• K N Ganesh

      Articles written in Journal of Chemical Sciences

    • Chemical modelling of photosynthesis: Intramolecular quinone-porphyrin complexes

      K N Ganesh

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      The strategies for the synthesis of covalently linked, flexible and rigid quinoneporphyrin complexes are described. Several anomalous chemical reactivities were observed in the quinone-capped porphyrins which may be attributed to the proximity of quinone and porphyrin moieties. Previous investigations by1Hnmr spectroscopy have demonstrated that the metal ion in capped metalloporphyrins is 5 co-ordinate, bound intramolecularly to quinone carbonyls and can accept a sixth ligand from the unhindered side. Here, additional evidence from13CNMR spectroscopy is presented to support the intramolecular co-ordination of the quinone and establish the cooperativity in binding of an external ligand; this process involves the movement of the metal ion into the porphyrin plane, pulling the quinone chromophore closer to the porphyrin. Electrochemical results reveal that the quinone in capped metalloporphyrins are better electron acceptors than simple quinones. The intramolecular quinone-porphyrin complexes promise to be potential model compounds to demonstrate the primary photosynthetic eventin vitro.

    • Chemical synthesis of oligonucleotides. 3: Synthesis and characterization of N,O-protected ribophosphoesters for applications in RNA synthesis

      Vidhya Gopalakrishnan K N Ganesh

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      The chemical synthesis of RNA, in contrast to that of DNA, poses problems due to fi) additional requirement of 2′-hydroxyl protection of the ribose moieties, and (ii) high lability of inter-ribophosphate bonds. Herein we report the synthesis and characterisation of N, O-protected ribophosphoesters 1 which are key monomeric derivatives in phosphotriester methodology for RNA synthesis. Both the isomeric 2′ and 3′-O-phosphates have been obtained and characterised. The utility of the t-butyl dimethylsilyl group for 2′-hydroxyl protection in the phosphotriester method is demonstrated by the synthesis of r(AUAU),r (UAUA) andr (CACA).

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      K N Ganesh

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    • Metallodesferals as a new class of DNA cleavers: Specificity, mechanism and targetting of DNA scission reactions

      R R Joshi K N Ganesh

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      Interaction of metal complexes with nucleic acids is currently attracting wide attention due to their potential utility as drugs, regulators of gene expression and tools for molecular biology. Many metal complexes exhibit nucleolytic activity, the most important examples being Cu(II)-OP, Fe(H)-BLM, Fe(II)-EDTA, metalloporphyrins, Ru and Co complexes of 4,7-diphenyl-l,10-phenanthroline and more recently by Ni(II) complexes. Desferal, a well known siderophore and a highly effective drug in chelation therapy of iron overload diseases, forms a stable octahedral co-ordination Fe(III) complex Eerrioxamine B. We have been interested in the DNA damaging properties of metallodesferals and this paper describes the DNA cleaving ability of metallodesferals, metal-dependent base selectively in DNA scission reactions, mechanistic studies on DNA cleavage by CuDFO and targetting of DNA cutting by covalent MDFO conjugates. This paper reports the synthesis of Cu(II), Co (III) and Ni(II) complexes of a siderophore chelating drug desferal, the studies on cleavage of plasmid DNA, the sequence preference of cleavage reactions, and C1’ as the primary site of hydroxyl radical attack in the reactions. Oligonucleotides covalently linked with this molecular scissor can direct the cleavage of either single or double strand DNA’s, mediated by duplex or triple helix structures respectively. Such targetting of DNA cleavage reactions, mediated by oligonucleotide-Cu(II)/Co(III) desferal conjugates has demonstrated reasonable site specificity and efficiency

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