Complexes of general formulation [Cr(Schiff-base)(H₂O)₂]X, where Schiff-base=1, 2-bis(salicylideneamino)ethane (salen), 1, 3-bis(salicylideneamino) propane (salprn) and 1, 4-bis(salicylideneamino)butane (salbuen) and X=ClO₄ or Cl have been prepared and characterised. Single-crystal structure of the complexrans[Cr(salprn)(H₂O)₂]Cl has been resolved. Evidence for less distorted coordination geometry around chromium in the salprn analogue as compared to that intrans-[Cr(salen)(H₂O)₂]⁺ has been presented. The kinetics of the aqua ligand substitution in the complexes Cr(Schiff-base)(H₂O)₂⁺ by thiocyanate have been investigated under pseudo-first order conditions with [NCS⁻]≫[Cr(III)],T=10–50°C, [H⁺]=10⁻⁸−10⁻¹ M,I=1.0M (LiClO₄). An attempt has been made to discuss the anomalous lability oftrans-[Cr(salen)(H₂O)₂]⁺ reported earlier in comparison to the reactivities of salprn and salbuen analogues. Bimolecular rate constants for the aqua ligand substitution by NCS⁻ in [Cr(Schiff-base)(H₂O)₂]⁺ at 25°C vary by more than two orders of magnitude depending on the nature of the Schiff-base ligand. The reactivity order is discussed in terms of the possible steric strain imposed by the equatorially coordinated quadridentate ligand.

Mechanistic insight has been gained into the diverse roles played by some chromium(III) ions in biosystems. Experimental evidence to show that chromium may serve to assemble insulin rather than insulin-receptor units has been obtained. A proposal that stabilisation of insulin by Cr(III) may be responsible for the beneficial role of Cr(III) in glucose metabolism has also been made. Although one of the well-known industrial applications of chromium(III) salts has been in the stabilisation of the collagen in skin to produce leather, it has remained difficult to provide a molecular basis to tanning. Results of model studies involving the reactions of collagen with a series of complexes of chromium(III) have been presented and an attempt to provide a molecular basis to the stabilisation of collagen by the metal ion have been made. In view of the growing concern about the ecological consequences as well as the occupational hazards of using chromium, abnormalities induced by a series of chromium complexes on the proliferation of human lymphocytes have been investigated. Evidence for apoptosis by Cr(III) has been obtained. Although chromium plays diverse functional roles in biosystems, a perspective discussion of some common features in the nature of interactions of the metal ion with biomolecules has been attempted.

The charge transfer spectral properties of group IV A tetrahalides (where M=Ti, Zr or Hf and X=F, Cl, Br or I) have been calculated using the Ms-Xα method and compared with experimental values. The order of ligand-to-metal charge transfer energies corresponds to the one-electron oxidation potential of X→X+e⁻(F⁻/F, Cl⁻/Cl, Br⁻/Br and I⁻/I). The dependence of the ligand-to-metal charge transfer energies on the optical electronegativity of the ligand has been demonstrated. The nature of bonding of the group IVA tetrahalides has been analysed using the MS-Xα method.

Theoretical calculations have been performed on Si₂C using density functional theories (DFT) and conventionalab initio method employing 6-311G* basis set. Present calculations indicate that some of the DFT methods (B3LYP, B3P86, BHandH, BHandHLYP) employed in this study cannot predict the observed bent structure in the case of Si₂C cluster whereas, MP2, SVWN5 and B3PW91 calculations predict the bent structure, as observed by experiment.

A molecular insight into the mechanism of stabilisation of collagen against the action of collagenase and wet heat leading to tanning has been gained. The variations in the extent of stabilisation of collagen with the nature of the molecular species of chromium(III) have been demonstrated experimentally. A case has been made to conceive tanning as emerging from an increase in long-range order and chromium(III)-induced molecular assembly of collagen.

Systematic investigation has been carried out to calculate critical points, charge density,ρ(r_c), and Laplacian of charge density, ∇²ρ(r_c), for weak complexes in the framework of MP2 and density functional theory (DFT). This study helps in assigning structures to van der Waals complexes such as Rg-HF, Rg-HCl, Rg-Li⁺ and Rg-Mg⁺, where Rg=He, Ne and Ar. The presence of (3, −1) critical points (bond critical points) in the complexes and the typical values ofρ(r) and ∇²ρ(r) at critical points indicate that closed-shell type of interaction is present in the molecules. The possible difference between the two types of bonding, rare gas-hydrogen bond interaction (Rg-H-X) and rare gas-halogen bond interaction (Rg-X-H), (where X=F and Cl) has also been analysed by computing the properties of charge density and Laplacian of charge density at the bond critical points.

Spreading behaviour of the dimeric surfactant polyethylene-glycoldistearate (PEGDS) monolayer at air/water interface has been studied using surface pressure-area (π-A) isotherms as a function of temperature. The isotherms show a plateau suggesting a transition between a liquid expanded (LE) and a condensed state. The condensed state possibly arises due to nucleation and growth of multilayers from the monolayer. Isobaric measurements of bothA-T and π-T at constant area show transitions atT = 295 K. These plots suggest a melting followed by formation of condensed microcrystallites. Structure optimization carried out using various angles of orientation of the alkyl tails with respect to the backbone in PEGDS reveals tilt transitions of the tails in different states which can be related to the packing behaviour seen in the isotherms. Optical microscopy has been used to confirm the structures in these states.

Copper sulphide clusters were prepared in Langmuir-Blodgett films of copper complexes of amphiphilic Schiff bases-3,4-dimethoxy-N-benzylidene hexadeylamine (I) and 3,4-dimethoxy-N-benzylidene-4’-(hexadecylamino) benzylamine (II) The clusters obtained were analysed using UV-Vis spectroscopy and optical microscopy. Brewster angle microscopic studies on monolayers ofI andII at air/water interface showed formation of needle-like domains which seem to cluster faster inI than inII. Atomic force microscopy (AFM) studies also showed fairly uniform sized clusters inII whereas in the case ofI they seem to show varying sizes. From the results it is concluded that π-elongation in the polar head groups leads to controlled cluster sizes in compoundII as compared to those in compoundI.