Crystal structure and identification of amino acid residues for catalysis and binding of GH3 AnBX ß-xylosidase from Aspergillus niger.

ß-Xylosidases catalyze the hydrolysis of xylooligosaccharides to xylose in the final step of hemicellulose degradation. AnBX, which is a GH3 ß-xylosidase from Aspergillus niger, has a high catalytic efficiency toward xyloside substrates. In this study, we report the three-dimensional structure and the identification of catalytic and substrate binding residues of AnBX by performing site-directed mutagenesis, kinetic analysis, and NMR spectroscopy-associated analysis of the azide rescue reaction. The structure of the E88A mutant of AnBX, determined at 2.5-Å resolution, contains two molecules in the asymmetric unit, each of which is composed of three domains, namely an N-terminal (ß/α)8 TIM-barrel-like domain, an (α/ß)6 sandwich domain, and a C-terminal fibronectin type III domain. Asp288 and Glu500 of AnBX were experimentally confirmed to act as the catalytic nucleophile and acid/base catalyst, respectively. The crystal structure revealed that Trp86, Glu88 and Cys289, which formed a disulfide bond with Cys321, were located at subsite -1. Although the E88D and C289W mutations reduced catalytic efficiency toward all four substrates tested, the substitution of Trp86 with Ala, Asp and Ser increased the substrate preference for glucoside relative to xyloside substrates, indicating that Trp86 is responsible for the xyloside specificity of AnBX. The structural and biochemical information of AnBX obtained in this study provides invaluable insight into modulating the enzymatic properties for the hydrolysis of lignocellulosic biomass. KEY POINTS: • Asp288 and Glu500 of AnBX are the nucleophile and acid/base catalyst, respectively • Glu88 and the Cys289-Cys321 disulfide bond are crucial for the catalytic activity of AnBX • The W86A and W86S mutations in AnBX increased the preference for glucoside substrates.

Recent advances in supported acid/base ionic liquids as catalysts for biodiesel production.

Biodiesel is considered a potential substitute for fossil diesel because of its unique environmentally friendly and renewable advantages. The efficient and durable heterogeneous catalysts are vital to greenly and efficiently drive the biodiesel production process. The ionic liquid-functionalized materials, possessing the characteristics of both homogeneous and heterogeneous catalysts, are one of the promising substitutions for conventional homogeneous acid/base catalysts for producing biodiesel. This mini-review focuses on recent advances in supported acid/base ionic liquids to synthesize ionic liquid-functionalized materials for producing biodiesel. The methods of immobilizing ionic liquids on supports were summarized. The merits and demerits of various supports were discussed. The catalytic activities of the ionic liquid-functionalized materials for biodiesel production were reviewed. Finally, we proposed the challenges and future development direction in this area.

Titanate Nanotubes-Based Heterogeneous Catalyst for Efficient Production of Biomass Derived Chemicals.

The development of efficient heterogeneous catalytic system to convert plentiful biomass to renewable bio-chemicals is urgent need. Titanate nanotubes-based materials obtained from hydrothermal treatment have been reported as low-cost and efficient catalytic materials in chemical syntheses for bio-based chemicals production with interesting catalytic performance. This mini-review expressly revealed the significance and potential of using titanate nanotubes based material as sustainable and environmentally benign solid catalysts/supports for synthesis of various bio-based chemicals, including glycerol-derived solketal, jet fuel range alkanes precursors, biomass-derived esters, aldehydes, aromatic compounds and so on. From the current knowledge on titanate nanotubes-based material via hydrothermal method here summarized, the future lines of research in the field of catalysis/supports for bio-based chemicals production are outlined.

The Role of the Surface Acid-Base Nature of Nanocrystalline Hydroxyapatite Catalysts in the 1,6-Hexanediol Conversion.

Hydroxyapatite is known to have excellent catalytic properties for ethanol conversion and lactic acid conversion, and their properties are influenced by the elemental composition, such as Ca/P ratio and sodium content. However, few reports have been examined for the surface acid-base nature of hydroxyapatites containing sodium ions. We prepared nanocrystalline hydroxyapatite (Ca-HAP) catalysts with various Ca/P ratios and sodium contents by the hydrothermal method. The adsorption and desorption experiments using NH3 and CO2 molecules and the catalytic reactions for 2-propenol conversion revealed that the surface acid-base natures changed continuously with the bulk Ca/P ratios. Furthermore, the new catalytic properties of hydroxyapatite were exhibited for 1,6-hexanediol conversion. The non-stoichiometric Ca-HAP(1.54) catalyst with sodium ions of 2.3 wt% and a Ca/P molar ratio of 1.54 gave a high 5-hexen-1-ol yield of 68%. In contrast, the Ca-HAP(1.72) catalyst, with a Ca/P molar ratio of 1.72, gave a high cyclopentanemethanol yield of 42%. Both yields were the highest ever reported in the relevant literature. It was shown that hydroxyapatite also has excellent catalytic properties for alkanediol conversion because the surface acid-base properties can be continuously controlled by the elemental compositions, such as bulk Ca/P ratios and sodium contents.

In-situ catalytic pyrolysis upgradation of microalgae into hydrocarbon rich bio-oil: Effects of nitrogen and carbon dioxide environment.

Pyrolysis of Spirulina Platensis (SP) microalgae was carried out under different reaction environment such as nitrogen (N2) and carbon dioxide (CO2) at different reaction temperatures of 300, 350, 400, 450 and 500 °C. Catalytic upgradations were examined over solid acid (ZSM-5) and solid base (MgO) catalyst, and with ZSM-5-MgO catalysts mixtures. Results showed, pyrolysis of non-catalytic biomass yielded maximum bio-oil of 43.6% under N2. However catalytic upgradation in CO2 environment produced lower bio-oil due to the coke formation. Maximum bio-oil (46.2 wt%) was obtained with basic metal MgO catalyst in N2 environment compared to other catalyst and environments. Mixture of MgO-ZSM-5 catalyst improved the bio-oil yield (37.8-48.6 wt%) compared to individual catalytic reaction under N2 and CO2. Higher high heating value (HHV) was observed in catalytic bio-oil 36.8 MJ/Kg. Bio-oil (catalytic) analysis revealed that 64-70% of compounds are in hydrocarbon range. Bio-oil was rich in hydrocarbons of C7-C18 range with less oxygenated compounds.

A Chemist's Perspective on the Role of Phosphorus at the Origins of Life.

The central role that phosphates play in biological systems, suggests they also played an important role in the emergence of life on Earth. In recent years, numerous important advances have been made towards understanding the influence that phosphates may have had on prebiotic chemistry, and here, we highlight two important aspects of prebiotic phosphate chemistry. Firstly, we discuss prebiotic phosphorylation reactions; we specifically contrast aqueous electrophilic phosphorylation, and aqueous nucleophilic phosphorylation strategies, with dry-state phosphorylations that are mediated by dissociative phosphoryl-transfer. Secondly, we discuss the non-structural roles that phosphates can play in prebiotic chemistry. Here, we focus on the mechanisms by which phosphate has guided prebiotic reactivity through catalysis or buffering effects, to facilitating selective transformations in neutral water. Several prebiotic routes towards the synthesis of nucleotides, amino acids, and core metabolites, that have been facilitated or controlled by phosphate acting as a general acid-base catalyst, pH buffer, or a chemical buffer, are outlined. These facile and subtle mechanisms for incorporation and exploitation of phosphates to orchestrate selective, robust prebiotic chemistry, coupled with the central and universally conserved roles of phosphates in biochemistry, provide an increasingly clear message that understanding phosphate chemistry will be a key element in elucidating the origins of life on Earth.