GENERATION OF SUPEROXIDE ANION WITH A PHOTOREDUCED PHENOXAZINE DERIVATIVE

Abstract. 1-Hydroxy-5-oxo-5H-pyrido [3,2 a ] phenoxazine-3-carboxylic acid was found to be reduced when it was irradiated with visible light in the presence of certain electron donors such as tetramethyl ethylenediamine and reduced glutathione. Upon illuminating this compound with either of the above electron donors under aerobic conditions, the coexisting nitroblue tetrazolium was reduced. The reduction was inhibited by superoxide dismutase, which indicated that superoxide anion was generated during the photoinduced reaction.     

Ultra-high-vacuum in situ electron microscopy of growth processes of epitaxial thin films

Extracts from recent results of ultra-high-vacuum in-situ electron microscopy of growth processes of epitaxial thin films are given. As a modified monolayer-by-monolayer mode, the growth process in Fe/(111)Au of the initial Frank-van der Merwe type, followed by the intrinsic γ → α transformation of Fe is mentioned. For the nucleation and growth mode, a systematic selection of epitaxial orientation according to interfacial lattice fitting, nucleation and coalescence features, the validity of Cabrera's suggestion extending Frank and van der Merwe's idea, the cluster mobility and effects of grown-in dislocations in substrate crystals are discussed on the basis of the observations.     

Brillouin scattering in KH3 (SeO3)2 above the transition temperature

The Brillouin scattering measurement in KH₃(SeO₃)₂ above the transition temperature shows a large anomaly in hypersonic velocity of the transverse wave with the wave vector q = [010] and the polarization ξ = [001], which indicates acoustic phonon softening.     

Solvent effect on helicity induction of zinc bilinone bearing a chiral auxiliary at the helix terminal

Solvent effects on helicity induction in zinc bilinone (ZnBL) derivatives bearing chiral auxiliaries at their 19-positions were investigated by using circular dichroic spectroscopy and (1)H NMR experiments. In ZnBLs 1 and 2, which possess (R)-2-methyl-1-phenylpropyloxy and (R)-1-phenylethyloxy groups at their 19-positions, respectively, the efficiency of helicity induction was significantly affected by employed solvents (78-95% de in 1 and 33-89% de in 2). The free energy changes of the P-M interconversion of 1 and 2 were linearly in proportion to reduction in polarizability of solvents: lower polarizability of solvents led to better efficiency of helicity induction in 1 and 2. With the support of the (1)H NMR study in addition to the molecular modeling previously reported, it was indicated that the solvophobic van der Waals interaction between the alkyl group in the chiral auxiliary and the A-ring of the bilinone skeleton in the preferred conformer plays a crucial role in determining the efficiency of helicity induction in 1 and 2.     

New insights on the mechanisms of the pH-independent reactions of benzo[a]pyrenes 7,8-diol 9,10-epoxides.

The rates and products of the reactions of (+/-)-7beta,8alpha-dihydroxy-9beta,10beta-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (1) and (+/-)-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (2) in water and dioxane-water mixtures have been determined over a pH range wider than that of earlier studies. This study provides additional insight on the mechanisms of the pH-independent reactions of 1 and 2. The rate profile for reaction of 1 shows acid-catalyzed hydrolysis at pH <5, a rate plateau at pH 5-9.5, a negative inflection at pH 10-11.5, and a rate increase at pH >11.5. The rate decrease between pH 10 and pH 11.5 is accompanied by a decrease in the yield of tetrols from 60% (pH 8) to 29% (pH 11.2) and is interpreted to be the result of a partial change in mechanism brought about by attack of hydroxide ion acting as a base to deprotonate a carbocation intermediate and regenerate 1 at pH >10, thus reducing the contribution of the pathway for tetrol formation in which water attacks the carbocation. The rate profile for the reaction of 2 exhibits only a single rate plateau at intermediate pH, along with increases in rate at low and high pH because of second-order reactions of 2 with H+ and HO-, respectively. The lack of a rate depression at pH >10 and the product studies for the reaction of 2 in dilute sodium azide solutions suggest that the tetrol-forming reactions of the pH-independent reaction of 2 are concerted or near-concerted.     

Reliability study on high-power 638nm broad stripe laser diode

High-power laser diodes (LDs) are strongly demanded as a light source of display applications. In this work, the reliability of a high-power 638 nm broad stripe (BS) LD was studied from the viewpoint of not only gradual degradation but also catastrophic optical degradation (COD) at a front facet. Long term acceleration aging tests for the 638 nm BS-LD with the window-mirror structure by using Zn diffusion were performed. It was confirmed that COD only occurs at a high output power and this mode was dominant compared with gradual degradation. The result also revealed that the mean time to failure due to COD was proportional to optical density to the power of ?3:2. It is clarified that maintaining a low optical output power density is essential to develop high-power and highly reliable red BS-LDs.     

Visible‐Light‐Induced Morphological Changes of Giant Vesicles by Photoisomerization of a Ruthenium Aqua Complex

Visible‐ and red‐light responsive vesicles were prepared by incorporating a ruthenium aqua complex having two alkyl chains on tridentate and asymmetrical bidentate ligands (proximal‐ 2 : [Ru(C₁₀tpy)(C₁₀pyqu)OH₂]²⁺, C₁₀tpy=4′‐decyloxy‐2,2′;6′,2“‐terpyridine, C₁₀pyqu=2‐[2′‐(6′‐decyloxy)‐pyridyl]quinoline). The ruthenium complex of proximal‐ 2 with closed alkyl chain geometry and a cylinder‐like molecular shape exhibited photoisomerization to distal‐ 2 with an open alkyl chain geometry and a cone‐like shape, both in an aqueous solution and in vesicle dispersions. We observed that light irradiation of giant vesicles containing proximal‐ 2 induced diverse morphological changes.