Methylaminopropylviologen (MAV) was covalently attached to glassy carbon electrodes via cyuranic chloride. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of bound MAV on the electrode surfaces. Electrochemical experiments of these electrodes indicated that the bound MAV was stable and electrochemically active for extended periods of time in aqueous media. The surface coverage of MAV was in the range, of 2.0–3.0×10?10 mol cm?2. 相似文献
Two novel 25,27-dihydroxy-26,28-bis(3-phenylthiapropxy)-calix[4]arene(3) and 25,27-dihydroxy-26,28-bis(3-phenylthiapropoxy)-5,11,17,23-tetra-tert-butylcalix[4] arene (4) were synthesized for the evaluation of their ion-selectivity in ion-selective electrodes(ISEs).ISEs based on 3 and 4 as neutral ionophores were prepared,and their selectivity coefficients for Ag^ (lg KAg,M^pot)were investigated against other alkali metal,alkaline-earth metal,aluminum,thallium(Ⅰ),Lead and some transition metal ions using the separate solution method (SSM).These ISEs showed excellent Ag^ seletivity over most of the interfering cations examined,except for Hg^2 and Fe^2 having relative smaller interference(lg KAg,M^pot≤-2.1). 相似文献
The purpose of the work presented here was to prepare a support material for enzymes and “affinity ligands” with the following characteristics: low cost, durability, rigidity, and high capacity. Our study encompassed conjugates of porous and nonporous silicas with organic polymers and macroporous ion-exchange resins. Poly-ethyleneimine (PEI), polyacrylic acid (PAA), poly (methyl vinyl ether/maleic anhydride) were attached to porous glass and silica in various combinations. The composite of silica beads with PEI and PAA is a good support for the enzyme trypsin as judged by the activity against N-α-benzoyl-L-arginine ethyl ester.
Amberlyst (macroporous, sulfonated polystyrene) was activated by treatment with thionyl chloride; the resulting resin was either used directly or reacted with a diamine. The diamine derivative was used for enzyme coupling or transformed further to the succinyl or p-aminobenzoyl derivative. None of these derivatives were particularly good as supports for the enzyme trypsin. Duolite converted to a PAA, succinyl, or succinimide derivative was a good support. The enzyme-resin adduct has good activity and stability.
The resin is quite durable and of low cost. The Duolite-trypsin has good activity against protein. In addition, this derivative was active in 7 M urea. The proteolytic activity was nearly doubled by urea, presumably as a result of substrate (casein) denaturation. The michaelis constants and pH dependences are compared for trypsin conjugates with Duolite A-7, Silica-PEI-PAA, agarose, and porous glass. A cost comparison reveals that the Duolite and silica derivatives are much less expensive than agarose and glass. 相似文献
A laser self-focused channel formation into overdense plasmas was observed using a soft x-ray laser probe system with a grid image refractometry (GIR) technique. 1.053 &mgr;m laser light with a 100 ps pulse duration was focused onto a preformed plasma at an intensity of 2x10(17) W/cm (2). Cross sections of the channel were obtained which show a 30 &mgr;m diameter in overdense plasmas. The channel width in the overdense region was kept narrow as a result of self-focusing. Conically diverging density ridges were also observed along the channel, indicating a Mach cone created by a shock wave due to the supersonic propagation of the channel front. 相似文献
The influence of surface roughness on surfactant adsorption was studied using a quartz crystal microbalance with dissipation (QCM-D). The sensors employed had root-mean-square (R) roughness values of 2.3, 3.1, and 5.8 nm, corresponding to fractal-calculated surface area ratios (actual/nominal) of 1.13, 1.73, and 2.53, respectively. Adsorption isotherms measured at 25 °C showed that adsorbed mass of cetyltrimethylammonium bromide per unit of actual surface area below 0.8 cmc, or above 1.2 cmc, decreases as the surface roughness increases. At the cmc, both the measured adsorbed amount and the measured dissipation increased dramatically on the rougher surfaces. These results are consistent with the presence of impurities, suggesting that roughness exacerbates well-known phenomena reported in the literature of peak impurity-related adsorption at the cmc. The magnitude of the increase, especially in dissipation, suggests that changes in adsorbed amount may not be the only reason for the observed results, as aggregates at the cmc on rougher surfaces are more flexible and likely contain larger amounts of solvent. Differences in adsorption kinetics were also found as a function of surface roughness, with data showing a second, slower adsorption rate after rapid initial adsorption. A two-rate Langmuir model was used to further examine this effect. Although adsorption completes faster on the smoother surfaces, initial adsorption at zero surface coverage is faster on the rougher surfaces, suggesting the presence of more high-energy sites on the rougher surfaces. 相似文献
Laboratory quality assurance provides a rationale for laboratory credibility and reliability of results if quality assurance principles are applied and the procedures for implementation and assessment are documented. 相似文献