Replica of a Fishy Enzyme: Structure–Function Analogue of Trimethylamine-N-Oxide Reductase

Delving into the catalytic mechanism of molybdenum cofactors: a novel coupled cluster study

In this work, we use modern electronic structure methods to model the catalytic mechanism of different variants of the molybdenum cofactor (Moco). We investigate the dependence of various Moco model systems on structural relaxation and the importance of environmental effects for five critical points along the reaction coordinate with the DMSO and NO3- substrates. Furthermore, we scrutinize the performance of various coupled-cluster approaches for modeling the relative energies along the investigated reaction paths, focusing on several pair coupled cluster doubles (pCCD) flavors and conventional coupled cluster approximations. Moreover, we elucidate the Mo-O bond formation using orbital-based quantum information measures, which highlight the flow of σM-O bond formation and σN/S-O bond breaking. Our study shows that pCCD-based models are a viable alternative to conventional methods and offer us unique insights into the bonding situation along a reaction coordinate. Finally, this work highlights the importance of environmental effects or changes in the core and, consequently, in the model itself to elucidate the change in activity of different Moco variants.

Ag/AgBr-oxygen enriched g-C3N4 for efficient photocatalytic degradation of trimethylamine

In this study, Ag/AgBr-O-gCN samples with ternary Z-type heterojunctions were prepared by in situ photoreduction using water as the reducing agent for generating Ag/AgBr active species and oxygen doping. The experimental results indicated that Ag/AgBr-O-gCN degraded trimethylamine by nearly 100% in half an hour and maintained 90% of its original activity after five cycles. The kinetic constant of Ag/AgBr-O-gCN was excellent at 0.0928 min-1, 3.8 times that of gCN, 2.3 times that of Ag/AgBr-gCN, and 1.9 times that of O-gCN. Unlike Ag/AgBr-gCN photoreduced by methanol, gCN was used as an electron donor in the aqueous solution during the photoreduction process, and oxidation sites between the gCN skeleton and Ag/AgBr were formed for constructing the heterojunction system. The Z-type heterojunction system was established by introducing a suitable size of Ag nanoparticles as the recombination center to keep indirect contact between gCN and AgBr. This effectively reduced the electron-hole recombination rate and caused activity enhancement. This study offers a novel idea for the construction of a ternary heterojunction.

Inspired by Nature-Functional Analogues of Molybdenum and Tungsten-Dependent Oxidoreductases

Throughout the previous ten years many scientists took inspiration from natural molybdenum and tungsten-dependent oxidoreductases to build functional active site analogues. These studies not only led to an ever more detailed mechanistic understanding of the biological template, but also paved the way to atypical selectivity and activity, such as catalytic hydrogen evolution. This review is aimed at representing the last decade’s progress in the research of and with molybdenum and tungsten functional model compounds. The portrayed systems, organized according to their ability to facilitate typical and artificial enzyme reactions, comprise complexes with non-innocent dithiolene ligands, resembling molybdopterin, as well as entirely non-natural nitrogen, oxygen, and/or sulfur bearing chelating donor ligands. All model compounds receive individual attention, highlighting the specific novelty that each provides for our understanding of the enzymatic mechanisms, such as oxygen atom transfer and proton-coupled electron transfer, or that each presents for exploiting new and useful catalytic capability. Overall, a shift in the application of these model compounds towards uncommon reactions is noted, the latter are comprehensively discussed.

Oxygen Activation by a Copper Complex with Sulfur-Only Coordination Relevant to the Formylglycine Generating Enzyme

Synthesizing hydrosulfido Cu thiolate complexes is quite challenging. In this report, two new and rare hydrosulfido Cu thiolate complexes, [Et₄N]₂[(mnt)Cu-SH] (2, mnt = maleonitrile dithiolene = S₂C₂(CN)₂) and [Et₄N]₃[(mnt)Cu-(μ-SH)-Cu(mnt)] (3), have been synthesized. Coordination sites and O₂ activation by complex 2 resemble the formylglycine generating enzyme (FGE), an enzyme recently crystallographically characterized with sulfur-only coordination around Cu (three thiolate ligands). The function of this enzyme (and complex 2) is surprising because vulnerable thiolates should not be well suited for O₂ activation rationally. Indeed, activation of oxygen by such an all-sulfur-coordinated Cu complex 2 is lacking in the literature. Aerial O₂ (ambient O₂ from the air) activation by complex 2 could proceed through a superoxide radical intermediate and a sulfur radical intermediate detected by resonance Raman (rR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, respectively. The chemistry of 2 has been examined by its reactivity, crystal structure, and spectroscopic and cyclic voltammetric analyses. In addition, the results have been complemented with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations.

