Ultrafast photosynthetic reduction of elemental sulfur by Au nanoparticle-loaded TiO2

Nanometer-sized gold particles with varying mean size from 3.2 to 12.2 nm were loaded on the surfaces of TiO2 particles in a highly dispersed state with the loading amount maintained constant (0.46 +/- 0.02 mass %) using the deposition-precipitation method. Light irradiation (lambda(ex) > 300 nm) to a deaerated ethanol TiO2 particle suspension containing elemental sulfur (S8) led to the energetically uphill reduction of S8 to H2S. It has been found that this reaction is dramatically enhanced with such a low level of Au loading on TiO2 and that the zero-order rate constant of reaction increases with decreasing mean size of Au nanoparticles (d). The effects of reaction parameters (substrate concentration, light intensity, temperature) on the rate of reaction were studied to infer the essential reaction mechanism. Further, a kinetic analysis has led to a conclusion that the increase in the rate of reaction with decreasing d results from the improvement of the charge separation efficiency.     

Helical structures of N-alkylated poly(p-benzamide)s

Poly(p-benzamide)s 1 bearing a chiral side chain on the nitrogen atom were synthesized by chain-growth polycondensation methodology. The polyamides exhibited well-defined molecular weights with narrow polydispersities. Solutions of the polyamides in several organic solvents (CH(3)CN, CHCl(3), and CH(3)OH) showed dispersion type CD signals characteristic of coupled-oscillator and much larger as compared with the corresponding monomer. The CD signals were dependent on the temperature and molecular weight of the polyamides but independent of the solvent, as far as examined. An exciton model analysis of the absorption and CD spectra provided a clear-cut picture for the secondary structure of these polyamides in solution that the N-alkylated poly(p-benzamide)s possess a right-handed helical conformation ((P)-helix). In the solid states, the results of X-ray crystallographic analysis of 4-(methylamino)benzoic acid oligomers substantiated that they have a helical conformation with three monomer units per turn.     

Oxidation-active flavin models: oxidation of alpha-hydroxy acids by benzo-dipteridine bearing metal-binding site in the presence of divalent metal ion and base in organic solvents.

The oxidizing ability of benzo-dipteridine bearing a bipyridin-6-ylmethyl moiety (4) was found to be increased with Zn(2+) by approximately 10(3)-fold for sulfite addition in MeOH and approximately 10(2)-fold for oxidation of an NADH model in MeCN. It was found for the first time that 4 is able to oxidize alpha-hydroxy acids to alpha-keto acids in the presence of a divalent metal ion such as Zn(2+), Co(2+), and Ni(2+) and an amine base in MeCN or t-BuOH, whereas benzo-dipteridine having a bipyridin-5-ylmethyl moiety (3) is unable to oxidize them under the same conditions. The oxidation reaction was kinetically investigated including the kinetic isotope effect for deuterated mandelic acids (k(H)/k(D) = 2.1-3.7) and the Hammett plots for substituted mandelic acids (V-shaped plots). In the reaction of alpha-substituted alpha-hydroxy acids such as alpha-methyl mandelic and benzylic acids with 4, novel oxidative decarboxylation was found to take place, giving acetophenone and benzophenone, respectively. The oxidation mechanism for mandelic acid was proposed to proceed via a ternary complex of 4.Zn(2+).PhCH(OH)CO(2)(-), in which alpha-oxyanion of mandelate attacks C(4a)-position of 4 to form an adduct followed by 1,2-elimination to afford benzoyl formate and 2e-reduced 4. The roles of the metal ion were proposed as follows; (i) activation of 4, (ii) substrate-binding site, and (iii) activation of the bound alpha-hydroxy acid by lowering pK(a)'s of alpha-OH and alpha-CH. This is a first example that a flavin model oxidizes alpha-hydroxy acids in the presence of a metal ion.     

Efficient peroxide decoloration of azo dye catalyzed by polyethylene glycol-linked manganese chlorin derivative

We reported here that polyethylene glycol (PEG)-linked manganese pyrochlorophyllide a (PEG-MnPChlide a) possesses remarkable catalytic activity comparable to horseradish peroxidase (HRP). The PEG-MnPChlide a catalyzed the oxidation decoloration reaction of C.I. Acid Orange 7 by hydrogen peroxide under a mild aqueous condition, pH 8.0 at 25 °C. The manganese pyrochlorophyride a methylester (MnPChlide a ME) dissolved in a Triton X-100 micellar solution also exhibited the catalytic activity, indicating the micellar environment plays an important role in the catalytic reaction. The reaction rate was accelerated by addition of imidazole. The catalytic reactions were analyzed by Michaelis–Menten kinetics, revealing that the higher reactivity of catalyst–substrate complex is responsible for the present catalytic reaction system.     

Naphtho[2,1-b:6,5-b']difuran: a versatile motif available for solution-processed single-crystal organic field-effect transistors with high hole mobility

We here report naphtho[2,1-b:6,5-b']difuran derivatives as new p-type semiconductors that achieve hole mobilities of up to 3.6 cm(2) V(-1) s(-1) along with high I(on)/I(off) ratios in solution-processed single-crystal organic field-effect transistors. These features originate from the dense crystal packing and the resulting large intermolecular π-orbital overlap as well as from the small reorganization energy, all of which originate from the small radius of an oxygen atom.     

Development of an energy‐domain 57Fe‐Mössbauer spectrometer using synchrotron radiation and its application to ultrahigh‐pressure studies with a diamond anvil cell

An energy‐domain ⁵⁷Fe‐Mössbauer spectrometer using synchrotron radiation (SR) with a diamond anvil cell (DAC) has been developed for ultrahigh‐pressure measurements. The main optical system consists of a single‐line pure nuclear Bragg reflection from an oscillating ⁵⁷FeBO₃ single crystal near the Néel temperature and an X‐ray focusing device. The developed spectrometer can filter the Doppler‐shifted single‐line ⁵⁷Fe‐Mössbauer radiation with a narrow bandwidth of neV order from a broadband SR source. The focused incident X‐rays make it easy to measure a small specimen in the DAC. The present paper introduces the design and performance of the SR ⁵⁷Fe‐Mössbauer spectrometer and its demonstrative applications including the newly discovered result of a pressure‐induced magnetic phase transition of polycrystalline ⁵⁷Fe₃BO₆ and an unknown high‐pressure phase of Gd⁵⁷Fe₂ alloy placed in a DAC under high pressures up to 302 GPa. The achievement of Mössbauer spectroscopy in the multimegabar range is of particular interest to researchers studying the nature of the Earth's core.