• P T Manoharan

      Articles written in Journal of Chemical Sciences

    • A theoretical study of the Jorgensen’s nephelauxetic effect in some simple transition metal halo-complexes from a molecular orbital computation

      S Vijaya P T Manoharan

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      A theoretical study of Jorgensen's nephelauxetic effect in some simple high spin transition metal halo-complexes has been made with an unrestricted Hartree-Fock-SCF-INDO MO calculation. The nephelauxetic spectroscopic parameters—the Racah integralB and the covalency factor β- have been theoretically evaluated from the above MO analysis results. For this a pseudo-atom model and an eigen-MO model have been employed. The results allow a comparison to be made between the experimental and theoretical results, which indicate the relative success of the pseudo-atom model over the other. It has also been pointed out that the results from both models would have improved considerably if the use of metal valence basis orbitals corresponding to its final oxidation state had been resorted to. The concept of differential covalency and its effect on nephelauxetic parameters are also discussed.

    • Magnetic properties of some exchange coupled [Ni(mnt)2] dimers

      P Kuppusamy P T Manoharan

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      The metal dithiolenes exhibit interesting solid state properties owing to the presence of columnar crystallographic packing. Particularly, thebis(maleonitriledithiolato)-nickel(III) systems with a variety of organic and inorganic counter ions seem to possess low-dimensional magnetic interactions and charge-transfer properties. The metal chelates show strong alternation in their packing and result in reduced magnetic moments as a consequence of antiferromagnetic exchange coupling between the pairs. We have studied a few interesting dimers through x-ray structure and magnetic susceptibility measurements and the results are used to arrive at a correlation between the observed magnetic behaviour and the structure of the dimeric units.

    • Surfactant-induced stabilization of four-coordinated hemes in reconstituted hemoglobins

      B Venkatesh S Ramasamy V Swarnalatha J Santhanalakshmi R Asokan J M Rifkind P T Manoharan

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      A transition from 5-coordination to 4-coordination metal centres of porphyrins in carbonmonoxy Fe(II), Cu(II) and Ni(II) hemoglobins is observed as a consequence of ionic surfactant interactions with metalloproteins through UV-Vis studies. SDS (anionic) and CTAB (cationic) surfactants are used. Values of heme partition coefficient (K) between globin and surfactant show that, in both CTAB and SDS, partitioning increases proportionately with surfactant concentration for a fixed concentration of hemoglobin. The interactions seem to be mainly hydrophobic in nature with metalloproteins, though coordination and coulombic interactions may also play a minor role in CTAB and SDS respectively. The present study provides new insight into reconstituted hemoglobin-surfactant interaction.

    • Interesting properties of some iron(II), copper(I) and copper(II) complexes with tridentate ligands

      P T Manoharan

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    • Metal ion coordination in ‘R’ and ‘T’ state hybrid hemoglobins as revealed by optical, EPR and sulphhydryl reactivity studies

      S Ramasamy Swarnalatha Venkateshrao J M Rifkind P T Manoharan

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      The sulphhydryl environment in various mixed-metal hybrid hemoglobins, viz. α2(Cu)-β2(FeCO), α2(FeCO)-β2(Cu), α2(Cu)-β2(Ni), α2(Ni)-β2(Cu), was studied by reacting them with the sulphhydryl reagent, 4,4′-dithiodipyridine (4-PDS). The reactivity was compared with that of HbCO, NiHb and CuHb. It is found that there exists a correlation between conformational change and metal ion environment, not only at the extreme R and T states but also the intermediate conformations. EPR examinations of these hybrids show that both in R state-[Cu(II)-Fe(II)] and T state-[Cu(II)-Ni(II)] hybrids at neutral pH and in the absence of IHP, CuPPIX, irrespective of the subunit in which it is present, has a mixed-metal ion environment: Species 1, a five-coordinated Cu2+ complex with strong proximal histidine bond and species 2, a four-coordinated complex without any covalent linkage with Nε F8-histidine.

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