Multivariate analysis on the structure-activity parameters for nano CuO-catalyzed reduction reactions.

Understanding the origin of enhanced catalytic activity is critical to heterogeneous catalyst design. This is especially important for non-noble metal-based catalysts, notably metal oxides, which have recently emerged as viable alternatives for numerous thermal catalytic processes. For thermal catalytic reduction/hydrogenation using metal oxide nanoparticles, enhanced catalytic performance is typically attributed to increased surface area and oxygen vacancies.

Activity assays of NnlA homologs suggest the natural product -nitroglycine is degraded by diverse bacteria.

Linear nitramines (R-N(R')NO; R' = H or alkyl) are toxic compounds, some with environmental relevance, while others are rare natural product nitramines. One of these natural product nitramines is -nitroglycine (NNG), which is produced by some strains and exhibits antibiotic activity towards Gram-negative bacteria. An NNG degrading heme enzyme, called NnlA, has recently been discovered in the genome of strain JS1663 ( NnlA).

Synergistic Steric and Electronic Effects on the Photoredox Catalysis by a Multivariate Library of Titania Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) that display photoredox activity are attractive materials for sustainable photocatalysis. The ability to tune both their pore sizes and electronic structures based solely on the choice of the building blocks makes them amenable for systematic studies based on physical organic and reticular chemistry principles with high degrees of synthetic control. Here, we present a library of eleven isoreticular and multivariate (MTV) photoredox-active MOFs, UCFMOF-, and UCFMTV--% with a formula TiO[], where the links are linear oligo--arylene dicarboxylates with number of -arylene rings and mol% of multivariate links containing electron-donating groups (EDGs).

Particle Swarm Fitting of Spin Hamiltonians: Magnetic Circular Dichroism of Reduced and NO-Bound Flavodiiron Protein.

A particle swarm optimization (PSO) algorithm is described for the fitting of ground-state spin Hamiltonian parameters from variable-temperature/variable-field (VTVH) magnetic circular dichroism (MCD) data. This PSO algorithm is employed to define the ground state of two catalytic intermediates from a flavodiiron protein (FDP), a class of enzymes with nitric oxide reductase activity. The bimetallic iron active site of this enzyme proceeds through a biferrous intermediate and a mixed ferrous-{FeNO} intermediate during the catalytic cycle, and the MCD spectra of these intermediates are presented and analyzed.

Reduction of a Heme Cofactor Initiates -Nitroglycine Degradation by NnlA.

Linear nitramines are potentially carcinogenic environmental contaminants. The NnlA enzyme from sp. strain JS1663 degrades the nitramine -nitroglycine (NNG)-a natural product produced by some bacteria-to glyoxylate and nitrite (NO).

The hemerythrin-like diiron protein from Mycobacterium kansasii is a nitric oxide peroxidase.

The hemerythrin-like protein from Mycobacterium kansasii (Mka HLP) is a member of a distinct class of oxo-bridged diiron proteins that are found only in mycobacterial species that cause respiratory disorders in humans. Because it had been shown to exhibit weak catalase activity and a change in absorbance on exposure to nitric oxide (NO), the reactivity of Mka HLP toward NO was examined under a variety of conditions. Under anaerobic conditions, we found that NO was converted to nitrite (NO) via an intermediate, which absorbed light at 520 nm.

The Ferric-Superoxo Intermediate of the TxtE Nitration Pathway Resists Reduction, Facilitating Its Reaction with Nitric Oxide.

TxtE is a cytochrome P450 (CYP) homologue that mediates the nitric oxide (NO)-dependent direct nitration of l-tryptophan (Trp) to form 4-nitro-l-tryptophan (4-NO-Trp). A recent report showed evidence that TxtE activity requires NO to react with a ferric-superoxo intermediate. Given this minimal mechanism, it is not clear how TxtE avoids Trp hydroxylation, a mechanism that also traverses the ferric-superoxo intermediate.

The emergence of nitric oxide in the biosynthesis of bacterial natural products.

