 and deuterium 1D and 2D-NMR spectroscopies at natural abundance and at various magnetic fields when in the nematic phase, the isotropic phase close to the nematic-isotropic phase transition, and as a solute in the chiral nematic solution comprised of the polypeptide PBLG dissolved in chloroform. It is concluded that 95% of conformers have a trans arrangement about the central C-C bond of the ethane fragment in all phases. |
| 24. | Giuseppe Pileio, Marina Carravetta, Malcolm H Levitt: Extremely Low-Frequency Spectroscopy in Low-Field Nuclear Magnetic
Resonance. In: PHYSICAL REVIEW LETTERS, vol. 103, no. 8, 2009, ISSN: 0031-9007. (Type: Journal Article | Abstract | Links)@article{ISI:000269288500030,We demonstrate a new phenomenon in nuclear magnetic resonance spectroscopy, in which nuclear spin transitions are induced by radio frequency irradiation at extremely low frequencies (of the order of a few Hz). Slow Rabi oscillations are observed between spin states of different exchange symmetry. These ``forbidden'' transitions are rendered weakly allowed by differential electronic shielding effects on the radio frequency field. We generate coherence between the singlet and triplet states of (15)N-labeled nitrous oxide in solution, and estimate the scalar coupling between the two (15)N nuclei with a precision of a few mHz. |
| 23. | Giuseppe Pileio, Malcolm H Levitt: Theory of long-lived nuclear spin states in solution nuclear magnetic
resonance. II. Singlet spin locking. In: JOURNAL OF CHEMICAL PHYSICS, vol. 130, no. 21, 2009, ISSN: 0021-9606. (Type: Journal Article | Abstract | Links)@article{ISI:000266674400022,In a previous paper [M. Carravetta and M. H. Levitt, J. Chem. Phys. 122, 214505 (2005)], we presented the theory of long-lived nuclear spin singlet states in low magnetic field. In this paper, we consider the spin locking of long-lived singlet states in high magnetic field by the application of resonant radio frequency irradiation. We present theoretical results for unmodulated irradiation, including approximate analytical expressions for the singlet decay rate constants. We show the results of numerical simulations, which indicate that modulated radio frequency fields may be used to achieve broadband spin locking of singlet states but only in the case of a small difference in Larmor frequencies between the members of the spin pair. |
| 22. | Giuseppe Pileio, Marina Carravetta, Eric Hughes, Malcolm H Levitt: The long-lived nuclear singlet state of N-15-nitrous oxide in solution. In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 130, no. 38, pp. 12582+, 2008, ISSN: 0002-7863. (Type: Journal Article | Abstract | Links)@article{ISI:000259295400016,A N-15 nuclear singlet lifetime of over 26 min has been observed in a solution of (N2O)-N-15, by using a field-cycling NMR pulse sequence. This observation suggests applications of hyperpolarized (N2O)-N-15 in medical imaging and for flow and diffusion studies. |
| 21. | Giuseppe Pileio, Salvatore Mamone, Giulia Mollica, Ildefonso Marin Montesinos, Axel Gansmueller, Marina Carravetta, Steven P Brown, Malcolm H Levitt: Estimation of internuclear couplings in the solid-state NMR of
multiple-spin systems. Selective spin echoes and off-magic-angle sample
spinning. In: CHEMICAL PHYSICS LETTERS, vol. 456, no. 1-3, pp. 116-121, 2008, ISSN: 0009-2614. (Type: Journal Article | Abstract | Links)@article{ISI:000255554600024,Internuclear couplings between selected homonuclear spin pairs in a multiply-labelled spin system are determined by NMR spin echo experiments in the solid-state. The spin echoes are induced by an amplitude-modulated shaped pulse. The time shift in the echo modulation curve is treated by average Hamiltonian theory and verified by numerical simulation. The J-couplings may be estimated by experiments on samples spinning at the magic-angle, while the direct dipole-dipole couplings may be estimated by off-magic-angle spinning. The concept is tested on a uniformly C-13-enriched sample of L-histidine hydrochloride monohydrate. (C) 2008 Elsevier B.V. All rights reserved. |
| 20. | Giuseppe Pileio, Malcolm H Levitt: Isotropic filtering using polyhedral phase cycles: Application to
singlet state NMR. In: JOURNAL OF MAGNETIC RESONANCE, vol. 191, no. 1, pp. 148-155, 2008, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000253500700017,A technique is described for filtering out the components of an NMR signal that have passed through an isotropic spin order term. The method involves a coordinated cycle of three radiofrequency phase angles, where two of the phases correspond to the polar angles describing the vertices of a regular polyhedron, and the third angle is stepped around a circle. The most economical isotropic filtering scheme involves a 12-step phase cycle based on tetrahedral symmetry. The method is used to filter out NMR signals that have passed through singlet populations in a solution NMR experiment. (C) 2007 Elsevier Inc. All rights reserved. |
