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Li C.-Y.,South China Agricultural University | Li C.-Y.,Maoming Vocational Technical College | Huang Z.-L.,South China Agricultural University | Li L.-J.,South China Agricultural University | And 3 more authors.
Gaodeng Xuexiao Huaxue Xuebao/Chemical Journal of Chinese Universities

In order to approach the effects and action mechanism of dimethyl sulfoxide(DMSO) and tetrahydrofuran(THF) on pepsin, the catalytic activity, kinetics parameters, ultraviolet absorption spectra, ultraviolet differential spectra, and fluorescence emission spectra of pepsin were investigated. It was indicated that pepsin activity was enhanced by 83.4% as the enzyme was treated with 9%DMSO. But when pepsin was treated with 1% THF the enzyme activity was enhanced only by 3.59%. In hydrochloric acid solution the kinetics parameter of the enzyme, K m=2.22 mg/mL, v max=1.1×10 6 U/mg Pro. In 9%DMSO, K m=1.50 mg/mL, v max=0.5×10 6 U/mg Pro. In 1% THF, K m=1.91 mg/mL and v max=0.51×10 6 U/mg Pro. In 9% DMSO the ultraviolet absorption of pepsin peptide bonds was strongly inhibited. But the ultraviolet absorption of aromatic amino acids of pepsin was not inhibited. The ultraviolet absorption of pepsin molecules was not influenced obviously in 1% THF. Both in 9% DMSO and in 1% THF the ultraviolet differential spectra of pepsin showed obvious positive and negative peaks. The fluorescence emission peak of pepsin enzyme moved to short wavelength direction by 1 nm in 9% DMSO. But in 1% THF the fluorescence emission spectrum did not change obviously. It was concluded from these results that the conformation of pepsin molecules changed obviously in both 9% DMSO and 1% THF. This led the K m value of the enzyme descended and the affinity of the enzyme to substrates enhanced. So the catalysis activities of the enzyme were increased in some extent in these solutions. Source

Zhang H.-Y.,University of Rhode Island | Chen S.-F.,Maoming Vocational Technical College | Lin Q.-Y.,Hezhou University
Chinese Journal of Inorganic Chemistry

This study evaluates the effect of water condition on the physicochemical properties of silver nanoparticles (AgNPs) with/without capping agent. The results show that the average particle size of AgNPs increases with increasing in electrolyte concentration. Divalent cation (Ca 2+) can more effectively increase the size and ζ-potential of AgNP aggregates than monovalent cation (Na +). This study also indicates that PVP, humic acid or natural organic matters can increase the stability of AgNP suspension. Larger AgNPs aggregates are formed in seawater than in lake water. Source

Chen S.-F.,Maoming Vocational Technical College | Zhang H.,University of Rhode Island
Advances in Natural Sciences: Nanoscience and Nanotechnology

In this study the effect of different water conditions on the aggregation kinetics of nanosilver (nAg) is evaluated. The obtained results show that the aggregation rate of nAg increases with increasing electrolyte concentration. Divalent cation (Ca2+) can more effectively induce aggregation than monovalent cation (Na+). Critical coagulation concentration of nAg in NaCl solution is about 40 times higher than that in CaCl2 solution. This study also indicates that aggregation rate of nAg in water condition containing high Ca2+ concentration in presence of humic acid is higher than that without humic acid due to the bridging effect of humic acid-Ca2+ complex. Finally, aggregation rate of nAg in seawater is higher than that in lake water. © 2012 Vietnam Academy of Science & Technology. Source

Chen S.-F.,Maoming Vocational Technical College | Zhang H.,University of Rhode Island
Asian Journal of Chemistry

Silver nanoparticle nanosuspension was prepared by Tollen's method using sodium citrate as stabilizing agent. Particle size and zeta potential of silver nanoparticles in different electrolyte solutions containing anionic ligands and humic acid solution were characterized by zetasizer. Dissolution of silver nanoparticels was evaluated using ICP-MS. Toxicity of silver nanoparticles on Escherichia coli were measured using a plate count method. The obtained results showed that toxicity of silver nanoparticles in electrolyte solution containing Cl- ligands was significantly reduced. Among all the conditions, toxicity of silver nanoparticles in humic acid solution was the lowest. Source

Chen S.F.,Maoming Vocational Technical College | Zhang H.,University of Rhode Island
Asian Journal of Chemistry

This study shows the synthesis of citrate capped nanosilver using Tollens method and the effect of seawater on its physcochemical properties. The results show that the average particle size of nanosilver is 66 nm in deionized water condition and 1800 nm in seawater condition. ζ-Potentials of nanosilver in deionized water is more negative than that in seawater. This study also indicates that aggregation rate of nanosilver in seawater is higher than that in deionized water. At last, more dissolution of nanosilver was measured in deionized water than that in seawater. Source

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