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Quadrupolar Couplings (quadrupolar + coupling)
Selected AbstractsThe interaction of water molecules with purple membrane suspension using 2H double-quantum filter, 1H and 2H diffusion nuclear magnetic resonanceBIOPOLYMERS, Issue 1 2004Limor Frish Abstract Bacteriorhodopsin is a membrane protein of the purple membrane (PM) of Halobacterium salinarum, which is isolated as sheets of highly organized two-dimensional hexagonal microcrystals and for which water molecules play a crucial role that affects its function as a proton pump. In this paper we used single- and double-quantum 2H NMR as well as 1H and 2H diffusion NMR to characterize the interaction of water molecules with the PM in D2O suspensions. We found that, under the influence of a strong magnetic field on a concentrated PM sample (0.61 mM), the PM sheets affect the entire water population and a residual quadrupolar splitting (,q ,5.5 Hz, 298 K, at 11.7 T) is observed for the D2O molecules. We found that the residual quadrupolar coupling, the creation time in which a maximal DQF signal was obtained (,max), and the relative intensity of the 2H DQF spectrum of the water molecules in the PM samples (referred to herein as NMR order parameters) are very sensitive to temperature, dilution, and chemical modifications of the PM. In concentrated PM samples in D2O, these NMR parameters seem to reflect the relative organization of the PM. Interestingly, we have observed that some of these parameters are sensitive to the efficiency of the trimer packing, as concluded from the apo-membrane behavior. The data for dionized blue membrane, partially delipidated sample, and detergent-treated PM show that these D2O NMR order parameters, which are magnetic field dependent, are sensitive to the structural integrity of the PM. In addition, we revealed that heating the PM sample inside or outside the NMR magnet has, after cooling, a different effect on the NMR characteristics of the water molecules in the concentrated PM suspensions. The difference in the D2O NMR order parameters for the PM samples, which were heated and cooled in the presence and in the absence of a strong magnetic field, corroborates the conclusions that the above D2O order parameters are indirect reflections of both microscopic and macroscopic order of the PM samples. In addition, 1H NMR diffusion measurements showed that at least three distinct water populations could be identified, based on their diffusion coefficients. These water populations seem to correlate with different water populations previously reported for the PM system. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004 [source] Probing the Local Structure of Pure Ionic Liquid Salts with Solid- and Liquid-State NMR,CHEMPHYSCHEM, Issue 1 2010Peter G. Gordon Abstract Room-temperature ionic liquids (RTILs) are gaining increasing interest and are considered part of the green chemistry paradigm due to their negligible vapour pressure and ease of recycling. Evidence of liquid-state order, observed by IR and Raman spectroscopy, diffraction studies, and simulated by ab initio methods, has been reported in the literature. Here, quadrupolar nuclei are used as NMR probes to extract information about the solid and possible residual order in the liquid state of RTILs. To this end, the anisotropic nature and field dependence of quadrupolar and chemical shift interactions are exploited. Relaxation time measurements and a search for residual second-order quadrupolar coupling were employed to investigate the molecular motions present in the liquid state and infer what kind of order is present. The results obtained indicate that on a timescale of ,10,8 sec or longer, RTILs behave as isotropic liquids without residual order. [source] Motional smearing of electrically recovered couplings measured from multipulse transientsCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2001Scott A. Riley Abstract The measurement of residual dipolar and quadrupolar coupling constants in the liquid phase by using an electric field to destroy the isotropic nature of molecular tumbling is complicated by charge-induced turbulent motion. In many cases this motion is due to charge injection at electrode surfaces, an effect that leads to an apparent removal of electrically recovered anisotropic spectral splittings when measured from a spin-echo envelope modulation produced by a train of radio frequency (rf) pulses. To understand this averaging, the effect of quadrupolar couplings and enhanced molecular diffusion on free-induction, spin-echo, and Carr,Purcell signals is analytically