• Sabyasachi Sarkar

Articles written in Journal of Chemical Sciences

• Abstracts of posters presented at the symposium

• Synthesis of the active sites of molybdoenzymes: MoO2(VI) and MoO(IV)-dithiolene complexes mimicking enzymatic reactions of sulphite oxidase with saturation kinetics

[MoVIO2(S2C2(CN)2)2]2− (┘1) and [MoIVO(S2C2(CN)2)2]2− (2) mimick oxidoreductase enzymatic activities of sulphite oxidase with biological electron donor, SO32−, andin vitro electron acceptor, [Fe(CN)6]3−, demonstrating proton coupled electron transfer reaction in water and inhibition of the oxidation of (2) in the presence of KCN. The sulphite exidizing system is characterized by substrate saturation kinetics indicating the biological significance of the reactions

• CO2 fixation by [WIVO(S2C2(CN)2)2]2−: functional model for the tungsten-formate dehydrogenase ofClostridium thermoaceticum

(NEt4)2[WIVO(S2C2(CN)2)2] (1), isolated by reaction of Na2 WO4, Na2S2C2(CN)2 (Na2mnt) in acidified (pH5.5) aqueous medium in the presence of excess of sodium dithionite and NEt4Br, reduces CO2/HCO3 (pH 7.5) to yield HCOO and (NEt4)2[WVIO2(S2C2(CN)2)2] (2) mimicking tungsten-formate dehydrogenase (W-FDH) activity. (1) reacts with Na2MoO4 in acidic medium to produce [MoIvO(S2C2(CN)2)2]2− implicating the displacement of tungsten by molybdenum from the cofactor complex in W-FDH.

• Sunlight induced synthesis of tricarbonylhexahaptobuckminsterfullerenetungsten

[W(CO)3(η6-C60)] has been synthesized by sunlight irradiation of a benzene solution of C60 and W(CO)6 or [W(CO)3(η6-C6H6)] as a red-brown solid. This compound has been characterized by elemental analysis and by FAB mass spectroscopy (parent ion peak centred at 988 (30%)). Chemical reactivity and IR spectroscopy indicate a hexahapto mode of bonding in this complex according to the 18-electron rule. XPS and cyclic voltammetric data support the electron acceptor/donor properties of bonded C60 and the electron donor/acceptor properties of W(CO)3 moiety respectively in this compound.

• Modelling non-redox enzymes: Anaerobic and aerobic acetylene hydratase

• Oxidation of phosphine by sulfur or selenium involving a catalytic cycle in the interconversion of monomer and tetramer forms of copper-maleonitriledithiolate complexes

The addition of triphenylphosphine (PPh3), into [Et4N]4[Cu4(mnt)4] shifted its characteristic electronic spectral band at 377 nm to 372 nm which is identical to that of the monomeric species, [Et4N][Cu(mnt)(PPh3)]. This reaction was followed by electrochemical study and also by 31P NMR spectroscopy. Such interconversion with the participation of breaking of bridging copper-$\mu_3$-sulfur bond with the formation of new copper-phosphorous bond led to the development of a catalytic cycle using excess PPh3 and S or Se as the reacting substrates. The turnover number for the oxidation of PPh3 by S was found to be $0.8 \times 10^{-2} s^{-1}$ and that with Se was $0.6 \times 10^{-2} s^{-1}$ using this catalytic system.

• NO2-induced synthesis of nitrato-iron(III) porphyrin with diverse coordination mode and the formation of isoporphyrin

Two nitrato-iron(III) porphyrinates [Fe(4-Me-TPP)(NO3)] 1 and [Fe(4-OMe-TPP)(NO3)] 2 are reported. Interestingly, [Fe(4-Me-TPP)(NO3)] 1 has nitrate ion coordinated as monodentate (by single oxygen atom), while [Fe(4-OMe-TPP)(NO3)] 2 has nitrate coordination through bidentate mode. Compound 1 was found serendipitously in the reaction of [Fe(4-Me-TPP)Cl] with nitrous acid, which was performed for the synthesis of nitro-iron(III) porphyrin, [Fe(4-Me-TPP)NO2]. The compound 2 was synthesized by passing NO2 gas through a solution of [Fe(4-OMe-TPP)]2O. Upon passing NO2 gas through a solution of a 𝜇-oxo-dimer, [Fe(4-Me-TPP)]2O also produces 1. It is interesting that in more electron-rich porphyrin 2, binding of the nitrate in a symmetrical bidentate way while in less electron-rich porphyrin 1, binding of the anion is unidentate by a terminal oxygen atom. However, it is expected that the energy difference between the monodentate and bidentate coordination mode is very small and the interchange between these coordination is possible. Upon passing NO2 gas through a solution of 𝜇-oxo-dimeric iron(III) porphyrin, the nitrato-iron(III) porphyrin forms first, that later gets oxidized to 𝜋-cation radical to yield hydroxy-isoporphyrin in the presence of trace amount of water. These nitrato-iron(III) porphyrinates in moist air slowly converted back to their respective 𝜇-oxo-dimeric iron(III) porphyrins.

• # Journal of Chemical Sciences

Volume 132, 2020
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019