| 19. | G De Luca, M Egan, J W Emsley, E K Foord, M Longeri, G Pileio: Do the molecules which form discotic liquid crystals have disc-like
structures? The conformation of a simple model compound,
1,2-dihydroxydiacetylbenzene, determined from the NMR spectra of samples
dissolved in liquid crystalline solvents. In: LIQUID CRYSTALS, vol. 35, no. 2, pp. 205-212, 2008, ISSN: 0267-8292. (Type: Journal Article | Abstract | Links)@article{ISI:000254630500013,Many discotic mesogens are molecules with a central aromatic ring with adjacent alkylcarboxylate substituents. The simplest such molecule, 1,2-dihydroxydiacetylbenzene, which is not mesogenic, is studied by NMR spectroscopy as a solute in a nematic solvent. The spectra are analysed to give sets of residual dipolar couplings, D-ij , which are then used to test models for the conformation adopted by the acetate side groups. The conformations and geometry of an isolated molecule are calculated by the ab initio MP2/6-311G method and also by the DFT approach using the B3LYP functional with the 6-311++G** basis set. The quantum chemical calculations find that the minimum energy conformer has the acetate groups rotated in opposite directions out of the ring plane, and this kind of structure is also consistent with the NMR data. |
| 18. | James W Emsley, Philippe Lesot, Giuseppina De Luca, Anne Lesage, Denis Merlet, Giuseppe Pileio: A comparison of proton-detected C-13 local field experiments with
deuterium NMR at natural abundance for studying liquid crystals. In: LIQUID CRYSTALS, vol. 35, no. 4, pp. 443-464, 2008, ISSN: 0267-8292. (Type: Journal Article | Abstract | Links)@article{ISI:000256955800009,A comparison is made between the information which can be derived on structure, conformation and orientational order of the molecules in a nematic liquid crystal 4-pentyl-4'-cyanobiphenyl (5CB) from the NMR spectra of the deuterium atoms at natural abundance (NAD NMR), and the two-dimensional proton-detected C-13 local field experiment (PDLF). The nine residual quadrupolar splittings, Delta v(k), obtained experimentally have been compared with quadrupolar tensors and a geometry and conformational potentials calculated by the DFT method B3LYP/6-311G**. The PDLF experiment yielded 42 scaled C-13-H-1 residual dipolar couplings, kD(CiHj). The scaling factor, k, is determined experimentally by comparing unscaled and scaled residual dipolar couplings in a sample of fluorobenzene dissolved in a nematic liquid crystalline solvent. The corrected residual dipolar couplings, D-CiHj, are used to investigate the structure and rotational potentials about each bond in the molecule. |
| 17. | Giuseppe Pileio, Ying Guo, Tran N Pham, John M Griffin, Malcolm H Levitt, Steven P Brown: Residual dipolar couplings by off-magic-angle spinning in solid-state
nuclear magnetic resonance Spectroscopy. In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 129, no. 36, pp. 10972+, 2007, ISSN: 0002-7863. (Type: Journal Article | Abstract | Links)@article{ISI:000249372400004,A solid-state NMR analogue of the solution-state residual dipolar coupling effect is demonstrated. A small misset of the spinning axis by less than 0.5 degrees changes the modulation frequency of spin-echoes, allowing the estimation of internuclear dipole-dipole couplings and hence internuclear distances. |
| 16. | Giuseppe Pileio, Malcolm H Levitt: J-Stabilization of singlet states in the solution NMR of multiple-spin
systems. In: JOURNAL OF MAGNETIC RESONANCE, vol. 187, no. 1, pp. 141-145, 2007, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000247982800018,Long-lived singlet states have been observed in the solution NMR of spin systems containing more than two coupled spins, despite the fact that the singlet state is expected to be quenched by small long-range J-couplings. We show that the stability of localized singlet states may be explained by taking into account the intra-pair J-coupling between the two spins which participate in the singlet state. The relatively strong intra-pair J-coupling protects the singlet state against quenching by weaker out-of-pair J-couplings. (C) 2007 Elsevier Inc. All rights reserved. |
| 15. | Giuseppe Pileio, Maria Concistre, Neville McLean, Axel Gansmulller, Richard C D Brown, Malcolm H Levitt: Analytical theory of gamma-encoded double-quantum recoupling sequences
