共查询到20条相似文献,搜索用时 500 毫秒
1.
Dr. Stanislav L. Veinberg Zachary W. Friedl Austin W. Lindquist Brianna Kispal Dr. Kristopher J. Harris Dr. Luke A. O'Dell Prof. Robert W. Schurko 《Chemphyschem》2016,17(23):4011-4027
14N ultra‐wideline solid‐state NMR (SSNMR) spectra were obtained for 16 naturally occurring amino acids and four related derivatives by using the WURST–CPMG (wideband, uniform rate, and smooth truncation Carr–Purcell–Meiboom–Gill) pulse sequence and frequency‐stepped techniques. The 14N quadrupolar parameters were measured for the sp3 nitrogen moieties (quadrupolar coupling constant, CQ, values ranged from 0.8 to 1.5 MHz). With the aid of plane‐wave DFT calculations of the 14N electric‐field gradient tensor parameters and orientations, the moieties were grouped into three categories according to the values of the quadrupolar asymmetry parameter, ηQ: low (≤0.3), intermediate (0.31–0.7), and high (≥0.71). For RNH3+ moieties, greater variation in N?H bond lengths was observed for systems with intermediate ηQ values than for those with low ηQ values (this variation arose from different intermolecular hydrogen‐bonding arrangements). Strategies for increasing the efficiency of 14N SSNMR spectroscopy experiments were discussed, including the use of sample deuteration, high‐power 1H decoupling, processing strategies, high magnetic fields, and broadband cross‐polarization (BRAIN‐CP). The temperature‐dependent rotations of the NH3 groups and their influence on 14N transverse relaxation rates were examined. Finally, 14N SSNMR spectroscopy was used to differentiate two polymorphs of l ‐histidine through their quadrupolar parameters and transverse relaxation time constants. The strategies outlined herein permitted the rapid acquisition of directly detected 14N SSNMR spectra that to date was not matched by other proposed methods. 相似文献
2.
Monitoring and Understanding the Paraelectric–Ferroelectric Phase Transition in the Metal–Organic Framework [NH4][M(HCOO)3] by Solid‐State NMR Spectroscopy
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Dr. Jun Xu Dr. Bryan E. G. Lucier Regina Sinelnikov Dr. Victor V. Terskikh Prof. Viktor N. Staroverov Prof. Yining Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(41):14348-14361
The paraelectric–ferroelectric phase transition in two isostructural metal–organic frameworks (MOFs) [NH4][M(HCOO)3] (M=Mg, Zn) was investigated by in situ variable‐temperature 25Mg, 67Zn, 14N, and 13C solid‐state NMR (SSNMR) spectroscopy. With decreasing temperature, a disorder–order transition of NH4+ cations causes a change in dielectric properties. It is thought that [NH4][Mg(HCOO)3] exhibits a higher transition temperature than [NH4][Zn(HCOO)3] due to stronger hydrogen‐bonding interactions between NH4+ ions and framework oxygen atoms. 25Mg and 67Zn NMR parameters are very sensitive to temperature‐induced changes in structure, dynamics, and dielectric behavior; stark spectral differences across the paraelectric–ferroelectric phase transition are intimately related to subtle changes in the local environment of the metal center. Although 25Mg and 67Zn are challenging nuclei for SSNMR experiments, the highly spherically symmetric metal‐atom environments in [NH4][M(HCOO)3] give rise to relatively narrow spectra that can be acquired in 30–60 min at a low magnetic field of 9.4 T. Complementary 14N and 13C SSNMR experiments were performed to probe the role of NH4+–framework hydrogen bonding in the paraelectric–ferroelectric phase transition. This multinuclear SSNMR approach yields new physical insights into the [NH4][M(HCOO)3] system and shows great potential for molecular‐level studies on electric phenomena in a wide variety of MOFs. 相似文献
3.
