The photoreaction of the photoactive yellow protein domain in the light sensor histidine kinase Ppr is influenced by the C-terminal domains

To study the role of the C-terminal domains in the photocycle of a light sensor histidine kinase (Ppr) having a photoactive yellow protein (PYP) domain as the photosensor domain, we analyzed the photocycles of the PYP domain of Ppr (Ppr-PYP) and full-length Ppr. The gene fragment for Ppr-PYP was expressed in Escherichia coli, and it was chemically reconstituted with p-coumaric acid; the full-length gene of Ppr was coexpressed with tyrosine ammonia-lyase and p-coumaric acid ligase for biosynthesis in cells. The light/dark difference spectra of Ppr-PYP were pH sensitive. They were represented as a linear combination of two independent difference spectra analogous to the PYP(L)/dark and PYP(M)/dark difference spectra of PYP from Halorhodospira halophila, suggesting that the pH dependence of the difference spectra is explained by the equilibrium shift between the PYP(L)- and PYP(M)-like intermediates. The light/dark difference spectrum of Ppr showed the equilibrium shift toward PYP(L) compared with that of Ppr-PYP. Kinetic measurements of the photocycles of Ppr and Ppr-PYP revealed that the C-terminal domains accelerate the recovery of the dark state. These observations suggest an interaction between the C-terminal domains and the PYP domain during the photocycle, by which light signals captured by the PYP domain are transferred to the C-terminal domains.     

A new taxane composed of two N-formyl rotamers from Taxus canadensis

A taxane with an amino-side chain on C-5 was identified for the first time from rooted cuttings of the Canadian yew, Taxus canadensis. The structure was characterized as 7β,9α,10β,13α-tetraacetoxy-5α-[3′-(N-formyl-N-methylamino)-3′-phenylpropanoyl]oxytaxa-4(20),12-diene (1) on the basis of 1D-, 2D-NMR data, and HR-FABMS analyses. The spectra revealed that in CDCl₃ solution 1 was composed of two rotamers (1a and 1b) in a ratio of approximately 2:1.     

Effect of benzothiophene on tetralin hydrogenation over supported rhodium catalyst in supercritical carbon dioxide solvent

The hydrogenation behavior of tetralin in the presence and absence of benzothiophene was studied over a charcoal-supported rhodium catalyst in supercritical carbon dioxide solvent. The catalyst activity, as well ascis-decalin selectivity, decreased in the presence of benzothiophene.     

Evaluation of kinetics parameters for poly(l-lactic acid) hydrolysis under high-pressure steam

In order to evaluate more precise kinetics parameters: rate constant k and E_a values for poly(l-lactic acid) hydrolysis, the reaction was carried out under high-pressure steam in a temperature range of 100-130 °C. Molecular weights of hydrolyzates were calculated by the universal calibration method without being influenced by any weight loss. The changes in molecular weight could be successfully explained according to the auto-catalytic hydrolysis mechanism, clearly indicating the critical point. Resulting k and E_a values were estimated as 8.4 × 10⁻⁵-7.2 × 10⁻⁴ s⁻¹ and 87.2 kJ mol⁻¹ with high R² values, respectively. Moreover, to determine the deviation of the parameter values, influences of four factors on the measurements and calculation: (1) use of number-average molecular weight value alone, (2) use of relative molecular weight based on polystyrene standards, (3) weight loss during the hydrolysis, and (4) selection of reaction mechanism were evaluated quantitatively.     

Elucidation of inhibitors in the dimerization of acrylonitrile using [RuCl2(DMSO)4/CH3CH2COONa/DMSO/o-benzoylbenzoic acid] as catalyst

A study of inhibitors in the dimerization of acrylonitrile using the novel catalytic system of [RuCl₂(DMSO)₄/CH₃CH₂COONa/DMSO/o-benzoylbenzoic acid] was carried out by examining the effect of reaction products on the catalytic activity. 1,4-Dicyanobuta-1,3-diene (3), one of the linear dimer products of acrylonitrile, inhibited the Ru-catalyzed reaction. Methylthiomethyl o-benzoylbenzoate (8), a by-product which was produced from carboxylic acid and DMSO under the reaction conditions, also acted as an inhibitor.     

