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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]

Iron derivatives have emerged as valuable catalysts for a variety of transformations, as well as for biological and photophysical applications, and iminophosphorane can be considered an ideal ligand scaffold for modulating electronic and steric parameters in transition metal complexes. In this report, we aimed to synthesize dichloride and dibromide iron(II) complexes supported by symmetric bis(iminophosphorane)pyridine ligands, starting from readily available ferrous halides. The ease of synthesis of this class of ligands served to access several derivatives with distinct electronic and steric properties imparted by the phosphine moiety. The ligands and the resulting iron(II) complexes were characterized by 31P and 1H NMR spectroscopy and DART or ESI mass spectrometry. While none of these iron(II) complexes could be characterized by single-crystal X-ray diffraction, suitable crystals of a µ-O bridged dinuclear iron complex bearing an iminophosphorane ligand were obtained, confirming a κ3 binding motif. The bis(iminophosphorane)pyridine ligands in the obtained iron(II) complexes are labile, as demonstrated by their facile substitution by terpyridine. Cyclic voltammetry studies revealed that the oxidation of bis(iminophosphorane)pyridine iron(II) complexes to iron(III) species is quasi-reversible, suggesting the strong thermodynamic stabilization of the iron(III) center imparted by the σ-donating iminophosphorane ligands. [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.

A cyclic voltammetry study of a series of iron(III) TAML activators of peroxides of several generations in acetonitrile as solvent reveals reversible or quasireversible FeIII/IV and FeIV/V anodic transitions, the formal reduction potentials (E°′) for which are observed in the ranges 0.4–1.2 and 1.4–1.6 V, respectively, versus Ag/AgCl. The slope of 0.33 for a linear E°′(IV/V) against E°′(III/IV) plot suggests that the TAML ligand system plays a bigger role in the FeIII/IV transition, whereas the second electron transfer is to a larger extent an iron‐centered phenomenon. The reduction potentials appear to be a convenient tool for analysis of various properties of iron TAML activators in terms of linear free energy relationships (LFERs). The values of E°′(III/IV) and E°′(IV V−1) correlate 1) with the pKa values of the axial aqua ligand of iron(III) TAMLs with slopes of 0.28 and 0.06 V, respectively; 2) with the Stern–Volmer constants KSV for the quenching of fluorescence of propranolol, a micropollutant of broad concern; 3) with the calculated ionization potentials of FeIII and FeIV TAMLs; and 4) with rate constants kI and kII for the oxidation of the resting iron(III) TAML state by H2O2 and reactions of the active forms of TAMLs formed with donors of electrons S, respectively. Interestingly, slopes of log kII versus E°′(III/IV) plots are lower for fast‐to‐oxidize S than for slow‐to‐oxidize S. The log kI versus E°′(III/IV) plot suggests that the manmade TAML catalyst can never be as reactive toward H2O2 as a horseradish peroxidase enzyme. [ABSTRACT FROM AUTHOR]

The bis-sulfonamide TAML activator of peroxides [Fe{4-NO2C6H3-1,2-(NCOCMe2NSO2)2CHMe}]- (2) catalyzes the H2O2 oxidation of microcystin-LR (m-LR), a common surface water contaminant produced by cyanobacteria that is toxic at very low concentrations. The major reaction product is by 16 Da heavier than m-LR, suggesting that the first oxidative step involves addition of oxygen to one of m-LRs three C = C units to form an epoxide. The kinetic data suggest that the m-LR → m + 16 conversion occurs without any kinetically meaningful intermediate with the catalytic rate constant kII of 2.5 × 105 M−1 s−1, which characterizes the interaction of m-LR with the oxidized, active form of the catalyst. The primary m + 16 product undergoes much slower further catalytic oxidation in the aqueous reaction medium. This communication describes a potential utility of TAML/H2O2 catalysis for microcystin detoxification that calls for further research. [ABSTRACT FROM AUTHOR]

Bis‐sulfonamide bis‐amide TAML activator [Fe{4‐NO2C6H3‐1,2‐(NCOCMe2NSO2)2CHMe}]− (2) catalyzes oxidative degradation of the oxidation‐resistant neonicotinoid insecticide, imidacloprid (IMI), by H2O2 at pH 7 and 25 °C, whereas the tetrakis‐amide TAML [Fe{4‐NO2C6H3‐1,2‐(NCOCMe2NCO)2CF2}]− (1), previously regarded as the most catalytically active TAML, is inactive under the same conditions. At ultra‐low concentrations of both imidacloprid and 2, 62 % of the insecticide was oxidized in 2 h, at which time the catalyst is inactivated; oxidation resumes on addition of a succeeding aliquot of 2. Acetate and oxamate were detected by ion chromatography, suggesting deep oxidation of imidacloprid. Explored at concentrations [2]≥[IMI], the reaction kinetics revealed unusually low kinetic order in 2 (0.164±0.006), which is observed alongside the first order in imidacloprid and an ascending hyperbolic dependence in [H2O2]. Actual independence of the reaction rate on the catalyst concentration is accounted for in terms of a reversible noncovalent binding between a substrate and a catalyst, which usually results in substrate inhibition when [catalyst]≪[substrate] but explains the zero order in the catalyst when [2]>[IMI]. A plausible mechanism of the TAML‐catalyzed oxidations of imidacloprid is briefly discussed. Similar zero‐order catalysis is presented for the oxidation of 3‐methyl‐4‐nitrophenol by H2O2, catalyzed by the TAML analogue of 1 without a NO2‐group in the aromatic ring. [ABSTRACT FROM AUTHOR]

The dissolution of dimeric chloro-bridged Pd(II) and Pt(II) derivatives of N,N-dimethylbenzylamine and a related acetophenone complex in minimum amount of benzene followed by reaction with N-((tert-butyloxy)-carbonyl)-L-methionine p-nitrophenyl ester gives crystals of a monomeric compound with S,N-trans geometry. UV-vis spectrophotometry of the aquation of these monomers reveals the departure of p-nitrophenolate ion. The stoichiometric analysis of these species through analytical data shows close agreement with 1H and 13C NMR measurements.

The design and structural and kinetic characterization of a second generation of iron(III)-TAML activators with unprecedented peroxidase-mimicking abilities is described. The studies have shown that the new catalyst can decolorize Orange II without loss of activity for at least 10 half-lives, attesting to its exceptional properties as an oxidizing enzyme mimic.