Outer-sphere hexacyanoferrate(III) oxidation of organic substrates

Potential application of Micellar nanoreactor for electron transfer reactions mediated by a variety of oxidants: A review

Surfactant, either natural or synthetic, forms a different type of aggregates among which 'Micelle' is truly an important dynamic surfactant aggregate, having a different region to interact with several organic, inorganic, and biomolecules; therefore the practical use of micelle is rapidly growing day-to-day. Surfactant-micelle, looks like a reactor of nano-dimension, govern a variety of reactions in aqueous media extensively. Oxidation is one of the vital reaction, take a part in the course of several organic transformations which are not very easy to execute in water media alone due to the solubility problem. Moreover, in order to achieve a quick transformation overcoming several difficulties the utility of micellar media became an excellent innovation, that's why nowadays, the surfactant and its aggregates are a focus of interest to the researcher of synthetic field and thus its practical applicability has been tremendously cultivated over the few decades. It is, therefore, useful to introduce some basic concepts regarding the aggregation of surfactants. Subsequently, we emphasize the importance of micellar media on the kinetics of oxidation reactions mediated by several metal ions with a special emphasis on their catalytic role.

Mechanistic insights into the in vitro metal-promoted oxidation of (di)azine hydroxamic acids: evidence of HNO release and N,O-di(di)azinoyl hydroxylamine intermediate

HNO is released through a one-electron oxidation of the hydroxamic acid along with the N,O-di(di)azinoylhydroxylamine intermediate.

Rapid and Sensitive Detection of Aspergillus niger Using a Single-Mediator System Combined with Redox Cycling

Rapid and sensitive mold detection is becoming increasingly important, especially in indoor environments. Common mold detection methods based on double-mediated electron transfer between an electrode and molds are not highly sensitive and reproducible, although they are rapid and simple. Here, we report a sensitive and reproducible detection method specific to Aspergillus niger ( A. niger), based on a single-mediator system combined with electrochemical-chemical (EC) redox cycling. Intracellular NAD(P)H-oxidizing enzymes in molds can convert electro-inactive hydroxy-nitro(so)arenes into electro-active hydroxy-aminoarenes. Since the membrane and wall of A. niger is well permeable to both a substrate (4-nitro-1-naphthol) and a reduced product (4-amino-1-naphthol) in tris buffer (pH 7.5) solution, the electrochemical signal is increased in the presence of A. niger due to two reactions: (i) enzymatic reduction of the substrate to the reduced product and (ii) electrochemical oxidation of the reduced product to an oxidized product. When a reducing agent (NADH) is present in the solution, the oxidized product is reduced back to the reduced product and then electrochemically reoxidized. This EC redox cycling significantly amplifies the electrochemical signal. Moreover, the background level is low and highly reproducible because the substrate and the reducing agent are electro-inactive at an applied potential of 0.20 V. The calculated detection limit for A. niger in a common double-mediator system consisting of Fe(CN)₆^3- and menadione is ∼2 × 10⁴ colony-forming unit (CFU)/mL, but the detection limit in the single-mediator system combined with EC redox cycling is ∼2 × 10³ CFU/mL, indicating that the newly developed single-mediator system is more sensitive. Importantly, the detection method requires only an incubation period of 10 min and does not require a washing step, an electrode modification step, or a specific probe.

Is IQG-607 a Potential Metallodrug or Metallopro-Drug With a Defined Molecular Target in Mycobacterium tuberculosis?