in solid-state nuclear magnetic resonance. In: JOURNAL OF MAGNETIC RESONANCE, vol. 186, no. 1, pp. 65-74, 2007, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000246494300007,Many important double-quantuin recoupling techniques in solid-state NMR are classified as being gamma-cncoded. This means that the phase of the double-quantum effective Hamiltonian, but not its amplitude, depends on the third Euler angle defining the orientation of the molecular spin system in the frame of the magic-angle-spinning rotor. In this paper, we provide closed analytical solutions for the dependence of the powder-average double-quantum-filtered signal on the recoupling times, within the average Hamiltonian approximation for gamma-encoded pulse sequences. The validity of the analytical Solutions is tested by numerical simulations. The internuclear distance in a C-13(2)-labelled retinal is estimated by fitting the analytical Curves to experimental double-quantum data. (C) 2007 Elsevier Inc. All rights reserved. |
| 14. | J W Emsley, G De Luca, A Lesage, D Merlet, G Pileio: The structure and conformation of a mesogenic compound between almost
zero and almost complete orientational order. In: LIQUID CRYSTALS, vol. 34, no. 9, pp. 1071-1093, 2007, ISSN: 0267-8292. (Type: Journal Article | Abstract | Links)@article{ISI:000250006900008,The conformational distributions in molecules that form liquid crystalline phases are predicted to depend strongly on orientational order. Results are presented here to test this hypothesis. The mesogen 4-hexyloxy-4'-cyanobiphenyl (6OCB) has been studied by NMR spectroscopy in the isotropic phase and in the nematic phase. In the isotropic phase the field-induced orientational ordering produces small dipolar couplings between C-13 and H-1 nuclei, which were determined from the 13 C spectra. Couplings between H-1 nuclei were also obtained using 2D selective refocusing experiments. In the nematic phase, both H-1-H-1 dipolar couplings and quadrupolar splittings for deuterium nuclei were measured for partially-deuterated samples. Both proton and deuterium spectra were also obtained for 6OCB in an equimolar mixture with 4-(ethoxybenzylidene)-4'-butylaniline (EBBA). This mixture exhibits SmA and SmB phases. The data obtained from these experiments has been analysed to yield the probability distribution of the conformations in this molecule generated by rotations about bonds. It is found that there is a substantial influence of the orientational order of the molecules on these distributions. |
| 13. | Giorgio Celebre, Giuseppina De Luca, Marcello Longeri, Giuseppe Pileio: Calculated versus ``Experimental'' force fields: The influence in the
structure determination of benzene by NMR spectroscopy in liquid crystal
solvents. In: MOLECULAR CRYSTALS AND LIQUID CRYSTALS, vol. 465, pp. 289-299, 2007, ISSN: 1542-1406, (7th National Meeting of the Italian-Liquid-Crystal-Society/3rd
Italian-Japanese Workshop on Liquid Crystals, Castiglioncello, ITALY,
JUN 04-09, 2006). (Type: Journal Article | Abstract | Links)@article{ISI:000246070600028,Very accurate bond distances can be derived from dipolar couplings, D-ij, obtained by analysis of the NMR spectra of samples dissolved in anisotropic solvents (LXNMR). To do this, however, the couplings must be corrected for the averaging produced by vibrational motion. The vibrational corrections require a knowledge of the force field, which may be obtained by fitting experimental vibrational frequencies or, much more easily, from quantum-mechanical computations. In the present study, the reliability of the methods used to calculate the force field and the effects on the accuracy of the vibrational corrections to the D-ij is tested on benzene for which a very accurate structural study is available. |
| 12. | Ildefonso Marin-Montesinos, Giulia Mollica, Marina Carravetta, Axel Gansmueller, Giuseppe Pileio, Matthias Bechmann, Angelika Sebald, Malcolm H Levitt: Truncated dipolar recoupling in solid-state nuclear magnetic resonance. In: CHEMICAL PHYSICS LETTERS, vol. 432, no. 4-6, pp. 572-578, 2006, ISSN: 0009-2614. (Type: Journal Article | Abstract | Links)@article{ISI:000243067000036,We describe a solid-state NMR concept for the estimation of individual spin-spin couplings in strongly-coupled homonuclear spin systems. A radiofrequency pulse sequence, synchronised with the magic-angle sample rotation recouples zero-quantum dipolar interactions as well as a frequency-dispersing interaction such as the chemical shift anisotropy. The combination of these two recoupled interactions causes the spin system to behave in an approximately weakly-coupled fashion. Individual spin-spin couplings may then be disentangled by using frequency-selective radiofrequency pulses. Theoretical results and numerical simulations are compared with experimental data for the (13)C nuclei in [(2)H(7), (13)C(3),(15)N]-L-alanine. (c) 2006 Elsevier B.V. All rights reserved. |
