Photocatalyst of lamellar aggregates of RuOx-loaded perovskite nanosheets for overall water splitting

Overall photocatalytic splitting of water was achieved using a restacked aggregate of exfoliated nanosheets of Ca(2)Nb(3)O(10), which was synthesized by flocculating a colloidal suspension of the nanosheets with alkali-metal ions and a trace amount of ruthenium red, a trinuclear complex of ([(NH(3))(5)Ru-O-Ru(NH(3))(4)-O-Ru(NH(3))(5)]Cl(6). The as-restacked material showed the evolution of H(2) gas from water immediately after UV irradiation, while O(2) evolution was observed only after some induction time, which may be understood by the possible oxidation of ruthenium red to RuO(x) in the initial stage. The restacked aggregate, which was heated at 773 K to convert the ruthenium complex to the oxide, underwent the stoichiometric splitting of water upon initiation of UV illumination, verifying the hypothesis. Total decomposition of water could not be attained with the bulk layered host of KCa(2)Nb(3)O(10) as well as its RuO(x)-loaded forms obtained via a conventional impregnation procedure. This clearly demonstrates the effectiveness of the present exfoliation-restacking route for loading RuO(x) to improve and enhance the photocatalytic activities of layered semiconducting materials. A homogeneous distribution of RuO(x)was suggested by XPS depth-profile analysis on the materials obtained through the exfoliation-restacking process.     

Allylation of phenoxides by crown ethers and their polymers

Allylation of sodium phenoxide in the presence of crown ethers produces a high ratio of O/O + C allylation when conducted in water, phenol, benzene, or diethyl ether. The striking increase in the product ratios is attributed to specific complexation of the crown ethers that facilitate the dissociation of the ion pair aggregate of the sodioderivative in benzene or diethyl ether. The crown ethers may act as a phase transfer catalyst when the reaction is run in water. Furthermore, the O/O + C ratios of the allylation strongly depend on the kind of crown ethers used. To examine their effect the allylation of sodium phenoxide was studied with various crown ethers, such as 18-crown-6, benzo-18-crown-6, benzo-15-crown-5, poly(vinylmonobenzo-15-crown-5), and poly(vinylmono-benzo-18-crown-6), as catalysts. It was found that among these crown ethers poly(vinylmono-benzo-15-crown-5) was the most effective catalyst.     

Silazanes/catalytic bases: mild,powerful and chemoselective agents for the preparation of enol silyl ethers from ketones and aldehydes

We have developed an efficient method for the preparation of enol silyl ethers using novel agents, silazanes together with NaH or DBU catalyst, wherein TMS and TBDMS groups were smoothly and chemoselectively introduced into ketones and aldehydes under mild conditions.     

Interesterification activity of Rhizopus delemar lipase in phospholipid microemulsions

The interesterification of olive oil with palmitic acid catalyzed by Rhizopus delemar lipase was investigated in phospholipid microemulsion systems. Soybean lecithin was used as the amphiphilic component. The maximal reaction rate was obtained at a buffer pH of 5.5–6.0. The reaction rate was also dependent on the W_L (= [H₂O]/[lecithin]) value and attained a maximum at W_L = 5. The reaction rate reached a maximum at a palmitic acid concentration of 350 mM. The molar fraction of the interesterified product 1,3-dipalmitoyl-3-oleoyl glycerol (POP) in the olive oil was enhanced from 2.8 to 65.6 mol% after 24 h of the reaction.     

New synthetic routes to biscarbonylbipyridinerhenium(I) complexes cis,trans-[Re(X2bpy)(CO)2(PR3)(Y)n+ (X2bpy = 4,4'-X2-2,2'-bipyridine) via photochemical ligand substitution reactions, and their photophysical and electrochemical properties

Photochemical ligand substitution of fac-[Re(X2bpy)(CO)3(PR3)]+ (X2bpy = 4,4'-X2-2,2'-bipyridine; X = Me, H, CF3; R = OEt, Ph) with acetonitrile quantitatively gave a new class of biscarbonyl complexes, cis,trans[Re(X2bpy)(CO)2(PR3)(MeCN)]+, coordinated with four different kinds of ligands. Similarly, other biscarbonylrhenium complexes, cis,trans-[Re(X2bpy)(CO)2(PR3)(Y)]n+ (n = 0, Y = Cl-; n = 1, Y = pyridine, PR'3), were synthesized in good yields via photochemical ligand substitution reactions. The structure of cis,trans-[Re(Me2bpy)(CO)2[P(OEt)3](PPh3)](PF6) was determined by X-ray analysis. Crystal data: C38H42N2O5F6P3Re, monoclinic, P2(1/a), a = 11.592(1) A, b = 30.953(4) A, c = 11.799(2) A, V = 4221.6(1) A3, Z = 4, 7813 reflections, R = 0.066. The biscarbonyl complexes with two phosphorus ligands were strongly emissive from their 3MLCT state with lifetimes of 20-640 ns in fluid solutions at room temperature. Only weak or no emission was observed in the cases Y = Cl-, MeCN, and pyridine. Electrochemical reduction of the biscarbonyl complexes with Y = Cl- and pyridine in MeCN resulted in efficient ligand substitution to give the solvento complexes cis,trans-[Re(X2bpy)(CO)2(PR3)(MeCN)]+.     

