Intermediates involved in the reduction of SO: insight into the mechanism of sulfite reductases.

Sulfite reductases (SiRs) catalyze the reduction of SO to HS in biosynthetic sulfur assimilation and dissimilation of sulfate. The mechanism of the 6e/6H reduction of SO at the siroheme cofactor is debated, and proposed intermediates involved in this 6e reduction are yet to be spectroscopically characterized. The reaction of SO with a ferrous iron porphyrin is investigated, and two intermediates are trapped and characterized: an initial Fe(III)-SO species, which undergoes proton-assisted S-O bond cleavage to form an Fe(III)-SO species.

Iron Dioxygen Adduct Formed during Electrochemical Oxygen Reduction by Iron Porphyrins Shows Catalytic Heme Dioxygenase Reactivity.

Heme dioxygenases oxidize the indole ring of tryptophan to kynurenine which is the first step in the biosynthesis of several important biomolecules like NAD, xanthurenic acid, and picolinic acid. A ferrous heme dioxygen adduct (or Fe-O) is the oxidant, and both the atoms of O are inserted in the product and its catalytic function has been difficult to emulate as it is complicated by competing rapid reactions like auto-oxidation and/or formation of the μ-oxo dimer. In situ resonance Raman spectroscopy technique, SERRS-RDE, is used to probe the species accumulated during electrochemical ORR catalyzed by site-isolated imidazole-bound iron porphyrin installed on a self-assembled monolayer covered electrode.

Silver nanostructure-modified graphite electrode for in-operando SERRS investigation of iron porphyrins during high-potential electrocatalysis.

In-operando spectroscopic observation of the intermediates formed during various electrocatalytic oxidation and reduction reactions is crucial to propose the mechanism of the corresponding reaction. Surface-enhanced resonance Raman spectroscopy coupled to rotating disk electrochemistry (SERRS-RDE), developed about a decade ago, proved to be an excellent spectroscopic tool to investigate the mechanism of heterogeneous oxygen reduction reaction (ORR) catalyzed by synthetic iron porphyrin complexes under steady-state conditions in water. The information about the formation of the intermediates accumulated during the course of the reaction at the electrode interface helped to develop better ORR catalysts with second sphere residues in the porphyrin rings.

Second-Sphere Hydrogen-Bond Donors and Acceptors Affect the Rate and Selectivity of Electrochemical Oxygen Reduction by Iron Porphyrins Differently.

The factors that control the rate and selectivity of 4e/4H O reduction are important for efficient energy transformation as well as for understanding the terminal step of respiration in aerobic organisms. Inspired by the design of naturally occurring enzymes which are efficient catalysts for O and HO reduction, several artificial systems have been generated where different second-sphere residues have been installed to enhance the rate and efficiency of the 4e/4H O reduction. These include hydrogen-bonding residues like amines, carboxylates, ethers, amides, phenols, etc.

Bioinorganic Chemistry on Electrodes: Methods to Functional Modeling.

One of the major goals of bioinorganic chemistry has been to mimic the function of elegant metalloenzymes. Such functional modeling has been difficult to attain in solution, in particular, for reactions that require multiple protons and multiple electrons (H/e). Using a combination of heterogeneous electrochemistry, electrode and molecule design one may control both electron transfer (ET) and proton transfer (PT) of these H/e reactions.

Visualization of ceramide channels by transmission electron microscopy.

Functional studies have shown that the sphingolipid ceramide, self-assembles in phospholipid membranes to form large channels capable of allowing proteins to cross the membrane. Here these channels are visualized by negative stain transmission electron microscopy. The images contain features consistent with stain-filled pores having a roughly circular profile.

Role of pepsin in modifying the allergenicity of bhetki (Lates calcarifer) and mackerel (Rastrelliger kanagurta) fish.

The effect of pepsin digestion on the allergenicity of raw and thermally processed (boiled and fried) fish muscle extracts of two widely consumed fishes bhetki (Lates calcarifer) and mackerel (Rastrelliger kanagurta) was studied. Sere were collected from 110 patients who were hypersensitive to fish, as evidenced by their clinical history, symptoms and positive skin-prick test results. The various extracts after digestion with pepsin at different times of incubation were tested for specific IgE-binding activity by ELISA and immunoblotting with patients' sera.