| 11. | Giuseppe Pileio, Maria Concistre, Marina Carravetta, Malcolm H Levitt: Long-lived nuclear spin states in the solution NMR of four-spin systems. In: JOURNAL OF MAGNETIC RESONANCE, vol. 182, no. 2, pp. 353-357, 2006, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000241203900022,The existence of long-lived nuclear spin states in four-spin systems is explored by solution-state NMR experiments. Long-lived states are proved to exist in three different natural product molecules, each containing either a AA'BB' or a AA'XA' proton spin system. The measured state lifetimes are between four and eight times the spin-lattice relaxation time constants. (c) 2006 Elsevier Inc. All rights reserved. |
| 10. | Giorgio Celebre, Maria Concistre, Giuseppina De Luca, Marcello Longeri, Giuseppe Pileio: Intrinsic information content of NMR dipolar couplings: A conformational
investigation of 1,3-butadiene in a nernatic phase. In: CHEMPHYSCHEM, vol. 7, no. 9, pp. 1930-1943, 2006, ISSN: 1439-4235. (Type: Journal Article | Abstract | Links)@article{ISI:000240668700015,The conformational equilibrium of 1,3-butadiene in a condensed fluid phase is investigated by liquid-crystal NMR spectroscopy. The full set of D-HH and D-CH dipolar couplings is determined from the analysis of the H-1 spectra of the three 1,3-butadiene most-abundant isotopomers (i.e. the all C-12 and the two single-labeled C-13 isotopomers) for a total of 21 independent dipolar couplings. A very good starting set of spectral parameters for the analysis of the H-1 spectrum is determined in a semiautomated way by the analysis of the (N - 1) (specifically |
| 9. | JW Emsley, M Longeri, D Merlet, G Pileio, N Suryaprakash: An investigation of the structure and bond rotational potential of some
fluorinated ethanes by NMR spectroscopy of solutions in nematic liquid
crystalline solvents. In: JOURNAL OF MAGNETIC RESONANCE, vol. 180, no. 2, pp. 245-255, 2006, ISSN: 1090-7807. (Type: Journal Article | Abstract | Links)@article{ISI:000237875300011,NMR spectra of 1,2-dibromo-1,1-difluoroethane and 1-bromo-2-iodo-tetrafluoroethane dissolved in nematic liquid crystalline solvents have been analysed to yield the magnitudes and signs of the scalar couplings, J(ij), and total anisotropic couplings, T-ij, between all the H-1, F-19, and C-13 nuclei, except for those between two C-13 nuclei. The values obtained for Tij in principle contain a contribution from J(ij)(aniso), the component along the static applied magnetic field of the anisotropic part of the electron-mediated spin-spin coupling. Neglecting this contribution allows partially averaged dipolar couplings, D-ij, to be extracted from the T-ij, and these were used to determine the structure, orientational order, and the conformational distribution generated by rotation about the C-C bond. The values obtained are compared with the results of calculations by ab initio and density functional methods. The differences found are no greater than those obtained for similar compounds which do not contain fluorine, so that there is no definitive evidence for significant contributions from J(CF)(aniso) or J(FF)(aniso) in the two compounds studied. (c) 2006 Elsevier Inc. All rights reserved. |
| 8. | G Celebre, G De Luca, JW Emsley, M Longeri, D Merlet, G Pileio, N Suryaprakash: Obtaining the structure and bond rotational potential of a substituted
ethane by NMR spectroscopy of solutions in nematic liquid-crystalline
solvents. In: JOURNAL OF CHEMICAL PHYSICS, vol. 123, no. 19, 2005, ISSN: 0021-9606. (Type: Journal Article | Abstract | Links)@article{ISI:000233353200044,Partially averaged dipolar couplings (also referred to as residual dipolar couplings) D-ij can be obtained from the analysis of the NMR spectra of molecules dissolved in liquid-crystalline solvents. Their values for a nonrigid molecule depend upon the bond lengths and angles, the rotational potentials, and the orientational order of the molecules. The molecule studied, 1-chloro-2-bromoethane, is one of the simplest example of a substituted alkane in which the rotational potential has three minimum-energy positions, trans and gauche +/- conformations, and the present investigation explores the problems inherent in deriving the form of the potential and the molecular geometry from the set of partially averaged couplings between the protons, and between protons and C-13 nuclei. The geometrical parameters and the rotational potential obtained are compared with the results from a density-functional theory method. (c) 2005 American Institute of Physics. |
