This review summarizes progress in capillary ion chromatography. Theoretical aspects and practical limitations of packed and open tubular capillary columns are considered. Applications of packed and open tubular capillary IC are described. Emerging technologies such chip-scale IC and the use of monolithic columns are discussed. 相似文献
A series of 6‐azacytosines 4a‐4k and 5a‐5c were prepared by nucleophilic cleavage of furan ring of [1]benzofuro[2,3‐e][1,2,4]triazine derivative 1 . Some of them were used for the preparation of derivatives of [1,2,4]triazolo[4,3‐d][1,2,4]triazine ( 6a‐6d ) and tetrazolo[1,5‐d][1,2,4]triazine (7). The reaction of 1 with hydrogen sulfide afforded the corresponding 6‐(2‐hydroxyphenyl)‐2‐phenyl‐5‐thioxo‐4,5‐dihydro‐1,2,4‐tri‐azin‐3(2H)‐one ( 8 ), while with hydrogen selenide 6‐(2‐hydroxyphenyl)‐2‐phenyl‐4,5‐dihydro‐1,2,4‐triazin‐3(2H)‐one ( 9 ) was formed. The prepared compounds were tested for biological activity. 相似文献
A mixture of both geometrical isomers of hydrazones 3a‐3e was obtained by the coupling reactions of pyrazole‐3‐diazonium salts 2a‐2d and benzenediazonium chloride 2e with 2‐pyridylacetonitrile 1 . Hydrazones 3a‐3d were cyclized to the corresponding 4‐amino‐3‐(2‐pyridyl)pyrazolo[5,1‐c][1,2,4]triazines 4a‐4d. 相似文献
Titanocene 1,8-dithiolato-naphthalene and titanocene 2,2'-dithiolato biphenyl are produced by the reaction of naphtho[1,8-cd]-1,2-dithiole [or the biphenyl] with titanocene dicarbonyl (Ti(II)) in toluene at room temperature. The pro-ligands 2,7-di(tert-butyl)naphtho[1,8-cd]-1,2-dithiole, 5,6-dihydroacenaphtho[5,6-cd]-1,2-dithiole, 4,5-dithioacephenanthrylene, and 13,14-dithiapicene have been used in similar reactions with titanocene dicarbonyl to investigate the effect of steric bulk and of varying the naphthalene backbone on the final complex. The resulting Cp(2)TiS(2)Ar complexes (Ar = naphthalene) have been shown by temperature-dependent (1)H NMR spectroscopy to exist in solution in an envelope conformation with the six-membered TiS(2)C(3) rings undergoing inversion on the NMR time scale while the similar Cp(2)TiS(2)Ar complexes (Ar = biphenyl, binaphthalene) interconvert more rapidly. Titanocene 2,2'-disulfinato biphenyl has been synthesized by the salt elimination reaction of titanocene dichloride (Ti(IV)) and the disodium salt of biphenyl 2,2'-disulfinic acid. Finally, the effect of using pro-ligands where the sulfur atoms have been mono- or di-oxidized has been studied, and an interesting oxygen elimination reaction is observed for the S=O fragments but not for the SO(2) groups. All complexes have been characterized spectroscopically and seven X-ray structures are reported. 相似文献
[Chemical reaction: See text] Enantiomerically or diastereomerically pure 4-(purin-6-yl)phenylalanines, a novel type of stable amino acid-purine conjugates, were synthesized by palladium-catalyzed cross-coupling reactions of protected 4-boronophenylalanines or 4-(trimethylstanyl)phenylalanines with diverse 6-halopurines (9-benzyl-6-halopurines and 9-(tetrahydropyran-2-yl)-6-halopurines as well as acyl- and silyl-protected 6-halopurine ribonucleosides and 2-deoxyribonucleosides). Free purine bases and nucleosides bearing (S)- or (R)-phenylalanine in position 6 were obtained after complete deprotection of the products of cross-coupling reactions. Reactivity trends for both of these cross-coupling and deprotection protocols have been compared in terms of practicability, efficiency, and stereoselectivity. 相似文献
Intermolecular association and ion-pair formation, respectively, between a cationic chiral selector, viz. o-9-(tert-butylcarbamoyl) quinine (CQN), and the both enantiomers of anionic N-(3,5-dinitrobenzoyl)leucine, (R)-DNB-Leu and (S)-DNB-Leu, were investigated by affinity capillary electrophoresis (ACE). Thus, binding constants of the both diastereomeric ion-pairs, (R) and (S)-DNB-Leu/CQN associates, were determined by different experimental setups and correction of nonlinear effects. A reciprocal setup was employed for the high-affinity (S)-enantiomer, and the experimental mobility data obtained for CQN at variable (S)-DNB-Leu concentrations in the background electrolyte were linearized and evaluated by advanced statistical model. A binding constant of KS=125.1 l mol−1 was afforded. The constant for the (R)-enantiomer, which is outside the range suitable for direct affinity CE, was obtained from indirect affinity CE utilizing the separation of the DNB-Leu racemate at a single appropriate CQN concentration in the BGE (resolution method) taking advantage of the known constant for the (S)-enantiomer yielding a binding constant of KR=2.51 l mol−1. Thereby, the so-called “constant time method” was adopted for the required precise measurement of the effective mobilities of the both enantiomers. A combined approach of reciprocal affinity CE with racemic DNB-Leu as additive and the resolution method confirmed the results. The resulting constants evidence excellent enantioselectivity of the tert-butylcarbamoyl derivative of the cinchona alkaloid quinine as chiral selector for N-(3,5-dinitrobenzoyl) derivatives of amino acids. 相似文献
