Direct observation of the one-electron reduction of methyl viologen mediated by the CO2 radical anion during TiO2 photocatalytic reactions

The one-electron reduction of methyl viologen (MV(2+)) mediated by the carbon dioxide radical anion (CO(2)(*-)) during photocatalytic reactions in a colloidal TiO(2) aqueous solution (pH 2) has been investigated by time-resolved absorption spectroscopy. The formation of MV(*+) generated from the one-electron reduction reaction with CO(2)(*-), which is generated from the one-electron oxidation reactions with the photogenerated holes (h(+)), was directly observed. The spectral features of the photogenerated charge carriers and the kinetic analysis of the formation process of MV(*+) revealed that the CO(2)(*-), desorbed from the surface, reacts with MV(2+) via a homogeneous electron-transfer process in the bulk solution.     

Kinetics of transient end-to-end contact of single-stranded DNAs

The formation of the pyrene (Py) dimer radical cation (Py(2)(*+)) was used to measure the kinetics of the intrastrand end-to-end contact rates of single-stranded DNAs (ssDNAs) in the 10 nanoseconds to the tens of microseconds time range. ssDNAs labeled with Py at both ends with the lengths of 3, 6, and 9 mer were synthesized, and the two-photon ionization method was employed to generate a Py(*+), which enables the measurements of the end-to-end contact rates from 10 ns. The formation rate of Py(2)(*+) depended on the length and the sequence of the ssDNAs, and about 1 order of magnitude faster rates were observed for the T-rich ssDNAs compared to those for the corresponding length of A-rich ssDNAs, showing that ssDNA made from adenines is much more rigid than that composed of thymidines. As for the T-rich ssDNAs, the formation of Py(2)(*+) attributed to the misfolded structures was also observed, which is consistent with the configurational diffusion model suggested by Ansari and co-workers.     

Photocatalytic Reduction of NO with C2H6 on a Hollandite-Type Catalyst

The photocatalytic reduction of nitrogen monoxide (NO) with ethane on the hollandite type catalyst (K₂Ga₂Sn₆O₁₆KGSO) was investigated. Using a closed-gas circulating system equipped with a Q-MASS detector and in-situ diffuse reflectance FT-IR spectroscopy. The reactant gases of NO and ¹³C₂H₆ decreased with the increasing irradiation time. In contrast, the N₂ yield increased proportionally to the conversion of ¹³C₂H₆. Nitrogen oxides such as N₂O did not reach their detectable levels. The NO adsorbed on KGSO was found to change to its activated species by UV irradiation. The oxidized products of C₂H₆ such as CH₃CHO increased in proportion to the reaction time. The present results strongly suggest that KGSO has remarkable photocatalytic activity for the reduction of NO with C₂H₆.     

Inhibitory effects of 1,3-selenazol-4-one derivatives on mushroom tyrosinase

This study reports depigmenting potency of 1,3-selenazol-4-one derivatives, which would be based upon the finding of direct inhibition to mushroom tyrosinase. 1,3-Selenazol-4-one derivatives exhibited inhibitory effect on dopa oxidase activity of mushroom tyrosinase. In this study, inhibitory effects of six kinds of 1,3-selenazol-4-one derivatives (A, B, C, D, E and F) on mushroom tyrosinase were investigated. Compounds at a concentration of 500 microM exhibited 33.4-62.1% of inhibition on dopa oxidase activity of mushroom tyrosinase. Their inhibitory effects were higher than that of kojic acid (31.7%), a well known tyrosinase inhibitor. 2-(4-Methylphenyl)-1,3-selenazol-4-one (A) exhibited the strongest inhibitory effect among them dose-dependently and in competitive inhibition manner.     

Synthesis of 1-alkylselenocyclobutene via intermediate allenyl selenoketene

Reactions of 2-alkynyl arylethynyl selenide 1 with alkyl iodides 3 in the presence of lithium aluminium hydride via allenyl selenoketene 2 afforded cyclobutene 4. Allenyl group of the intermediate allenyl selenoketene 2 was monitored by React IR.     

