Masahiko Kodama

Quantum-mechanical study on the photodimerization of aromatic molecules

Abstract Distinct parallelism is found between the quantum-mechanical index, the π delocalization energy and the degrees of dimer-forming ability of thymine, uracil and other aromatic compounds. It is surprising that the π delocalization energies for thymine and uracil are larger than those of well-known photodimer-forming compounds such as anthracene and acenaphthacene. The possible structures of thymine dimer isomers in vitro and in vivo , are postulated from considerations of, for example, the π delocalization energy and steric properties. Biological inactivation by photo-irradiation is discussed in relation to the energy liberation due to the thymine dimer formation.

Non-covalent interaction with DNA of the mutagens 2-amino-dipyrido[1,2-a:3′,2′-d]imidazole and methyl-substituted isomers

Abstract The interactions of 2-amino-6-methyldipyrido[1,2-a:3′,2′-d]imidazole (Glu-P-1) and its analog 2-amino-dipyrido[1,2-a:3′,2′-d]imidazole (Glu-P-2) which are potent mutagens isolated from a L-glutamic acid pyrolysate, with calf thymus DNA were studied spectroscopically. Scatchard plots obtained by optical titration gave association constants, K, of 2.7 ∼ 17 × 10 3 M −1 for several derivatives. Flow dichroism studies showed that Glu-P-1 and other derivatives are oriented in parallel to the planes of base pairs of DNA. The correlation between the association constants and degrees of mutagenicity is discussed.

The semi-empirical SCF Treatment of σ-π system I. Peptide molecule

Abstract The semi-empirical ASMO SCF method has been applied to the peptide molecule. In this treatment, σ and π electrons are explicitly taken into account. With regard to σ electrons, the molecular orbital originally used by Sandorfy (1955) and extensively developed by Fukui et al. (1962) in the Huckel MO method is employed, and the integrals involved in this treatment are estimated semi-empirically. The calculated absorption maximum, its oscillator strength, ionization potential and dipole moment are compared with experimental data and good agreement is found. The important role of the hydrogen atom in semiconductivity of protein and the possibility of σ-σ ∗ , π-σ ∗ and σ-π ∗ transitions of the peptide molecule are pointed out.

Photosensitizing effects of aromatic hydrocarbons and quinolines upon DNA

Abstract (1) The photosensitizing action of aromatic hydrocarbons, carcinogenic quinoline derivatives and aromatic amines were tested in ethanol solution containing DNA as the cetyltrimethylammonium salt. Except for aromatic amines, all these compounds were found to have photosensitizing actions to DNA by visible light photoirradiation, and the guanine residue was specifically degraded. Correlation of the photosensitizing action of these compounds to DNA with their photodynamic actions to Paramecium candatum was not so good, probably due to the difference of irradiation conditions such as solvents used and light doses. Correlation with carcinogenicities also was not satisfactory, but among aromatic hydrocarbons such potent carcinogens as 3,4-benzpyrene, 3,4,8,9-dibenzpyrene and 20-methylcholanthrene were found to have strong photosensitizing action to DNA. (2) In aqueous solution, single-stranded DNA was more susceptible to the photosensitizing action of 4-nitroquinoline 1-oxide than the double-stranded DNA, indicating that intercalation of the quinoline compound between the base pairs in DNA is not necessary for the photosensitizing action to DNA. The same was true for aromatic hydrocarbons, tricycloquinazoline and methylene blue which were proved to be good photosensitizers to the single-stranded DNA. (3) During photoirradiation, aromatic hydrocarbons were found to bind covalently to the guanine residue in DNA, although the binding was not necessarily correlated with the photosensitizing action. The spectra of the bound 3,4-benzpyrene, 3,4,8,9-dibenzpyrene, anthanthrene and 5-acetoxy-3,4-benzpyrene were similar to those of the free hydrocarbons, respectively, though they were shifted to ths longer wavelength by about 10 mμ. On the other hand, bound 3,4-benzpyrenequinone, 9,10-dimethyl-l,2-benzanthracene, 20-methylcholanthrene, 5-nitro-, and