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A b i n i t i o SCF and CI calculations of the dipole moment function of ozoneAb initio self-consistent field and configuration interaction (SCF-CI) calculations with a minimal basis set are carried out on a few lower 1T-1T* states of free base porphin and free base chlorin. Excitation energies and oscillator strength of these states are calculated and are compared with observed values. For the two lowest states of porphin and chlorin, the calculated excitation energies and oscillator strength are in good agreement with the observed ones. In particular, a characteristic of chlorin spectra is reproduced by the calculation. Namely, the oscillator strength of the lowest transition is several times larger than that of porphin but the oscillator strength of the second transition is similar to that of porphin. Such differences of the oscillator strength between chlorin and porphin are explained by an interchange of the order of two highest occupied orbitals and that of the two lowest unoccupied orbitals. Those differences are caused by a change of orbital shapes of chlorin due to the addition of two hydrogen atoms to the porphin skeleton.

Small-angle X-ray scattering profiles for an amylose fragment (maltoheptaose) in aqueous solution were observed and compared with the theoretical profiles calculated for an ensemble of chain conformations generated by molecular dynamics simulations and Monte Carlo simulations. The Monte Carlo results based on the disaccharide conformation energy map obtained without explicitly considering surrounding water molecules were in satisfactory agreement with the experimental results, provided that the effective dielectric constant was set to four. In contrast, the results of the fully solvated molecular dynamics simulations performed using the Cff91, Cff, Gromos, Glycam93, and Glycam99 force-fields were unexpectedly different from each other. Among them, Cff91 gave most satisfactory agreement with experiment, but the other fields yielded conformations that were somewhat or highly extended. It was also shown that recently developed Glycam99 is a significant improvement over Glycam 93. The representative snapshots of the two successful simulations resembled the regular helical structure reported by Goldsmith et al. (J. Mol. Biol. 1982, 156, 411). The source of the large force-field dependence was investigated by examining the various Ramachandran-like plots for the glycosidic torsion angles. For comparison, similar plots of ab initio energy for maltose (i.e., a fragment with two glucose units) were also calculated at the Hartree-Fock level, although in a simplified manner. These plots suggest that the extended conformation arises from too strong a preference for a certain rotational isomeric state of the glycosidic linkage. A procedure to remedy this over-preference can be devised, although a need of further elaboration of the force-field is indicated. The significance of force-fields is also illustrated in modeling a cyclodextrin composed of 14 glucose units.