Sigeo Yomosa

Dynamics of the Protons in One-Dimensional Hydrogen-Bonded Systems

We have studied some dynamical properties of the protons in one-dimensional H-bonded system whose polarization field Hamiltonian is strongly anharmonic. We find solitary wave solutions. Kink and antikink solutions correspond to ionic D t default (H 3 O + ) and ionic L t default (OH - ), respectively. Thus ionic defaults are described as solitary excitations in H-bonded systems.

Theory of the Excited State of Molecular Complex in Solution

The excited equilibrium state of molecular complex in solution is described by the use of the nonlinear Schrodinger equation presented in our previous paper. The excited equilibrium state of charge-transfer molecular complex or the equilibrium state of exciplex in polar solvents is quite polar and quite different from the excited Franck-Condon state, and has large tendency to dissociate to solvated ions. These theoretical results are confirmed by the laser photolysis experiments on the excited states of the molecular complexes.

Physical Methods for Treating the π-Electron Systems of Biopolymers such as Polypeptides and Polynucleotides in the Hückel Approximation

Two simple physical methods are presented for calculating the electronic band structures of biopolymers such as hydrogen-bonded polypeptides or homopolynucleotides in the Huckel approximation. One is an extended LCAO MO method, or a method of Linear Combination of Molecular Orbitals, and the other is an extended Bloch wave method where the crystal orbitals are constructed from the molecular orbitals of elementary group with the aid of group theoretical considerations. The extended Bloch orbital method seems to be the most simple and powerful tool for dealing with the electronic structures of the multiple conjugate π-electron systems. The brief applications of these two methods to actual biopolymers are made only for the illustration.

On the Basic Equation for the Equilibrium Electronic States in Polar Solvents –Broken Symmetry–

The basic equation to determine the equilibrium electronic structure ψ of the solute system (the solvated electron or the solute molecule or the solute molecular complex) in polar solvent is proposed in the form of variational equation δ( F t (ψ)-κ f )=0 which states that the free energy of the total system F t (ψ) consisting of the solute system and the solvent is minimum for an arbitrary variation of ψ in accordance with the normalization condition f = -1=0; here κ denotes a Lagrange undetermined multiplier. The nonlinear wave equations derived from the basic equation for the dimeric molecules or their radicals yield the broken symmetry solutions (self-trapping states). The simple description of the solvated electron is presented as another example of the application of the basic equation.

Solitary Waves in One-Dimensional Hydrogen-Bonded Systems

We have studied again the dynamical properties of protons in one-dimensional H-bonded system, taking account of the coupling between the proton motion and the lattice deformation. We find that the solitary waves of the proton-polarization are accompanied by the local lattice-deformations. Kink and antikink solutions correspond to ionic D t default (H 3 O + ion) and L t default (OH - ion), respectively. Two modes of solitary waves and two modes of phonons are found in the four respective regions of wave velocities.

Statistical Mechanics of Antiferromagnetic Layer Crystal, FeCl2

For the spin system in FeCl 2 we developed a statistical theory with Bethe-Peierls method and performed the numerical calculations to compare the results with experimental data of antiferro-ferro transition. Our results are also compared with those obtained by the molecular field approximation. The short range correlation gives rise to the following effects: the decrease of the Neel temperature, more rapid increase of the sublattice magnetization with decreasing temperature, and larger critical magnetic field of antiferro-ferro transition. From the experimental data of the critical magnetic field of antiferro-ferro transition, the values of two exchange coupling constants are estimated. For these values, it is concluded from theoretical considerations that the antiferro-ferro transition is of the first kind in almost whole the temperature region below the Neel point.

Charge-Transfer Molecular Compounds in Biological Systems

In order to investigate the feature of the charge-transfer molecular compound forme:! in biological environment, we develop a simple theory on the charge-transfer molecular compound in a local field; the polarization or the dipole moment, the binding energy and the maximum wave length and the oscillator strength of the spectrum are estimated as functions of the strength of the local field. In the biological system the local field consists of the Coulombic field due to free charges and permanent dipoles in the structural biopolymers and the reaction field due to the polarization induced in the surrounding medium by the dipole moment of the compound. By the additional effect of these two sorts of local fields the compound in biological system can be polarized strongly. Especially, an interesting phenomenon can be expected where the polarization and the absorption maximum change discontinuously for the variation of the Coulombic field or the dielectric constant of the medium. Such a strongly polarized state is considered as the first important stage of the biochemical reaction and the abrupt polarization initiated by a small change of the Coulombic field or of the dielectric constant of the surroundings seems to suggest a control mechanism in the biological functions.

Valence Bond Study of the Hydrogen Bond. : III. Formation and Migration of Ionic Defects in Water and Ice

Potential energy curves of the proton for the formation and migration of the ionic defects in water and ice are calculated by a valence bond method. In order to explain the thermodynamical data on the dissociation of water and ice, the reaction field concept of Onsager is introduced. The potential energy for the migration of positive and negative defects is calculated with six valence bond structures. The resulting height of the potential barrier for the positive defect is lower than that for the negative one, and this agrees with the experimental fact that the mobility of the positive defect is much greater than the negative one. The experimental data on the mobility of the positive defect in ice can be explained by Gosars theory if the O–O distance is taken to be 2.63 A

Energy Band Structures in Polypeptides

Using the MOs for π-electrons in an isolated peptide group which are determined such that the ASMO-SCF-CI calculation reproduces the observed wavelength of the optical absorption maximum, the energy bands for both the H -bonded and the main polypeptide-chain in the case of the β-structures and of the α-helix are calculated in terms of the LCMO and the nearest-neighbor approximation. It is shown that the shifts of bands for main peptide chains are of the considerable order of -0.2∼-0.8 eV, and that in each case the band widths for main peptide chain are generally far larger than those for H -bonded polypeptide, especially those of the highest valence and the conduction band for main chain in α-helix have remarkably large values of the order of 1∼2 eV. The π-electronic structure of H -bonded di- and tri-peptide are also studied by means of the ASMO-SCF method, in comparison with those obtained by Suard et al. .

π-Electronic Structures of DNA-Bases with Normal, Tautomeric and Ionized Forms

ASMO-SCF-CI calculations on the DNA-bases with both the normal and the tautomeric forms are carried out within the framework of the π-electron approximation and in terms of the Pariser-Parr-Pople approximation. The comparison between the electronic structures of the two forms is systematically made. The electronic structures for the anion, the cation and the first-triplet states of the bases are also calculated by means of the unrestricted Hartree-Fock method. It is shown that there is a close resemblance between the electronic states of the normal bases and those of the tautomeric ones: A↔G * , U↔C * , G↔A * and C↔U * . It is also shown for each of the bases that the excitation to triplet states and the ionization lead to large redistributions of π-electron densities whereas the excitation to singlet states does not. The calculated excitation energies for singlet states are in close agreement with observed ultra-violet absorption date on the lowest three absorption bands.