Iron and Zinc Porphyrin Linked MoO(dithiolene) Complexes in Relevance to Electron Transfer between Mo-cofactor and Cytochrome b5 in Sulfite Oxidase

Oxo-molybdenum (dithiolene) complex covalently linked individually to iron and zinc porphyrin have been synthesized to show an electron transfer between the two metal centres in relevance to electron transfer from...

Zinc protoporphyrin-trimethylamine-N-oxide complex involves cholesterol oxidation causing atherosclerosis

Metabolism of food protein by gut microbes produce trimethylamine which on oxidation by hepatic flavin-containing monooxygenases is transformed to trimethylamine-N-oxide (TMAO). TMAO has recently been implicated as a biomarker for atherosclerosis. TMAO, as (CH₃)₃N⁺-O^-), is ionic and so a hydrophilic molecule that is freely available in blood plasma. For the effective interaction with lipid-soluble molecules, TMAO should be phase transferred to the lipid site. We show that the free TMAO is effectively bonded to zinc protoporphyrin IX dimethyl ester [ZnPPDME] to yield [TMAOZnPPDME] using phase transfer reaction. The zinc protoporphyrin IX, [ZnPP], in general, available in blood may form [TMAOZnPP] complex. The nature of such interaction between TMAO and [ZnPP] has been structurally shown using a model complex, [TMAOZnTPP] (TPP = tetraphenylporphyrin). These complexes readily move from the polar plasma to the non-polar (lipid) site to act as the oxo-transfer agent to oxidize cholesterol causing atherosclerosis. Chromatographic and circular dichroism (CD) studies show that either TMAO or [ZnPP] alone cannot oxidize cholesterol. Free TMAO bonded with zinc-protoporphyrin IX, [ZnPP], in blood plasma as [TMAOZnPP] is transported to the lipid site and this is the reacting species to oxidize cholesterol causing atherosclerosis.

Selective Detection of Nitrogen-Containing Compound Gases

N-containing gaseous compounds, such as trimethylamine (TMA), triethylamine (TEA), ammonia (NH₃), nitrogen monoxide (NO), and nitrogen dioxide (NO₂) exude irritating odors and are harmful to the human respiratory system at high concentrations. In this study, we investigated the sensing responses of five sensor materials—Al-doped ZnO (AZO) nanoparticles (NPs), Pt-loaded AZO NPs, a Pt-loaded WO₃ (Pt-WO₃) thin film, an Au-loaded WO₃ (Au-WO₃) thin film, and N-doped graphene—to the five aforementioned gases at a concentration of 10 parts per million (ppm). The ZnO- and WO₃-based materials exhibited n-type semiconducting behavior, and their responses to tertiary amines were significantly higher than those of nitric oxides. The N-doped graphene exhibited p-type semiconducting behavior and responded only to nitric oxides. The Au- and Pt-WO₃ thin films exhibited extremely high responses of approximately 100,000 for 10 ppm of triethylamine (TEA) and approximately −2700 for 10 ppm of NO₂, respectively. These sensing responses are superior to those of previously reported sensors based on semiconducting metal oxides. On the basis of the sensing response results, we drew radar plots, which indicated that selective pattern recognition could be achieved by using the five sensing materials together. Thus, we demonstrated the possibility to distinguish each type of gas by applying the patterns to recognition techniques.

Structurally characterized one oxo–desoxo bridged Mo2–bis(dithiolene) complex and its interconversion to a discrete oxo or desoxo DMSOR model

The dissymmetric binuclear complex1acts as a precursor of the molybdoenzyme models of the dimethylsulfoxide reductase (DMSOR) class.

Synthesis and characterization of cyano and isocyano complexes of bis(dithiolato) molybdenum using Me3SiCN: a route to a cyanide-bridged multimer to a monomer

The Mo(iv) bis (dithiolate) complex showed diverse reactions with Me₃SiCN in the presence and absence of a coligand and under protic and aprotic media.

