Wrightiamines A and B,two new cytotoxic pregnane alkaloids from Wrightia javanica

Two new pregnane alkaloids, wrightiamines A (1) and B (2), were isolated from the extract of the tropical Apocynaceous plant Wrightia javanica collected in Thailand, and their structures were elucidated by spectral data. Wrightiamine B (2) was preparaed from 3beta-hydroxy-5alpha-pregnan-20-one to establish the configuration of the C-20 position as S. Wrightiamine A (1) exhibited cytotoxic activity against vincristine-resistant murine leukemia P388 cells.     

Etude par RPE des radicaux libres daus le tétraoxane irradié

The free radicals induced in tetraoxane at liquid nitrogen temperatures by ⁶⁰Co γ-rays have been studied by ESR. The powder spectrum as well as he spectra of the single crystal rotated around the b axis have been studied through their modifications from ?196°C up to + 80°C. These spectra show that at low temperatures two radicals exist conserving the cyclic nature of the parent molecule. During the course of annealing, starting at ?140°C and towards ?85°C they are gradually replaced by radicals with a linear structure, this being the first step in the post-polymerization process of tetraoxane. Further increase in temperature leads to radical sites situated on the polymer chains. At low temperatures evidence has also been found for the formyl radical, radical pairs, and a photo-sensitive radical.     

The orbital relaxation energy for single and double ionizations from valence shells of CH4, NH3, H2O and HF

The orbital relaxation energy is defined for single and double ionizations of valence electrons, and is calculated for CH₄, NH₃, H₂O and HF molecules with the ab initio SCF method. It is shown that the orbital relaxation energy for the ionization from a bonding orbital is about half of that for a non-bonding orbital, and the orbital relaxation energy for the double ionization is about double of that for the single ionization. This result gives a theoretical foundation for the empirical method of interpret Auger electron spectra by using experimental single ionization potentials.     

Correlation of the zero-field splittings with the n,π* and π,π* triplet levels of benzaldehydes

The n,π^* and π,π^* triplet state energies of p-chlorobenzaldehyde and p-mathoxybenzaldehyde were determined in several hosts with the aid of phosphorescence and phosphorescence excitation spectra. A linear relationship expected from the theory considering spin-orbit interaction between the closely located n,π^* and π,π^* triplet states was found to be satisfied. The spin—orbit interaction parameter, <vb>G₂>vb>² was found to be 83 cm^?2 for benzaldehydes.     

A novel axially chiral 2,2'-bipyridine N,N'-dioxide. Its preparation and use for asymmetric allylation of aldehydes with allyl(trichloro)silane as a highly efficient catalyst

[reaction: see text] New axially chiral 2,2'-bipyridine N,N'-dioxides were obtained by a new method that does not involve any procedures for the separation of enantiomers. One of the dioxides, (R)-3,3'-bis(hydroxymethyl)-6,6'-diphenyl-2,2'-bipyridine N,N'-dioxide, exhibited extremely high catalytic activity for the asymmetric allylation of aldehydes with allyl(trichloro)silane. The allylation of aromatic aldehydes proceeded in the presence of 0.01 or 0.1 mol % of the dioxide catalyst to give the corresponding homoallyl alcohols of up to 98% ee.     

THEORETICAL STUDY OF COLOR CONTROL MECHANISM IN RETINAL PROTEINS. I. ROLE OF THE TRYPTOPHAN RESIDUE, TYROSINE RESIDUE and WATER MOLECULE

Abstract –We calculated the opsin shift due to the electrostatic interaction between tryptophan or tyrosine residues and the chromophore by the perturbation method for various mutual configurations. The obtained opsin shift maps for these configurations demonstrated that when the above residues reside around the ionone ring side, the positive opsin shift (bathochromic shift) is obtained, and when they reside around the Schiff-base side, the negative opsin shift (hypsochromic shift) is obtained. These properties hold true, irrespective of the orientation of those residues, indicating that higher order multipoles of the group play a central role. The maximum value of the opsin shift by these groups amounts to several hundred wavenumbers. These results indicate that the location of some of those amino acid residues at proper positions around the chromophore can cause a considerable opsin shift. We also calculated opsin shift maps for the various mutual configurations between a water molecule and the chromophore for comparison.     

