Nuclear magnetic resonance studies

NMR studies have also been carried out on active cyclohexyl analogs of taxol (779), on the taxol analogs 2 -deoxytaxol and 2 -methoxytaxol, which were shown to adopt conformations similar to those of taxol (486), and on D-secotaxol analogs (208) as noted earlier in section 5.4. 

REDOR technique on the quadmply labeled analog 15.3.2 (489), and these results coupled with fluorescence data led to the proposal of stmcture 15.3.3 as the most probable conformation of taxol on tubulin. 

Nuclear Magnetic Resonance Studies.— The relationship between B n.m.r. chemical shifts in compounds of the general type R3B and n.m.r. chemical shifts for the corresponding cationic centre in the ions RaC is not so simple as had been previously reported. Nevertheless, the comparative data are useful. n.m.r. chemical shifts have been quoted as evidence for the hyper-conjugative interaction of allylic borates, which may therefore be represented as shown in structure (40), or more generally as shown in (41).  

Wisian-Nielson and D. R. Martin, J. Inorg. Nucl, Chem., 1979, 41, 1545. 

A combination of and n.m.r. data allows the investigation of complex formation between 9-BBN and its derivatives with amines. Four types of behaviour can be identified (a) the formation of stable complexes with no observable exchange of amine (b) the formation of stable complexes, but with rapid exchange of amine with free amine (c) the formation of partially dissociated complexes, accompanied by rapid exchange and (d) a lack of interaction between the borane and the amine. There is a regular progression from (a) to (d) with increasing steric requirements of the system. 

studies indicate that diphenylguanidine [(PhNH)2C=NH] co-ordinates to triarylboranes through the imine nitrogen atom. Several B-O 

Proton and n.m.r. studies suggest major differences between the abilities of lithium (weak) and potassium (strong) enolates to complex to tri-alkylboranes.  

The diffusion constant of the surface water obtained from such studies was found to be lower than that of the bulk value by a factor of 5. Nevertheless, it remains orders of magnitude faster than motions in a rigid ice lattice, even in samples hydrated to levels well below what is generally thought to be the full hydration level of the protein. 

Nuclear Overhauser effect (NOE) is another techiuque used to study the dynamics of water near a heterogeneous surface. NOE intensities are modulated by dipole-dipole interactions between protons of protein and water in the hydration layer. This interaction varies as where R is the separation between the two protons. Measurements of magnetization transfer using NOE have been used to obtain the residence time of the hydration water. The residence time of water molecules in the hydration layer immediate to the protein is not easily available by other techniques and is valuable information in quantifying the rigidity of the layer. 

NOE studies predict long residence times, of the order of 300-500 ps, for water molecules in the hydration layer. Such long residence times can be appropriate only for water molecules strongly bound to the cavity of a protein. In fact, these initial estimates from NOE have not been properly explained even today. It was pointed out recently by Halle that all earlier NOE measurements derived significant contributions from distant water molecules as well, because the number of contributing water molecules increases as and the characteristic time for orientational modulation of the intemuclear vector also increases as 1. Thus, earlier estimates from NOE might not be reliable for the residence time of the water molecules. 

More recent nuclear magnetic relaxation dispersion (NMRD) studies involving water oxygen-17 find a much shorter residence time, in the range 10-50 ps [7]. These results are in better agreement with recent studies that seemed to rule out the existence of slower dynamics. 

However, it is important to note that the MRD experiments do not measure an explicit time correlation function that could characterize water dynamics occurring at different timescales. Thus it extracts only the average relaxation time of the system. It is interesting to note how these recent developments (particularly results from the NMRD technique and computer simulations) have changed our perception about the dynamics of the hydration layer, from a rigid ice-like layer to a dynamically mobile, somewhat slower than bulk but still active region. 

Although NMR is a powerful tool for studying solvation, it suffers the same limitation outlined above for ESR spectroscopy, namely, that systems are almost always in fast exchange. In our experience, the only way to reach unambiguous interpretations of NMR shift data is to link the results with infrared studies, when possible. (Shifts are by far the most widely studied parameters coupling constants are generally relatively insensitive to solvent changes.) 

As usual, one can study changes in the shifts for selected nuclei in solutes, neutral or ionic, or one can study solvent shifts, generally the sensitive H resonances of protic solvents. 

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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... 