Mechanistic investigation of trimethylamine-N-oxide reduction catalysed by biomimetic molybdenum enzyme models

In this paper, we report a theoretical investigation of the reduction reaction mechanism of Me3NO using molybdenum containing systems that are functional and structural analogues of trimethylamine N-oxide reductase mononuclear molybdenum enzyme. The reactivity of the monooxomolybdenum(IV) benzenedithiolato complex and its derivatives to carbamoyl (t-BuNHCO) and acylamino (t-BuCONH) substituents on the benzene rings in both cis and trans arrangements was explored. The calculated energy profiles describing the steps of two mechanisms of attack considered viable (named cis- and trans-attack) by the Me3NO substrate at cis and trans positions with respect to the oxo ligand show that the attack on cis is energetically more favourable than the attack on trans. Along the pathway for the cis-attack the first step of the reaction, that is rate-determining for all the studied compounds, is the approach of the substrate to the Mo centre in cis to the oxo ligand that causes a distortion of the initial square-pyramidal geometry of the complex. The reaction steps involved in the trans position attack were also explored. Calculations confirm that, as previously suggested, the introduction of ligands able to form intramolecular NH···S hydrogen bonds accelerates the reduction of the Me3NO substrate and contributes to the tuning of the reactivity of molybdoenzyme models.

Molybdenum trioxide nanopaper as a dual gas sensor for detecting trimethylamine and hydrogen sulfide

The dual function of a free-standing, flexible, and semi-transparent MoO₃ nanopaper sensor to detect TMA and H₂S in a highly selective manner.

Mononuclear bis(dithiolene) Mo(iv) and W(iv) complexes with P,P; S,S; O,S and O,O donor ligands: a comparative reactivity study

Comparative redox reactions of eight Mo^IV/W^IVcomplexes with P,P; S,S; S,O and O,O donor ligands are presented.

Structural and functional models in molybdenum and tungsten bioinorganic chemistry: description of selected model complexes, present scenario and possible future scopes

A brief description about some selected model complexes in molybdenum and tungsten bioinorganic chemistry is provided. The synthetic strategies involved and their limitations are discussed. Current status of molybdenum and tungsten bioinorganic modeling chemistry is presented briefly and synthetic problems associated therein are analyzed. Possible future directions which may expand the scope of modeling chemistry are suggested.

Synthesis and structural characterization of dioxomolybdenum and dioxotungsten hydroxamato complexes and their function in the protection of radiation induced DNA damage

The synthesis and structural characterization of two novel dioxomolybdenum(VI) (1) and dioxotungsten(VI) (2) complexes with 2-phenylacetylhydroxamic acid (PAHH) [M(O)2(PAH)2] [M = Mo, W] have been accomplished. The dioxomolybdenum(VI) and dioxotungsten(VI) moiety is coordinated by the hydroxamate group (-CONHO(-)) of the 2-phenylacetylhydroxamate (PAH) ligand in a bi-dentate fashion. In both the complexes the PAHH ligand is coordinated through oxygen atoms forming a five membered chelate. The hydrogen atom of N-H of the hydroxamate group is engaged in intermolecular H-bonding with the carbonyl oxygen of another coordinated hydroxamate ligand, thereby forming an extended 1D chain. The ligand as well as both the complexes exhibit the ability to protect from radiation induced damage both in CTDNA as well as in pUC19 plasmid DNA. As the damage to DNA is caused by the radicals generated during radiolysis, its scavenging imparts protection from the damage to DNA. To understand the mechanism of protection, binding affinities of the ligand and the complex with DNA were determined using absorption and emission spectral studies and viscosity measurements, whereby the results indicate that both the complexes and the hydroxamate ligand interact with calf thymus DNA in the minor groove. The intrinsic binding constants, obtained from UV-vis studies, are 7.2 × 10(3) M(-1), 5.2 × 10(4) M(-1) and 1.2 × 10(4) M(-1) for the ligand and complexes 1 and 2 respectively. The Stern-Volmer quenching constants obtained from a luminescence study for both the complexes are 5.6 × 10(4) M(-1) and 1.6 × 10(4) M(-1) respectively. The dioxomolybdenum(VI) complex is found to be a more potent radioprotector compared to the dioxotungsten(VI) complex and the ligand. Radical scavenging chemical studies suggest that the complexes have a greater ability to scavenge both the hydroxyl as well as the superoxide radicals compared to the ligand. The free radical scavenging ability of the ligand and the complexes was further established by EPR spectroscopy using a stable free radical, the DPPH, as a probe. The experimental results of DNA binding are further supported by molecular docking studies.

A cyanide-bridged molybdenum bis(maleonitriledithiolate) square

[Et4N]2[Mo(IV)O(mnt)2] (mnt = maleonitriledithiolate) reacts, as a synthon, with Me3SiCN under an acidic medium to produce the square complex [Et4N]4[Mo4(μ-CN)4(mnt)8] (1) in high yield. Complex 1 shows strong antiferromagnetic interactions between adjacent Mo atoms in the cluster. The presence of redox-active mnt as a capping ligand strongly influences the magnetic property of 1. The physicochemical properties of 1 have been rationalized by density functional theory level of calculations.