The emergence of strains of Mycobacterium tuberculosis resistant to isoniazid (INH) has underscored the need for the development of new anti-tuberculosis agents. INH is activated by the mycobacterial katG-encoded catalase-peroxidase, forming an acylpyridine fragment that is covalently attached to the C4 of NADH. This isonicotinyl-NAD adduct inhibits the activity of 2-trans-enoyl-ACP(CoA) reductase (InhA), which plays a role in mycolic acid biosynthesis. A metal-based INH analog, Na₃[Fe^II(CN)₅(INH)]·4H₂O, IQG-607, was designed to have an electronic redistribution on INH moiety that would lead to an intramolecular electron transfer to bypass KatG activation. HPLC and EPR studies showed that the INH moiety can be oxidized by superoxide or peroxide yielding similar metabolites and isonicotinoyl radical only when associated to IQG-607, thereby supporting redox-mediated drug activation as a possible mechanism of action. However, IQG-607 was shown to inhibit the in vitro activity of both wild-type and INH-resistant mutant InhA enzymes in the absence of KatG activation. IQG-607 given by the oral route to M. tuberculosis-infected mice reduced lung lesions. Experiments using early and late controls of infection revealed a bactericidal activity for IQG-607. HPLC and voltammetric methods were developed to quantify IQG-607. Pharmacokinetic studies showed short half-life, high clearance, moderate volume of distribution, and low oral bioavailability, which was not altered by feeding. Safety and toxic effects of IQG-607 after acute and 90-day repeated oral administrations in both rats and minipigs showed occurrence of mild to moderate toxic events. Eight multidrug-resistant strains (MDR-TB) were resistant to IQG-607, suggesting an association between katG mutation and increasing MIC values. Whole genome sequencing of three spontaneous IQG-607-resistant strains harbored katG gene mutations. MIC measurements and macrophage infection experiments with a laboratorial strain showed that katG mutation is sufficient to confer resistance to IQG-607 and that the macrophage intracellular environment cannot trigger the self-activation mechanism. Reduced activity of IQG-607 against an M. tuberculosis strain overexpressing S94A InhA mutant protein suggested both the need for KatG activation and InhA as its target. Further efforts are suggested to be pursued toward attempting to translate IQG-607 into a chemotherapeutic agent to treat tuberculosis.

Hydrogen-bonded assemblies of ruthenium(ii)-biimidazole complex cations and cyanometallate anions: structures and photophysics

The complex cations [RuL2(H2biim)]2+ (L=bipy, 4,4'-tBu2-bipy) interact with cyanometallate anions via a chelating hydrogen-bonding interaction between the two N-H donors of the complex cation and the N lone pair of one cyanide ligand in the complex anion; the anion hexacyanoferrate(III) quenches the Ru(II)-based luminescence in CH2Cl2 solution by photoinduced electron-transfer within the H-bonded assembly, whereas hexacyanocobaltate(III) enhances the Ru(II)-based luminescence.

Modification phenomena of solid-state lignin caused by electron-abstracting oxidative systems

Oxidative treatments of wood pulp lignin by one-electron-abstracting enzymatic or chemical systems result in modification phenomena which are not fully described in terms of those known from lignin model compound studies. The generation of, e.g., long-lived radicals necessitates nondestructive spectroscopic analysis of the lignin polymer for a proper characterization of these. The present work exposes a complexity of spectroscopic modification phenomena, which has not previously been realized. This is achieved by a laccase-mediator system, where the mediator is an aromatic low-molecular-weight compound, which mediates the electron abstraction between the lignin and the enzyme laccase. It is demonstrated that the modification generated exhibits qualitatively different temporal phases. The mechanisms are partly explained in terms of Marcus electron transfer theory, and it is suggested that these may play a role in the in vivo synthesis and degradation of lignin.

Filling a void: isolation and characterization of tetracarboxylato dimolybdenum cations

Dimolybdenum tetracarboxylato cations have been prepared and structurally characterized for the first time. The reactions of the new, quadruply bonded compound, Mo(2)(TiPB)(4), where TiPB = 2,4,6-triisopropylphenyl carboxylate, with NOPF(6) and NOBF(4) give the ionic compounds [Mo(2)(TiPB)(4)]PF(6) and [Mo(2)(TiPB)(4)]BF(4), respectively. Each product crystallizes in space group P2(1)/n and displays an elongation of the Mo-Mo bond of 0.060 and 0.068 A, respectively, over that of the parent compound (2.076(1) A). Each complex displays a characteristic EPR signal, showing hyperfine coupling to the spin active isotopes (95)Mo and (97)Mo, with g( parallel) = g( perpendicular) = 1.936, that is consistent with the presence of an unpaired electron. Electronic spectroscopy indicates the expected red shift in the delta --> delta(*) transition for the cations, due to the loss of exchange energy in going from the two-electron to one-electron system. We have also obtained a small amount of crystalline [Mo(2)(O(2)CC(4)H(9))(4)]PF(6) from the reaction of Mo(2)(O(2)CC(4)H(9))(4) with AgPF(6). This product crystallizes in the space group C2/c, and the Mo-Mo bond is elongated by 0.063 A over that of the neutral parent compound. These ionic compounds have the first isolated and characterized [Mo(2)(O(2)CR)(4)](+) cationic species.

Kinetics and mechanism of osmium (VIII) catalysed oxidation of formic acid by hexacyanoferrate (III) in aqueous alkaline medium

The kinetics of osmium (VIII) catalysed oxidation of formic acid by hexacyanoferrate (III) in alkaline medium is investigated.