Nuclear magnetic resonance chemical exchange

Woessner D E 1996 Relaxation effects of chemical exchange Encyclopedia of Nuclear Magnetic Resonance ed D M Grant and R K Harris (Chichester Wiley) pp 4018-28... 

Reeves L W and Shaw K N 1970 Nuclear magnetic resonance studies of multi-site chemical exchange. I. Matrix formulation of the Bloch equations Can. J. Chem. 48 3641-53... 

Physical Chemical Characterization. Thiamine, its derivatives, and its degradation products have been fully characterized by spectroscopic methods (9,10). The ultraviolet spectmm of thiamine shows pH-dependent maxima (11). H, and nuclear magnetic resonance spectra show protonation occurs at the 1-nitrogen, and not the 4-amino position (12—14). The H spectmm in D2O shows no resonance for the thiazole 2-hydrogen, as this is acidic and readily exchanged via formation of the thiazole yUd (13) an important intermediate in the biochemical functions of thiamine. Recent work has revised the piC values for the two ionization reactions to 4.8 and 18 respectively (9,10,15). The mass spectmm of thiamine hydrochloride shows no molecular ion under standard electron impact ionization conditions, but fast atom bombardment and chemical ionization allow observation of both an intense peak for the patent cation and its major fragmentation ion, the pyrimidinylmethyl cation (16). 

Isab, A.A. and Sadler, P.J. (1982) A carbon-13 nuclear magnetic resonance study of thiol exchange reactions of gold(l) thiomalate ( Myocrisin ) including applications to cysteine derivatives. Journal of the Chemical Society, Dalton Transactions, (1), 135—141. 

Nuclear magnetic resonance (NMR) experiments are used to study the exchange kinetics of chemical systems in equilibrium.28,68,69 As is the case for fluorescence correlation spectroscopy no perturbation of the chemical system in equilibrium is required to obtain kinetic information from NMR experiments. However, NMR is not very sensitive to concentration changes. 

The same nucleus (say methyl protons) in different chemical environments A and B will generally have nuclear magnetic resonances at different frequencies. If the exchange of pro-... 

J.I. Kaplan and G. Fraenkel, NMR of Chemically Exchanging Systems (Academic Press, New York, 1980). L.M. Jackman and F.A. Cotton, Dynamic Nuclear Magnetic Resonance Spectroscopy (Academic Press, New York, 1975). 

Human bile sample (500 pi) is placed into a 5-mm nuclear magnetic resonance (NMR) tube. The pH of the solution is adjusted at 6 0.5 using HC1. This range of pH is the optimal value to avoid lowering of the amide integral due to the chemical exchange (alkaline pH) or to precipitation of bile salts (acidic pH). 

Aksnes, D.W., Hutchison, S.M. and Packer, K.J. (1968) Nuclear spin relaxation and chemical exchange effects in the 19F nuclear magnetic resonance spectrum of the hexafluoroniobate ion. Mol. Phys., 14, 301-309. 

Lastly, molecular motion affects solid-state spectra just as chemical exchange does in solution (Chapter 10 and Section 14.2). Nuclear magnetic resonance provided the proof that benzene molecules, structure 15-2, rotate in place about their sixfold axes (Example 4.3) in the crystal above 90 K (Kelvins absolute temperature 0°C = 273 K) ... 

Various physical techniques, i.e., nuclear magnetic resonance (NMR), x-ray diffraction, and chemical probes (exchange of H by D), indicate that there is a layer of water bound to protein molecules, phospholipid bilayers, and nucleic acids, as well as at the surface of the cell membranes and other organelles. 

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