| 7. | M Concistre, L De Lorenzo, G De Luca, M Longeri, G Pileio, G Raos: Conformational analysis of 2,2 `-bithiophene: A H-1 liquid crystal NMR
study using the C-13 satellite spectra. In: JOURNAL OF PHYSICAL CHEMISTRY A, vol. 109, no. 44, pp. 9953-9963, 2005, ISSN: 1089-5639. (Type: Journal Article | Abstract | Links)@article{ISI:000233342300006,We have obtained a very large data set of spectral parameters from the analysis of H-1 NMR and C-13 satellite spectra of 2,2'-bithiophene dissolved in anisotropic, partially orienting mesophases. In particular, this parameter set includes 33 dipolar couplings, which are directly related to the interatomic distances, the dihedral angle 0 between the two thiophenic rings, and the anisotropic solute-solvent interaction potential. This allows an exhaustive investigation of the conformational equilibrium of 2,2'-bithiophene in a liquidlike phase. Comparison with the predictions of high-level theoretical calculations for the isolated molecule provides evidence of a strong flattening as well as the sharpening effect of the medium on the conformer population. The approximations needed to apply vibrational corrections to flexible molecules are discussed in detail and some general conclusions concerning their effect on structure and conformational equilibria are proposed. |
| 6. | G De Luca, M Longeri, G Pileio, P Lantto: NMR spectroscopy investigation of the cooperative nature of the internal
rotational motions in acetophenone. In: CHEMPHYSCHEM, vol. 6, no. 10, pp. 2086-2098, 2005, ISSN: 1439-4235. (Type: Journal Article | Abstract | Links)@article{ISI:000232725900015,The proton NMR spectrum of the doubly enriched acetophenone-carbonyl,methyl-C-13(2) isotopomer dissolved in a liquid-crystalline solvent (LXNMR) was analyzed to yield a data set of 19 dipolar couplings. The presence of so many couplings, and in particular the dependence of some of them on the acetyl carbons enabled the investigation of the structure of the acetyl moiety and of possible cooperative motions about the aryl-carbonyl and carbonylmethyl bonds. Methodological aspects, and approximations relating to the application of the vibrational correction procedure in the presence of large-amplitude torsional motions, are discussed. Results show that it is possible to discriminate between a continuous and a discrete conformer distribution about the angle, but not among a few proposed continuous shapes of U-iso(phi). In this study, the use of dipolar couplings with a non-negligible contribution from the indirect spin-spin coupling tensor J, (D-C8C9 in our case), for structural determination is extended from rigid to flexible molecules. The 1/2J(C8C9)(aniso) contribution was derived theoretically using the density functional theory linear response (DFT-LR) first-principles calculation of the J(C8C9) spin-spin coupling tensor. |
| 5. | M Concistre, G De Luca, M Longeri, G Pileio, JW Emsley: The structure and conformations of 2-thiophenecarboxaldehyde obtained
from partially averaged dipolar couplings. In: CHEMPHYSCHEM, vol. 6, no. 8, pp. 1483-1491, 2005, ISSN: 1439-4235. (Type: Journal Article | Abstract | Links)@article{ISI:000231378900009,The proton NMR spectra of samples of 2-thiophenecarboxalde-hyde dissolved in a nematic liquid crystalline solvent, including those from all five singly labelled C-13 isotopomers, have been obtained. These have been analysed to yield sets of partially averaged dipolar couplings which have been used to determine the structure and the relative amounts of the cis and trans forms, which are the two minimum-energy structures generated by rotation about the ring-aldehyde bond. A procedure for applying vibrational corrections to the dipolar couplings in the presence of large amplitude motions is discussed. |
| 4. | G Celebre, M Concistre, G De Luca, M Longeri, G Pileio, JW Emsley: The structure of acrolein in a liquid crystal phase. In: CHEMISTRY-A EUROPEAN JOURNAL, vol. 11, no. 12, pp. 3599-3608, 2005, ISSN: 0947-6539. (Type: Journal Article | Abstract | Links)@article{ISI:000229729300014,The H-1 NMR spectrum of a sample of acrolein dissolved in the nematic liquid crystal phase 152 has been analysed to yield 18 dipolar couplings between all the magnetic nuclei in the molecule; moreover, the C-13 and C-13[H-1] NMR spectra of a sample of acrolein in CDCl3 were recorded and analysed to determine the indirect J(ij) couplings. The data were used to obtain the relative positions of the carbon and hydrogen atoms, assuming that these are independent of the conformations generated by rotation around the C-C bond through an angle phi, and to obtain a probability distribution P(phi). It has been found that in the liquid phase, the distribution is a maximum at the trans form whereas the abundance of the cis form is significantly smaller compared with that found by microwave spectroscopy or high level quantum mechanical calculations. Such calculations produced also a suitable force field needed to develop suitable strategies for vibrational correction procedure in the case of flexible molecules. |
