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The protonation/deprotonation reaction is one of the most fundamental processes in solutions and biological systems. Compounds with dissociative functional groups change their charge states by protonation/deprotonation. This change not only significantly alters the physical properties of a compound itself, but also has a profound effect on the surrounding molecules. In this paper, we review our recent developments of the methods for predicting the K a , the equilibrium constant for protonation reactions or acid dissociation reactions. The p K a , which is a logarithm of K a , is proportional to the reaction Gibbs energy of the protonation reaction, and the reaction free energy can be determined by electronic structure calculations with solvation models. The charge of the compound changes before and after protonation; therefore, the solvent effect plays an important role in determining the reaction Gibbs energy. Here, we review two solvation models: the continuum model, and the integral equation theory of molecular liquids. Furthermore, the reaction Gibbs energy calculations for the protonation reactions require special attention to the handling of dissociated protons. An efficient method for handling the free energy of dissociated protons will also be reviewed. [ABSTRACT FROM AUTHOR]

The synthesis, structures, optical and redox properties, and reactivity of phosphaporphyrins prepared via acid-promoted dehydrative condensation is presented. The incorporation of a phosphorus atom into the core is found to be a highly promising way to modify the fundamental properties of the porphyrin 18[pi] system which could also be used as reliable tool to stabilize uncommon 22[pi] and 20[pi] systems through the chemical modifications at the core phosphorus atom.

Frozen-core four-component multiconfigurational quasidegenerate perturbation theory was used to study the electronic structure of the molecules La[F.sup.+] and LaF. The findings provide insight into excitation energies of La[F.sup.+] based on electronic correlations between the outermost valence electrons and ionic core electrons.

The activation mechanism of NH3 in the selective catalytic reduction of NO by NH3 on a V2O7H4 cluster is investigated. A complete active space self-consistent field method is used for this purpose.

The excited states (Q and B bands) of free-base porphyrins (FBP), Mg-porphyrin and Zn-porphyrin and their derivatives were investigated. The results of multireference Moller-Plesset perturbation studies with complete active space self-consistent field reference that the weakness of the Q band of FBP is due to pseudoparity-forbidden status that came from the pairing properties of alternant hydrocarbons. It was shown that breaking the pairing properties results in the strengthening of the Q band intensity, which can be accomplished by the substitution of C atoms with N atoms in the meso position.

The role of water in host-ligand binding was investigated using a combination of molecular dynamics simulation and three-dimensional reference interaction site model theory. Three different hosts were selected (CB6, CB7, and CB8). Six organic molecules were used as representative ligands: dimethyl sulfoxide (DMSO), N , N -dimethylformamide (DMF), acetone, 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), cyclopentanone (CPN), and pyrrole. From the binding free energy and its components, we divided the ligands into two groups: those with relatively small molecular size (DMSO, DMF, acetone, and pyrrole) and those with relatively large molecular size (DBO and CPN). We established that the solvent water in the CB6 cavity can be completely displaced by small ligands, resulting in a greater binding affinity compared with larger CBs, except in the case of the small pyrrole ligand, due to outstanding intrinsic properties such as the relatively high hydrophobicity and low dipole moment. In the case of the large ligands, the solvent water can be displaced by DBO and CPN in both CB6 and CB7; there were similar tendencies in their binding affinities, with the greatest affinity in the CB7 complexes. However, the tendencies of the binding affinity components are completely different due to the difference between the complex structure and the solvation structure when a ligand binds with a CB structure. The binding affinities suggest that the size fit between the ligand and CB cannot guarantee the greatest binding affinity gain because the binding structure and intrinsic properties of CB and ligand equally play a crucial role.