ion from a primary OH group of glyc-erol. 223,231 A similar mechanism was proposed manyyears ago for alcohol oxidation on Pt/C, involving asecond step, the transfer of a hydride ion to the Ptsurface (Scheme 11). 8,87,237 We consider it more feasible that the rate-deter-mining step is the cleavage of the C-H bond at theR-carbon atom. A similar mechanism is now generallyaccepted for Au electrodes (Scheme 12). 238 Despite thestructural differences between Au nanoparticles andan extended Au electrode surface, there are alsosimilarities, such as the critical role of aqueousalkaline medium and the absence of deactivation dueto decomposition products (CO and C x H y frag-ments). 239,240 An important question is the nature of active siteson Au nanoparticles. Electrooxidation of ethanol onAu nanoparticles supported on glassy carbon re-quired the partial coverage of Au surface by oxides. 241 Another analogy might be the model proposed for COoxidation. 219,242,243 According to this suggestion, theactive site consists of an ensemble of metallic Auatoms and a cationic Au

Oxidation of Alcohols with Molecular Oxygen on Solid Catalysts

Treatment of a stoichiometric hydroxyapatite (HAP), Ca10(PO4)6(OH)2, with PdCl2(PhCN)2 gives a new type of palladium-grafted hydroxyapatite. Analysis by means of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX), IR, and Pd K-edge X-ray absorption fine structure (XAFS) proves that a monomeric PdCl2 species is chemisorbed on the HAP surface, which is readily transformed into Pd nanoclusters with a narrow size distribution in the presence of alcohol. Nanoclustered Pd0 species can effectively promote the alcohol oxidation under an atmospheric O2 pressure, giving a remarkably high turnover number (TON) of up to 236,000 with an excellent turnover frequency (TOF) of approximately 9800 h(-1) for a 250-mmol-scale oxidation of 1-phenylethanol under solvent-free conditions. In addition to advantages such as a simple workup procedure and the ability to recycle the catalyst, the present Pd catalyst does not require additives to complete the catalytic cycle. The diameters of the generated Pd nanoclusters can be controlled upon acting on the alcohol substrates used. Oxidation of alcohols is proposed to occur primarily on low-coordination sites within a regular arrangement of the Pd nanocluster by performing calculations on the palladium crystallites.

Hydroxyapatite-Supported Palladium Nanoclusters: A Highly Active Heterogeneous Catalyst for Selective Oxidation of Alcohols by Use of Molecular Oxygen

Clays and catalysis: a promising future

Mg-Al mixed oxides as highly active acid-base catalysts for cycloaddition of carbon dioxide to epoxides

New developments in catalytic alcohol oxidations for fine chemicals synthesis

Heterogeneous oxidation of allylic and benzylic alcohols catalyzed by ru-al-mg hydrotalcites in the presence of molecular oxygen

Heterogeneous Baeyer-Villiger oxidation of ketones using m-chloroperbenzoic acid catalyzed by hydrotalcites

Heterogeneous Oxidation of Allylic and Benzylic Alcohols Catalyzed by Ru—Al—Mg Hydrotalcites in the Presence of Molecular Oxygen.

Heme-containing proteins, the heme proteins, are known to have physiologic functions in humans, mammalians, fish, plants, and bacteria. For example, hemoglobin and myoglobin, which belong to the globin family, have been studied in terms of their structures and functions with spectroscopic and mutagenic methods. Recently, a new class of heme proteins has been discovered, referred to as gas sensors. These are heme-based sensor proteins that play important roles in transcriptional activation, histidinekinase activities, phosphodiesterase activities, etc. CooA is a CO-sensing transcriptional activator derived from the photosynthetic bacterium Rhodospirillum rubrum. FixL is a rhizobial oxygen sensor protein, and we have targeted Bj FixL derived from Bradyrhizobium japonicum. Dos from Escherichia coli is an oxygen sensor protein, which senses oxygen in the heme-containing domain and induces phosphodiesterase activity in other domains. In previous work, we studied the axial ligands and C-helix of CooA to clarify the activation mechanism. Moreover, FixL and Dos were investigated using time-resolved spectroscopic methods. Whereas FixL has a pentacoordinate heme in the ferrous deoxy form, there are a proximal histidine (His 77) and a distal methionine (Met 95) as axial ligands to coordinate to the heme iron in EcDos. However almost all gas sensors show mono-exponential rebinding (6-7 ps), while EcDosH and full-length Dos show biexponential rebinding (7 ps and 35 ps) on the internal ligand. The results were also supported by molecular dynamic simulation. Here we discuss recent work on gas sensors with implications provided by our research.

Toyokazu Yamashita

Papers

Heterogeneous oxidation of allylic and benzylic alcohols catalyzed by ru-al-mg hydrotalcites in the presence of molecular oxygen

Heterogeneous Baeyer-Villiger oxidation of ketones using m-chloroperbenzoic acid catalyzed by hydrotalcites

Heterogeneous Oxidation of Allylic and Benzylic Alcohols Catalyzed by Ru—Al—Mg Hydrotalcites in the Presence of Molecular Oxygen.

[Recent studies on gas sensors, CooA, FixL, and Dos].

Recent Studies on Gas Sensors, CooA, FixL, and Dos