Extended hypervalent 5c-6e interactions: linear alignment of five C-Se---O---Se-C atoms in anthraquinone and 9-methoxyanthracene bearing arylselanyl groups at the 1,8-positions

The structures of 1,8-bis(phenylselanyl)anthraquinone (1a), 1,8-bis(phenylselanyl)-9-methoxyanthracene (2a), and 1,8-bis(phenylselanyl)anthracene (3a) are determined by X-ray crystallographic analysis, together with the derivatives. The Se-C(i) (Ph) bonds in 1a are placed on the anthraquinone plane (both type B) and the phenyl planes are perpendicular to the anthraquinone plane. The structure around the Se atoms in 2a is very close to that of 1a: the conformations of the PhSe groups are both type B. Consequently, the five C(i)-Se- - -O- - -Se-C(i) atoms in 1a and 2a align linearly. The nonbonded Se- - -O distances in 1a and 2a are 2.673-2.688 and 2.731-2.744 A, respectively, which are about 0.7 A shorter than the sum of van der Waals radii of the atoms. The extended hypervalent sigma*(C(i)-Se)- - -n(p)(O)- - -sigma*(Se-C(i)) 5c-6e interactions are strongly suggested for the origin of the linear alignment of the five atoms in 1a and 2a. The 5c-6e must be constructed by the connection of the two hypervalent n(p)(O)- - -sigma*(Se-C(i)) 3c-4e interactions through the central n(p)(O). The five C(i)-Se- - -H- - -Se-C(i) atoms never align linearly in 3a. To reveal the nature of 5c-6e in 1a and 2a, QC calculations are performed on H(a)H(b)(A)Se- - -O([double bond]CH(2))- - -(B)SeH(a')H(b') (model a) and H(a)H(b)(A)Se- - -OH(2)- - -(B)SeH(a')H(b') (model b) with the B3LYP/6-311++G(3df,2pd) method, where the nonbonded Se- - -O distances are fixed at 2.658 A. Four conformers, a (AA-cis), a (AA-trans), a (AB), and a (BB), are optimized to be stable for model a, where a (AA) shows both type A for the (A)Se-H(b) and (B)Se-H(b') bonds in model a. Three conformers, b (AA-cis), b (AB), and b (BB), are stable for model b. The bonding models in AA, AB, and BB correspond to 3c-6e, 4c-6e, and 5c-6e, respectively. The models become more stable by 42 +/- 5 kJ mol(-1), if the type A conformation of each Se-H bond changes to type B. No noticeable saturation is observed in the stabilization for each change. QC calculations are also performed on 1a-3a at the B3LYP level. Three conformers are evaluated to be stable for 1a and 2a. The relative energies of 1a (AA-trans), 1a (AB), and 1a (BB) are 0.0, -31.5, and -60.6 kJ mol(-1), respectively, and those of 2a (AA-cis), 2a (AB), and 2a (BB) are 0.0, -24.4, and -36.5 kJ mol(-1), respectively. These results demonstrate that the origin of the linear alignment of the five C-Se- - -O- - -Se-C atoms in 1a and 2a is the energy lowering effect by the extended hypervalent 5c-6e interactions of the sigma*(C-Se)<--n(p)(O)-->sigma*(Se-C) type. The pi-conjugation between pi(C[double bond]O) and n(pz)(Se) through the pi-framework of anthraquinone must also contribute to stabilize the BB structure of 1a, where z is the direction perpendicular to the anthraquinone plane.     

Nanometer-sized gelatin particles prepared by means of gamma-ray irradiation

Nanometer-sized gelatin particles have been prepared by means of gamma-ray irradiation and characterized by static and dynamic light scattering combined with circular dichroism (CD) measurements. The molecular weight of the nanoparticles was much larger than that of the original gelatin molecules, whereas the hydrodynamic radius was much smaller. Radius of gyration evaluated from the angular dependence of the static light scattering intensity decreased with increasing irradiation dose. CD spectra of the gelatin nanoparticles were independent of temperature, and it is suggested that the nanoparticles consist of highly and randomly packed gelatin and their conformation is stable against the temperature change.     

Multinuclear macromolecule metal complexes 2. Preparation and characterization of Prussian blue and its analogs bonded to pofy(vinylamine hydrochloride)

Prussian blue and its analogs bonded to poly(vinylamine hydrochloride) (PVAm · HCl) containing Fe^II or Fe^III and M²⁺ (M=Fe, Co, Cu) in a 11 molar ratio were obtained by the reaction of [Fe(CN)₆] ^n– (n=3,4) with M²⁺ ion-PVAm · HCl mixture in aqueous solution. Under a limited polymer concentration (T_VAm/T_Fe over 10), these polymer complexes thus obtained were stable and soluble in water. By casting these solutions, colored films can be produced. The formation of Prussian blue and its analogs bonded to PVAm · HCl was also investigated by the Benesi-Hildebrand method. The molar extinction coefficients of intervalence charge transfer (Fe^IIFe^III, Co^IIFe^III, Fe^IICu^II) band for MFe(CN)₆]^(n–2)– bound to PVAm · HCl (M=Fe, Co, Cu) were found to be 10,100–9601 · mol^–1 · cm^–1 at 25 C. The formation constants were found to be in the range of 10⁷ to 10¹⁰ M^–1. The changes of enthalpy (H) and entropy (S) were found to be in the range of –10.4 to –22.5 kJ · mol^–1 and 5.7 to 52.9 J · K^–1 mol^–1 respectively, at 25C.