Biomedical subjects

T K Ghanty

Publications and source records attributed to T K Ghanty.

5 recordsLinked to original sources

PubMed2006

Insertion of rare gas atoms into BF3 and AlF3 molecules: an ab initio investigation.

The structure, stability, charge redistribution, and harmonic vibrational frequencies of rare gas inserted group III-B fluorides with the general formula F-Rg-MF(2) (where M=B and Al; Rg=Ar, Kr, and Xe) have been investigated using ab initio quantum chemical methods. The Rg atom is inserted in one of the M-F bond of MF(3) molecules, and the geometries are optimized for ground as well as transition states using the MP2 method. It has been found that Rg inserted F-Rg-M portion is linear in both F-Rg-BF(2) and F-Rg-AlF(2) species. The binding energies corresponding to the lowest energy fragmentation products MF(3)+Rg (two-body dissociation) have been computed to be -670.4, -598.8, -530.7, -617.0, -562.1, and -494.0 kJmol for F-Ar-BF(2), F-Kr-BF(2), F-Xe-BF(2), F-Ar-AlF(2), F-Kr-AlF(2), and F-Xe-AlF(2) species, respectively. The dissociation energies corresponding to MF(2)+Rg+F fragments (three-body dissociation) are found to be positive with respect to F-Rg-MF(2) species, and the computed values are 56.3, 127.8, and 196.0 kJmol for F-Ar-BF(2), F-Kr-BF(2), and F-Xe-BF(2) species, respectively. The corresponding values for F-Ar-AlF(2), F-Kr-AlF(2), and F-Xe-AlF(2) species are also found to be positive. The decomposition of F-Rg-MF(2) species into the MF(3)+Rg (two-body dissociation) channel typically proceeds via a transition state involving F-Rg-M out-of-plane bending mode. The transition state barrier heights are 35.5, 62.7, 89.8, 22.0, 45.6, and 75.3 kJmol for F-Ar-BF(2), F-Kr-BF(2), F-Xe-BF(2), F-Ar-AlF(2), F-Kr-AlF(2), and F-Xe-AlF(2) species, respectively. The calculated geometrical parameters and the energy values suggest that these species are metastable and may be prepared and characterized using low temperature matrix isolation techniques, and are possibly the next new candidates for gas phase or matrix experiments.

Journal Article↗

PubMed2006

Structure and stability of xenon insertion compounds of hypohalous acids, HXeOX [X=F, Cl, and Br]: an ab initio investigation.

The structure and stability of xenon-inserted hypohalous acids HXeOX (X=F, Cl, and Br) have been investigated theoretically using ab initio molecular orbital calculations. All these molecules are found to consist of a nearly linear HXeO moiety and a bend XeOX fragment. Geometrical parameters of HXeOX are comparable with that of experimentally observed HXeOH species. The dissociation energies corresponding to the lowest-energy fragmentation products, HOX+Xe have been computed to be -398.1, -385.5, and -386.7 kJmol for HXeOF, HXeOCl, and HXeOBr, respectively, at the MP2 level of theory. The respective barrier heights corresponding to the bent transition states (H-Xe-O bending mode) have been calculated to be 138.1, 138.4, and 138.2 kJmol with respect to HXeOX minimum. These species are found to be metastable in their respective potential-energy surface, and the dissociation energies corresponding to the H+Xe+OX products are found to be 56.8, 66.0, and 80.8 kJmol for HXeOF, HXeOCl, and HXeOBr, respectively. The energies corresponding to the H+Xe+O+X dissociation channel have been computed to be 272.0, 309.3, and 299.7 kJmol for HXeOF, HXeOCl, and HXeOBr, respectively, at the same level of theory. Energetics as well as geometrical considerations suggests that it may be possible to prepare these species experimentally similar to that of HXeOH species at low-temperature laser photolysis experiments.

Journal Article↗

PubMed2005

Photoionization of CH(3)I mediated by the C state in the visible and ultraviolet regions.