Electrochemical elucidation on the mechanism of uncoupling caused by hydrophobic weak acids

Uncoupler-mediated cation transport has been investigated by cyclic voltammetry for the ion transfer from one aqueous phase (W1) to another (W2) across a bilayer lipid membrane (BLM) in the presence of typical uncouplers, 3,5-di(tert-butyl)-4-hydroxybenzylidenemalononitril (SF6847) and 2,4-dinitrophenol (DNP). The voltammograms for the ion transfer were in a steady state and exhibited a rotated sigmoidal shape that was almost symmetrical about the origin (0 V, 0 A). The plot of the ion transfer current against pH was a bell-type curve centered on pH approximately = pK(a) + 1, K(a) being the dissociation constant of the uncouplers in the aqueous phase. Taking into account the ion transfer reactions at the W1|BLM and the BLM|W2 interfaces, these properties were well explained by our proposed model which considers that the ion transfer current is attributable to the facilitated transfers of H(+) and Na(+). The buffer action in the aqueous phase was found to play an important role in the facilitated H(+)-transfer across the BLM. The nature of the pH-dependence of the ion transfer current was reasonably explained from an electrochemical viewpoint based on the distribution coefficient of the anionic and neutral forms of SF6847, as estimated from its absorption spectra in liposomal membrane. The proposed model is also valuable for understanding the pH-dependence of uncoupling activity in mitochondria in the literature.     

Asymmetric addition of arylboronic acids to glyoxylate catalyzed by a ruthenium/Me-BIPAM complex

The enantioselective synthesis of α-hydroxy esters by ruthenium-catalyzed 1,2-addition of arylboronic acids to tert-butyl glyoxylate is described. The use of RuCl(2)(PPh(3))(3) with (R,R)-Me-BIPAM gave optically active mandelic acids of up to 99% ee. Addition of a fluoride salt such as potassium fluoride (KF) or caesium fluoride (CsF) was effective for achieving high enantioselectivities.     

Four new epoxy taxanes from needles of Taxus cuspidata (Taxaceae)

Four new epoxy taxoids were isolated from the needles of Taxus cuspidata. Their structures were established as 2a,9a-diacetoxy-5a-cinnamoyloxy-11,12-epoxy-10ss-hydroxytax-4(20)-en-13-one (1), 2a,10ss-diacetoxy-5a-cinnamoyloxy-11,12-epoxy-9a-hydroxytax-4(20)-en-13-one (2), 2a,9a-diacetoxy-11,12-epoxy-10ss,20-dihydroxytax-4-en-13-one (3) and 2a,10ss-diacetoxy-11,12-epoxy-9a,20-dihydroxytax-4-en-13-one (4) on the basis of spectral analysis including 1H-NMR, 13C-NMR, 1H-1H-COSY, HSQC, HMBC and HRFABMS. Compounds 3 and 4 are the first example of 11,12-epoxy taxoids with C-4 double bond found in T. cuspidata.     

Effects of thermal treatments on the recovery of adsorbed water and photocatalytic activities of TiO2 photocatalytic systems

The effects of thermal treatments on the rehydration process and photocatalytic activity were investigated by 1H NMR spectroscopy for six anatase abundant TiO2 photocatalysts with different properties. Acetic acid and benzoic acid were employed for photodecomposition in aqueous suspension. After the calcinations at 973 K, physisorbed water layers recovered relatively fast for P25, F4, and AMT-600 (shorter than 24 h) with no significant enhancement of the photocatalytic decomposition. On the other hand, for ST-01, UV-100, and AMT-100, the recovery was very slow (longer than 1 week) and only partially reversible, and the photocatalytic decomposition was considerably enhanced but retarded with rehydration. In the presence of adsorbed water, the binding of a carboxyl group of the molecules with adsorbed water is considered to compete with the direct adsorption on the surface, which reduces the amount of the direct adsorption and results in the reduction in the photocatalytic efficiency. In addition, the photocatalytic decomposition of benzoic acid with an aromatic ring was much faster in all of the TiO2 aqueous suspensions and more enhanced for the fully dehydroxylated TiO2 than that of acetic acid. These results suggest that the most efficient photocatalytic sites should be the hydrophobic sites on the TiO2 surface. The difference among the rehydration rates of different TiO2 is discussed in terms of thermally induced changes of surface morphology.     

Growth and characterization of pyrene crystals on carbon nanofibers

Pyrene crystals were grown on carbon nanofibers (CNFs) by dispersing pyrene polycrystals and CNFs in water during ultrasonic irradiation, and they were characterized by scanning electron microscopy, X-ray diffractometry (XRD) and spectroscopy. The XRD measurements indicated that the orientation and size of the pyrene crystals on the CNF aggregates were different from that of the added pyrene polycrystals. Based on the spectroscopic properties of the pyrene crystals on the CNFs, the pyrene crystals on the CNF aggregates and on the individual CNFs were determined to be polycrystals and single crystals, respectively. These results indicate that pyrene crystals are produced on the CNFs by recrystallization of the added pyrene polycrystals and their crystal states depend on the aggregation state of the CNFs.