Limiting interdiffusion coefficients of Tris(acetylacetonato)cobalt(III) in water and in organic solvents

The diffusion coefficients of tris(acetylacetonato)-cobalt(III) in water (5, 15, 25, and 40°C), methanol (25°C), ethanol (15, 25, and 45°C), 1-propanol (25°C), 1-butanol (45°C), acetone (25 and 40°C), 2-butanone (25°C), acetonitrile (25°C), tetrahydrofuran (25°C), benzen (25°C), toluene (25°C), and carbon tetrachloride (25°C) have been measured at concentrations close to infinite dilution. The Stokes-Einstein coefficient (f=kT/Dr) has been calculated for Co(acac)₃ in each solvent and is found to be larger in water than in organic solvents. Furthermore, it increases as the temperature is lowered (or as the viscosity is increased) in water while it decreases with increasing viscosity of organic solvents. The differences are discussed in terms of the enhancement of the water structure by the solute.     

Development of novel diastereoselective alkenylation of enolates using alkenylselenonium salts

[reaction: see text] A novel alkenylation of enolates using alkenylselenonium salts is described. A reaction of lithium enolates, which were prepared in situ by the reaction of LiHMDS and carbonyl compounds, with alkenylselenonium salts gave the ethenylation products of carbonyl compounds in high yield. Diastereoselective alkenylation was also accomplished by the reaction of the enolates derived from N-acyl-1,3-oxazolidin-2-ones with the alkenylselenonium salt to afford good results (up to 92% yield and up to 95% de).     

A highly potent non-nucleoside adenosine deaminase inhibitor: efficient drug discovery by intentional lead hybridization

We disclose herein the rapid discovery of the first highly potent (Ki = 7.7 nM) non-nucleoside adenosine deaminase (ADA) inhibitor based on the rational hybridization of two structurally distinct leads. Two micromolar inhibitors were discovered by a parallel rational design and random screening program, and individual crystal structures of bovine ADA in complexation with these inhibitors revealed several unknown binding sites and distinct binding modes. Using this information as the starting point, highly effective lead hybridization was achieved in only two structure-based drug design iterations. The conceptual approach illustrated by this example promises to be broadly useful in the search for new chemical entities and can contribute greatly to improve the overall efficiency and speed of drug discovery.     

Photocurrent generation from semiconducting manganese oxide nanosheets in response to visible light

Unilamellar nanosheet crystallites of manganese oxide generated the anodic photocurrent under visible light irradiation (lambda < 500 nm), while the nanosheets themselves were stable as revealed by in-plane XRD and UV-visible absorption spectra. The band gap energy was estimated to be 2.23 eV on the basis of the photocurrent action spectrum. The molecular thickness of approximately 0.5 nm may facilitate the charge separation of excited electrons and holes, which is generally very difficult for strongly localized d-d transitions. The monolayer film of MnO2 nanosheets exhibited the incident photon-to-electron conversion efficiency of 0.16% in response to the monochromatic light irradiation (lambda = 400 nm), which is comparable to those for sensitization of monolayer dyes adsorbed on a flat single-crystal surface. The efficiency declined with increasing the layer number of MnO2 nanosheets, although the optical absorption was enhanced. The recombination of the excited electron-hole pairs may become dominant when the carriers need to migrate a longer distance than 1 layer through multilayered nanosheets.     

FEMTOSECOND STUDIES OF PRIMARY PHOTOPROCESSES IN OCTOPUS RHODOPSIN

Abstract— Femtosecond spectroscopy of octopus rhodopsin in H₂O and D₂O was performed over a very wide spectral region of 400–1000 nm. Transient gain and absorption from the excited state were observed for the first time around 650 and 700 nm, respectively, just after 300 fs pulse excitation. Bathorhodopsin was formed within 400 fs from the excited state; therefore, the cis-trans isomerization completes within 400 fs. The first intermediate "primerhodopsin" found in our previous paper is most likely "quasi-thermal" bathorhodopsin, in which the local thermalization of the chromophore is achieved. Then cooling down of the chromophore to the surrounding protein temperature takes place with 20 ± 10 ps along with blue-shifting of a spectrum of 10 ± 5 nm. In addition to these observations, a prominent gain in the region of > 850 nm was observed and decayed with 2–3 ps in H₂O. A similar time constant was estimated for a partial decay of an induced absorption around 600 nm. This process may be related with two forms of bathorhodopsin reported previously. In this scheme, two forms of bathorhodopsin are formed with time constants of about 400 fs and 2 ps. In the sample in D₂O, time constant of 3–4 ps was obtained for the slower process.