Masanobu Kojima

Mechanistic considerations on photoreaction of organic compounds via excitation of contact charge transfer complexes with oxygen

Abstract Reactions of various organic compounds induced by excitation of their contact charge transfer (CCT) pairs with oxygen were classified into three types of behaviour on the basis of reaction products. It is proposed that the excited state of the CCT pairs gives the products through the most isoenergetic course along the plausible exothermic pathway.

The role of oxygen as an electron acceptor in dimerization of some styrene derivatives

Abstract Irradiation of the CT bands of p -methoxy- and p -methylstyrene with oxygen induced the dimerization of the olefins through their cation radicals generated by electron transfer on CT excitation.

Photooxygenation of stilbenes in zeolite by excitation of their contact charge transfer complexes with oxygen

Abstract Contact charge transfer (CCT) complexes of trans -stilbenes with oxygen molecules were formed in zeolite NaY. Excitation of the CCT bands by a 313-nm wavelength light produced the corresponding benzaldehydes through an electron transfer reaction to generate stilbene cation radicals and superoxide anion radical. Irradiation of the CCT complexes by a 254-nm wavelength light, by contrast, gave rise to isomerization and formation of phenanthrene without yielding any oxygenation products, as in the photoreaction under oxygen in solution.

Regulation of Primary Metabolic Pathways in Oyster Mushroom Mycelia Induced by Blue Light Stimulation: Accumulation of Shikimic Acid

Shikimic acid is a key intermediate in the aromatic amino acid pathway as well as an important starting material for the synthesis of Tamiflu, a potent and selective inhibitor of the neuraminidase enzyme of influenza viruses A and B. Here we report that in oyster mushroom (Pleurotus ostreatus) mycelia cultivated in the dark, stimulation with blue light-emitting diodes induces the accumulation of shikimic acid. An integrated analysis of primary metabolites, gene expression and protein expression suggests that the accumulation of shikimic acid caused by blue light stimulation is due to an increase in 3-deoxy-D-arabinoheptulosonate 7-phosphate synthase (DAHPS, EC2.5.1.54), the rate-determining enzyme in the shikimic acid pathway, as well as phosphofructokinase (PFK, EC2.7.1.11) and glucose-6-phosphate dehydrogenase (G6PD, EC1.1.1.49), the rate-determining enzymes in the glycolysis and pentose phosphate pathways, respectively. This stimulation results in increased levels of phosphoenolpyruvic acid (PEP) and erythrose-4-phosphate (E4P), the starting materials of shikimic acid biosynthesis.

Identification of Blue-Light Photoresponse Genes in Oyster Mushroom Mycelia

Using the characteristics of light-emitting diodes, we studied the effects of light quality, light intensity, and repeated light-dark cycles on the growth of oyster mushroom mycelia. Blue-light stimulation suppressed growth in oyster mushroom mycelia, and this effect was remarkably dependent on light intensity. Random amplified polymorphic DNA differential display analysis enabled the identification for the first time of 15 upregulated and 13 downregulated genes induced by blue-light stimulation. On the basis of a homologous search using BLASTX and the Interpro database, the transcription products were analyzed to identify the putative proteins. In addition, by real-time PCR analysis, the time courses of the expression levels of eight of the genes identified were found to include intrinsic induction time.

Cationic Dye–sensitized Degradation of Sodium Hyaluronate Through Photoinduced Electron Transfer in the Upper Excited State¶

Abstract The formation of ground-state complexes of methylene blue (MB) and thionine (TN) with sodium hyaluronate (NaHA) was clearly observed by means of absorption spectra in aqueous solution. Irradiation of the complexes using 313 nm light caused significant degradation of NaHA under oxygen and argon. However, the use of visible light over 400 nm, which gives the lowest excited singlet state of the cationic dyes, caused no degradation. MB and TN were more efficient sensitizers for the degradation of NaHA than rose bengal (RB), although RB is a more efficient singlet oxygen (1O2) sensitizer than the cationic dyes. Under similar conditions the polysaccharides with carboxyl groups, such as alginic acid and polygalacturonic acid, also photodecomposed. However, the polysaccharides without carboxyl groups, such as pullulan and methyl cellulose, did not. The irradiation of the polysaccharides in the presence of powdered titanium dioxide as a photocatalyst to generate the hydroxyl radical (·OH) in aerated aqueous solution caused the fragmentation of all the polymers. It was confirmed that methyl viologen, an electron-accepting sensitizer, formed a charge-transfer complex with NaHA, the irradiation of which caused the efficient degradation of NaHA. In the presence of β- and γ-cyclodextrins the MB- and TN-sensitized photodegradation of NaHA was markedly suppressed. This was probably due to the formation of the inclusion complexes comprising the cationic dyes and the cyclodextrins. On the basis of the results obtained we propose that the cationic dye–sensitized degradation of NaHA involves a photoinduced electron-transfer process between the upper excited dyes and the ground-state NaHA and that ·OH and 1O2 do not participate in the degradation.

