Helical superstructure and charged polarons contributions to optical nonlinearity of 2-methyl-4-nitroaniline crystals studied by resonance Raman, electron paramagnetic resonance, circular dichroism spectroscopies, and quantum chemical calculations.

The Raman excitation profiles of solid 2-methyl-4-nitroaniline (MNA) reveal several band enhancements by intermolecular and intramolecular charge transfer states. Calculated excited- and ground-state molecular geometries and excited state distortions qualitatively determined from Raman spectra indicate multiple vibrations leading to MNA dissociation. Also, overtones and combination tones can generate charged polarons, as detected by electron paramagnetic resonance after the exposure to 980 and 1550 nm laser diodes. The MNA space group Ia (C(s)(4)) is nonchiral; however, the electronic circular dichroism (CD) spectra of solution, KBr pellet, and single crystal were recorded. The crystal chirality is elucidated by room-temperature dynamic disorder, possible helical superstructure along the [102] polar axis, and charged polarons presence. The CD spectra ab initio calculations for MNA neutral and negatively charged monomers, dimers, and trimers, lying along the helix, confirmed the chirality. The role of these findings toward efficient optical nonlinearity and electric conductivity failure is discussed.

Non-empirical quantum chemical studies on electron transfer reactions in trans- and cis-diamminedichloroplatinum(II) complexes.

The search was made for theoretical confirmation of hypothesis that mechanism of cisplatin cytotoxicity is based on dissociative electron transfer (ET) processes. Applying quantum chemical calculations based on supermolecular approach, the reactions mimicking presumed steps of cisplatin activation were evaluated. The electronic structure of model systems: cis- and transplatin with free electrons, hydrated electrons, and water, was studied by using density functional (DFT) within the Huzinaga basis set and GAUSSIAN-09 package. The respective energy was evaluated with the use of B3LYP density hybrid functional. The calculations were performed for gas phase and water solution; the solvent effects were studied by using the polarizable continuum model. Analysis of the energetic and structural parameters of cisplatin vs. transplatin behavior in the model systems leads to conclusion: there are two possible ways of cisplatin biotransformation, hydrolysis and hydrated electron impact, dependent on the medium redox state.

In silico approach to cisplatin toxicity. Quantum chemical studies on platinum(II)-cysteine systems.

The behaviour of cisplatin in serum, and the drastic differences between the properties of this drug and its trans-isomer were the main motivations for this work. In a search for model "thiol-platin(II)" interactions, the first steps of the following reaction systems were evaluated: (1) cisplatin-thiomethanol; (2) transplatin-thiomethanol; (3) cisplatin-cysteine; and (4) transplatin-cysteine. In each case, calculations for the associative mode of reactions were performed. The electronic structure of these molecular systems was studied at the non-empirical all-electron level using density functional theory (DFT) within the Huzinaga and WTBS basis sets including polarisation Gaussian functions and full geometry optimisation. B3LYP or EPBO density functionals were applied throughout. The calculated molecular electrostatic potentials are presented graphically. Assuming that electrostatic effects are dominant, cisplatin should interact more strongly with the sulfur atom of CH3S- and deprotonated CYS-S- than transplatin. This fact has been documented in the supermolecule model of the relevant interaction energies in both gas phase as well as within the solvent polarisable continuum model. The opposite relationship was observed when we compared values of energy differences between products and substrates for both isomers. The data obtained here could be applied to search for correlation between the biological activity of platinum complexes and their properties as estimated by various physico-chemical and in silico methodologies.

Proton transfer in some periodic molecular systems.

The electronic structure of representative hydrogen bonded systems: hydrogen cyanide, imidazole and malonic acid have been studied at the non-empirical level. The role of the dimensionality on the potential barrier for the proton transfer has been examined. It was shown that it depends on the crystal structure and only in some cases like hydrogen cyanide or imidazole the relevant crystals may be considered as one-dimensional. However, for more complicated crystallographic structures, e.g. malonic acid, the evaluated barrier is strongly dependent on the dimensionality taken into account in our calculations.

Structure, properties and in vitro cytotoxic activity of hexakis(2-cyanoethyl)ditin(III).

The structure of the tin(III) complex [Sn(2)(CH(2)CH(2)CN)(6)] has been determined. There are two independent molecules in the crystal, both adopt distorted eclipsed conformation. The molecular and electronic structures of this compound have been studied both at the semiempirical level and with the use of non-empirical ab initio methods. The calculated Sn-Sn distances agree well with those found crystallographically. The results of calculations showed that the eclipsed conformation of complex is more stable as compared with staggered conformation. The compound show modest cytotoxic activity against A549 and HSMC cells.

Helium-antihydrogen interaction: the Born-Oppenheimer potential energy curve.

The interaction of atomic antihydrogen with helium has been studied within the Born-Oppenheimer approximation. The linear combination of explicitly correlated Gaussian functions was used as the ansatz for the wave function of light particles. The potential energy curve with the minimum at 3.63 bohr and the barrier at 2.42 bohr has been obtained.