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941.
Oleg V. Mikhailov Marina A. Kazymova Tatyana A. Shumilova Galina A. Chmutova Svetlana E. Solovieva 《Transition Metal Chemistry》2005,30(3):299-304
The complexing process proceeding in the NiII–thiocarbohydrazide (H2N–H–NC(=S)–NH–NH2)–propanone triple system in EtOH solution and nickel(II)hexacyanoferrate(II) gelatin-immobilized matrix has been studied. It has been found that in the first case, template synthesis leading, as a minimum, to formation of three coordination compounds of NiII with (N,N,S,S)-donor tetradentate ligands having NiL1, NiL2 and NiL3compositions where L1 is 4,6,6-trimethyl-2,3,7,8-tetraazanonen-3-di(thiohydrazide)-1,9, L2 is 4,6,6,12-tetrametyl-1,9-dithio-2,3,7,8,10,11-hexaazatridekadien-3,11-hydrazide-1 and L3 is 2,8,10,10,16-pentamethyl-5,13-dithio-3,4,6,7,11,12,14,15-octaazaheptadekatrien-2,7,15 is observed, whereas in the gelatin-immobilized matrix, a complexing process in the system considered does not occur. 相似文献
942.
A simple and sensitive method for determination of benzodiazepines in plasma has been developed using high-performance liquid chromatography in a reverse-phase mode. The method is illustrated by application to plasma samples containing diazepam and N-desmethyldiazepam at concentrations which would be encountered during therapy, with limits of detection of 10 ng/ml and 2 ng/ml for diazepam and N-desmethyldiazepam, respectively. 相似文献
943.
[reaction: see text] The 3-quinuclidinone-catalyzed (pK(BH) = 7.5) enolization of cyclobutanone (1) in D(2)O at 25 degrees C, I = 1.0 (KCl) was followed by deuterium incorporation, which was determined by (1)H NMR. The second-order rate constant for the buffer-catalyzed deprotonation of 1 was found to be k(B) = 3.3 x 10(-4) M(-1) s(-1), which is compared to rates for acetone and 2-(2'-oxopropyl)benzaldehyde under similar conditions. The data shows that ring strain has very little effect on the energy barrier to deprotonation of 1 vs the unstrained systems. 相似文献
944.
James Murphy Phil Jones Steve J. Hill 《Spectrochimica Acta Part B: Atomic Spectroscopy》1996,51(14):1867-1873
A simple and accurate method has been developed for the determination of total mercury in environmental and biological samples. The method utilises an off-line microwave digestion stage followed by analysis using a flow injection system with detection by cold vapour atomic absorption spectrometry.
The method has been validated using two certified reference materials (DORM-1 dogfish and MESS-2 estuarine sediment) and the results agreed well with the certified values. A detection limit of 0.2 ng g−1 Hg was obtained and no significant interference was observed. The method was finally applied to the determination of mercury in river sediments and canned tuna fish, and gave results in the range 0.1–3.0 mg kg−1. 相似文献
945.
Single molecule experiments reveal intriguing phenomenon in chemical and biological systems. Several indicators of complex dynamics, including "intensity" correlations, "event" correlations, and characteristic functions have been proposed, but extraction of information from these indicators can be difficult since these indicators only observe certain characteristics of the system. Generally, for systems that follow Poisson kinetics, all of these indicators contain similar information about the relaxation times of the system and the connections between different relaxation times, but the information is convoluted in different ways so the strength of various indicators is system specific. The paper discusses the theoretical implications and information content of various data analysis methods for single molecule experiments and demonstrates the relationships between indicators. Under certain conditions, common indicators contain all available information about systems with Poisson kinetics between degenerate states, but extraction of this information is generally not numerically feasible. The paper also discusses practical issues associated with these analyses, which motivates a numerical study based on Bayes' formula in the companion paper [J. Witkoskie and J. S. Cao, J. Chem. Phys. 121, 6373 (2004), following paper]. 相似文献
946.
Addition of a small amount of polar solvent (i.e., modifier) to CO2 in packed column supercritical fluid chromatography (SFC) has shown major improvements in both polar analyte solubility and interaction of the polar analyte with the stationary phase. Recently, the addition of an ionic component (i.e., additive) to the primary modifier by one of us has been shown to extend even further the application of SFC to polar analytes. In this work, the effect of various ionic additives on the elution of ionic compounds, such as sodium 4-dodecylbenzene sulfonate and sodium 4-octylbenene sulfonate, has been studied. The additives were lithium acetate, ammonium acetate, tetramethylammonium acetate, tetrabutylammonium acetate, and ammonium chloride dissolved in methanol. Three stationary phases with different degrees of deactivation were considered: conventional cyanopropyl, deltabond cyanopropyl, and bare silica. The effect of additive concentration and additive functionality on analyte retention was investigated. Sodium 4-dodecylbenzene sulfonate was successfully eluted using all the additives with good peak shape under isocratic/isobaric/isothermal conditions. Different additives, however, yielded different retention times and in some cases different peak shapes. 相似文献
947.
