Catalytic and Direct Oxidation of Cysteine by Octacyanomolybdate(V)
摘要:
The oxidation of cysteine by [Mo(CN)(8)](3-) in deoxygenated aqueous solution at a moderate pH, is strongly catalyzed by Cu2+, to the degree that impurity levels of Cu2+ are sufficient to dominate the reaction. Dipicolinic acid (dipic) is a very effective inhibitor of this catalysis, such that with 1 mM dipic, the direct oxidation can be studied. UV-vis spectra and electrochemistry show that [Mo(CN)(8)](4-) is the Mo-containing product. Cystine and cysteinesulfinate are the predominant cysteine oxidation products, The stoichiometric ratio (Delta n(Mo(V))/Delta n(cysteine)) of 1.4 at pH 10.8 is consistent with this product distribution. At pH 1.5, the reaction is quite slow and yields intractable kinetics. At pH 4.5, the rates are much faster and deviate only slightly from pseudo-first-order behavior. With 2 mM PBN (N-phenyl-tert-butyl nitrone) present at pH 4.5, the reaction rate is about 20% less and shows excellent pseudo-first-order behavior, but the stoichiometric ratio is not significantly changed. The rates also display a significant specific cation effect. In the presence of spin-trap PBN, the kinetics were studied over the pH range 3.48-12.28, with [Na+] maintained at 0.09-0.10 M. The rate law is -d[Mo(V)]/dt = k[cysteine](tot)[Mo(V)], with k = {2(k(b)K(a1)K(a2)[H+] + k(c)K(a1)K(a2)K(a3))}/([H+](3) + K-a1[H+](2) + Ka1Ka2[H+] + Ka1Ka2Ka3), where K-a1, K-a2, and K-a3 are the successive acid dissociation constants of HSCH2CH(NH3+)CO2H. Least-squares fitting yields k(b) = (7.1 +/- 0.4) x 10(4) M-1 s(-1) and k(c) = (2.3 +/- 0.2) x 10(4) M-1 s(-1) at mu = 0.1 M (NaCF3SO3) and 25 degrees C. A mechanism is inferred in which k(b) and k(c) correspond to electron transfer to Mo(V) from the thiolate forms of anionic and dianionic cysteine.
Kinetics of the reversible photoaquation of the octacyanomolybdate(IV) ion
作者:Vilmos Gáspár、Mihály T. Beck
DOI:10.1016/s0277-5387(00)80796-2
日期:1987.1
The kinetics of the photoaquation of the octacyanomolybdate(IV) ion in aqueous solution were studied by potentiometric and spectrophotometric methods. In an alkaline medium a simple scheme analogous to the photoaquation of the hexacyanoferrate(II) ion describes the process. The values of the constants of the kinetic equation are: (Φ = 1.0, k8 = (6.55 ± 0.8) x 10−9 s−1, and k−8 = (7.88 ± 0.5) x 10−2
Pressure effect on photo-induced electron-transfer reactions between tris-(2,2′-bipyridine)ruthenium(<scp>II</scp>) and various metal complex ions
作者:Fumio B. Ueno、Yoichi Sasaki、Tasuku Ito、Kazuo Saito
DOI:10.1039/c39820000328
日期:——
The electron-transfer quenching of photo-excited [Ru(bpy)32+](bpy = 2,2′-bipyridine) by [Mo(CN)8]4– and Euaq2+ gives large positive and negative activation volumes (ΔV‡+ 24.7 and –11.0 cm3 mol–1), respectively, whereas quenching by other quenchers having quenching rate constants of > 109 mol–1 dm3 s–1 has a negligibly small pressure effect regardless of the charge of quencher.
[Mo(CN)8 ] 4–和Eu aq 2+对光激发的[Ru(bpy)3 2 + ](bpy = 2,2'-联吡啶)的电子转移猝灭产生较大的正和负激活量(分别为ΔV ‡ + 24.7和–11.0 cm 3 mol –1),而采用淬灭速率常数大于10 9 mol –1 dm 3 s –1的其他淬灭剂进行淬灭,无论加料量多少,其压力效应都可以忽略不计。淬灭剂。
Ligand-Field Photolysis of [Mo(CN)<sub>8</sub>]<sup>4−</sup> in Aqueous Hydrazine: Trapped Mo(II) Intermediate and Catalytic Disproportionation of Hydrazine by Cyano-Ligated Mo(III,IV) Complexes
investigated in detail. A molybdenum(II) intermediate, K5[Mo(CN)7].N2H4, is isolated in the primary stage of the reaction that involves the oxidation of N2H4 to N2, as evidenced by the analysis of evolving gases. The powder X-ray crystal structure of K5[Mo(CN)7].N2H4 indicates the pentagonal bipiramidal geometry of the anion and the presence of N2H4 in proximity to the CN(-) ligands. The salt is characterized
Kinetics and mechanism of the interaction of hexaaquochromium(III) with octacyanomolybdate(IV) ions
作者:S.I. Ali、Zakir Murtaza
DOI:10.1016/s0277-5387(00)87010-2
日期:1985.1
The kinetics of the interaction of hexaaquochromium(III) ion with potassium octacyanomolybdate(IV) have been studied using conductance and spectrophotometric data. The mechanism of the reaction is discussed and the effect of H+ ion and the ionic strength on the rate of the reaction determined. The reaction is found to be pseudo-first order with respect to potassium octacyanomolybdate(IV) and inverse
Electron-transfer reactions and the self-exchange rate of the perruthenate(<scp>VII</scp>)–ruthenate(<scp>VI</scp>) couple
作者:Tai-Chu Lau、Sophia L. L. Kong
DOI:10.1039/dt9950002221
日期:——
The kinetics of the reduction of perruthenate(VII) by [Fe(CN)6]4– and [W(CN)8]4– and the oxidation of ruthenate(VI) by [Mo(CN)8]3– and [Ru(CN)6]3– have been studied in aqueousalkaline solutions using stopped-flow techniques. The cross-reaction data have been treated according to the Marcus relations and yield a self-exchange rate constant of 10 ± 5 dm3 mol–1 s–1(25.0 °C, I= 1.0 mol dm–3) for the