Nitric oxide (NO) has a broad range of biological utilities including as a biosynthon for bacterial natural products (NPs). The biosyntheses of thaxtomin A and rufomycin require an NO-dependent nitration step where a bacterial NO synthase provides the necessary NO and nitration is catalyzed by a cytochrome P450 homolog. Undiscovered NO-dependent biosynthesis pathways are likely to have similar requirements: a pathway dedicated NO source and a metalloenzyme to catalyze the NO-dependent chemistry.

Influences of the heme-lysine crosslink in cytochrome P460 over redox catalysis and nitric oxide sensitivity.

Ammonia (NH)-oxidizing bacteria (AOB) derive total energy for life from the multi-electron oxidation of NH to nitrite (NO). One obligate intermediate of this metabolism is hydroxylamine (NHOH), which can be oxidized to the potent greenhouse agent nitrous oxide (NO) by the AOB enzyme cytochrome (cyt) P460. We have now spectroscopically characterized a 6-coordinate (6c) {FeNO} intermediate on the NHOH oxidation pathway of cyt P460.

Organometallic and radical intermediates reveal mechanism of diphthamide biosynthesis.

Diphthamide biosynthesis involves a carbon-carbon bond-forming reaction catalyzed by a radical S-adenosylmethionine (SAM) enzyme that cleaves a carbon-sulfur (C-S) bond in SAM to generate a 3-amino-3-carboxypropyl (ACP) radical. Using rapid freezing, we have captured an organometallic intermediate with an iron-carbon (Fe-C) bond between ACP and the enzyme's [4Fe-4S] cluster. In the presence of the substrate protein, elongation factor 2, this intermediate converts to an organic radical, formed by addition of the ACP radical to a histidine side chain.

Spectroscopy and DFT Calculations of a Flavo-diiron Enzyme Implicate New Diiron Site Structures.

Flavo-diiron proteins (FDPs) are non-heme iron containing enzymes that are widespread in anaerobic bacteria, archaea, and protozoa, serving as the terminal components to dioxygen and nitric oxide reductive scavenging pathways in these organisms. FDPs contain a dinuclear iron active site similar to that in hemerythrin, ribonucleotide reductase, and methane monooxygenase, all of which can bind NO and O. However, only FDP competently turns over NO to NO.

Nitric oxide is an obligate bacterial nitrification intermediate produced by hydroxylamine oxidoreductase.

Ammonia (NH)-oxidizing bacteria (AOB) emit substantial amounts of nitric oxide (NO) and nitrous oxide (NO), both of which contribute to the harmful environmental side effects of large-scale agriculture. The currently accepted model for AOB metabolism involves NH oxidation to nitrite (NO) via a single obligate intermediate, hydroxylamine (NHOH). Within this model, the multiheme enzyme hydroxylamine oxidoreductase (HAO) catalyzes the four-electron oxidation of NHOH to NO We provide evidence that HAO oxidizes NHOH by only three electrons to NO under both anaerobic and aerobic conditions.

Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission.

Ammonia oxidizing bacteria (AOB) are major contributors to the emission of nitrous oxide (NO). It has been proposed that NO is produced by reduction of NO. Here, we report that the enzyme cytochrome (cyt) P460 from the AOB Nitrosomonas europaea converts hydroxylamine (NHOH) quantitatively to NO under anaerobic conditions.

A diferrous-dinitrosyl intermediate in the N2O-generating pathway of a deflavinated flavo-diiron protein.

Flavo-diiron proteins (FDPs) function as anaerobic nitric oxide scavengers in some microorganisms, catalyzing reduction of nitric to nitrous oxide. The FDP from Thermotoga maritima can be prepared in a deflavinated form with an intact diferric site (deflavo-FDP). Hayashi et al.

The nitric oxide reductase mechanism of a flavo-diiron protein: identification of active-site intermediates and products.

