• Arun Kumar

      Articles written in Journal of Chemical Sciences

    • Preparation and characterization of free-standing pure porphyrin nanoparticles

      Arun Kumar Perepogu Prakriti Ranjan Bangal

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      Preparation and characterization of absolutely pure and stable nanoparticles of 5,10,15,20-meso-tetrakis phenyl porphyrin (TPP) and catalytically repute 5,10,15,20-meso-tetrakis pentaflurophenyl porphyrin (H2F20TPP) by improved ‘reprecipitation method’ is described. The innovation of this modified `reprecipitation method’ lies on the judicial selection of organic solvent and amount of porphyrin solution to be injected in the aqueous media. Exactly similar process produces relatively small nanoparticles for TPP than that of H2F20TPP while the stability of the H2F20TPP nanoparticles is bit higher than nanoparticles of TPP. Absorption and emission spectra reveal that the formation of nanoparticles for both the cases is induced by J- and H-type aggregation. DFT calculations predict the optimized geometries and frontier molecular orbital, which favours the strength of face-to-face interaction with neighbour molecules to be more facile for TPP than that of H2F20TPP helping the latter to form bigger and relatively more stable and free-standing nanoparticles. The use of no other compounds except dichloromethane, a highly volatile organic solvent and respective porphyrins give absolutely pure nanoparticles. This improved method will lead to produce organic nanoparticles of 𝜋-conjugated systems easily and efficiently.

    • Synthesis and unexpected reactivity of [Ru(𝜂6 -cymene)Cl2 (PPh2 Cl)], leading to [Ru(𝜂6 -cymene)Cl2 (PPh2H)] and [Ru(𝜂6-cymene)Cl2 (PPh2OH)] complexes

      Arun Kumar Pandiakumar Ashoka G Samuelson

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      The reaction of [Ru(𝜂6-cymene)Cl2]2 and PPh2Cl in the ratio 1:2 gives a stable [Ru(𝜂6-cymene) Cl2(PPh2Cl)] complex. Attempts to make the cationic [Ru(𝜂6-cymene)Cl(PPh2Cl)2]Cl with excess PPh2Cl and higher temperatures led to adventitious hydrolysis and formation of [Ru(𝜂6-cymene)Cl2 (PPh2OH)]. Attempts to make a phosphinite complex by reacting [Ru(𝜂6-cymene)Cl2]2 with PPh2Cl in the presence of an alcohol results in the reduction of PPh2Cl to give [Ru(𝜂6-cymene)Cl2(PPh2H)] and the expected phosphinite. The yield of the hydride complex is highest when the alcohol is 1-phenyl-ethane-1,2-diol. All three half-sandwich complexes are characterized by X-ray crystallography. Surprisingly, the conversion of chlorodiphenylphosphine to diphenylphosphine is mediated by 1-phenyl-ethane-1,2-diol even in the absence of the ruthenium half-sandwich precursor.

    • Photocytotoxic ternary copper(II) complexes of histamine Schiff base and pyridyl ligands

      Samya Banerjee Akanksha Dixit K Sesha Maheswaramma Basudev Maity Sanjoy Mukherjee Arun Kumar Anjali A Karande Akhil R Chakravarty

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      Ternary copper(II) complexes of salicylaldehyde-histamine Schiff base (HL) and pyridyl ligands, viz. [Cu(bpy)(L)](ClO4) (1) and [Cu(dppz)(L)](ClO4) (2), where bpy is 2,2′-bipyridine (in 1) and dppz is dipyrido[3,2-a:2′,3′-c]phenazine (in 2), were synthesized, characterized and their DNA binding, photo-activated DNA cleavage activity and photocytotoxicity studied. The 1:1 electrolytic one-electron paramagnetic complexes showed a d-d band near 670 nm in aqueous DMF (1:1 v/v). The crystal structure of complex 1 showed the metal in CuN4O distorted square-pyramidal geometry. Complex 2 intercalatively binds to calf-thymus (ct) DNA with a binding constant (𝐾b) of ∼105 M−1. It exhibited moderate chemical nuclease activity but excellent DNA photocleavage activity in red light of 647 nm forming $^{\bullet}\text{OH}$ radicals. It showed remarkable photocytotoxicity in human cervical cancer cells (HeLa) giving IC50 of 1.6 𝜇M in visible light (400-700 nm) with low dark toxicity. The photo-induced cell death is via generation of oxidative stress by reactive oxygen species.

    • Transfer hydrogenation reactions catalyzed by chiral half-sandwich Ruthenium complexes derived from Proline

      ARUN KUMAR PANDIA KUMAR ASHOKA G SAMUELSON

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      Chiral ruthenium half-sandwich complexes were prepared using a chelating diamine made from proline with a phenyl, ethyl, or benzyl group, instead of hydrogen on one of the coordinating arms. Three of these complexes were obtained as single diastereoisomers and their configuration identified by X-ray crystallography. The complexes are recyclable catalysts for the reduction of ketones to chiral alcohols in water. A ruthenium hydride species is identified as the active species by NMR spectroscopy and isotopic labelling experiments.Maximum enantio-selectivity was attained when a phenyl group was directly attached to the primary amine on the diamine ligand derived from proline.

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