Dr. Karen E. Johnston Christopher A. O'Keefe Dr. Régis M. Gauvin Dr. Julien Trébosc Dr. Laurent Delevoye Prof. Jean‐Paul Amoureux Dr. Nicolas Popoff Dr. Mostafa Taoufik Dr. Konstantin Oudatchin Prof. Robert W. Schurko 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12396-12414
A series of transition‐metal organometallic complexes with commonly occurring metal? chlorine bonding motifs were characterized using 35Cl solid‐state NMR (SSNMR) spectroscopy, 35Cl nuclear quadrupole resonance (NQR) spectroscopy, and first‐principles density functional theory (DFT) calculations of NMR interaction tensors. Static 35Cl ultra‐wideline NMR spectra were acquired in a piecewise manner at standard (9.4 T) and high (21.1 T) magnetic field strengths using the WURST‐QCPMG pulse sequence. The 35Cl electric field gradient (EFG) and chemical shielding (CS) tensor parameters were readily extracted from analytical simulations of the spectra; in particular, the quadrupolar parameters are shown to be very sensitive to structural differences, and can easily differentiate between chlorine atoms in bridging and terminal bonding environments. 35Cl NQR spectra were acquired for many of the complexes, which aided in resolving structurally similar, yet crystallographically distinct and magnetically inequivalent chlorine sites, and with the interpretation and assignment of 35Cl SSNMR spectra. 35Cl EFG tensors obtained from first‐principles DFT calculations are consistently in good agreement with experiment, highlighting the importance of using a combined approach of theoretical and experimental methods for structural characterization. Finally, a preliminary example of a 35Cl SSNMR spectrum of a transition‐metal species (TiCl4) diluted and supported on non‐porous silica is presented. The combination of 35Cl SSNMR and 35Cl NQR spectroscopy and DFT calculations is shown to be a promising and simple methodology for the characterization of all manner of chlorine‐containing transition‐metal complexes, in pure, impure bulk and supported forms. 相似文献
4.
Andrei V. Afonin Dmitry V. Pavlov Igor A. Ushakov Natalia A. Keiko 《Magnetic resonance in chemistry : MRC》2012,50(7):502-510
In the 13C NMR spectra of methylglyoxal bisdimethylhydrazone, the 13C‐5 signal is shifted to higher frequencies, while the 13C‐6 signal is shifted to lower frequencies on going from the EE to ZE isomer following the trend found previously. Surprisingly, the 1H‐6 chemical shift and 1J(C‐6,H‐6) coupling constant are noticeably larger in the ZE isomer than in the EE isomer, although the configuration around the –CH═N– bond does not change. This paradox can be rationalized by the C–H?N intramolecular hydrogen bond in the ZE isomer, which is found from the quantum‐chemical calculations including Bader's quantum theory of atoms in molecules analysis. This hydrogen bond results in the increase of δ(1H‐6) and 1J(C‐6,H‐6) parameters. The effect of the C–H?N hydrogen bond on the 1H shielding and one‐bond 13C–1H coupling complicates the configurational assignment of the considered compound because of these spectral parameters. The 1H, 13C and 15N chemical shifts of the 2‐ and 8‐(CH3)2N groups attached to the –C(CH3)═N– and –CH═N– moieties, respectively, reveal pronounced difference. The ab initio calculations show that the 8‐(CH3)2N group conjugate effectively with the π‐framework, and the 2‐(CH3)2N group twisted out from the plane of the backbone and loses conjugation. As a result, the degree of charge transfer from the N‐2– and N‐8– nitrogen lone pairs to the π‐framework varies, which affects the 1H, 13C and 15N shieldings. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
5.
HyperBIRD: A Sensitivity‐Enhanced Approach to Collecting Homonuclear‐Decoupled Proton NMR Spectra
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Dr. Kevin J. Donovan Prof. Lucio Frydman 《Angewandte Chemie (International ed. in English)》2015,54(2):594-598
Samples prepared following dissolution dynamic nuclear polarization (DNP) enable the detection of NMR spectra from low‐γ nuclei with outstanding sensitivity, yet have limited use for the enhancement of abundant species like 1H nuclei. Small‐ and intermediate‐sized molecules, however, show strong heteronuclear cross‐relaxation effects: spontaneous processes with an inherent isotopic selectivity, whereby only the 13C‐bonded protons receive a polarization enhancement. These effects are here combined with a recently developed method that delivers homonuclear‐decoupled 1H spectra in natural abundance samples based on heteronuclear couplings to these same, 13C‐bonded nuclei. This results in the HyperBIRD methodology; a single‐shot combination of these two effects that can simultaneously simplify and resolve complex, congested 1H NMR spectra with many overlapping spin multiplets, while achieving 50–100 times sensitivity enhancements over conventional thermal counterparts. 相似文献
6.
