• Sanjib Ghosh

      Articles written in Journal of Chemical Sciences

    • Triplet state sublevel spectroscopy applied to proteins

      Sanjib Ghosh L Zang A H Maki

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      Triplet state sublevel spectroscopy using optical detection of magnetic resonance (ODMR) in zero magnetic field can be successfully employed to study (i) the environment of tryptophan (Trp) residues in a protein by observing the position and structure of phosphorescence spectra, zero field ODMR transitions and triplet state sublevel kinetics, (ii) the energy transfer among Trp residues, and (iii) whether any cysteine (Cys) residue is within van der Waals distance of any Trp residue by studying the complex of the protein with methylmercury(II) iodide (CH3HgI) which binds to Cys residues. These studies are particularly important where crystal structure study is not possible. Study of the S1 state often gives ambiguous results since fluorescence is always broad and shows multi-exponential decay. Our results on bacteriophage lysozyme T4 which contains three Trp residues at positions 126, 138 and 158 are presented. Measurements were facilitated by the use of a mutated enzyme containing one or two Trp-Tyr substitutions. The results indicate that (i) Trp 126 and 158 are solvent exposed, whereas Trp 138 is buried in a hydrophobic environment, (ii)SS non-radiative energy transfer takes place predominantly from Trp 126 to Trp 158, and (iii) only Trp-158 undergoes a heavy atom perturbation, which affects selectively the z-sublevel (z is an out-of-plane axis of the indole plane) as a result of CH3HgI binding to nearby Cys 97. We suggest that the Hg atom is located on the z-axis of Trp 158 in the complex. This interpretation is based on our investigations on the effect of orientation of heavy atom perturbers in some naphthalene-crown ether metal ion complexes.

    • The lowest (n, π*) transition of indanetrione (anhydrous ninhydrin) in various ethers as solvents

      Jayanta Roy Surajit Bhattacharya Shampa Samanta Sanjib Ghosh

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      The lowestS1(n, π*) transition (absorption) of indanetrione having acis-vicinal triketo group exhibits a large blue-shift in cyclic saturated ethers compared to that in an open-chain saturated ether. This transition of indanetrione in mixed solvents containing a cyclic saturated ether (tetrahydrofuran, dioxane and tetrahydropyran) as one of the components and a non-polar or less polar solvent as the other component has been studied at room temperature. The spectra are also studied in pure cyclic saturated ethers as a function of temperature. These studies suggest a specific interaction between indanetrione and cyclic ethers in the ground state. Similar studies in open-chain saturated ethers indicate the absence of such an interaction. The nature of the specific interaction has been discussed.

    • Comparative photophysical behaviour of naphthalene-linked crown ethers and aza crown ethers of varying cavity dimensions

      Subhodip Samanta Pinki Saha Sardar Shyam Sundar Maity Anirban Pal Maitrayee Basu Roy Sanjib Ghosh

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      A comparative time-resolved emission studies of several naphtho-crown ethers I-V, where metal ions can be complexed in a predetermined orientation with respect to the naphthalene (Naph) 𝜋- plane and naphthalene-linked aza crown ethers (L1 and L2) have been presented. In both the systems, crown ethers and aza crown ethers, naphthalene fluorescence gets quenched. In the systems I to V, the quenching is mainly due to efficient spin-orbit coupling (SOC) leading to greater population of the lowest triplet state of naphthalene. This SOC depends on the orientation of the crown ring with respect to the Naph-𝜋-plane. However, in the systems L1 and L2, the quenching is due to photoinduced electron transfer (PET) from nitrogen lone pair of the aza crown ring to naphthalene moiety and consequent exciplex formation. The results have been interpreted using the time-resolved emission studies of all the compounds in various solvents, their alkali metal ion complexes, and protonated ligands.

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