| 3. | G Celebre, G De Luca, M Longeri, G Pileio, JW Emsley: Is styrene planar in liquid phases?. In: JOURNAL OF CHEMICAL PHYSICS, vol. 120, no. 15, pp. 7075-7084, 2004, ISSN: 0021-9606. (Type: Journal Article | Abstract | Links)@article{ISI:000220585300034,The proton NMR spectra of two C-13-labeled isotopomers of styrene dissolved in two liquid crystalline solvents have been obtained and analyzed to yield four sets each of 24 dipolar couplings. These couplings were then used to investigate the structure of the ring and the ene fragments of the molecule, and the position of the maximum, phi(0), in the ring-ene bond rotational probability distribution. To do this, the effect on the dipolar couplings of small-amplitude vibrational motion was taken into account using vibrational wave functions calculated by molecular orbital and density functional methods. It is concluded that the NMR data are consistent with the ring fragment, averaged over the ring-ene rotation, planar, while the ene fragment is not. The value of phi(0) is found to be 18.0degrees+/-0.2degrees for the two solutions, compared with a value of 27degrees calculated by the molecular method MP2/6-31G*. (C) 2004 American Institute of Physics. |
| 2. | G Celebre, G De Luca, JW Emsley, EK Foord, M Longeri, F Lucchesini, G Pileio: The conformational distribution in diphenylmethane determined by nuclear
magnetic resonance spectroscopy of a sample dissolved in a nematic
liquid crystalline solvent. In: JOURNAL OF CHEMICAL PHYSICS, vol. 118, no. 14, pp. 6417-6426, 2003, ISSN: 0021-9606. (Type: Journal Article | Abstract | Links)@article{ISI:000181834900036,The deuterium decoupled, proton nuclear magnetic resonance spectrum of a sample of diphenylmethane-d(3) dissolved in a nematic liquid crystalline solvent has been analyzed to yield a set of dipolar couplings, D-ij. These have been used to test models for the conformational distribution generated by rotation about the two ring-CH2 bonds through angles tau(1) and tau(2). Conformational distributions, particularly when obtained from a quantum chemistry calculation, are usually described in terms of the potential energy surface, V(tau(1),tau(2)), which is then used to define a probability density distribution, P(tau(1),tau(2)). It is shown here that when attempting to obtain P(tau(1),tau(2)) from experimental data it can be an advantage to do this directly without going through the intermediate step of trying to characterize V(tau(1,)tau(2)). When applied to diphenylmethane this method shows that the dipolar couplings are consistent with a conformational distribution centered on tau(1)=tau(2)=56.5+/-0.5degrees, which is close to the values calculated for an isolated molecule of 57.0degrees, and significantly different from the asymmetric structure found in the crystalline state. (C) 2003 American Institute of Physics. |
| 1. | [No title]. 0000. (Type: Bachelor Thesis | )@bachelorthesis{nokey, |
Publications
| 72. | : A dual-core NMR system for field-cycling singlet assisted diffusion NMR. In: Frontiers in Chemistry, vol. 11, 2023, ISSN: 2296-2646. |
| 71. | : Singlet-assisted diffusion-NMR (SAD-NMR): extending the scope of diffusion tensor imaging via singlet NMR. In: Frontiers in Chemistry, vol. 11, 2023, ISSN: 2296-2646. |
| 70. | : Theory and Simulation Framework for the Relaxation of Nuclear Spin Order in Porous Media. In: The Journal of Physical Chemistry B, vol. 126, no. 34, pp. 6536-6546, 2022, (PMID: 35976731). |
| 69. | : Single-scan measurements of nuclear spin singlet order decay rates. In: Phys. Chem. Chem. Phys., pp. -, 2021. |
| 68. | : Nuclear Spin Relaxation of Longitudinal and Singlet Order in Liquid-CO2 Solutions. In: Frontiers in Chemistry, vol. 9, pp. 243, 2021, ISSN: 2296-2646. |
| 67. | : Physical Characterisation of Chia Mucilage Polymeric Gel and its Implications on Rhizosphere Science - Integrating Imaging, MRI, and Modelling to Gain Insights into Plant and Microbial Amended Soils. In: Soil Biology and Biochemistry, pp. 108404, 2021, ISSN: 0038-0717. |
| 66. | : Chapter 7 Manipulating Spin Order by J-synchronised Echo Schemes. In: Long-lived Nuclear Spin Order: Theory and Applications, pp. 136-150, The Royal Society of Chemistry, 2020, ISBN: 978-1-78801-568-4. |