Steric effect on photochemistry of benzyl ester derivatives: 2. Effects of substituents and oxygen on photolysis of α-methyl-substituted benzyl alkanoates

Abstract The photochemistry of α-methyl-substituted benzyl acetates and pivalates, 1a–c and 2a–c , respectively, has been examined in methanol (MeOH). Sensitization and quenching experiments confirmed the predominance of the singlet-state photolysis of these esters. The product distribution depended on methyl groups, on the methylene carbon, and/or alkyl groups attached to the carbonyl group. Ester conversion decreased with methyl substitution. These results are explicable on the basis of steric hindrance, or conformational restriction, around the ester bond. We also found that the photolysis was markedly affected by oxygen, particularly for the most hindered ester 2c . It is likely that the effect of oxygen is attributed to the formation of an excited charge-transfer complex between the esters and an oxygen molecule.

Steric effect on photochemistry of benzyl ester derivatives: 1. Photolysis of 1-(naphthyl)ethyl alkanoates in methanol

Abstract The photochemistry of naphthylmethyl (NpM) and 1-(naphthyl)ethyl (NpE) alkanoates, 1a–d and 2a–d, has been examined in methanol (MeOH). Measurements of quantum yields for fluorescence and intersystem crossing and lifetimes for excited singlet and triplet states established similar photophysical behavior for all the esters studied here. The irradiation produced methyl NpM (or NpE) ether 3 and in-cage coupled product 4 as the major ionic and radical products, respectively. The conversion was found to be substituent-dependent, varying from 95% for 1c (2-NpMA) to 52% for 2b (1-NpEP). In contrast, a poorer correlation between the product distribution and ester structure was observed. The results indicate an important contribution of steric hindrance around the ester bond to the photocleavage. Steric effect on the stabilization of ionic and radical intermediates I–III in Scheme. 1 also perturbed the product distribution.

Light Stimulation Triggered Expression of Genes Coding for Vacuolar Proton-Pump Enzymes V-ATPase and V-PPase in Buckwheat

Although coloration in plants is ascribable to both the accumulation of anthocyanin pigments in vacuoles and to the acidification of vacuolar pH, the environmental factors causing the decrease in vacuolar pH are unknown. We found that blue-light irradiation of buckwheat seedlings using light-emitting diodes caused reddening on the surface of the hypocotyls. It has also been reported that light stimulation induces an accumulation of anthocyanin pigments. However, here we confirmed for the first time on the basis of real-time PCR analysis that light stimulation simultaneously triggers expression of the genes coding for subunit A of vacuolar H+-ATPase (V-ATPase) and vacuolar H+-pyrophosphatase (V-PPase).

Effect of co-adsorbed water on photodimerization and photooxygenation of 4-methoxystyrene included in NaY

Abstract Irradiation of 4-methoxystyrene ( 1 ) in zeolite NaY under vacuum, dry oxygen, and wet air yielded dimers and oxygenation products dependent on the atmosphere and co-adsorbed water. Head-to-head cis - and trans -cyclobutane dimers of 1 were produced at the isomer ratio of9/19under vacuum through excimer of 1 and38/62under wet air through cation radical of 1 , respectively. However, 4-methoxybenzaldehyde was a primary product under dry oxygen at the expense of production of the dimers (c/t=81/19). These results show significant differences in the photochemical behavior of 1 in solution and in NaY. Irradiation of 1 in NaY with co-adsorbed water yielded trans -cyclobutane dimer t - 4 as the primary product. Download full-size image