Local structure of Pt and Pd ions in Ce(1-x)TixO2: x-ray diffraction, x-ray photoelectron spectroscopy, and extended x-ray absorption fine structure

Ce(1-x-y)Ti(x)Pt(y)O(2-delta) (x=0.15; y=0.01) and Ce(1-x-y)Ti(x)Pd(y)O(2-delta) (x=0.25; y=0.02 and 0.05) are found to be good CO oxidation catalysts [T. Baidya et al., J. Phys. Chem. B 110, 5262 (2006); T. Baidya et al., J. Phys. Chem. C 111, 830 (2007)]. A detailed structural study of these compounds has been carried out by extended x-ray absorption fine structure along with x-ray diffraction and x-ray photoelectron spectroscopy. The gross cubic fluorite structure of CeO(2) is retained in the mixed oxides. Oxide ion sublattice around Ti as well as Pt and Pd ions is destabilized in the solid solution. Instead of ideal eight coordinations, Ti, Pd, and Pt ions have 4+3, 4+3, and 3+4 coordinations creating long and short bonds. The long Ti-O, Pd-O, and Pt-O bonds are approximately 2.47 A (2.63 A for Pt-O) which are much higher than average Ce-O bonds of 2.34 A.     

Synthesis of chiral and modifiable hexahydroxydiphenoyl compounds

A reliable method for synthesizing each enantiomer of the hexahydroxydiphenoyl (HHDP) compounds has been developed. The synthesis involved atropselective construction of the aryl-aryl bond of the HHDP compounds. This construction relied on the CuCl(2)·n-BuNH(2)-mediated intramolecular coupling of bis(4-O-benzylgallate) on two simple chiral auxiliaries, both of which were derived from l-(+)-tartaric acid. The coupling reaction realized complete or near-perfect atropselectivity. The two auxiliaries induced opposite axial chirality despite their identical origin. The diastereoselectivities of these couplings were probably controlled kinetically. Modifications of the free phenolic hydroxy groups and the carbonyl groups in the resulting HHDP compounds demonstrated the potential derivatization of a wide variety of HHDP analogues.     

In situ time-resolved XAFS study of the reaction mechanism of bromobenzene homocoupling mediated by [Ni(cod)(bpy)

A homocoupling reaction mechanism of bromobenzene mediated by the [Ni(cod)(bpy)] (cod = 1,5-cyclooctadiene; bpy = 2,2'-bipyridine) complex was investigated by means of in situ time-resolved X-ray absorption fine structure (XAFS) and factor analysis. A dimer intermediate [Ni(bpy)(Ph)Br](2) proposed in the previous studies by other groups is too dilute to observe with the XAFS technique; however, the structures and concentrations on the time course of a reactant [Ni(cod)(bpy)], an intermediate [Ni(bpy)(Ph)Br(dmf)(2)], and a byproduct [Ni(bpy)Br(2)(dmf)] during reaction are revealed by this combination.     

Alkali-Metal-Promoted Pt/TiO(2) Opens a More Efficient Pathway to Formaldehyde Oxidation at Ambient Temperatures

Addition of alkali metal ions significantly promotes the activity of the Pt/TiO(2) catalyst for the HCHO oxidation reaction by stabilizing an atomically dispersed Pt-O(OH)(x) alkali metal species and opening a new low-temperature reaction pathway. The atomically dispersed Na-Pt-O(OH)(x) species can effectively activate H(2) O and catalyze the facile reaction between surface OH and formate species to total oxidation products.     

Completely β-selective glycosylation using 3,6-O-(o-xylylene)-bridged axial-rich glucosyl fluoride

A completely β-selective glycosylation that does not rely on neighboring group participation is described. The novelty of this work is the design of the glycosyl donor locked into the axial-rich form by the o-xylylene bridge between the 3-O and 6-O of d-glucopyranose. The synthesized 2,4-di-O-benzyl-3,6-O-(o-xylyene)glucopyranosyl fluoride could efficiently react with various alcohols in a SnCl(2)-AgB(C(6)F(5))(4) catalytic system. The mechanism composed of the glycosylation and isomerization cycles was revealed through comparative experiments using acidic and basic molecular sieves. The achieved perfect stereocontrol is attributed to the synergy of the axial-rich conformation and convergent isomerization caused by HB(C(6)F(5))(4) generated in situ.     

