Alcohol stopped-flow spectrophotometry

Alcohol oxidation requires release of a proton, which formally comes from the alcohol. In other dehydrogenases such as lactate dehydrogenase, proton release occurs simultaneously with hydride transfer. In liver ADH proton release can be demonstrated, by reaction of the proton with an indicator such as thymol blue or phenol red in stopped-flow spectrophotometry, to be faster than hydride transfer, 270 vs. 150 s and unaffected by use of deuterated substrate, so it occurs before hydride transfer. Binding of the NAD+ nicotinamide ring is accompanied by a conformational change of ADH bringing the catalytic zinc about 0.1 nm closer to the... 

More recently, rate and equilibrium constants have been determined directly for the nitrosation by nitrosyl chloride of some alcohols in acetic acid using stopped-flow spectrophotometry (Dalcq and Bruylants, 1975). A second order term in [ROH] was noted for the O-nitrosation of methanol (and a corresponding term containing [ROH] for the reverse step), which was not significant for the other alcohols studied, so that the rate eqn(38) represented the kinetics. A mechanism was proposed involving attack by NOCl at the... 

Stopped flow spectrophotometry has also been used to measure the forward and reverse rate constants for the nitrosation of a number of alcohols and carbohydrates in aqueous solution (Aldred and Williams, 1980 Aldred et al., 1982). Both reactions were acid-catalysed and were also catalysed by added chloride and bromide ion. Structural effects were not marked but the sequence MeOH > EtOH > i-PrOH > t-BuOH was established for the forward reaction and was attributed to a steric effect, whilst for the reverse reaction the rate constants were not very dependent on the alcohol structure. The halide ion-catalysed reactions were believed to involve equilibrium concentrations of reactive NOCl and NOBr rate constants for the bimolecular process (39) were determined as 2.1x10 and 2.0 x 10 dm mol s for NOCl and NOBr respectively, for reaction with methanol at 25°C. Thus, as... 

The kinetics of ligand substitution in bis(N-tert-butylsalicylaldiminato)-copper(II) [Cu(SA=N-t-Bu)2] in various alcoholic media and specially the solvent dependence of this reaction was studied by Elias et al [El 80]. N-ethylsalicylal-dimine (HSA=N-t-Et) served as substituting ligand. Stopped-flow spectrophotometry has been used for these investigations. It was concluded that the mechanism of the solvent effect is made up of the following steps (i) fast equilibrium Cu(SA=N-t-Bu)2 + ROH Cu(SA=N-t-Bu)2. ROH (ii) fast proton transfer from... 

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See also in sourсe #XX -- [ ]

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