Applications of ab initio quantum chemistry: Gas phase stable polyanions and prediction of biological activities

Ab initio quantum chemistry methods were applied to several projects of scientific interest. The majority of the projects can be divided into two general groups. The first area of study concerned an investigation of gas phase stable polyanions. Two general structural motifs were explored for the construction of gas phase stable polyanions:;Carbon cluster tetra-anions with a novel geometry were investigated in which a central carbon atom joined four linear chains of carbon atoms resulting in a tetrahedral geometry. The minimum size for stability was found to be thirty-three carbon atoms, each branch being eight carbon atoms long. The carbon chains adopted alternating long and short bond lengths indicative of a polyalkyne structure and consistent with the linear geometry of the chains. The majority of the excess charge was found to be located on the terminal carbon atoms.;Several different families organic carboxcyclic acids were studied. Molecules with a central benzene structure and one through three carboxylate groups were investigated. Species with three acid groups were found to be unstable with respect to loss of an electron. Species with one or two acid groups were stable to electron loss, the benzoate anion having a binding energy large enough to qualify it as a superhalogen. Structures having two acid groups connected by alkene, alkene, and alkene chains of up to four carbon atoms were studied. Species with two or more connecting carbon atoms were found to be stable to electron loss. The relationship between the nature of the backbone and the magnitude of the electron binding energy was studied.;The second area of study concerned the relationship between complex biological properties such as carcinoginicity and easily calculated properties such as ionization energies. Certain physical properties of a large number of polycyclic aromatic hydrocarbons (PAHs) were calculated and the relationship between these properties, experimental values, and various biological activities were examined.;Several methods for calculating electronic excitation energies of PAHs were examined with the goal of relating excitation energy to phototoxicity. The single interaction configuration interaction (CIS) methods was found to provide the best tradeoff between computational cost and correlation with experiment. (Abstract shortened by UMI.).