| 65. | : Chapter 3 Relaxation Theory of Long-lived Spin Order. In: Long-lived Nuclear Spin Order: Theory and Applications, pp. 64-91, The Royal Society of Chemistry, 2020, ISBN: 978-1-78801-568-4. |
| 64. | : Chapter 15 Singlet-assisted Diffusion NMR. In: Long-lived Nuclear Spin Order: Theory and Applications, pp. 280-301, The Royal Society of Chemistry, 2020, ISBN: 978-1-78801-568-4. |
| 63. | : Chapter 16 Q-space Singlet NMR. In: Long-lived Nuclear Spin Order: Theory and Applications, pp. 302-319, The Royal Society of Chemistry, 2020, ISBN: 978-1-78801-568-4. |
| 62. | : A temperature-controlled sample shuttle for field-cycling NMR. In: Journal of Magnetic Resonance, pp. 106778, 2020, ISSN: 1090-7807. |
| 61. | : Nuclear singlet relaxation by scalar relaxation of the second kind in the slow-fluctuation regime. In: The Journal of Chemical Physics, vol. 150, no. 6, pp. 064315, 2019. |
| 60. | : Excitation of singlet-triplet coherences in pairs of nearly-equivalent spins. In: Phys. Chem. Chem. Phys., pp. -, 2019. |
| 59. | : Sub-minute kinetics of human red cell fumarase: 1H spin-echo NMR spectroscopy and 13C rapid-dissolution dynamic nuclear polarization. In: NMR in Biomedicine, vol. 31, no. 3, pp. e3870–n/a, 2018, ISSN: 1099-1492, (e3870 NBM-17-0125.R2). |
| 58. | : Singlet-assisted diffusion-NMR (SAD-NMR): redefining the limits when measuring tortuosity in porous media. In: Phys. Chem. Chem. Phys., vol. 20, pp. 13705-13713, 2018. |
| 57. | Correlative Visualization of Root Mucilage Degradation Using X-ray CT and MRI. In: Frontiers in Environmental Science, vol. 6, pp. 32, 2018, ISSN: 2296-665X. |
| 56. | : Accessing the long-time limit in diffusion NMR: The case of singlet assisted diffusive diffraction q-space. In: JOURNAL OF MAGNETIC RESONANCE, vol. 285, pp. 1-7, 2017, ISSN: 1090-7807. |
| 55. | : A pulse sequence for singlet to heteronuclear magnetization transfer: S2hM. In: JOURNAL OF MAGNETIC RESONANCE, vol. 277, pp. 169-178, 2017, ISSN: 1090-7807. |
| 54. | : Synthesis of carbon-13 labeled oxalates exhibiting extended nuclear singlet state lifetimes. In: JOURNAL OF LABELLED COMPOUNDS & RADIOPHARMACEUTICALS, vol. 60, no. 2, pp. 135-139, 2017, ISSN: 0362-4803. |
| 53. | : Singlet NMR methodology in two-spin-1/2 systems. In: PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY, vol. 98-99, pp. 1-19, 2017, ISSN: 0079-6565. |
| 52. | : Singlet order conversion and parahydrogen-induced hyperpolarization of C-13 nuclei in near-equivalent spin systems. In: JOURNAL OF MAGNETIC RESONANCE, vol. 274, pp. 163-172, 2017, ISSN: 1090-7807. |
| 51. | : Nuclear Singlet Spin States. In: Lindon, John C; Tranter, George E; Koppenaal, David W (Ed.): Encyclopedia of Spectroscopy and Spectrometry (Third Edition), pp. 456 - 462, Academic Press, Oxford, 2017, ISBN: 978-0-12-803224-4. |
| 50. | : Substituent interference on supramolecular assembly in urea gelators: synthesis, structure prediction and NMR. In: SOFT MATTER, vol. 12, no. 17, pp. 4034-4043, 2016, ISSN: 1744-683X. |
| 49. | : Synthesis of an Isotopically Labeled Naphthalene Derivative That Supports a Long-Lived Nuclear Singlet State. In: ORGANIC LETTERS, vol. 17, no. 9, pp. 2150-2153, 2015, ISSN: 1523-7060. |
| 48. | : A Nuclear Singlet Lifetime of More than One Hour in Room-Temperature Solution. In: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, vol. 54, no. 12, pp. 3740-3743, 2015, ISSN: 1433-7851. |
| 47. | : Real-space imaging of macroscopic diffusion and slow flow by singlet tagging MRI. In: JOURNAL OF MAGNETIC RESONANCE, vol. 252, pp. 130-134, 2015, ISSN: 1090-7807. |
| 46. | : Theory of long-lived nuclear spin states in methyl groups and quantum-rotor induced polarisation. In: JOURNAL OF CHEMICAL PHYSICS, vol. 142, no. 4, 2015, ISSN: 0021-9606. |
| 45. | : Enhancement of quantum rotor NMR signals by frequency-selective pulses. In: JOURNAL OF MAGNETIC RESONANCE, vol. 250, pp. 25-28, 2015, ISSN: 1090-7807. |
| 44. | : Long-lived nuclear spin states far from magnetic equivalence. In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, vol. 17, no. 8, pp. 5913-5922, 2015, ISSN: 1463-9076. |
| 43. | : Organophosphorus chemical warfare agent simulant DMMP promotes structural reinforcement of urea-based chiral supramolecular gels. In: RSC ADVANCES, vol. 5, no. 16, pp. 12287-12292, 2015, ISSN: 2046-2069. |
| 42. | : Long-lived localization in magnetic resonance imaging. In: JOURNAL OF MAGNETIC RESONANCE, vol. 246, pp. 27-30, 2014, ISSN: 1090-7807. |
