Nuclear magnetic resonance hydration

The following data were obtained during a kinetic study of the hydration of p-methoxyphenylacetylene by measuring the relative amounts of reactants and products by nuclear magnetic resonance (NMR). ... 

Nuclear magnetic resonance spectra of all four parent compounds have been measured and analyzed.The powerful potentialities of NMR as a tool in the study of covalent hydration, tautomerism, or protonation have, however, as yet received no consideration for the pyridopyrimidines. NMR spectra have been used to distinguish between pyrido[3,2-d]pyrimidines. and isomeric N-bridgehead compounds such as pyrimido[l,2- ]pyrimidines and in several other structural assignments (cf. 74 and 75). 

For a discussion of the use of polarography and nuclear magnetic resonance spectroscopy to detect covalent hydration, see the following... 

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

A review is given of the application of Molecular Dynamics (MD) computer simulation to complex molecular systems. Three topics are treated in particular the computation of free energy from simulations, applied to the prediction of the binding constant of an inhibitor to the enzyme dihydrofolate reductase the use of MD simulations in structural refinements based on two-dimensional high-resolution nuclear magnetic resonance data, applied to the lac repressor headpiece the simulation of a hydrated lipid bilayer in atomic detail. The latter shows a rather diffuse structure of the hydrophilic head group layer with considerable local compensation of charge density. 

These special features are explained by an interaction between the proton and one of the water molecules, which is not merely electrostatic but also covalent. This yields a new chemical species, the hydroxonium ion, HjO. The existence of such ions was demonstrated in the gas phase by mass spectrometry and in the solid phase by X-ray diffraction and nuclear magnetic resonance. The H -H20 bond has an energy of 712kJ/mol, which is almost two-thirds of the total proton hydration energy. 

F. Volke, A. Pampel 1995, (Membrane hydration and structure on a subnanometer scale as seen by high resolution solid state nuclear magnetic resonance POPC and P0PC/C12E04 model membranes), Biophys.J. 68, 1960-1965. 

Duce, S.L. and Hall, L.D. 1995. Visualisation of the hydration of food by nuclear magnetic resonance imaging. J. Food Engin. 26, 251-257. 

Nuclear magnetic resonance spectroscopy is often used to quantify the ratio of API and counter-ion in a pharmaceutical salt, together with the type and quantity of hydrate or solvate molecules. 

For suitable substances the average life-time of the hydrated or unhydrated species can be deduced from the broadening of nuclear magnetic resonance lines. This has recently been applied to acetaldehyde (Evans et al., 1965 Ahrens and Strehlow, 1965) and to isobuty-raldehyde (Hine and Houston, 1965) the velocities deduced for catalysis by hydrogen ions are in fair agreement with those obtained by other methods. 

Z. Zhou, B. G. Sayer, D. W. Hughes, R. E. Stark and R. M. Epand, Studies of phospholipid hydration by high-resolution magic-angle spinning nuclear magnetic resonance,... 

Mora-Gutierrez, A., Kumosinski, T.F., Farrell, Jr., H.M. (1997). Oxygen-17 nuclear magnetic resonance studies of bovine and caprine casein hydration and activity in deuterated sugar solutions. Journal of Agricultural and Food Chemistry, 45, 4545-4553. 

Male Fischer 344 rats were exposed by inhalation to 1% 2-chloro-1,1,1 -trifluoroethane for 2 h and then urine was collected for 24 h. Urinary metabolites identified by 19F nuclear magnetic resonance and gas chromatography/mass spectrometry were 2,2,2-trifluoroethyl glucuronide (16%), trifluoroacetic acid (14%), trifluoroacetaldehyde hydrate (26%), trifluoroacetaldehyde-urea adduct (40%) and inorganic fluoride (3%). A minor, unidentified metabolite was also detected. No covalent binding of fluorine-containing metabolites was observed in the liver and kidney from the exposed rats (Yin et al., 1995). In-vitro incubation of 2-chloro-1,1,1-trifluoroethane with rat liver microsomes and an NADPH-generating system has been shown to involve a dechlorination reaction (Salmon et al., 1981) that produced trifluoroacetaldehyde hydrate as the only metabolite (Yin et al., 1995). 

Belton, P.S. (2000) Nuclear magnetic resonance studies of the hydration of proteins and DNA. Cell. Mol. Life Sci. 57, 993-998. 

Nuclear magnetic resonance studies of methane hydrate dissociation suggest that intrinsic kinetics is not likely to play a dominant role in the dissociation process (Gupta et al., 2006). Methane hydrate dissociation was shown to progress in the absence of an intermediate state (or activated state), with no preferential decay of large to small cavities. Similar measurements have been performed for Xe hydrate dissociation (Moudrakovski et al., 2001b). 

Nuclear magnetic resonance logging presents a new and efficient means of hydrate detection. Dallimore and Collett (2005, p. 21) summarize theNMR method as follows ... 

Having introduced the correlation of Fig. 1, we may return to the stabilities of alkyl cations. Rate constants for the hydration of secondary and primary alkenes have been measured in concentrated solutions of aqueous sulfuric acid by Lucchini and Modena97 and by Tidwell and Kresge42 using proton nuclear magnetic resonance (NMR) or UV to monitor progress of the reactions. It is conceivable that the reactions involve a concerted addition of a proton and water molecule to the alkenyl double bonds. However, the very weak basicity of water under the conditions of reaction makes this unlikely, and the steep acidity dependences of the reactions (e.g., m =-1.65) is... 

In protein solutions the water protons may be considered to reside in two different environments, i.e. the bulk water, and the hydration spheres of the protein molecules. If there is fast exchange of protons between these environments a single proton nuclear magnetic resonance will be observed, which corresponds to the average of the resonances in the different environments. Following McConnell (74) the observed longitudinal relaxation time is to a good approximation... 

Syntheses of several annulated 1,2,3-triazepine structures have been reported recently <2000EJC421>. Compound 7 (m.p. 245 °C, 68% yield) was obtained by reaction of benzoxazinone 6 with hydrazine hydrate in boiling ethanol (Scheme 1). The stmcture was confirmed by its IR u 1670 (C=0), 1620 (C=N), 3250 (NH) cm-1], 111 NMR (NMR - nuclear magnetic resonance), and combustion data. Furthermore, treatment of 6 with P2S5 in dry xylene resulted in the formation of 8. Subsequent reaction of 8 with hydrazine hydrate in boiling ethanol gave 9 in a 50% overall yield. The reported infrared (IR) data for 9 are as follows 1240 (C=S), 1640 (C=N), and 3250 (NH) cm-1. 

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