determined in the special case of homogeneous rf pulses. Additional signal damping due to rf inhomogeneity and coupling constant heterogeneity is determined by numerically extending the kernel formalism introduced by Herzog and Hahn to understand spin diffusion in solids. Finally, the merit of the numerical approach is tested by comparison with analytical results for homogeneous rf pulses and experimental results for perdeuterated nitrobenzene involving inhomogeneous rf pulses and coupling heterogeneity. © 2001 John Wiley & Sons, Inc. Concepts Magn Reson 13: 171,189, 2001 [source] An ENDOR study of oxomolybdenum(V) tris(pyrazolyl)borate complexes; identification of couplings to boron and other heteroatomsMAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2002Robert D. Farley Abstract 11B hyperfine and quadrupolar couplings have been observed by the electron magnetic resonance techniques electron nuclear double resonance and hyperfine sublevel correlation spectroscopy for some tris(pyrazolyl)borato-oxomolybdenum(V) and related nitrosyl complexes including a dinuclear B,B linked complex. The spectra are interpreted according to the electron delocalization onto the ligands, especially the pyrazolylborate. Copyright © 2002 John Wiley & Sons, Ltd. [source] The application of 23Na double-quantum-filter (DQF) NMR spectroscopy for the study of spinal disc degenerationMAGNETIC RESONANCE IN MEDICINE, Issue 2 2008Kristopher J. Ooms Abstract Degenerative disc disease is an irreversible process that leads to a loss of mechanical integrity and back pain in millions of people. In this report, 23Na double-quantum-filtered (DQF) NMR spectroscopy is used to study disc tissues in two stages of degeneration. Initial results indicate that the 23Na DQF signal may be useful for determining the degree of degeneration. The spectral analysis reveals the presence of sodium environments with different residual quadrupolar couplings and T2 relaxation times that we attribute to different regions, or compartments, corresponding to different biochemical regions in the tissue. In general it is found that there are compartments with no residual quadrupolar couplings, compartments with moderate couplings (200 to 1000 Hz), and compartments with couplings ranging from 1500 to 3000 Hz. The results indicate that 23Na DQF NMR spectroscopy provides a probe of the degenerative state of the intervertebral disc tissues, and might hold potential as a novel diagnostic method for detection of disc degeneration. Magn Reson Med 60:246,252, 2008. © 2008 Wiley-Liss, Inc. [source] An EPR and ENDOR Investigation of a Series of Diazabutadiene,Group 13 ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2005Robert J. Baker Dr. Abstract Paramagnetic diazabutadienegallium(II or III) complexes, [(Ar-DAB)2Ga] and [{(Ar-DAB.)GaX}2] (X=Br or I; Ar-DAB={N(Ar)C(H)}2, Ar=2,6-diisopropylphenyl), have been prepared by reactions of an anionic gallium N-heterocyclic carbene analogue, [K(tmeda)][:Ga(Ar-DAB)], with either "GaI" or [MoBr2(CO)2(PPh3)2]. A related InIII complex, [(Ar-DAB.)InCl2(thf)], has also been prepared. These compounds were characterised by X-ray crystallography and EPR/ENDOR spectroscopy. The EPR spectra of all metal(III) complexes incorporating the Ar-DAB ligand, [(Ar-DAB.)MX2(thf)n] (M=Al, Ga or In; X=Cl or I; n=0 or 1) and [(Ar-DAB)2Ga], confirmed that the unpaired spin density is primarily ligand centred, with weak hyperfine couplings to Al (a=2.85 G), Ga (a=17,25 G) or In (a=26.1 G) nuclei. Changing the N substituents of the diazabutadiene ligand to tert -butyl groups in the gallium complex, [(tBu-DAB.)GaI2] (tBu-DAB={N(tBu)C(H)}2), changes the unpaired electron spin distribution producing 1H and 14N couplings of 1.4 G and 8.62 G, while the aryl-substituted complex, [(Ar-DAB.)GaI2], produces couplings of about 5.0 G. These variations were also manifested in the gallium couplings, namely aGa ,1.4 G for [(tBu-DAB.)GaI2] and aGa ,25 G for [(Ar-DAB.)GaI2]. The EPR spectra of the gallium(II) and indium(II) diradical complexes, [{(Ar-DAB.)GaBr}2], [{(Ar-DAB.)GaI}2], [{(tBu-DAB.)GaI}2] and [{(Ar-DAB.)InCl}2], revealed doublet ground states, indicating that the GaGa and InIn bonds prevent dipole,dipole coupling of the two unpaired electrons. The EPR spectrum of the previously reported complex, [(Ar-BIAN.)GaI2] (Ar-BIAN=bis(2,6-diisopropylphenylimino)acenaphthene) is also described. The hyperfine tensors for the imine protons, and the aryl and tert -butyl protons were obtained by ENDOR spectroscopy. In [(Ar-DAB.)GaI2], gallium hyperfine and quadrupolar couplings were detected for the first time. [source] | |||||||||||||