A photo-assisted fuel cell (photofuel cell; PFC) consisting of a porous TiO 2 photoanode and a Pt cathode in an aqueous electrolyte containing an organic fuel has been developed to generate an electric power by photoelectrochemically decomposing the fuel. Although direct utilization of cellulose as a fuel should be preferable, photocatalytic direct decomposition of cellulose, polymeric macromolecules, has been rarely reported. In the present study, a cellulose thin film deposited onto the TiO 2 photoanode was used as the fuel. It was revealed that the cellulose was decomposed into CO 2 through small carbonyl hydrocarbon intermediates. The complete decomposition of cellulose into CO 2 implies that almost all the Gibbs free energy of cellulose can be converted into an electric power with the assistance of the photon energy. The PFC composed of the cellulose-deposited TiO 2 and Pt-deposited Ni foam exhibited excellent photovoltaic performances (1.1 V of photovoltage and quantum efficiency up to 52 %). The present study should represent a potential means of electric power generation based on renewable energy sources by effectively treating waste biomass.

The genus Pestalotiopsis are endophytic fungi that have recently been identified as cellulolytic system producers. We herein cloned a gene coding for a xylanase belonging to glycoside hydrolase (GH) family 10 (PesXyn10A) from Pestalotiopsis sp. AN-7, which was isolated from the soil of a mangrove forest. This protein was heterologously expressed by Pichia pastoris as a host, and its enzymatic properties were characterized. PesXyn10A was produced as a glycosylated protein and coincident to theoretical molecular mass (35.3 kDa) after deglycosylation by peptide-N-glycosidase F. Purified recombinant PesXyn10A exhibited maximal activity at pH 6.0 and 50 °C, and activity was maintained at 90 % at pH 5.0 and temperatures lower than 30 °C for 24 h. The substrate specificity of PesXyn10A was limited and it hydrolyzed glucuronoxylan and arabinoxylan, but not β-glucan. The final hydrolysis products from birchwood xylan were xylose, xylobiose, and 1,2 3-α-D-(4-O-methyl-glucuronyl)-1,4-β-Dxylotriose. The addition of metallic salts (NaCl, KCl, MgCl 2 , and CaCl 2) activated PesXyn10A for xylan degradation, and maximal activation by these divalent cations was approximately 160 % at a concentration of 5 mM. The thermostability of PesXyn10A significantly increased in the presence of 50 mM NaCl or 5 mM MgCl 2. The present results suggest that the presence of metallic salts at a low concentration, similar to brackish water, exerts positive effects on the enzyme activity and thermal stability of PesXyn10A.

The reaction mechanisms occurring during the electrocatalytic oxidation of cellulose dissolved in a highly alkaline aqueous electrolyte were elucidated by hydrodynamic voltammetry using a Pt rotating disk electrode as well as product analyses. The charge-transfer limited current associated with the multielectron process in which macromolecules are cleaved into relatively short hydrocarbons was found to be dominant at relatively negative potentials, whereas further decomposition of the hydrocarbons proceeded at more positive potentials. Au was shown to facilitate the cleavage of cellulose macromolecules, while Pd and Ni promoted additional oxidative decomposition of the short-chain hydrocarbons. A fuel cell composed of Pt-deposited Ni foam electrodes as both the anode and cathode was capable of generating electricity in an external circuit while directly utilizing cellulose as a fuel, even at ambient temperature and pressure. The present study provides new insights into these reaction mechanisms and will assist in the design of catalytic materials intended for the effective utilization of biomass energy sources.

The assembly of discrete active species to form periodical nanostructures is essential in realizing low-cost artificial enzymes that mimic natural enzymatic functions in extraordinary bio(chemo)selective reactions. In this study, we developed artificial bifunctional glucose/gluconic acid dehydrogenase from naturally abundant resources: L-aspartic acid (Asp) and montmorillonite (a subgroup of smectite natural clay minerals). β-D-Glucose (Glc) was dehydrogenated to 2-keto-D-gluconate (2-KGA) at 25 and 30 °C in an aqueous acidic solution (pH = 3, 4, and 5). The reaction involved sequential steps that yielded D-gluconic acid (GA) as an intermediate. The second step of the dehydrogenation (GA to 2-KGA) occurred at a higher rate than the first (Glc to GA), which is comparable to the natural process. A negatively charged carboxylate in Asp was required for the dehydrogenation, which donates an electron pair (COO: − ) to the hydroxyl group bonded to the C(1)-position of Glc. The acidic sites in clay served as coenzymatic sites (electron acceptor), promoting the Glc dehydrogenation as the Glc reduced by Asp approached the clay coenzymatic sites. The active coenzymatic structures were developed in 48 h (induction period) through the rearrangement of the adsorbed Asp and Glc molecules on montmorillonite in water (intermediate structure). The spontaneous assembling of the intermediate structures facilitated the one-pot dehydrogenation of Glc to 2-KGA via periodic "hydrated stacked layers" comprising clay nanosheets, Asp, and Glc. The facile synthetic route proposed here is inexpensive and would be beneficial without using both GDH and GADH enzymes bound to a cell membrane.

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