| 41. | : Long-Lived Nuclear Spin States in Methyl Groups and Quantum-Rotor-Induced Polarization. In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 135, no. 50, pp. 18746-18749, 2013, ISSN: 0002-7863. |
| 40. | : Hyperpolarized singlet lifetimes of pyruvate in human blood and in the mouse. In: NMR IN BIOMEDICINE, vol. 26, no. 12, pp. 1696-1704, 2013, ISSN: 0952-3480. |
| 39. | : Grid-free powder averages: On the applications of the Fokker-Planck equation to solid state NMR. In: JOURNAL OF MAGNETIC RESONANCE, vol. 235, pp. 121-129, 2013, ISSN: 1090-7807. |
| 38. | : Anisotropic nuclear spin interactions in H2O@C-60 determined by solid-state NMR. In: PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, vol. 371, no. 1998, 2013, ISSN: 1364-503X. |
| 37. | : Lineshape-based polarimetry of dynamically-polarized (N2O)-N-15 in solid-state mixtures. In: JOURNAL OF MAGNETIC RESONANCE, vol. 234, pp. 90-94, 2013, ISSN: 1090-7807. |
| 36. | : Recycling and Imaging of Nuclear Singlet Hyperpolarization. In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 135, no. 13, pp. 5084-5088, 2013, ISSN: 0002-7863. |
| 35. | : Long-Lived Nuclear Singlet Order in Near-Equivalent C-13 Spin Pairs. In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 134, no. 42, pp. 17494-17497, 2012, ISSN: 0002-7863. |
| 34. | : Hyperpolarized singlet NMR on a small animal imaging system. In: MAGNETIC RESONANCE IN MEDICINE, vol. 68, no. 4, pp. 1262-1265, 2012, ISSN: 0740-3194. |
| 33. | : Direct Enhancement of Nuclear Singlet Order by Dynamic Nuclear Polarization. In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 134, no. 18, pp. 7668-7671, 2012, ISSN: 0002-7863. |
| 32. | : Sensitivity enhancement and low-field spin relaxation in singlet NMR. In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, vol. 14, no. 46, pp. 16032-16040, 2012, ISSN: 1463-9076. |
| 31. | : Singlet state relaxation via scalar coupling of the second kind. In: JOURNAL OF CHEMICAL PHYSICS, vol. 135, no. 17, 2011, ISSN: 0021-9606. |
| 30. | : Measurements of the Persistent Singlet State of N(2)O in Blood and Other Solvents-Potential as a Magnetic Tracer. In: MAGNETIC RESONANCE IN MEDICINE, vol. 66, no. 4, pp. 1177-1180, 2011, ISSN: 0740-3194. |
| 29. | : Singlet state relaxation via intermolecular dipolar coupling. In: JOURNAL OF CHEMICAL PHYSICS, vol. 134, no. 21, 2011, ISSN: 0021-9606. |
| 28. | : Storage of nuclear magnetization as long-lived singlet order in low magnetic field. In: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, vol. 107, no. 40, pp. 17135-17139, 2010, ISSN: 0027-8424. |
| 27. | : Orientational Sampling Schemes Based on Four Dimensional Polytopes. In: SYMMETRY-BASEL, vol. 2, no. 3, pp. 1423-1449, 2010, ISSN: 2073-8994. |
| 26. | : Relaxation theory of nuclear singlet states in two spin-1/2 systems. In: PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY, vol. 56, no. 3, pp. 217-231, 2010, ISSN: 0079-6565. |
| 25. | : The conformation and orientational order of a 1,2-disubstituted ethane nematogenic molecule (I22) in liquid crystalline and isotropic phases studied by NMR spectroscopy. In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, vol. 12, no. 12, pp. 2895-2914, 2010, ISSN: 1463-9076. |
| 24. | : Extremely Low-Frequency Spectroscopy in Low-Field Nuclear Magnetic Resonance. In: PHYSICAL REVIEW LETTERS, vol. 103, no. 8, 2009, ISSN: 0031-9007. |
| 23. | : Theory of long-lived nuclear spin states in solution nuclear magnetic resonance. II. Singlet spin locking. In: JOURNAL OF CHEMICAL PHYSICS, vol. 130, no. 21, 2009, ISSN: 0021-9606. |
| 22. | : The long-lived nuclear singlet state of N-15-nitrous oxide in solution. In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 130, no. 38, pp. 12582+, 2008, ISSN: 0002-7863. |
| 21. | : Estimation of internuclear couplings in the solid-state NMR of multiple-spin systems. Selective spin echoes and off-magic-angle sample spinning. In: CHEMICAL PHYSICS LETTERS, vol. 456, no. 1-3, pp. 116-121, 2008, ISSN: 0009-2614. |
| 20. | : Isotropic filtering using polyhedral phase cycles: Application to singlet state NMR. In: JOURNAL OF MAGNETIC RESONANCE, vol. 191, no. 1, pp. 148-155, 2008, ISSN: 1090-7807. |
| 19. | : Do the molecules which form discotic liquid crystals have disc-like structures? The conformation of a simple model compound, 1,2-dihydroxydiacetylbenzene, determined from the NMR spectra of samples dissolved in liquid crystalline solvents. In: LIQUID CRYSTALS, vol. 35, no. 2, pp. 205-212, 2008, ISSN: 0267-8292. |
| 18. | : A comparison of proton-detected C-13 local field experiments with deuterium NMR at natural abundance for studying liquid crystals. In: LIQUID CRYSTALS, vol. 35, no. 4, pp. 443-464, 2008, ISSN: 0267-8292. |
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