Three/two-photon resonant multiphoton ionization (MPI) of the CH3I monomer has been studied in the gas phase at 532 and 355 nm using time-of-flight mass spectrometry. Under low laser intensity (approximately 10(9) W/cm2) the mass spectra showed peaks at m/z 15, 127 and 142, corresponding to [CH3]+, [I]+ and [CH3I]+ species, at both these wavelengths. The laser power dependence for [CH3I]+, [I]+ and [CH3]+ ions showed a three-photon dependence at 532 nm. For the same three ions, photoionization studies at 355 nm gave a power dependence of 2. Both these results suggest that a vibronic energy level at approximately 7 eV, lying in the Rydberg C state, acts as a resonant intermediate level in ionization of CH3I. In the case of 355 nm, with increasing intensity additional peaks at m/z 139 and 141 were observed which could be assigned to [CI]+ and [CH2I]+ fragments. In contrast, for high intensity radiation at 532 nm ( approximately 2 x 10(10) W/cm2), only the [CI]+ fragment was observed. At these wavelengths, fragment ions observed in mass spectra mainly arise from photodissociation of the parent ion. Experiments at another wavelength in the visible region (564.2 nm) confirmed the results obtained at 532 nm. In order to assess the role of the A state in these MPI experiments, additional experiments were performed at 266 and 282.1 nm, which access the A state directly via a one-photon transition, and showed absence of a surviving precursor ion. Reaction energies for various possible dissociation channels of CH3I/[CH3I]+/[CH2I]+ were calculated theoretically at the MP2 level using the GAMESS electronic structure program.

Journal Article↗

PubMed2004

Is molecular rotation really influenced by subtle changes in molecular shape?

In an attempt to seek out whether the reorientation time of a solute molecule is influenced by marginal changes to its shape, rotational relaxation of four coumarin solutes that are almost identical in size but subtly distinct in shape has been investigated in a viscous nonpolar solvent as a function of temperature. It has been observed that the reorientation times of the four coumarins differ significantly from one another. The four solutes have been treated as asymmetric ellipsoids and Stokes-Einstein-Debye hydrodynamic theory has been employed to calculate the shape factors and boundary condition parameters. The measured reorientation times when normalized by respective shape factors and boundary condition parameters can be scaled on a common curve, which is an indication that ellipsoid based hydrodynamic theory is adequate to model the reorientation times even when the differences in the shapes of the solute molecules are minimal.

Journal Article↗

PubMed2003

Antioxidant activity of bakuchiol: experimental evidences and theoretical treatments on the possible involvement of the terpenoid chain.

The protective activity of the plant-derived meroterpene, bakuchiol [1-(4-hydroxyphenyl)-3,7-dimethyl-3-vinyl-1,6-octadiene, 1], against oxidative damages to lipids and proteins has been investigated and rationalized based on the scavenging activity of 1 against various oxidizing radicals (Cl(3)CO(2)(*), linoleic acid peroxyl radicals, LOO(*), DPPH radicals, (*)OH, and glutathiyl radicals). The rate constants of the scavenging reactions, transients formed in these reactions, and their mechanistic pathways have been probed using optical pulse radiolysis technique. Besides 1, its methyl ether derivative 2 also could prevent lipid peroxidation in rat brain homogenate, indicating the probable participation of their terpenoid chains in scavenging LOO(*). This was further corroborated from the pulse radiolytic studies on the reaction between the glutathiyl radicals and the compounds 1 and 2 as well as two other congeners, 3 and 4, which showed transient absorptions at approximately 300 nm attributable to some C-centered allylic radicals. On the basis of the strong signals at approximately 300 nm with 1-3 as compared to compound 4, formation of the allylic radical adjacent to the trisubstituted olefin function in 1-3 was envisaged. This was confirmed by quantum chemical calculations of the relative energies of the probable radical species derivable from 2 using Hartree-Fock and density functional theory along with self-consistent reaction field model. In the case of 1, the allylic radical was found to be transformed into the phenoxyl radical at a later stage. All of these data revealed, for the first time, the importance of the terpenoid moiety of bakuchiol in controlling its antioxidant action via radical scavenging.

Animals↗