• MAHESH SUNDARARAJAN

      Articles written in Journal of Chemical Sciences

    • Can uranyl complexes encapsulate to carbon nanotubes? A periodic DFT study

      K SRINIVASU MAHESH SUNDARARAJAN

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      Periodic density functional theory (DFT)-based calculations were carried out on a series of uranyl complexes encapsulated within single walled (SW)-CNT to understand their encapsulation affinities. We find that uranyl-aqua complex ([UO₂(H₂O)₅]²⁺) binds stronger as compared to uranyl-hydroxo-complex ([UO₂(OH)₄]²⁻) due to the variable overall charge of the complex. Further, binding affinities of uranyl formate complexes with different formate stoichiometries (1:1, 1:2 and 1:3) with SW-CNT are considered. Here again, due to variable charges, cationic mono-‘formate-uranyl ([UO2(FM)(H₂O)₃]¹⁺) complex binds stronger as compared to anionic tri-formate uranyl ([UO2(FM)₃]¹⁻). Further, due to the very weak binding commonly found in [UO₂(FM)₃]¹⁻ to CNT, the tubular ends of SW-CNT are sealed with functionalized C₃₆ fullerene. The binding affinity of uranyl complex is not improved when C₃₆ fullerene is used to seal to the SW-CNT as compared to its unsealed counterpart. However, upon functionalizing (at the hub carbon) the C36 cork, the binding affinity of [UO₂(FM)3]¹⁻ is larger inside the CNT due to favorable hydrogen bonding interactions with the uranyl oxygens. Our findings are consistent with the experimental observations which will help to design novel nanomaterials for nuclear waste management processes.

    • Quantum chemical studies of structures and spin Hamiltonian parameters of iron transferrin using isolated and embedded clusters models

      LOKPATI MISHRA MAHESH SUNDARARAJAN

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      Density functional theory (DFT) based calculations using large cluster models are used to elucidate the ground state electronic structure of iron bound transferrin. Explicit incorporation of second coordination amino acid residues and crystallographic water molecules anchors the active site. Our calculations clearlysuggest that tyrosine amino acid (Tyr188) residue is bound to iron when the structures are optimized within the continuum solvation model. However, in the gas phase optimized structure, we note that Tyr188 is unbound to Fe (by more than 3 Å). The Mössbauer isomer shift (δ) and quadrupolar splitting (ΔEq) of iron transferrin are in line with the experimental data only when Tyr188 is bound to Fe(III). Further, the computed oxygen hyperfine coupling constant value is very large (−14.5 MHz) when bound to iron which can be verified through 17O NMR experiments. We propose that Tyr188 is strongly bound to Fe(III) at physiological pH, which needs to be protonated (acidic pH) to weaken this bond, thus the metal release pathway can be possible only in acidic conditions.

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