Shulman, R. G., and Rothman, D. L., 1996. Nuclear magnetic resonance studies of muscle and applications to exercise and diabetes. Diabetes 45 S93-S98. 

The 9ai7-quinolizine structure (82) for the labile adduct from 3,5-dimethylpyridine was clearly established by the nuclear magnetic resonance studies of Richards and Higham, and subsequent work showed the labile adduct from 3-methylpyridine was analogous. As the labile adducts from all the pyridines and benzopyridines so far examined have very similar infrared absorption spectra in the 5-7 yn. (carbonyl and aromatic) region and within quite close limits very similar ultraviolet absorption spectra, it can be concluded that all are derivatives of 9aH-quinolizine,... 

Glasel, J. A. Nuclear Magnetic Resonance Studies on Water and Ice, in Water — a Comprehensive Treatise, Vol. 1, chapter 6, New York, Plenum Press 1972... 

Hydronium ion, HjO+, is a structural unit in solid perchloric acid hydrate, HCKVHjO, as shown by nuclear magnetic resonance studies. 

Wachtell (Ref 23) worked on the application of this principle. However, early in his work a major problem was encountered in finding the quadrupole resonance of the chlorine nucleus which did not exist in the frequency range in which it had been expected (20—40 megacycles). Nuclear Magnetic Resonance studies finally have shown that this quadrupole resonance should exist around 150 kilocycles. Future studies of single crystals of AP should reveal the presence and the exact location of this resonance. If this can be done, then the analysis of particle size, based on the shift of the quadrupole resonance frequency, may be possible... 

Lazo ND, Meine JG, Downing DT (1995) Lipids are covalently attached to rigid corneocyte protein envelope existing predominantly as beta-sheets a solid state nuclear magnetic resonance study. J Invest Dermatol 105 296-300... 

Flohr S, Kurz M, Kostenis E, Brkovich A, Fournier A, Klabunde T. Identification of nonpeptidic urotensin II receptor antagonists by virtual screening based on a pharmacophore model derived from structure-activity relationships and nuclear magnetic resonance studies on urotensin II. J Med Ghent 2002 45 1799-805. 

Molecular orbital calculations" and nuclear magnetic resonance studies " revealed that C-2 in indole and related compounds," the phenyl... 

Gakh, E.G., Dougall, D.K., and Baker, D.C., Proton nuclear magnetic resonance studies of monoacylated anthocyanins from the wild carrot part 1. Inter- and intramolecular interactions in solution, Phytochem. Anal., 9, 28, 1998. 

Lohmeier-Vogel EM, KT Leung, H Lee, JT Trevors HJ Vogel (2001) Phosphorus-31 nuclear magnetic resonance study of the effect of pentachlorophenol on the physiologies of PCP-degrading microorganisms. Appl Environ Microbiol 67 3549-3556. 

Halpin RA, GD Hegeman, GL Kenyon (1981) Carbon-13 nuclear magnetic resonance studies of mandelate metabolism in whole bacterial cells and in isolated, in vivo cross-linked enzyme complexes. Biochemistry 20 1525-1533. 

Steiert JG, WJ Thoma, K Ugurbil, RL Crawford (1988) P nuclear magnetic resonance studies of effects of some chlorophenols on Escherichia coli and apentachlorophenol-degrading bacterium. J Bacterial 170 4954-4957. 

Strohhacker J, AA de Graaf, SM Schoberth, RM Wittig, H Sahm (1993) P nuclear magnetic resonance studies of ethanol inhibition in Zymomonas mobilis. Arch Microbiol 159 484 90. 

Connick, R. E. Poulsen, R. E. (1957). Nuclear magnetic resonance studies of aluminium fluoride complexes. Journal of the American Chemical Society, 79, 5153-7. 

Vaughan, L.G. and Sheppard, W.A. (1969) New organogold chemistry. I. Synthesis and fluorine-19 nuclear magnetic resonance studies of some fluoroorganogold compounds. Journal of the American Chemical Society, 91(22), 6151-6156. 

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. 

Malik, N.A., Otiko, G. and Sadler, P.J. (1980) Control of intra- and extra-cellular sulfhydryl-disulfide balances with gold phosphine drugs Phosphorus-31 nuclear magnetic resonance studies of human blood. Journal of Inorganic Biochemistry, 12, 317-322. 

