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.     

On the eigenvalues of compact operators in a Hilbert space

Summary This paper contains several remarks concerning the behavior of the eigenvalues of compact operators in a Hilbert space. The results are related to the theorem for a finite matrix obtained as Theorem 1 in my previous paper[5].This work was partially supported by a research grant of the Sakkokai Foundation.     

Precise retinal shape measurement by alignment error and eye model calibration

Optical Review - To evaluate the repeatability of the optical coherence tomography (OCT) retinal shape measurement with and without alignment correction in children and adults. 62 eyes of the 31...     

STRUCTURE-REACTIVITY RELATIONSHIPS IN REDOX-PHOTOSENSITIZED SPLITTING OF PYRIMIDINE DIMERS AND UNUSUAL ENHANCING EFFECT OF MOLECULAR OXYGEN *

Abstract Redox photosensitization using the phenanthrene-p-dicyanobenzene pair in acetonitrile has been applied to the respective four isomeric dimers of N.N′-dimethylthymine (DMT) and N,N′-dimethyluracil (DMU) as well as to several related cyclobutane compounds. The head-to-head (syn) dimers of both DMT and DMU can undergo photosensitized splitting in the following order of efficiency: cis, syn dimer of DMT > cis, syn dimer of DMU > trans, syn dimer of DMT. On the other hand, the head-to-tail (anti) dimers are totally unreactive and have higher oxidation potentials than the corresponding syn dimers. It is suggested that the key mechanistic pathway is the formation of π complexes between the dimers and the photo-generated cation radical of phenanthrene by way of which splitting of the cyclobutane ring catalytically occurs without the formation of the discrete cation radical of the dimers. Structure-reactivity relationships are interpreted in terms of through-bond interactions between the n orbitals of N(l) and N(l′) involving the C(6)-C(6′) bond, as well as in terms of steric repulsion. It was found that aeration of solution greatly enhances the quantum yields of photosensitized splitting; the limiting quantum yield for splitting of the cis, syn dimer of DMT is 100.     

Three-dimensional Lie group actions on compact (4n+3)-dimensional geometric manifolds

The (4n+3)-dimensional sphere S⁴ⁿ⁺³ can be viewed as the boundary of the quaternionic hyperbolic space and the group PSp(n+1,1) of quaternionic hyperbolic isometries extends to a real analytic transitive action on S⁴ⁿ⁺³. We call the pair (PSp(n+1,1),S⁴ⁿ⁺³) a spherical Q C-C geometry. A manifold M locally modelled on this geometry is said to be a spherical Q C-C manifold. We shall classify all pairs (G,M) where G is a three-dimensional connected Lie group which acts smoothly and almost freely on a compact spherical Q C-C manifold M, preserving the geometric structure. As an application, we shall determine all compact 3-pseudo-Sasakian manifolds admitting spherical Q C-C structures.     

Novel Chiral Building Block: (2R,3S)-2-(1,3-Dithian-2-yl)-3-hydroxybutanoates. Highly Diastereo- and Enantioselective Baker's Yeast Reduction of 2-(1,3-Dithian-2-yl)-3-oxobutanoates

The baker's yeast reduction of 2-(1,3-dithian-2-yl)-3-oxobutanoates gave (2R,3S)-2-(1,3-dithian-2-yl)-3-hydroxybutanoates in good yiels and in high diastereo- and enantioselectivity.     

Reactions of copper(II)-phenol systems with O2: models for TPQ biosynthesis in copper amine oxidases

Copper(II) complexes supported by a series of phenol-containing bis(pyridin-2-ylmethyl)amine N(3) ligands (denoted as L(o)H, L(m)H, and L(p)H) have been synthesized, and their O(2) reactivity has been examined in detail to gain mechanistic insights into the biosynthesis of the TPQ cofactor (2,4,5-trihydroxyphenylalaninequinone, TOPA quinone) in copper-containing amine oxidases. The copper(II) complex of L(o)H (ortho-phenol derivative) involves a direct phenolate to copper(II) coordination and exhibits almost no reactivity toward O(2) at 60 °C in CH(3)OH. On the other hand, the copper(II) complex of L(m)H (meta-phenol derivative), which does not involve direct coordinative interaction between the phenol moiety and the copper(II) ion, reacts with O(2) in the presence of triethylamine as a base to give a methoxy-substituted para-quinone derivative under the same conditions. The product structure has been established by detailed nuclear magnetic resonance (NMR), infrared (IR) spectroscopy, and electrospray ionization-mass spectroscopy (ESI-MS) (including (18)O-labeling experiment) analyses. Density functional theory predicts that the reaction involves (i) intramolecular electron transfer from the deprotonated phenol (phenolate) to copper(II) to generate a copper(I)-phenoxyl radical; (ii) the addition of O(2) to this intermediate, resulting in an end-on copper(II) superoxide; (iii) electrophilic substitution of the phenolic radical to give a copper(II)-alkylperoxo intermediate; (iv) O-O bond cleavage concomitant with a proton migration, giving a para-quinone derivative; and (v) Michael addition of methoxide from copper(II) to the para-quinone ring and subsequent O(2) oxidation. This reaction sequence is similar to that proposed for the biosynthetic pathway leading to the TPQ cofactor in the enzymatic system. The generated para-quinone derivative can act as a turnover catalyst for aerobic oxidation of benzylamine to N-benzylidene benzylamine. Another type of copper(II)-phenol complex with an L(p)H ligand (para-phenol derivative) also reacts with O(2) under the same experimental conditions. However, the product of this reaction is a keto-alcohol derivative, the structure of which is qualitatively different from that of the cofactor. These results unambiguously demonstrate that the steric relationship between the phenol moiety and the supported copper(II) ion is decisive in the conversion of active-site tyrosine residues to the TPQ cofactor.     

Control Mechanism for cis Double‐Bond Formation by Polyunsaturated Fatty‐Acid Synthases

Polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) are essential fatty acids for humans. Some microorganisms biosynthesize these PUFAs through PUFA synthases composed of four subunits with multiple catalytic domains. These PUFA synthases each create a specific PUFA without undesirable byproducts, even though the multiple catalytic domains in each large subunit are very similar. However, the detailed biosynthetic pathways and mechanisms for controlling final‐product profiles are still obscure. In this study, the FabA‐type dehydratase domain (DH_FabA) in the C‐subunit and the polyketide synthase‐type dehydratase domain (DH_PKS) in the B‐subunit of ARA synthase were revealed to be essential for ARA biosynthesis by in vivo gene exchange assays. Furthermore, in vitro analysis with truncated recombinant enzymes and C₄‐ to C₈‐acyl ACP substrates showed that ARA and EPA synthases utilized two types of DH domains, DH_PKS and DH_FabA, depending on the carbon‐chain length, to introduce either saturation or cis double bonds to growing acyl chains.