First-Principle Study on the Interaction of Ligands with Gold and Effects on Catalytic Activities

The extensive use of fossil fuels has increased the atmospheric concentration of CO2, resulting in global climate change. One way to mitigate the CO2 challenge is to convert it into useful chemicals electrocatalytically using renewable energies. Recent studies suggest that ligand-modified gold electrodes can enhance the Faradaic efficiency (FE) and selectivity of the electrochemical CO2 reduction reaction (CO2RR). This theoretical research, primarily based on density functional theory (DFT), has been carried out to understand the interactions of ligands with Au and possible effects on electrocatalytic activities. We systematically modeled and studied the adsorption of three different types of ligands, which bond through C, N, and S respectively, on Au surfaces in conjunction with various experimental techniques to clarify how the type of ligand, bonding site on Au surfaces, and many environmental factors such as electrode potential and aqueous solution influence the strength of the interaction. In addition, we theoretically investigated the enhancement of catalytic activity of Au electrode induced by the interaction between thiol ligands and Au electrode. We demonstrated that thiol ligands, such as 2-phenylethanethiol (2-PET) and 2-mercaptopropionic acid (2-MPA), modified Au electrodes by reconstructing the electrode surfaces to generate active Au defect sites, which promoted CO and hydrogen evolution reactions (HER). Our studies provide strong theoretical evidence for future research on the synthesis of novel ligand-Au catalysts

NMR analysis of the dynamic exchange of the NS2B cofactor between open and closed conformations of the West Nile Virus NS2B-NS3 protease

BACKGROUND The two-component NS2B-NS3 proteases of West Nile and dengue viruses are essential for viral replication and established targets for drug development. In all crystal structures of the proteases to date, the NS2B cofactor is located far from the substrate binding site (open conformation) in the absence of inhibitor and lining the substrate binding site (closed conformation) in the presence of an inhibitor. METHODS In this work, nuclear magnetic resonance (NMR) spectroscopy of isotope and spin-labeled samples of the West Nile virus protease was used to investigate the occurrence of equilibria between open and closed conformations in solution. FINDINGS In solution, the closed form of the West Nile virus protease is the predominant conformation irrespective of the presence or absence of inhibitors. Nonetheless, dissociation of the C-terminal part of the NS2B cofactor from the NS3 protease (open conformation) occurs in both the presence and the absence of inhibitors. Low-molecular-weight inhibitors can shift the conformational exchange equilibria so that over 90% of the West Nile virus protease molecules assume the closed conformation. The West Nile virus protease differs from the dengue virus protease, where the open conformation is the predominant form in the absence of inhibitors. CONCLUSION Partial dissociation of NS2B from NS3 has implications for the way in which the NS3 protease can be positioned with respect to the host cell membrane when NS2B is membrane associated via N- and C-terminal segments present in the polyprotein. In the case of the West Nile virus protease, discovery of low-molecular-weight inhibitors that act by breaking the association of the NS2B cofactor with the NS3 protease is impeded by the natural affinity of the cofactor to the NS3 protease. The same strategy can be more successful in the case of the dengue virus NS2B-NS3 protease.The project was funded by the Australian Research Council (http://www.arc.gov.au), grant DP0877540

A spectral method to estimate fatigue life under broadband non-Gaussian random vibration loading

The aim of this study is to propose a spectral method for assessing the fatigue lives of mechanical components under non-Gaussian random vibration loadings. Efforts are made to extend the Dirlik’s method to non-Gaussian vibration field by introducing the Gaussian mixture model. A symmetric non-Gaussian random vibration can be decomposed into a series of Gaussian components through Gaussian mixture model. Then the rainflow cycle distributions of the Gaussian components can be obtained using Dirlik’s method. The cycle distribution of the underlying non-Gaussian process is derived by compounding the distributions of Gaussian components together. The non-Gaussian cycle distribution, combined with Palmgren-Miner rule is used to predict the fatigue lives of specimens. Comparisons among the proposed method, Dirlik’s solution, nonlinear model in literature, and the experimental data, are carried out extensively. The results have confirmed good accuracy of the proposed method

Limit cycles in a Kolmogorov-type model

In this paper, a Kolmogorov-type model, which includes the Gause-type model (Kuang and Freedman, 1988), the general predator-prey model (Huang 1988, Huang and Merrill 1989), and many other specialized models, is studied. The stability of equilibrium points, the existence and uniqueness of limit cycles in the model are proved