Characterization of a Water-Dispersed Biodegradable Polyurethane-Silk Composite Sponge Using 13C Solid-State Nuclear Magnetic Resonance as Coating Material for Silk Vascular Grafts with Small Diameters

Recently, Bombyx mori silk fibroin (SF) has been shown to be a suitable material for vascular prostheses for small arteries. In this study, we developed a softer SF graft by coating water-dispersed biodegradable polyurethane (PU) based on polycaprolactone and an SF composite sponge on the knitted SF vascular graft. Three kinds of ¹³C solid-state nuclear magnetic resonance (NMR), namely carbon-13 (¹³C) cross-polarization/magic angle spinning (MAS), ¹³C dipolar decoupled MAS, and ¹³C refocused insensitive nuclei enhanced by polarization transfer (r-INEPT) NMR, were used to characterize the PU-SF coating sponge. Especially the ¹³C r-INEPT NMR spectrum of water-dispersed biodegradable PU showed that both main components of the non-crystalline domain of PU and amorphous domain of SF were highly mobile in the hydrated state. Then, the small-diameter SF artificial vascular grafts coated with this sponge were evaluated through implantation experiments with rats. The implanted PU-SF-coated SF grafts showed a high patency rate. It was confirmed that the inside of the SF grafts was covered with vascular endothelial cells 4 weeks after implantation. These results showed that the water-dispersed biodegradable PU-SF-coated SF graft created in this study could be a strong candidate for small-diameter artificial vascular graft.     

Experimental evidence and theoretical analysis for the chiral symmetry breaking in the growth front of conglomerate crystal phase of 1,1'-binaphthyl

Chirally asymmetric states, chemical oscillations, propagating chemical waves, and spatial patterns, are examples of far-from-equilibrium self-organization. We have found that the crystal growth front of 1,1(')-binaphthyl shows many of the characteristics of an open system in which chiral symmetry breaking has occurred. From its supercooled molten phase, 1,1(')-binaphthyl crystallizes as a conglomerate of R and S crystals when the temperature is above 145 degrees C. In addition, 1,1(')-binaphthyl in its molten phase is always racemic due to its high racemization rate. Under appropriate conditions, bimodal probability distribution of enantiomeric excess (ee) with maxima around 60% was observed. The ee was mass independent, indicating that the growth front maintains a constant ee. A kinetic model that theoretically analyzes the chiral symmetry breaking transition in the growth front of a conglomerate crystal phase was formulated. Computer simulation of the model reproduced not only the average but also the large variation of the ee observed in crystallization experiments.     

Premodified Surface Method to Obtain Ultra‐Highly Dispersed Metals and their 3D Structure Control on an Oxide Single‐Crystal Surface

Precise control of the three‐dimensional (3D) structure of highly dispersed metal species such as metal complexes and clusters attached to an oxide surface has been important for the development of next‐generation high‐performance heterogeneous catalysts. However, this is not easily achieved for the following reasons. (1) Metal species are easily aggregated on an oxide surface, which makes it difficult to control their size and orientation definitely. (2) Determination of the 3D structure of the metal species on an oxide powder surface is hardly possible. To overcome these difficulties, we have developed the premodified surface method, where prior to metal deposition, the oxide surface is premodified with a functional organic molecule that can strongly coordinate to a metal atom. This method has successfully provided a single metal dispersion on an oxide single‐crystal surface with the 3D structure precisely determined by polarization‐dependent total reflection fluorescence X‐ray absorption fine structure (PTRF‐XAFS). Here we describe our recent results on ultra‐high dispersions of various metal atoms on TiO₂(110) surfaces premodified with mercapto compounds, and show the possibility of fine tuning and orientation control of the surface metal 3D structures.     

Extraction of object position from in-line holograms by using single wavelet coefficient

A novel digital method for tracking position of objects from in-line holograms by using single wavelet coefficient is proposed. In the proposed method, a wavelet transform is used to analyze the holograms. An axial position of the object being studied is determined by using a real value of a resultant wavelet coefficient appears at a center position of interference fringes. A feasibility of this method is experimentally verified by analyzing holograms of an optical fiber.