Fabricating mechanically strong hydrogels that can withstand the conditions in internal tissues is a challenging task. We have designed hydrogels based on multicomponent systems by combining chitosan, starch/cellulose, PVA, and PEDOT:PSS via one-pot synthesis. The starch-based hydrogels were homogeneous, while the cellulose-based hydrogels showed the presence of cellulose micro- and nanofibers. The cellulose-based hydrogels demonstrated a swelling ratio between 121 and 156%, while the starch-based hydrogels showed higher values, from 234 to 280%. Tensile tests indicated that the presence of starch in the hydrogels provided high flexibility (strain at break?>?300%), while combination with cellulose led to the formation of stiffer hydrogels (elastic moduli 3.9–6.6 MPa). The ultimate tensile strength for both types of hydrogels was similar (2.8–3.9 MPa). The adhesion and growth of human osteoblast-like SAOS-2 cells was higher on hydrogels with cellulose than on hydrogels with starch, and was higher on hydrogels with PEDOT:PSS than on hydrogels without this polymer. The metabolic activity of cells cultivated for 3 days in the hydrogel infusions indicated that no acutely toxic compounds were released. This is promising for further possible applications of these hydrogels in tissue engineering or in wound dressings.
A contactless conductometric detection (CCD) system for capillary electrophoresis (CE) with a flexible detection cell was applied for the simultaneous determination of small anions and/or cations in rain, surface and drainage water samples. The applied frequency, the amplitude of the input signal, the electrolyte conductivity and electrode distance were found to be the most significant factors affecting the detection sensitivity. 2-(N-Morpholino)ethanesulfonic acid/histidine-based (MES/His) electrolytes were used for direct conductivity detection of anions and cations, while ammonium acetate was selected for indirect conductivity determination of alkylammonium salts. For the simultaneous separation procedure, involving dual-opposite end injection, an electrolyte consisting of 20 mM MES/His, 1.5 mM 18-crown-6 and 20 microM cetyltrimethylammonium bromide provided baseline separation of 13 anions and cations in less than 6 min. The detection limits achieved were 7-30 micrograms/l for direct conductometric detection of various common inorganic cations and anions, excluding F- (62 micrograms/l) and H2PO4- (250 micrograms/l), and 35-178 micrograms/l for indirect conductometric detection of alkyl ammonium cations. The developed electrophoretic method with conductometric detection was compared to ion chromatography. 相似文献
In this article the methodology of the design of suitable background electrolytes (BGEs) in capillary zone electrophoresis (CZE) is described. The principal aspects of the role of a BGE in CZE are discussed with respect to an appropiate migration behavior of analytes, including the transport of the electric current, the buffering of pH, the Joule heat, the electro-endosmotic flow (EOF) and the principal migration and detection modes. The impact of the composition of the BGE upon migration and detection is discussed. It is shown that the total concentration of the BGE is a principal factor and the adjustment of migrating analyte zones according to the Kohlrausch regulating function (KRF) is the principal effect in most of the sample stacking techniques. The number of co-ions and their properties are of key importance for peak shapes of the analyte peaks and for the existence of system zones. The detection of UV-transparent analytes may advanteously be done in the indirect UV mode, by using UV-absorbing co-ions, however, both peaks and dips may be expected in the UV trace in case of multiple co-ionic BGEs. Properties of BGEs can be predicted applying mathematical models and it is shown that with SystCharts, predictions can be given concerning the existence of system zones, detection modes and the peak shapes of analytes for a given BGE. Practical examples of methodological considerations are given in the design of suitable BGEs for four principal combinations of migration and detection modes. The properties of the BGEs selected are exemplified with experimental results. Golden rules are summarized for the preparation of suitable BGEs in CZE. 相似文献
Simulation-based fitting has been applied to data analysis and parameter determination of complex experimental systems in many areas of chemistry and biophysics. However, this method is limited because of the time costs of the calculations. In this paper it is proposed to approximate and substitute a simulation model by an artificial neural network during the fitting procedure. Such a substitution significantly speeds up the parameter determination. This approach is tested on a model of fluorescence resonance energy transfer (FRET) within a system of site-directed fluorescence labeled M13 major coat protein mutants incorporated into a lipid bilayer. It is demonstrated that in our case the application of a trained artificial neural network for the substitution of the simulation model results in a significant gain in computing time by a factor of 5 x 10(4). Moreover, an artificial neural network produces a smooth approximation of the noisy results of a stochastic simulation. 相似文献