Natural Abundance 15N NMR by Dynamic Nuclear Polarization: Fast Analysis of Binding Sites of a Novel Amine‐Carboxyl‐Linked Immobilized Dirhodium Catalyst
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Torsten Gutmann Jiquan Liu Niels Rothermel Yeping Xu Eva Jaumann Mayke Werner Hergen Breitzke Snorri T. Sigurdsson Gerd Buntkowsky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(9):3798-3805
A novel heterogeneous dirhodium catalyst has been synthesized. This stable catalyst is constructed from dirhodium acetate dimer (Rh2(OAc)4) units, which are covalently linked to amine‐ and carboxyl‐bifunctionalized mesoporous silica (SBA‐15?NH2?COOH). It shows good efficiency in catalyzing the cyclopropanation reaction of styrene and ethyl diazoacetate (EDA) forming cis‐ and trans‐1‐ethoxycarbonyl‐2‐phenylcyclopropane. To characterize the structure of this catalyst and to confirm the successful immobilization, heteronuclear solid‐state NMR experiments have been performed. The high application potential of dynamic nuclear polarization (DNP) NMR for the analysis of binding sites in this novel catalyst is demonstrated. Signal‐enhanced 13C CP MAS and 15N CP MAS techniques have been employed to detect different carboxyl and amine binding sites in natural abundance on a fast time scale. The interpretation of the experimental chemical shift values for different binding sites has been corroborated by quantum chemical calculations on dirhodium model complexes. 相似文献
7.
《Magnetic resonance in chemistry : MRC》2002,40(5):353-360
The 15N NMR chemical shifts of N7‐ and N9‐substituted purine derivatives were investigated systematically at the natural abundance level of the 15N isotope. The NMR chemical shifts were determined and assigned using GSQMBC, GHMBC, GHMQC and GHSQC experiments in solution. 15N cross‐polarization magic angle spinning data were recorded for selected compounds in order to study the principal values of the 15N chemical shifts. Geometric parameters obtained by using RHF/6–31G** and single‐crystal x‐ray structural analysis were used to calculate the chemical‐shielding constants (GIAO and IGLO) which were then used to assign the nitrogen resonances observed in the solid‐state NMR spectra and to determine the orientation of the principal components of the shift tensors. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
8.
E. R. deAzevedo A. M. I. B. Ayrosa G. C. Faria H. J. Cervantes D. Huster T. J. Bonagamba R. N. M. Pitombo S. R. Rabbani 《Magnetic resonance in chemistry : MRC》2010,48(9):704-711
This article describes a solid‐state NMR (SSNMR) investigation of the influence of hydration and chemical cross‐linking on the molecular dynamics of the constituents of the bovine pericardium (BP) tissues and its relation to the mechanical properties of the tissue. Samples of natural phenetylamine‐diepoxide (DE)‐ and glutaraldehyde (GL)‐fixed BP were investigated by 13C cross‐polarization SSNMR to probe the dynamics of the collagen, and the results were correlated to the mechanical properties of the tissues, probed by dynamical mechanical analysis. For samples of natural BP, the NMR results show that the higher the hydration level the more pronounced the molecular dynamics of the collagen backbone and sidechains, decreasing the tissue's elastic modulus. In contrast, in DE‐ and GL‐treated samples, the collagen molecules are more rigid, and the hydration seems to be less effective in increasing the collagen molecular dynamics and reducing the mechanical strength of the samples. This is mostly attributed to the presence of cross‐links between the collagen plates, which renders the collagen mobility less dependent on the water absorption in chemically treated samples. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
9.
10.
《Magnetic resonance in chemistry : MRC》2002,40(3):219-224
An extensive study of both liquid‐ and solid‐state NMR spectroscopy was undertaken in order to elucidate the structural features of a phenyleneterephthalamide oligomer (OPTA) and of some related diarylamides. 1D‐ and 2D‐COSY measurements allowed us to assign completely the proton signals of the title compounds in solution, while 1D‐, 2D‐HETCOR and 2D‐COLOC measurements were used to assign 13C resonances. Solid‐state 13C NMR experiments, by conventional cross‐polarization (CP) at different contact times and with the dipolar dephased CP technique, were used to characterize these molecules in the solid state. Such techniques allowed us to differentiate among different carbon atoms; in the resulting spectra it was then possible to observe the selective appearance of signals from protonated and quaternary carbon atoms. It was also ascertained that the limited structural mobility of the insoluble OPTA, existing as a single monophasic species, can be explained in terms of hydrogen‐type bonds present in the solid state. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
11.
