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Zhang X.,Chinese Institute of Materia Medica | Zhao Y.,Xiamen University | Yan H.,Michigan State UniversityEast Lansing | Cao Z.,Xiamen University
Journal of Computational Chemistry | Year: 2016

Extensive combined quantum mechanical (B3LYP/6-31G*) and molecular mechanical (QM/MM) molecular dynamics simulations have been performed to elucidate the hydrolytic deamination mechanism of cytosine to uracil catalyzed by the yeast cytosine deaminase (yCD). Though cytosine has no direct binding to the zinc center, it reacts with the water molecule coordinated to zinc, and the adjacent conserved Glu64 serves as a general acid/base to shuttle protons from water to cytosine. The overall reaction consists of several proton-transfer processes and nucleophilic attacks. A tetrahedral intermediate adduct of cytosine and water binding to zinc is identified and similar to the crystal structure of yCD with the inhibitor 2-pyrimidinone. The rate-determining step with the barrier of 18.0 kcal/mol in the whole catalytic cycle occurs in the process of uracil departure where the proton transfer from water to Glu64 and nucleophilic attack of the resulting hydroxide anion to C2 of the uracil ring occurs synchronously. © 2016 Wiley Periodicals, Inc.


Qin W.,Donghua UniversityShanghai201620 China | Vautard F.,Michigan State UniversityEast Lansing | Askeland P.,Michigan State UniversityEast Lansing | Yu J.,State Key Laboratory for Modification of Chemical Fibers and Polymer Materials | Drzal L.T.,Michigan Science Center
Polymer Composites | Year: 2015

Functionalized silicon dioxide nanoparticles (nano-fSiO2) were uniformly deposited on the surface of carbon fibers (CFs) using a coating process which consisted of immersing the fibers directly in a suspension of nano-fSiO2 particles and epoxy monomers in 1-methyl-2-pyrrolidinone (NMP). The 0° flexural properties, 90° flexural properties, and Interlaminar shear strength (ILSS) mechanical properties of unidirectional epoxy composites made with nano-fSiO2+epoxy sized carbon fibers, with control fibers, and with epoxy-only sized fibers were measured and compared. An obvious increase of the fiber/matrix adherence strength was obtained with the nano-fSiO2+epoxy coating. The nano-fSiO2+epoxy sized CF/epoxy composites showed a relative increase of 15%, 50%, and 22% in comparison to control fibers, for the Interlaminar shear strength, the 90° flexural strength and the 90° flexural modulus, respectively but little e difference was measured between the different systems for the 0° flexural properties. The observation of the fracture surfaces by scanning electron microscopy of composite fracture confirmed the improvement of the interfacially dependent mechanical properties. © 2015 Society of Plastics Engineers.


Yu Z.,Hohai UniversityNanjing China | Kalin D.A.,Michigan State UniversityEast Lansing
Water Resources Research | Year: 2014

Soil temperature plays an important role in hydrology, agriculture, and meteorology. In order to improve the accuracy of soil temperature simulation, a soil temperature data assimilation system was developed based on the Ensemble Particle Filter (EnPF) and the Common Land Model (CLM), and then applied in the Walnut Gulch Experimental Watershed (WGEW) in Arizona, United States. Surface soil temperature in situ observations and Moderate Resolution Imaging Spectroradiometer Land Surface Temperature (MODIS LST) data were assimilated into the system. In this study, four different assimilation experiments were conducted: (1) assimilating in situ observations of instantaneous surface soil temperature each hour, (2) assimilating in situ observations of instantaneous surface soil temperature once per day, (3) assimilating verified MODIS LST once per day, and (4) assimilating original MODIS LST once per day. These four experiments reflect a transition from high-quality and more frequent in situ observations to lower quality and less frequent remote sensing data in the data assimilation system. The results from these four experiments show that the assimilated results are better than the simulated results without assimilation at all layers except the bottom layer, while the superiority gradually diminishes as the quality and frequency of the observations decrease. This demonstrates that remote sensing data can be assimilated using the ensemble particle filter in poorly gauged catchments to obtain highly accurate soil variables (e.g., soil moisture, soil temperature). Meanwhile, the results also demonstrate that the ensemble particle filter is effective in assimilating soil temperature observations to improve simulations, but the performance of the data assimilation method is affected by the frequency of assimilation and the quality of the input data. © 2014. American Geophysical Union.


Shen Z.,Michigan State UniversityEast Lansing | Ghasemlou M.,Michigan State UniversityEast Lansing | Kamdem D.P.,Michigan State UniversityEast Lansing
Journal of Applied Polymer Science | Year: 2014

In this study, interaction and compatibility between sugar-beet pulp (SBP) and polyvinyl alcohol (PVA) in blend films was assessed. Film-forming dispersions of different ratios of SBP to PVA (100/0, 75/25, 50/50, and 25/75) were cast at room temperature. The effects of adding PVA to SBP on the resulting film's physical, mechanical and barrier properties and thermal stability were investigated. X-ray diffraction and environmental scanning electron microscopy (ESEM) were used to characterize the structure and morphology of the composites. When PVA was also added to the composite films, the films became softer, less rigid and more stretchable than pure SBP films. The addition of PVA gave significantly greater elongation at break (12.45%) and lower water vapor permeability (1.55 × 10-10 gs-1m-1Pa-1), but tensile strength did not markedly change, remaining around 59.68 MPa. Thermogravimetric analysis also showed that SBP/PVA film had better thermal stability than SBP film. The ESEM results showed that the compatibility of SBP50/PVA50 was better than those of other composite films. These results suggest that when taking all the studied variables into account, composite films formulated with 50% PVA are most suitable for various packaging applications. © 2014 Wiley Periodicals, Inc.


Flores-Valdez M.A.,Biotecnologia Medica rmaceuticaresearch Center istencia En Tecnologia Y Diseno Del Estado Of Jalisco | de Jesus Aceves-Sanchez M.,Biotecnologia Medica rmaceuticaresearch Center istencia En Tecnologia Y Diseno Del Estado Of Jalisco | Pedroza-Roldan C.,University of Guadalajara | Vega-Dominguez P.J.,Biotecnologia Medica rmaceuticaresearch Center istencia En Tecnologia Y Diseno Del Estado Of Jalisco | And 6 more authors.
IUBMB Life | Year: 2015

Bacteria living in a surface-attached community that contains a heterogeneous population, coated with an extracellular matrix, and showing drug tolerance (biofilms) are often linked to chronic infections. In mycobacteria, the pellicle mode of growth has been equated to an in vitro biofilm and meets several of the criteria mentioned above, while tuberculosis infection presents a chronic (latent) phase of infection. As mycobacteria lack most genes required to control biofilm production by other microorganisms, we deleted or expressed from the hsp60 strong promoter the only known c-di-GMP phosphodiesterase (PDE) gene in Mycobacterium bovis BCG. We found changes in pellicle production, cellular protein profiles, lipid production, resistance to nitrosative stress and maintenance in lungs and spleens of immunocompetent BALB/mice. Our results show that pellicle production and capacity to remain within the host are linked in BCG. © 2015 International Union of Biochemistry and Molecular Biology.

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