The investigation of hydrogen bonding, protonation, and lithium cation association in systems of biochemical significance will be extended through the application of our findings and of recent developments in ab initio molecular orbital theory. Through and systematic studies will be performed to detemrine the structures and stabilization energies of (1) the complexes of the bases O=CHR and HHN=CHR with Li+ and the hydration of the resulting complexes and of the corresponding protonated complexes; (2) the complexes of other small molecules containing the functional groups -COOH, -COO-, -NH2 and -NH3+ with H20, H+, and Li+, and with each other; and (3) associated oxygen and nitrogen bases in which the hybridization of the basic site (O or N) varies. In this phase of the research, Hartree-Fock and Moller-Plesset correlation energies will be computed with different basis sets, and zero-point vibrational energy contributions will be evaluated. Changes in vibraitonal, rotational, and translational energies, and the PV work term at 298 K will also be computed so that calculated and experimental enthalpies may be compared. The systems chosen for this part of the study contain the same chemical moieties which are present in larger biochemical systems, but which have not yet been investigated at this level of theory. These studies are of interest in themselves and as a guide for further extension of ab initio studies to (1) determine the optimized structures and stabilization energies of the complexes of the DNA and RNA bases and base pairs with Li+ and the hydration of these complexes and of the protonated bases and base pairs; (2) study the association of small amino acids and small heterocyclic rings with both neutral and charged species; and (3) investigate the successive hydration of allcomplexes. Analyses of the structural, energetic, and electronic properties of the isolated and associated systems will be made, nonadditivities of interaction energies will be evaluated, and trends will be established. The stabilities of these complexes in low-energy excited electronic states will also be investigated. The results of this research will provide new and important information concerning the same types of associations (intermolecular, ion-molecule, and ion pair) in living systems, and will lead to a better understanding of their role in biological functions and processes. In this way, this research will contribute toward future progress in biochemistry and molecular biology.
