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Abstract: Human pancreatic α-amylase (HPA) catalyzes the hydrolysis of α-d-(1,4) glycosidic linkages in starch and is one of the major therapeutic targets for type II diabetes. Several acarviostatins isolated from Streptomyces coelicoflavus var. nankaiensis previously showed more potent inhibition of HPA than acarbose, which has been successfully used in clinical therapy. However, the molecular mechanisms by which acarviostatins inhibit HPA remains elusive. Here we determined crystal structures of HPA in complexes with a series of acarviostatin inhibitors (I03, II03, III03, and IV03). Structural analyses showed that acarviostatin I03 undergoes a series of hydrolysis and condensation reactions in the HPA active site, similar to acarbose, while acarviostatins II03, III03, and IV03 likely undergo only hydrolysis reactions. On the basis of structural analysis combined with kinetic assays, we demonstrate that the final modified product with seven sugar rings is best suited for occupying the full active site and shows the most efficient inhibition of HPA. Our high resolution structures reported here identify first time an interaction between an inhibitor and subsite-4 of the HPA active site, which we show makes a significant contribution to the inhibitory effect. Our results provide important information for the design of new drugs for the treatment of type II diabetes or obesity. [Copyright &y& Elsevier]

Abstract: α-Mn2O3 nanocrystals with uniform morphology prepared by calcining a self-assembled Mn3O4 precursor have proved active (ca. 0.14moleculenm-2 s-1 at 153°C) toward CO oxidation at low temperatures. The reaction orders with respect to CO and O2 were measured in the temperature range 100–190°C. Operando and in situ Raman spectroscopy are used to determine the near-surface structure of α-Mn2O3 nanocrystals during the adsorption and oxidation of CO for the first time. A surface phase transformation from α-Mn2O3 to Mn j O k (1< j <2, 1< k <3, and 1< k/j <1.5) intermediate species was observed in gaseous CO with the change in temperature. In addition, with the combination of the temperature-programmed desorption of O2, temperature-programmed surface reaction of CO oxidation, operando Raman spectra, and kinetics parameters, we conclude that the oxidation of CO may proceed through the Langmuir–Hinshelwood mechanism (<200°C) to the Mars–van Krevelen mechanism (>350°C) with increasing reaction temperature. In particular, the adsorbed oxygen is deduced to be responsible for CO oxidation at lower temperatures. [Copyright &y& Elsevier]

Abstract: Mechanistic study of the preferential CO oxidation was carried out over a Pt(1.0wt.%)/NaY zeolite catalyst from 300 to 523K by combination of kinetics and spectroscopy. The mechanism of CO oxidation at 300K was proposed on the basis of spectroscopic study, and the activity at low temperatures was assumed to originate from small Pt clusters. The analysis of XPS and TEM revealed that metallic state of Pt was rather stable after the reaction. The kinetics suggests a Langmuir–Hinshelwood mechanism in the oxygen-limited low-rate branch (O2 adsorption/dissociation is strongly depressed by adsorbed CO), being responsible for CO oxidation in H2-rich gas in the temperature range of 423–523K. In situ DRIFT spectra show that the Pt surface is dominated by linearly bound CO species, and the presence of H2 leads to a significant red-shift of the C frequency, which indicates a Had-induced modification of the Ptnot just a coverage-dependent frequency shift. Consequently, CO oxidation was significantly enhanced in H2-rich gas. [Copyright &y& Elsevier]