Wu‐Jang Huang Feng‐Chih Chang Peter Po‐Jen Chu 《Journal of Polymer Science.Polymer Physics》2000,38(19):2554-2563
In this article, we have applied solid‐state 13C NMR techniques, cross‐polarization/magic‐angle spinning (CP/MAS), and single‐pulse 13C NMR to characterize the NB conformation of the cyclo‐olefin copolymer. The copolymers containing higher NB contents produce more NB blocks according to 13C CP/MAS spectral analysis. In addition, NB‐dyad‐based conformations are able to induce peak splitting in the region of 49–52 ppm. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2554–2563, 2000 相似文献
12.
PSYCHE CPMG–HSQMBC: An NMR Spectroscopic Method for Precise and Simple Measurement of Long‐Range Heteronuclear Coupling Constants
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István Timári Prof. Dr. László Szilágyi Prof. Dr. Katalin E. Kövér 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):13939-13942
Among the NMR spectroscopic parameters, long‐range heteronuclear coupling constants convey invaluable information on torsion angles relevant to glycosidic linkages of carbohydrates. A broadband homonuclear decoupled PSYCHE CPMG–HSQMBC method for the precise and direct measurement of multiple‐bond heteronuclear couplings is presented. The PSYCHE scheme built into the pulse sequence efficiently eliminates unwanted proton–proton splittings from the heteronuclear multiplets so that the desired heteronuclear couplings can be determined simply by measuring frequency differences between peak maxima of pure antiphase doublets. Moreover, PSYCHE CPMG–HSQMBC can provide significant improvement in sensitivity as compared to an earlier Zangger–Sterk‐based method. Applications of the proposed pulse sequence are demonstrated for the extraction of nJ(1H,77Se) and nJ(1H,13C) values, respectively, in carbohydrates; further extensions can be envisioned in any J‐based structural and conformational studies. 相似文献
13.
Natural Abundance 15N and 13C Solid‐State NMR Chemical Shifts: High Sensitivity Probes of the Halogen Bond Geometry
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Paolo Cerreia Vioglio Luca Catalano Dr. Vera Vasylyeva Prof. Carlo Nervi Prof. Michele R. Chierotti Prof. Giuseppe Resnati Prof. Roberto Gobetto Prof. Pierangelo Metrangolo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16819-16828
Solid‐state nuclear magnetic resonance (SSNMR) spectroscopy is a versatile characterization technique that can provide a plethora of information complementary to single crystal X‐ray diffraction (SCXRD) analysis. Herein, we present an experimental and computational investigation of the relationship between the geometry of a halogen bond (XB) and the SSNMR chemical shifts of the non‐quadrupolar nuclei either directly involved in the interaction (15N) or covalently bonded to the halogen atom (13C). We have prepared two series of X‐bonded co‐crystals based upon two different dipyridyl modules, and several halobenzenes and diiodoalkanes, as XB‐donors. SCXRD structures of three novel co‐crystals between 1,2‐bis(4‐pyridyl)ethane, and 1,4‐diiodobenzene, 1,6‐diiodododecafluorohexane, and 1,8‐diiodohexadecafluorooctane were obtained. For the first time, the change in the 15N SSNMR chemical shifts upon XB formation is shown to experimentally correlate with the normalized distance parameter of the XB. The same overall trend is confirmed by density functional theory (DFT) calculations of the chemical shifts. 13C NQS experiments show a positive, linear correlation between the chemical shifts and the C?I elongation, which is an indirect probe of the strength of the XB. These correlations can be of general utility to estimate the strength of the XB occurring in diverse adducts by using affordable SSNMR analysis. 相似文献
14.