SPECTRAL ANALYSIS OF CHLOROPHYLL a AGGREGATES IN THE PRESENCE OF WATER-SOLUBLE MACROMOLECULES

Abstract— The absorption and fluorescence spectra of chlorophyll a (Chi a) aggregates formed in aqueous solutions of polyvinyl alcohol) (PVA), polyvinyl pyrrolidone) (PVP), and bovine serum albumin (BSA) were analyzed by curve-fitting methods in the wavelength region from 650 to 800 nm. The results indicated that the aggregation of Chi a to polymeric forms such as (Chia–2H₂0), was suppressed in the presence of the macromolecules. The suppression was due to a coordination of macromolecule bound ligands to Chi a and was strongest in BSA and weaker in PVA. There were differences in the spectra even though the same types of polymeric Chi a forms were observed due to characteristically different composition of these forms. Fluorescence patterns indicated that energy was transferred from the shorter to the longer wavelength forms.     

The absorption and circular dichroism bandshapes of chromophore aggregates as studied by a modified Green's function theory

A modified Green's function method is applied to calculating the aggregate bandshape whereby a decoupling approximation for vibrationally averaging the Green's function is used to include thermal and static effects as well in terms of the correction shift of the chromophore bandshape. The utility of the present method is shown by a sample calculation of the absorption and circular dichroism bandshapes of a model dimer.     

Higher triplet excited states of benzophenones and bimolecular triplet energy transfer measured by using nanosecond-picosecond two-color/two-laser flash photolysis

The lifetimes of benzophenone in the higher triplet excited state (BP(T(n))) and several BP derivatives in the T(n) states were measured directly to be tau(T(n))=37+/-7 ps and 20-33 ps, respectively, by using the nanosecond-picosecond (ns-ps) two-color/two-laser flash photolysis method. Based on the direct measurements of tau(T(n)) of BP(T(n)), the triplet energy transfer (TET) from BP(T(n)) to quenchers (Q), such as carbon tetrachloride (CCl4), benzene (Bz), and p-dichlorbenzene (DCB), was investigated. The fast TET from BP(T(n)) to Q can be attributed to the lifetime-dependent quenching process, according to the Ware theoretical model of the bimolecular energy transfer reaction. The contribution of the lifetime-dependent term on k(TET) was 27, 60, and 86% for CCl4, Bz, and DCB as the Q of BP(T(n)), respectively, indicating that the TET from BP(T(n)) to Q is influenced not only by tau(T(n)), but also by the size of Q.     

Saccharide-branched Cyclodextrins as Targeting Drug Carriers

A synthetic series of heptakis-galactose-branched cyclodextrins (termed CDs) having a longer spacer arm using two amino-caproic acids as an enlarging unit were prepared. Starting with heptakis-amino-β-CD or heptakis-amino-caproic-amide-β-CD, treated with galactosyl-glucono-amide-caproic acid, the new compounds heptakis (Gal-cap1)-CD (4) or heptakis (Gal-cap2)-CD (5) were obtained. The longer galactose spacer arm extremely favors the PNA association. The effect of branch length on K with PNA was enhanced up to 138-fold 3 as well as with DXR enhanced up to 81-fold. Hexakis (Gal-cap2)-CD (6) was prepared and the association constants with rat liver cells were observed to be 2.5 × 10¹⁰ M⁻¹. A multi-high mannose type oligosaccharide branched CD (7) showed a large association constant with DXR up to 1.1 × 10⁹ M⁻¹. The two-dimensional map for the association constants of newly synthesized oligosaccharide-branched CDs toward lectin or liver cells versus the association constants toward a drug (doxorubicin) suggested a method of finding a better targeting drug carrier. The structural effect of the oligosaccharide-CDs showed that the number and length of the branch were dominant factors in designing for enhanced dual recognition.     

Lifetime regulation of the charge-separated state in DNA by modulating the oxidation potential of guanine in DNA through hydrogen bonding

A series of naphthalimide (NI)- and 5-bromocytosine ((br)C)-modified oligodeoxynucleotides (ODNs) were prepared, and their lifetimes of the charge-separated states during the photosensitized one-electron oxidation of DNA were measured. Various lifetimes of the charge-separated states were observed depending on the sequence and the incorporation sites of (br)C, and the oxidation potential of G in the (br)C:G base-pair relative to that of G in the C:G base-pair and in the GGG sequence was determined by comparing the lifetimes of the charge-separated states. The change in the cytosine C5 hydrogen to bromine resulted in a 24 mV increase in the oxidation potential of G in the (br)C:G base-pair as compared to that of G in the C:G base-pair, the value of which is comparable to a 58 mV decrease in the oxidation potential of G in the GGG sequence. These results clearly demonstrate that hole transfer in DNA can be controlled through hydrogen bonding by introducing a substituent on the cytosine.