Stopped-flow kinetic studies

The procedure which had originally been used by Lehn et al. involved slow addition (over a period of ca. 8 h) of ca. 0.1 M solutions of diamine and diacyl halide in benzene. Dye et al. found that the reactions could be conducted more rapidly as long as stirring was kept efficient. This observation suggested the use of a mixing chamber of the type normally used for stopped-flow kinetic studies. Utilizing this type of set-up, the latter authors were able to obtain a 70% yield for 1, slightly inferior to the yield reported by Lehn, but a similar yield of 3 which is better than that previously ob-tained. Note that the chemical features of this synthetic method are essentially identical to the approach shown in Eq. (8.1) and differ primarily in the mechanics. 

Coles, B., Wilson, I. and Wardman, P. (1988). The spontaneous and enzymatic reaction of N-acetyl-/>-benzoquinone imine with glutathione, a stopped flow kinetic study. Arch. Biochem. Biophys. 264, 253-260. 

A study similar to that of Hersey and Robinson has been reported by Seiyama and coworkers.From a stopped-flow, kinetic study of the interaction of various azo dyes and some azo dye-metal complexes with alpha cyclodextrin, they observed two kinetic processes. The dependence of the observed rate-constants for these two processes on the alpha cyclodextrin concentration was found to be explainable in terms of a mechanism identical to that proposed earlier by Hersey and Robinson. In the case of the guests used by Seiyama and coworkers, however, values for the rate constants of the binding step could be determined from the concentration dependence of kobs for the faster process thus,... 

Stopped flow kinetic studies show that metal ions react with the dimer of Flox and FIH2 resulting in the formation of neutral and chelated semiquinone. Subsequent chelation of the neutral semiquinone by metal ions occurs at a much slower rate. 

Each of the forms of ETF isolated from the different sources contain FAD as coenzyme and form an anionic semiquinone on one-electron reduction. Stopped-flow kinetic studies on the pig liver ETF showed the anionic flavin semiquinone to be formed at times faster than catalytic turnover and thus demonstrate the participation of the anionic FAD semiquinone as an intermediate in the acceptance of reducing equivalents from the dehydrogenase. These studies would also imply the intermediacy of the semiquinone form of the acyl CoA dehydrogenase which would have been expected to form a neutral flavin semiquinone at the time the studies of Hall and Lambeth were performed, however, no spectral evidence for its formation were found. Recent studies have shown that the binding of CoA analogs to the dehydrogenase results in the perturbation of the pKa of the FAD semiquinone such that an anionic (red) rather than the neutral (blue) semiquinone is formed. This perturbation was estimated to reduce the pKa by at least 2.5 units to a value of... 

The steady state and stopped-flow kinetic studies on the horse liver enzyme are now considered classic experiments. They have shown that the oxidation of alcohols is an ordered mechanism, with the coenzyme binding first and the dissociation of the enzyme-NADH complex being rate-determining.15,26,27 Both the transient state and steady state methods have detected that the initially formed enzyme-NAD+ complex isomerizes to a second complex 27,28 In the reverse reaction, the reduction of aromatic aldehydes involves rate-determining dissociation of the enzyme-alcohol complex,27,29 whereas the reduction of acetaldehyde is... 

Khalifah, R. G. The carbon dioxide hydration activity of carbonic anhydrase. I. Stop-flow kinetic studies on the native human isoenzymes B and C. J. Biol. Chem. 246, 2561-2573(1971). 

Stopped-flow kinetic studies of Amadoriase I using fructosylpropylamine and oxygen as substrates in 10 mM Tris hydrochloride buffer (pH 7.9) at 4 °C pointed to the pyranose form as being the active configuration. The redox potentials were found to be + 48 and -52 mV for the oxidised enzyme/anionic quinone and anionic semi-quinone/reduced enzyme reactions, respectively, at pH 7.0 and 25 °C.620... 

Khan, M.J., Joginadha Swamy, M., Krishna Sastry, M.V., Umadevi Sajjan, S., Patanjali, S.R., Rao, P., Swarnalatha, G.V., Banerjee, P. and Surolia, A. (1988). Saccharide binding to three Gal/GalNac specific lectins Fluorescence, spectroscopic and stopped-flow kinetic studies. Glycoconjugate Journal, 5, 75-84. 

Zhang, K., Gonzalez, A. A., Mukerjee, S. L., Chou, S.-J., Hoff, C. D., Kubat-Martin, K. A., Barnhar, D. and Kubas, G. J. (1991). Solution calorimetric and stopped-flow kinetic study of ligand substitution for the complexes M(CO)3(PCy)2(L) (M = Cr, Mo, W). Comparison of first-, second- and third-row transition-metal-ligand bonds at sterically-crowded metal centres, J. Am. Chem. Soc. 113, 9170. 

