Photochromic kinetic spectra and intermediates of BR-D96N

BR-D96N is a kind of genetically site-specific mutant of bacteriorhodopsin (BR) with obvious photochromic effect. Compared to the wild type BR, the lifetime of M state of BR-D96N is prolonged to several minutes so that the photochromic kinetics and the intermediates formation can be studied by the conventional spectra analysis. In the experiment, the absorption spectra of the sample at different time after light illumination are measured with spectrophotometer. By fitting and analyzing the variation of the spectra, we suppose there-are three main states in the photochromic process, i.e. B state (light-adapted state), M state and D state (dark-adapted state). The absorption spectra of the B state, M state and D state are extracted from the experimental data based on this three-state model and the spectra at various time are fitted With the least square method. So, the variations of population percentages of the M state, B state and D state are obtained and the M state and B state lifetimes are estimated. In another,way, from measuring the absorption dynamics at 407 nm and 568 nm, the M state and B state lifetimes are also obtained by two exponential data fitting, which give coincident results with those of the spectra analysis.

Adsorbed silica in stalagmite carbonate and its relationship to past rainfall

IEECAS SKLLQG

Investigation on the catalytic roles of silver species in the selective catalytic reduction of NOx with methane

Silver impregnated H-ZSM-5 zeolite catalysts with silver loading from 3 to 15 wt.% were investigated for the selective catalytic reduction (SCR) of NOx with CH4 in the excess of oxygen. X-ray diffraction (XRD) and UV-Vis measurements established the structure of silver catalysts. A relationship between the structure of silver catalysts and their catalytic functions for the SCR of NOx by CH4 was clarified. The NO conversion to N-2 showed a S-shape dependence on the increase of Ag loading. No linear dependence of catalytic activity on the amount of silver ions in the zeolite cation sites was observed. Contrastively, the activity was significantly enhanced by the nano-sized silver particles formed on the higher Ag loading samples (greater than or equal to7 wt.%). Temperature programmed desorption (TPD) and temperature programmed reduction (TPR) studies showed that nano-silver particles provided much stronger adsorption centers for active intermediates NO3-(s) on which adsorbed NO3-(s) could be effectively reduced by the activated methane. Silver ions in the zeolite cation sites might catalyze the reaction through activation of CH4 at lower temperatures. Activated CH4 reacted with NO3-(s) adsorbed on nano-silver particles to produce N-2 and CO2. (C) 2003 Elsevier B.V. All rights reserved.

Recent progress in adsorbed stationary phases for capillary electrochromatography

This review surveys the recent progress in the adsorbed stationary phases for capillary electrochromatography (CEC). Adsorption-based methods for preparation of stationary phase are novel approaches in CEC, which allow rapid and facile preparing stationary phases with desirable selectivity onto an open-tubular fused-silica capillary, a baresilica or ion-exchange packed column or a monolithic silica or polymer column. A variety of adsorbing agents have been developed as adsorbed stationary phases, including ionic long-chain surfactant, protein, peptide, amino acid, charged cyclodextrin (CD), basic compound, aliphatic ionene, and ion-exchange latex particle. The adsorbed stationary phases have been applied to separation of neutral, basic and acidic organic compounds, inorganic anions and enantiomers. They have also been applied to on-line sample concentration, fast separation and study of the competitive binding of enantiomers with protein.