C. A. Fyfe, M. Cocivera, S. W. H. Damji 1975, (High resolution nuclear magnetic resonance studies of chemical reactions using flowing liquids. Investigation of the kinetic and thermodynamic intermediates formed by the attack of meth-oxide ion on l-X-3,5-dinitrobenzenes), J. Am. Chem. Soc. 97, 5707. 

J. J. Grimaldi, B. D. Sykes 1975, (Con-canavalin A a stopped flow nuclear magnetic resonance study of conformational changes induced by Mn++, Ca++, and alpha-methyl-D-mannoside),/. Biol. Chem. 250, 1618. 

J. Jonas 2002, (High-resolution nuclear magnetic resonance studies of proteins), Biochim. Biophys. Acta 1595, 145. 

Owens C, Karyannis NM, Pytlewski LL, et al. 1971. Infrared and proton nuclear magnetic resonance studies of adduct of tin(II) and (IV) and titanium(IV) halides with diisopropyl methylphosphonate. Journal of Physical Chemistry 75(5) 637-641. 

Thakkar, A.L., Self association of caffeine in aqueous solution IH nuclear magnetic resonance study, J. Chem. Soc. Chem. Commun., 9,524,1970. 

Carrington CD, Burt CT, Abou-Donia MB. 1988. In vivo 3 IP nuclear magnetic resonance studies on the absorption triphenyl phosphate and tri-ort/zo-cresyl phosphate following subcutaneous administration in hens. Drug Metab Distrib 104-109. 

Kelusky, E. C. Smith, I. C. R, Anethetic-membrane interaction A 2H nuclear magnetic resonance study of the binding of specifically deuterated tetracaine and procaine to phosphatidylcholine, Can. J. Biochem. Cell Biol. 62, 178-184 (1984). 

Nuclear magnetic resonance studies on spin labeled derivatives are not extremely useful due to the paramagnetism of the molecule. However, the NMR spectrum of spin labeled methylcobinamide confirms that the nitroxyl function is coordinated to the cobalt. It is possible in this compound to obtain good resolution of the methyl group resonance. 

C. Evidence from Nuclear Magnetic Resonance Studies. 178... 

Although relaxation measurements have been widely used in nuclear magnetic resonance studies of solid catalysts and adsorbed molecules, they have not found such favor in similar ESR work. Relaxation phenomena, however, do play a very important role in any magnetic resonance experiment, whether or not this aspect of the problem is studied. In fact, the temperature at which most ESR experiments are conducted is dictated by the relaxation process. Furthermore, even qualitative data on relaxation times can be used as supporting evidence in the identification of a paramagnetic species. 

Letellier M., Chevallier F., Clinard C., Frackowiak E., Rouzaud J.N., Beguin F. The first in situ 7Li nuclear magnetic resonance study of lithium insertion in hard-carbon anode materials for Li-ion batteries, J. Chem. Phys. 2003 118 6038-45... 

J. Karliner and C. Djerassi, Terpenoids. LVII. Mass spectral and nuclear magnetic resonance studies of pentacyclic triterpene hydrocarbons, J. Org. Chem., 31, 1945 1956 (1966). 

There are several systematic nuclear magnetic resonance studies of the interaction between the substituents and the protons and ring atoms of five-membered heterocycles. In some 2-substituted furans, thiophenes, selenophenes, and tellurophenes there is a linear correlation between the electronegativity of the chalcogen and several of the NMR parameters.28 As there also is a good correlation between the shifts of the corresponding protons and carbons in the four heterocycles, the shifts of unknown selenophene and tellurophene derivatives can be predicted when those of thiophene are known. This is of special interest for the tellurophene derivatives, since they are difficult to synthesize. In the selenophene series, where a representative set of substituents can be introduced in the 2- as well as in the 3-position, the correlation between the H and 13C shifts and the reactivity parameters according to Swain and Lupton s two-parameter equation... 

T. Yoshida, H. Okabayashi, K. Takahashi, and I.Ueda, A proton nuclear magnetic resonance study on the release of bound water by inhalation anesthetic in water-in-oil emulsion. Biochim. Biophys. Acta, 772,102-107 (1984). 

Yeagle PL (1982) 31P nuclear magnetic resonance studies of the phospholipid-protein interface in cell membranes. Biophys J 37 227-239... 

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