The unique active site of flavo-diiron proteins (FDPs) consists of a nonheme diiron-carboxylate site proximal to a flavin mononucleotide (FMN) cofactor. FDPs serve as the terminal components for reductive scavenging of dioxygen or nitric oxide to combat oxidative or nitrosative stress in bacteria, archaea, and some protozoan parasites. Nitric oxide is reduced to nitrous oxide by the four-electron reduced (FMNH2-Fe(II)Fe(II)) active site.

Studies of iron(III) porphyrinates containing silanethiolate ligands.

The chemistry of several iron(III) porphyrinates containing silanethiolate ligands is described. The complexes are prepared by protonolysis reactions of silanethiols with the iron(III) precursors, [Fe(OMe)(TPP)] and [Fe(OH)(H2O)(TMP)] (TPP = dianion of meso-tetraphenylporphine; TMP = dianion of meso-tetramesitylporphine). Each of the compounds has been fully characterized in solution and the solid state.

Histidine ligand variants of a flavo-diiron protein: effects on structure and activities.

Flavo-diiron proteins (FDPs) contain non-heme diiron and proximal flavin mononucleotide (FMN) active sites and function as terminal components of a nitric oxide reductase (NOR) and/or a four-electron dioxygen reductase (O(2)R). While most FDPs show similar structural, spectroscopic, and redox properties, O(2)R and NOR activities vary significantly among FDPs. A potential source of this variability is the iron ligation status of a conserved His residue that provides an iron ligand in all known FDP structures but one, where this His residue is rotated away from iron and replaced by a solvent ligand.

Treponema denticola superoxide reductase: in vivo role, in vitro reactivities, and a novel [Fe(Cys)(4)] site.

In vitro and in vivo results are presented demonstrating that superoxide reductase (SOR) from the air-sensitive oral spirochete, Treponema denticola (Td), is a principal enzymatic scavenger of superoxide in this organism. This SOR contains the characteristic non-heme [Fe(His)(4)Cys] active sites. No other metal-binding domain has been annotated for Td SOR.

Vibrational analysis of mononitrosyl complexes in hemerythrin and flavodiiron proteins: relevance to detoxifying NO reductase.

Flavodiiron proteins (FDPs) play important roles in the microbial nitrosative stress response in low-oxygen environments by reductively scavenging nitric oxide (NO). Recently, we showed that FMN-free diferrous FDP from Thermotoga maritima exposed to 1 equiv NO forms a stable diiron-mononitrosyl complex (deflavo-FDP(NO)) that can react further with NO to form N(2)O [Hayashi, T.; Caranto, J.

Adsorption kinetics of catalase to thin films of carbon nanotubes.

The adsorption conditions used to immobilize catalase onto thin films of carbon nanotubes were investigated to elucidate the conditions that produced films with maximum amounts of active catalase. The adsorption kinetics were monitored by spectroscopic ellipsometry, and the immobilized catalase films were then assayed for catalytic activity. The development of a volumetric optical model used to interpret the ellipsometric data is discussed.

Insights into the nitric oxide reductase mechanism of flavodiiron proteins from a flavin-free enzyme.

Flavodiiron proteins (FDPs) catalyze reductive scavenging of dioxygen and nitric oxide in air-sensitive microorganisms. FDPs contain a distinctive non-heme diiron/flavin mononucleotide (FMN) active site. Alternative mechanisms for the nitric oxide reductase (NOR) activity consisting of either protonation of a diiron-bridging hyponitrite or "super-reduction" of a diferrous-dinitrosyl by the proximal FMNH(2) in the rate-determining step have been proposed.

Reductive dioxygen scavenging by flavo-diiron proteins of Clostridium acetobutylicum.

Two flavo-diiron proteins (FDPs), FprA1 and FprA2, are up-regulated when the strictly anaerobic solvent producer, Clostridium acetobutylicum, is exposed to dioxygen. These two FDPs were purified following heterologous overexpression in Escherichia coli as N-terminal Strep-tag fusion proteins. The recombinant FprA1 and FprA2 were found to be homodimeric and homotetrameric, respectively, and both FDPs functioned as terminal components of NADH oxidases (NADH:O(2) oxidoreductases) when using C.