Squadrito, G. L., Jin, X., and Pryor, W. A., Stopped-flow kinetic study of the reaction of ascorbic acid with peroxynitrite. Arch. Biochem. Biophys. 322, 53-59 (1995). 

The hexacyanorhodate(III) anion was first prepared by the fusion of [Rh(NH3)5Cl]Cl2 with KCN,485 and Schmidtke prepared it by reacting RhCl3-3H20 with a five-fold excess of CN- aqueous KCN workup of the resulting Rh(CN)3 3H20 leads to K3[Rh(CN)6] 486 Wilkinson and co-workers reported that the reaction of an aqueous solution of CN with [Rh(CO)2Cl]2 leads to [Rh(CN)4(H)(H20)]2-,487 but Jewsbury later identified the product as [Rh(CN)5(H)]3", m An intermediate in this reaction was said to be polymeric [RhfCO CN],487 while Jewsbury later spoke of [Rh(CO)2(CN)Cl]-, tra .y-[Rh(CO)2(CN)2] and [Rh(CO)(CN)3]2" as intermediates in the same reaction.488 A stopped-flow kinetic study of the reaction of CN- with [Rh(CO)2Cl]2 indicated that successive CN substitutions lead to the tetracyanorhodate(I) anion, [Rh(CN)4]3", which then undergoes oxidative addition with HCN to give [Rh(CN)s(H)]3, 489 In the presence of Mel, pen-tacyanoalkylrhodium complexes are formed.4 ... 

The mechanism originally postulated by Segal and Boyer (180) (and shown schematically in Fig. 11) is in accord with the above-mentioned observations, and has since received extensive support from the stopped-flow kinetic studies of Trentham and colleagues (69, 83, 116, 117, 189, 190). 

Stopped flow kinetic studies by Hartmann and Klinman (1991) on bovine serum amine oxidase and by Olsson et al. (1976) on pig plasma amine oxidase showed that the substrate Schiff-base has an absorbance maximum at 350nm. 

Green, J., and Dalton, H., 1989, A stopped-flow kinetic study of the soluble methane monooxygenase from Methylococcus capsulatus (Bath), Biochem J. 259 167nl72. 

Seven-coordinate three-dimensional metal complexes are considered to be quite unstable and kinetically labile species, and their solution chemistry is largely undefined. Over the last few years it was shown that these species exhibit extremely interesting chemical properties and catalytic activity. They can catalyze disproportionation of deleterious superoxide radicals, even faster than natural enzymes, and therefore this became a challenging research area. Recently, Rudi van Eldik reported a detailed rapid-scan stopped-flow kinetic study of the substitution behavior of the seven-coordinate [Fe(dapsox)(L)2]C104 complex with thiocyanate as a function of the thiocyanate concentration, temperature, and pressure in protic and aprotic organic solvents. 

Lippard etal. presented the results of detailed double-mixing stopped-flow kinetic studies of the reaction of diiron(II) compoimds (Fe2(/r-02CAr ° )4(4-CNPy)2) with water and the subsequent interaction of the aqua species with dioxygen. 

Fendorf, S. E., Sparks, D. L., Franz, J. A., and Camaioni, D. M. (1993). Electron-paramagnetic resonance stopped-flow kinetic-study of manganese(II) sorption desorption on Bimessite. Soil Sci. Soc. Am. J. SI, Sl-d. 

Over the years there have been a number of mechanistic proposals for substrate oxidation by TMADH. An early proposal considered a carbanion mechanism in which an active site base deprotonates a substrate methyl group to form a substrate carbanion [69] reduction of the flavin was then achieved by the formation of a carbanion-flavin N5 adduct, with subsequent formation of the product imine and dihydroflavin. A number of active site residues were identified as potential bases in such a reaction mechanism. Directed mutagenesis and stopped-flow kinetic studies, however, have been used to systematically eliminate the participation of these residues in a carbanion-type mechanism [76-79], thus indicating that a proton abstraction mechanism initiated by an active site residue does not occur in TMADH. Early proposals also invoked the trimethylammonium cation as the reactive species in the enzyme-substrate complex, owing to the high (9.81) of free... 

In a later report,83 stopped-flow kinetic studies were combined with calorimetric studies to generate the data shown in Table 10.1 for PhEEPh (E = S, Se, Te). 

A stopped-flow kinetic study of this reaction yielded the results summarized in Table 9. The k values refer to general acid catalyzed MeO expulsion, most probably by a concerted process with a transition state such as 73 in the forward direction this would correspond to general base catalyzed addition of methanol. 

The stoichiometric reactions of 9 with halogens and halide ions and infrared stopped flow kinetic studies clearly show the importance of one-electron transfer in the oxidative elimination reactions between [Fe(CO)3L2] and X2 (X = Cl, Br, or I). The major steps in the mechanism are shown in... 

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