Kazuko Suzuki Charlotte Martineau Gerhard Fink Stefan Steuernagel Francis Taulelle 《Magnetic resonance in chemistry : MRC》2012,50(2):159-168
Cross polarization–magic angle spinning (CPMAS) is the most used experiment for solid‐state NMR measurements in the pharmaceutical industry, with the well‐known variant RAMP–CPMAS its dominant implementation. The experimental work presented in this contribution focuses on the entangled effects of the main parameters of such an experiment. The shape of the RAMP–CP pulse has been considered as well as the contact time duration, and a particular attention also has been devoted to the radio‐frequency (RF) field inhomogeneity. 13 C CPMAS NMR spectra have been recorded with a systematic variation of 13 C and 1H constant radiofrequency field pair values and represented as a Hartmann‐Hahn matching two‐dimensional map. Such a map yields a rational overview of the intricate optimal conditions necessary to achieve an efficient CP magnetization transfer. The map also highlights the effects of sweeping the RF by the RAMP–CP pulse on the number of Hartmann–Hahn matches crossed and how RF field inhomogeneity helps in increasing the CP efficiency by using a larger fraction of the sample. In the light of the results, strategies for optimal RAMP–CPMAS measurements are suggested, which lead to a much higher efficiency than constant amplitude CP experiment. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
15.
Dynamic Nuclear Polarization NMR Spectroscopy of Polymeric Carbon Nitride Photocatalysts: Insights into Structural Defects and Reactivity
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Dr. Xiaobo Li Dr. Ivan V. Sergeyev Dr. Fabien Aussenac Prof. Anthony F. Masters Prof. Thomas Maschmeyer Dr. James M. Hook 《Angewandte Chemie (International ed. in English)》2018,57(23):6848-6852
Metal‐free polymeric carbon nitrides (PCNs) are promising photocatalysts for solar hydrogen production, but their structure–photoactivity relationship remains elusive. Two PCNs were characterized by dynamic‐nuclear‐polarization‐enhanced solid‐state NMR spectroscopy, which circumvented the need for specific labeling with either 13C‐ or 15N‐enriched precursors. Rapid 1D and 2D data acquisition was possible, providing insights into the structural contrasts between the PCNs. Compared to PCN_B with lower performance, PCN_P is a more porous and more active photocatalyst that is richer in terminal N?H bonds not associated with interpolymer chains. It is proposed that terminal N?H groups act as efficient carrier traps and reaction sites. 相似文献
16.
《Magnetic resonance in chemistry : MRC》2003,41(6):466-474
This paper presents the high‐resolution 13C and 15N cross‐polarization magic angle spinning (CP/MAS) NMR spectra of three natural melanin solids: Sepia officinalis melanin, Sepia officinalis melanin free acid (MFA) and Human hair melanin. The functional group characterization of Human hair melanin by NMR is the first to date and the 13C CP/MAS NMR spectra reported here show improved resolution of chemically inequivalent sites. The observed spectral regions of the solid melanin samples can be assigned to the postulated structural unit of the polymer chain of Sepia MFA derived from solution‐state NMR studies. To assist in the assignment of functional groups in the spectra, the solid‐state CP/MAS NMR spectra are compared with high‐resolution 13C and 15N CP/MAS spectra of four model compounds, L ‐dopa, dopamine, 2‐methoxycarbonyl‐3‐ethoxycarbonyl‐4‐methylpyrrole and ethyl 5,6‐dimethoxyindole‐2‐carboxylate. To aid further in the assignment of protonated and non‐protonated carbon atoms, CP contact time dependence and non‐quaternary carbon suppression (NQS) experiments were performed on the melanin samples. The 15N CP/MAS spectra of the melanin samples confirm the presence of indole and pyrrole units in the melanin polymer chain. The NMR peaks observed in all of the melanin samples are relatively broad, presumably owing to the presence of free radicals. Electron spin resonance (ESR) data shows that all three melanin samples contain localized free radicals (g = 2.007), with the Sepia melanin containing a 10‐fold higher free radical density than Human hair melanin. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
17.