Yuan Ruo Cao ShuRui Chai YaQin Gao FengXian Zhao Qing Tang MingYu Tong ZhongQiang Xie Yi 《中国科学B辑(英文版)》2007,50(5):620-628
Alternate adsorption of positively charged colloid-Au nanoparticles (nano-Au⊕) and negatively charged hemoglobin (Hb) on L-cysteine (L-cys) modified gold electrode resulted in the assembly of {Hb/nano-Au⊕}n layer-by-layer films/L-cys modified gold electrode. The nano-Au⊕ was characterized by transmission electron micrograph (TEM) and microelectrophoresis. The modified electrode interface morphology was characterized by electrochemical impedance spectroscopy (EIS), atomic force mi- croscopy (AFM), cyclic voltammograms (CV) and chronoamperometry. Direct electron transfer between hemoglobin and gold electrodes was studied, and the apparent Michaelis-Menten constant ( km app) of the modified electrode was evaluated to be 0.10 mmol·L?1. Moreover, the higher activity of proteins in the nano-Au⊕ films could be retained compared with the electropolymerization membrane, since the pro- teins in nano-Au⊕ films retained their near-native structure. Direct electron transfer between hemoglo- bin and electrode and electrochemically catalyzed reduction of hydrogen peroxide on a modified elec- trode was studied, and the linear range was from 2.1×10-8 to 1.2 ×10?3 mol·L-1 (r = 0.994) with a detection limit of 1.1×10-8 mol·L-1 H2O2. 相似文献
948.
Barry LygoS.Russell James 《Tetrahedron letters》2003,44(30):5629-5632
A library of quaternary ammonium salts has been generated via reaction of simple chiral amines with a series of conformationally dynamic biphenyl units. Screening of this library against the alkylation of a glycine imine has led to the identification of a highly effective asymmetric phase-transfer catalyst derived from α-methylnaphthylamine. 相似文献
949.
Michael R. Detty James W. Hassett Bruce J. Murray George A. Reynolds 《Tetrahedron》1985,41(21):4853-4859
The O-, S-, Se- and Te-containing Δ4,4' -2,2?,6,6'-tetramethyl-, -tetra-t-butyl- and -tetraphenyl-4-(chalcogenapyranyl)-4H-chalcogenapyrans were prepared from the corresponding chalcogenapyran-4-ones. The thia-, selena- and tellurapyran-4-ones were prepared by sodium borohydride reduction of the appropriate chalcogen and addition of the disodium chalcogenide to a 1,4-diyn-3-one. The comparative electrochemistry of all three series was examined by cyclic voltammetry. Within each scries the first oxidation (E1) became more difficult with increasing chalcogen size. The radical-cation states of the tetra-t-butyl analogues were examined by ESR. The O and S analogues gave well-defined five-line spectra, but the Se and Te analogues gave broad single lines. The g value increased with increasing size of the heteroatom. A linear correlation exists between g value and spin-orbit coupling constants λ for the chalcogens, suggesting that the electron densities on the heteroatoms are similar in each heteroatom analogue. 相似文献
950.
2-[2-(5-Bromopyridyl)azol-4,5-dimethylphenol (BrPDMP) and 2-[2-benzothiazolylazo)-5-dimethylaminophenol (BTADAP) have been synthesised and compared, as reagents for cadmium, with the related dyes BrPADAP and BTDMP. The new dyes both form stable highly coloured 2:1 complexes with cadmium, with molar absorptivities (in o-xylene solution) of 3.8 x 10(4) 1.mole(-1).cm(-1) at 590 nm (BrPDMP) and 4.5 x 10(4) 1.mole(-1).cm(-1) at 600 nm (BTADAP). Cadmium can be determined by extraction under alkaline conditions with a solution of BTADAP in xylene. Beer's law is obeyed up to at least 16 mug of cadmium. A limit of detection of 0.15 mug has been estimated and a coefficient of variation of 3.3% at the 5 mug level was found. The only species which interfere seriously are Co(2+), Ni(2+), and Ca(2+). A 200-fold excess of zinc may be tolerated. The method has been applied to the determination of cadmium in water samples, plant materials and hair. Interferences were overcome by preliminary extraction into Aliquat/carbon tetrachloride. The acid dissociation constant of BTADAP (pK = 9.5) and formation constant of the cadmium-BTADAP complex (log beta = 15.1) have been determined. 相似文献