Contributions of various serum proteins to the binding of prasterone sulfate in humans.

The binding of prasterone sulfate (PS) in human plasma was investigated. Binding percentages of PS to human plasma, human serum albumin (HSA), human alpha 1-acid glycoprotein (AGP) and human gamma-globulin (GGL) were independent of the PS concentration between 0.1 and 8.0 micrograms/ml. The mean binding percentages were 99.1% for human plasma, 98.3% for HSA, 12.6% for AGP and 8.1% for GGL. Though PS is an acidic drug, binding of PS to AGP was observed. From the binding index, it was found that PS mainly bound to HSA in human plasma and that the contributions of AGP and GGL to PS in plasma were negligible.     

An ab initio MO study on the disulfide bond: properties concerning the characteristic S-S dihedral angle

The characteristics of disulfide groups concerning the S-S dihedral angle are represented by ab initio SCF calculations using the split-valence 6-31G(^*) basis set. It is shown that the hyperconjugation between the S-H bond and the electron pair on the other sulfur plays an important role in determining the characteristic S-S dihedral angle. The S 3d orbitals do not participate in such characteristics. The nature of the S-S bond is compared with that of the O-O bond. The S-S bond length varies largely depending on the S-S dihedral angle. This is related to the frequency-conformation correlation of the disulfide group.     

Metabolic activation of chemical carcinogens and binding of metabolites with nucleic acid bases

A free radical was produced enzymatically by incubating benzo(a)pyrene with liver microsomes. This radical, identified as the 6-oxybenzo(a) pyrene radical, was sufficiently reactive to bind covalently with nucleic acid bases. Similar reactive free radicals were produced enzymatically from anthanthrene and 10-aza-benzo(a)pyrene, which are carcinogenic in spite of lacking so-called “bay regions.” Hepatocarcinogens such as 3′-methyl-4-dimethylaminoazobenzene and related compounds, naphthylamines, and 2-acetylaminofluorene yield free radicals after being incubated with liver microsomes. Thus, various kinds of chemical carcinogens are found to be converted to free radicals, suggesting causal significance for the formation of free radicals in chemical carcinogenesis.     

Stilbene-cored poly(glutamate) dendrimers

A new class of photoresponsive poly(glutamate) dendrimers based on a stilbene core unit was successfully synthesized. The core stilbene was used to probe the polarity inside the dendrimer based on changes in the absorption and fluorescence spectra under various solvent conditions. Upon acidification of a solution of one of the dendrimers, wG1, the absorption band decreased with red-shift and the fluorescence band decreased with blue-shift, indicating that the groups at dendrimer periphery were protonated, resulting in shrinking of the dendrimer via hydrophobic interactions, and the inside of the dendrimer became more hydrophobic than under neutral pH conditions. In addition, the core stilbene unit underwent photoisomerization to give the cis-isomer with concomitant structural change in the poly(glutamate) dendrimer.     

Structure and hypochromism of (6,9) (9′,6′) purinophanes

The structure of the title compound 1a was determined to be a cross-stacking form with an interplanar distance of ca. 3.3 Å by X-ray analysis. On the basis of this structure, the hypochromicity of 1a was calculated by the ASMO SCF CI method.     

An ab initio molecular orbital study on the stacking interaction between nucleic acid bases: Dependence on the sequence and relation to the conformation

The stacking interaction energies between nucleic acid bases in A DNA and B DNA are calculated by means of the ab initio molecular orbital method. The calculated values agree well with the experimental values of stacking enthalpy changes. The stacking interaction energy is shown to be highly sequence dependent, particularly when the sequence includes guanine or cytosine. The possibility is shown that the conformation of a DNA double helix fragment is determined by the constituent stacking interaction. Electrostatic energy is the cause of the sequence dependency of the stacking energy, while charge transfer and dispersion energies contribute to the overall stability.