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Efficient base-free direct oxidation of glucose to gluconic acid over TiO2-supported gold clusters
No full textThe transformation of renewable natural resources is an appealing and sustainable protocol to minimize fossil fuel consumption. Here, a simple incipient wetness protocol is developed to prepare ultrasmall gold clusters, immobilized on TiO2 (particle size: 1.2-1.7 nm), using anthranilic acid as a stabilizing agent. The Au clusters can be reduced to metallic Au-0 (Au/TH-150 and Au/TH-200) during 150 and 200 degrees C annealing in the presence of H-2 gas, while the Au clusters are converted to Au+ species in air at 200 and 500 degrees C (Au/TA-200 and Au/TA-500), a conclusion supported by XPS and low-temperature (-150 degrees C) Operando-DRIFTS analysis. Au/TA-200 and Au/TA-500 showed inactivity in the base-free direct oxidation of glucose. For comparison, Au/TH-150 and Au/TH-200 exhibited salient catalytic performance (87-92% conversion and 95-97% selectivity for gluconic acid), revealing that glucose oxidation occurs preferentially on the Au-0 species. The turnover frequency (TOF) of Au/TH-150 reaches 1908 mol(reacted glucose) mol(Au)(-1) h(-1), which is much higher than that of commercial Pd-Bi/C under alkaline conditions (TOF: 1298 mol(reacted glucose) mol(Pd)(-1) h(-1), pH 9.5). The apparent activation energies are 37 (over Au/TH-150) and 47 kJ mol(-1) (Au/TH-200), comparable to the unsupported Au colloids, indicating that the oxidation should occur at the Au surface rather than at the perimeter interface between the Au clusters and the supports
Thiol-ene polymerization for hierarchically porous hybrid materials by adding degradable polycaprolactone for adsorption of bisphenol A
No full textHierarchically porous materials with multiple pore structures have the potential application in catalysis, separation or bioengineering. A concept was introduced to design and fabricate hierarchically porous hybrid materials (HPHMs) simultaneously containing mesopores and macropores. The proof-of-concept design was demonstrated by fabrication of several kinds of hybrid materials by adding degradable polycaprolactone (PCL) additive, which was simple and easy-operating. The specific surface areas of HPHMs prepared with polyhedral oligomeric vinylsilsesquioxanes (vinylPOSS) and 1,4-dithiothreitol (DTT) could reach 727 m(2)/g by adding 25% PCL additive, while the HPHMs were imperforate prior to degradation of PCL. The characterization further indicated that the macropores could be controlled by the amount of PCL additive. Moreover, the porous properties of HPHMs were influenced by the molecular weight of PCL. Other dithiols compounds were also successful in preparing HPHMs with high specific surface areas over 400 m2/g. Due to hydrophobic interaction and hydrogen bond interaction, the HPHM exhibited good adsorption ability for bisphenol A (BPA) in aqueous solution. Adsorption equilibrium could be achieved within 30 min, and the adsorption capacity was up to 157.4 mg/g. Meanwhile, the removal efficiency was found to be 95.37% for BPA
Youth Innovation Promotion Association CAS, Nanyang Technological University[M4080977.120]
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Characterization of the Specific Mode of Action of a Chitin Deacetylase and Separation of the Partially Acetylated Chitosan Oligosaccharides
No full textPartially acetylated chitosan oligosaccharides (COS), which consists of N-acetylglucosamine (GlcNAc) and glucosamine (GlcN) residues, is a structurally complex biopolymer with a variety of biological activities. Therefore, it is challenging to elucidate acetylation patterns and the molecular structure-function relationship of COS. Herein, the detailed deacetylation pattern of chitin deacetylase from Saccharomyces cerevisiae, ScCDA(2), was studied. Which solves the randomization of acetylation patterns during COS produced by chemical. ScCDA(2) also exhibits about 8% and 20% deacetylation activity on crystalline chitin and colloid chitin, respectively. Besides, a method for separating and detecting partially acetylated chitosan oligosaccharides by high performance liquid chromatography and electrospray ionization mass spectrometry (HPLC-ESI-MS) system has been developed, which is fast and convenient, and can be monitored online. Mass spectrometry sequencing revealed that ScCDA(2) produced COS with specific acetylation patterns of DAAA, ADAA, AADA, DDAA, DADA, ADDA and DDDA, respectively. ScCDA(2) does not deacetylate the GlcNAc unit that is closest to the reducing end of the oligomer furthermore ScCDA(2) has a multiple-attack deacetylation mechanism on chitin oligosaccharides. This specific mode of action significantly enriches the existing limited library of chitin deacetylase deacetylation patterns. This fully defined COS may be used in the study of COS structure and function