Molecular Level Characterization of the Structure and Interactions in Peptide‐Functionalized Metal–Organic Frameworks
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Dr. Tanya K. Todorova Dr. Xavier Rozanska Dr. Christel Gervais Dr. Alexandre Legrand Dr. Linh N. Ho Pierrick Berruyer Dr. Anne Lesage Prof. Lyndon Emsley Dr. David Farrusseng Dr. Jérôme Canivet Dr. Caroline Mellot‐Draznieks 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(46):16531-16538
We use density functional theory, newly parameterized molecular dynamics simulations, and last generation 15N dynamic nuclear polarization surface enhanced solid‐state NMR spectroscopy (DNP SENS) to understand graft–host interactions and effects imposed by the metal–organic framework (MOF) host on peptide conformations in a peptide‐functionalized MOF. Focusing on two grafts typified by MIL‐68‐proline ( ‐Pro ) and MIL‐68‐glycine‐proline ( ‐Gly‐Pro ), we identified the most likely peptide conformations adopted in the functionalized hybrid frameworks. We found that hydrogen bond interactions between the graft and the surface hydroxyl groups of the MOF are essential in determining the peptides conformation(s). DNP SENS methodology shows unprecedented signal enhancements when applied to these peptide‐functionalized MOFs. The calculated chemical shifts of selected MIL‐68‐NH‐ Pro and MIL‐68‐NH‐ Gly‐Pro conformations are in a good agreement with the experimentally obtained 15N NMR signals. The study shows that the conformations of peptides when grafted in a MOF host are unlikely to be freely distributed, and conformational selection is directed by strong host–guest interactions. 相似文献
18.
Middleton DA 《Magnetic resonance in chemistry : MRC》2011,49(2):65-69
Solid‐state nuclear magnetic resonance (SSNMR) is a powerful technique for the structural analysis of amyloid fibrils. With suitable isotope labelling patterns, SSNMR can provide constraints on the secondary structure, alignment and registration of β‐strands within amyloid fibrils and identify the tertiary and quaternary contacts defining the packing of the β‐sheet layers. Detection of 14N? 13C dipolar couplings may provide potentially useful additional structural constraints on β‐sheet packing within amyloid fibrils but has not until now been exploited for this purpose. Here a frequency‐selective, transfer of population in double resonance SSNMR experiment is used to detect a weak 14N? 13C dipolar coupling in amyloid‐like fibrils of the peptide H2N‐SNNFGAILSS‐COOH, which was uniformly 13C and 15N labelled across the four C‐terminal amino acids. The 14N? 13C interatomic distance between leucine and asparagine side groups is constrained between 2.4 and 3.8 Å, which allows current structural models of the β‐spine arrangement within the fibrils to be refined. This procedure could be useful for the general structural analysis of other proteins in condensed phases and environments, such as biological membranes. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
19.
Dissolution dynamic nuclear polarization (DNP) enables high‐sensitivity solution‐phase NMR experiments on long‐lived nuclear spin species such as 15N and 13C. This report explores certain features arising in solution‐state 1H NMR upon polarizing low‐γ nuclear species. Following solid‐state hyperpolarization of both 13C and 1H, solution‐phase 1H NMR experiments on dissolved samples revealed transient effects, whereby peaks arising from protons bonded to the naturally occurring 13C nuclei appeared larger than the typically dominant 12C‐bonded 1H resonances. This enhancement of the satellite peaks was examined in detail with respect to a variety of mechanisms that could potentially explain this observation. Both two‐ and three‐spin phenomena active in the solid state could lead to this kind of effect; still, experimental observations revealed that the enhancement originates from 13C→1H polarization‐transfer processes active in the liquid state. Kinetic equations based on modified heteronuclear cross‐relaxation models were examined, and found to well describe the distinct patterns of growth and decay shown by the 13C‐bound 1H NMR satellite resonances. The dynamics of these novel cross‐relaxation phenomena were determined, and their potential usefulness as tools for investigating hyperpolarized ensembles and for obtaining enhanced‐sensitivity 1H NMR traces was explored. 相似文献
20.
The temperature dependences of the chemical shifts and intensities of 1H, 13C, and 14N nuclei in tetramethylammonium tetrabromozincate, [N(CH3)4]2ZnBr4, were investigated using single-crystal nuclear magnetic resonance (NMR) and magic angle spinning (MAS) NMR spectroscopy to elucidate the structural geometry near the phase transition temperature. Based on the analysis of the 13C cross-polarization (CP)/MAS NMR and 14N NMR spectra, the two chemically inequivalent N(1) (CH3)4 and N(2) (CH3)4 ions were distinguished. Furthermore, the 14N NMR spectrum at the phase transition temperature indicated the existence of the ferroelastic characteristics of the N(CH3)4 ions. 相似文献