Search

AbstractThe kinetics of oxidation catalysis by TAML activators of peroxides [LFeIII(OH2)]− (TAML = tetraamido macrocyclic ligand) in water can be typically quantified by a mechanism comprised of two key steps: catalyst activation to the reactive state with rate constant kI, followed by substrate oxidation with rate constant kII. Usually, kI ≪ kII and the overall catalytic activity is limited by the first step. The second-order rate constant kI can be enhanced by changing structural features in the TAML macrocycle that make the iron site more electrophilic. Chemical interventions beyond changes at the catalyst itself should also be able to change kI. In examining potentially useful interventions, the effect of chloride on kI was explored and an intriguing fact was found. For the NewTAML catalyst, [FeIII{4-NO2C6H3-1,2-(NCOCMe2NSO2)2CHMe}(OH2)]−, increasing chloride concentration reduces the rate constant kI when the pH is below the pKa of the catalyst ([LFeIII(OH2)]− ⇄ [LFeIII(OH)]2− + H+), but increases kI when the pH > pKa. Mechanisms of the observed deceleration/acceleration effects are discussed. A linear dependence between KCl and pKa for iron(III) TAMLs is established: logKCl = 16 ± 2 – (1.6 ± 0.2) × pKa. [ABSTRACT FROM AUTHOR]

The kinetic and thermodynamic properties of the regioselective addition of bifunctional hydroxylaminooxime-type HO-nucleophiles to form Pt-complexed nitriles are described. The results of the synthetic, kinetic and theoretical studies have shown that the high regioselectivity of the reactions of the 1,2-hydroxylaminooximes with ligated nitriles is both kinetically and thermodynamically controlled.

A study shows that the activating effect of nitriles by platinum(IV) versus platinum(II) is 3 orders of magnitude when coordinated EtCN reacts with (p-ClC6H4CH2)2NOH. The results shows that the reactions are intramolecular in nature as proved by the independence of k2 on the concentrations of added EtC(triple bond)N and Cl(super -).

A biochemical and biomimetic study that highlights the ongoing need for synthetic iron compounds that can produce technologically useful O2 activation chemistry is discussed. It shows a promising development for the advancement of green oxidation technology as O2 is an abundant, clean and an inexpensive oxidizing agent.

Intact photosensitive cyclometalated [Ru.sup.II] derivatives of 2-phenylpyridine or N,N-dimethylbenzylamine cis-[Ru-(C~N) (LL)[X.sub.2]] [PF.sub.6][C~N : o-[C.sub.6][H.sub.4]-py or o-[C.sub.6][H.sub.4]C[H.sub.2]N[Me.sub.2]; LL = 1,10-phenanththroline (phen), 2,2'-bipyridine (bpy), or 4,4'-[Me.sub.2]-2,2'-bipyridine ([Me.sub.2]bpy); X = MeCN or pyridine (py)] are efficient mediators of glucose oxidase (GO) from Aspergillus niger and horseradish peroxidase (HRP). Their redox potentials in an aqueous buffer are in the range 0.15-0.35 V versus SCE, and the rate constants for the oxidation GO(red) (where red indicates reduced) by the electrochemically generated [Ru.sup.III] species equal (1.7-2.5) x [10.sup.6] [M.sup.-1] [s.sup.-1] at pH 7 and 25[degrees]C. The redox potentials of all complexes decrease cathodically by 0.4-0.6 V upon irradiation by visible light because of the photoinduced solvolysis of acetonitrile or py ligands. These in situ generated species display an even better mediating performance with HRP, although their behavior toward GO is different. The loading of a ruthenium unit into the protein interior brings about large catalytic currents in a self-assembled system GO--Ru--D-glucose. The estimated rate constant for intramolecular electron transfer from FAD[H.sub.2] of the active site at [Ru.sup.III], [k.sub.intra], equals 4.4 x [10.sup.3] [s.sup.-1]]. This suggests that the distance between the redox partners is around 19 [Angstrom]. The value of 21 [Angstrom] was obtained through the docking analysis of a possible closest-to-FAD localization of a Ru-containing fragment derived from the irradiated complex cis-[Ru(o-[C.sub.6][H.sub.4]-py)-(phen) [(MeCN).sub.2]][PF.sub.6]. The operational stability of the GO-Ru assemblies depends on the nature of complex used, the highest being observed for cis-[Ru(o-[C.sub.6][H.sub.4]-py)([Me.sub.2]bpy)[(MeCN).sub.2]][PF.sub.6] (2). UV--vis studies of interaction of 2 with GO revealed photomechanical oscillations in the system GO--Ru--D-glucose. When irradiated complex 2 is mixed with GO and D-glucose, the absorbance at 510 nm increases because of the enzymatic reduction of [Ru.sup.III] to [Ru.sup.II]. The absorbance drops rapidly and then increases as in the first cycle after shaking the reaction solution. Many cycles are possible, and the rate of absorbance increase does not depend on a cycle number. A plausible mechanism of the oscillations is presented.

Research has been conducted on the acetophenone and benzaldehyde oximes. The study of the oximes' orthoplatination carried out via platinum(II) sulfoxide and sulfide complexes in producing platinacycles is presented.

Research has been conducted on the family of cycloruthenated complexes. The synthesis of these complexes and the use of the cyclometalated compounds are discussed.

The reaction of amylose with NaH and FcC[H.sub.2]N[[Me.sub.3].sup.+][I.sup.-] in dimethyl sulfoxide brought about a redox-labeled polymer with a low degree of modification, viz. 1 ferrocene residue per 60 glucose units. The preparation, (0.017ferrocene)amylose, displays one-electron irreversible behavior at a pyrographite electrode in terms of the Delahay formalism, the formal redox potential E [degree] [prime] being equal to 0.38 V at pH 6 and 40 [degrees] C versus SCE. Specific to amylose enzymes endo-depolymerases, which carry out random hydrolysis, accept the labeled amylose providing a significant increase in the peak current on cyclic voltammograms. The absence of potential drifts suggests that the effect is due an increase in the diffusion coefficients of the amylose fragments in the course of enzymatic digestion of (0.017ferrocene)amylose. This proposal was confirmed by the simulation of experimental cyclic voltammograms. Several practical applications of the results of this study for electro-chemical assaying the amylolytic activity and evaluation of the mechanisms of the enzymatic catalysis by amylases have been demonstrated.

The photochemical synthesis and X-ray characterization of new complexes derived from the reaction of orthopalladated N, N-dimethylbenzylamine and azobenzene. The spectral and thermochroic properties of three complexes and the kinetics of thermal composition are also discussed. The behavior of cis-Azobenzene in reaction was notable in its role as a bridging, bidentate ligand. This resulted in two platinum centers in close proximity and platinum planes almost perpendicular to the plane of the N=N double bond.

Cyclopalladated aryl oximes were obtained via ligand exchange between the aryl oximes and cyclopalladated complexes of N, N-dimethylbenzylamine or (dimethylamino methyl)ferrocene chloro-bridged dimers. Cationic monomeric complexes were derived from the O-acylated complexes derived from corresponding chloro-bridged dimers. The cyclopalladated oxime ligands in the monomeric complexes are inert to substitution and contain their own deprotonated oxime hydroxyls. A multifunctional catalyst with oximato and hydroxo nucleophilic centers arises from the coordination sphere of the Pd.