摘要:

AbstractThe structures formed during the photodicosiation of CBr4in alcohol solution have been measured by means of a novel ultrafast time‐resolved x‐ray absorption fine structure (EXAFS) experimental system, suitable for the direct determination of ultrafast transient structures of molecules in the liquid and solid phase. The EXAFS spectra of the starting and final products of the reaction were measured and analy

ISSN:0009-4536    

DOI:10.1002/jccs.200100023

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe total synthesis of the non‐peptide fibrinogen receptor antagonists, sibrafiban (1) (Ro 48–3657) and lamifiban (2) (Ro 44–9883), is described. Both contain 4‐hydroxypiperidine unit and the same solid‐phase synthesis method was used as a key step. Connection of a secondary alcohol to the DHP‐resin, followed by iterative saponification and coupling sequences, provided

ISSN:0009-4536    

DOI:10.1002/jccs.200100024

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe Beckmann rearrangement of cyclohexanone oxime (CHO) to ϵ‐caprolactam (ϵ‐C) was studied in a plug flow reactor at 300–400°C under atmospheric pressure by using Hβ, ZSM‐5, and alumina pillared montmorillonite. With Hβ(X) Y zeolites, raising the SiO2/Al2O3molar ratio (X) results in the enhancement of catalyst acid strength with concomitant decrease of the total acid amount. In creasing the calcination temperature (Y) causes remarkable diminution of catalyst surface area, acid strength, and acid amount. A similar trend was found for AlPMY catalysts. In there action of CHO, the initial catalytic activity correlates well with the total acid amount of various catalysts except for Hβ(10) Y (Y>600°C). The reaction proceeds on both Brönsted and Lewis acid sites and the catalyst deactivation most likely occurs at the strong Brönsted acid sites. The effect of solvents in the feed on the catalytic results was also investigated; it was found that polar solvents such as ethanol or n‐butanol give high ϵ‐C yield and longer catalyst life time. In the reaction of CHO/C2H5OH over Hβ(10)800 at 400°C and W/F 74.6 gh/mol, the CHO conversion and ϵ‐C yield remain 100% and 92%, respectively, for at least 20 h time‐on‐stream. The reaction paths and the mechanism

ISSN:0009-4536    

DOI:10.1002/jccs.200100025

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe hydrogen‐bond energies of water dimer and water‐formaldehyde complexes have been studied using density functional theory (DFT). Basis sets up to aug‐cc‐pVXZ (X=D, T, Q) were used. It was found that counterpoise corrected binding energies using the aug‐cc‐pVDZ basis set are very close to those predicted with the aug‐cc‐pVQZ set. Comparative studies using various DFT functionals on these two systems show that results from B3LYP, mPW1PW91 and PW91PW91 functionals are in better agreements with those predicted using high‐levelab initiomethods. These functionals were applied to the study of hydrogen bonding between guanine (G) and cytosine (C), and between adenine (A) and thy mine (T) base pairs. With the aug‐cc‐pVDZ basis set, the predicted binding energies of base pairs are in good agreement with the most elab

ISSN:0009-4536    

DOI:10.1002/jccs.200100026

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThree ligands have been formed by the 1:2 molar condensation of o‐phenylenediamine with salicyldhyde, 2‐hydroxy‐1‐naphthaldhyde or o‐hydroxyacetophenone. The potentially tetradentate ligands are N,N′‐bis(salicyldhyde)‐o‐phenylenediamine(SalophH2), N,N′‐bis(2‐hydroxy‐1‐naphthaldhyde)‐o‐phenylenediamine (NophH2) and N,N′‐bis(o‐hydroxyacetophenone)‐o‐phenylenediamine (AophH2), respectively. These ligands form complexes (1:1 molar ratio) with nickel, copper and zinc ions. The complexes have been characterized by IR,1HNMR, MS, uv/vis spectra in addition to elemental analysis. The spectral data of the ligands and their complexes with nickel, copper and zinc are discussed in connection with the structura

ISSN:0009-4536    

DOI:10.1002/jccs.200100027

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractA combination of solid phase micro‐extraction (SPME) with attenuated total reflection (ATR) infrared spectrometry provides a fast and sensitive way to detect organic compounds in aqueous solutions. It is especially useful for detection of chlorinated organic compounds in environmental samples. Currently, analyses of organic compounds in aqueous solutions are limited to low‐polarity compounds by the SPME/ATR‐IR sensing method. This limitation was mainly caused by the low polarity nature of the SPME phase. To increase the capability of this method to detect more polar compounds and also to increase the sensitivity in detection of organic compounds, the principle of “like‐dissolve‐like” was used to design a specific SPME phase for a certain class of chlorinated compounds. To demonstrate this concept, chlorinated phenols were used as probe molecules and polyvinyl chloride was chemically modified with phenol, ‐naphthol and ‐naphthol to provide SPME phases with a similar chemical structure to chlorinated phenols. These polymers were used as SPME phases and their performance were compared with the commonly used SPME phases (i.e., polystyrene and polyisobutylene). Results indicated that naphthols attached to PVCs provided much lower compactness, which allows fast speed in absorption of phenols. Meanwhile, due to the structural similarity between naphthols attached to PVCs and phenols, much higher partition coefficients were found for these chemically modified PVCs than conventionally used polymers. To further increase the sensitivity for analysis of chlorinated phenols, the common influencing factors, such as pH values and salt effect were also investigated. Apparently, pH values of the solutions did not influence the structure of the modified PVCs significantly. In absorption of chlorinated phenols in aqueous solutions with different pH values, the observed IR signals were decreased greatly in pH higher than 6 due to the charged form of chlorinated phenols that were presented. Results of the salt effect indicated that three times stronger of IR signals can be obtained if 20% (w/vol)

ISSN:0009-4536    

DOI:10.1002/jccs.200100028

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractA polymer coated piezoelectric crystal detection system with a home‐made computer interface for signal acquisition and data processing was prepared as a liquid chromatographic detector for various proteins. Various polymers, e.g., polyvinyl aldehhyde (polyacrolein) (PVA), polyacrylamide/glutaldehyde (PAA/GA) and bio‐gel A, were used as coating materials on quartz crystals for adsorption of various protein molecules, e.g., catalase (CA), hemoglobin (Hb), α‐chymotrypsin (Ch), albumin (Ab). The frequency responses of the polyacrlein coated piezoelectric detector for various proteins were in the order: catalase>hemoglobin>α‐chymotrypsin>albumin. In contrast, the order of the frequency responses of bio‐gel A and polyacrylamide/glutaldehyde coated piezoelectric crystals for these proteins were: hemoglobin>catalase>α‐chymotrypsin ≥ albumin and hemoglobin>albumin>catalase. The polyacrolein coated piezoelectric crystal protein detector exhibited a good linear frequency response with a high sensitivity of about 2.5×103Hz/(mg/mL) for catalase. In addition, bio‐gel A and polyacrylamide/glutaraldehyde coated crystals were sensitive to hemoglobin with sensitivities of about 4.5×103Hz/(mg/mL) and 3.0×103Hz/(mg/mL), respectively. Study of the interference of various organic molecules, e.g., alcohols, amines, ketones and carboxylic acids, in the detection of proteins with theses polymer coated crystals was also made. The polyacrolein coated crystal for proteins under went less interference from various organic molecules than bio‐gel A or polyacrylamide/glutaraldehyde coated crystals. Effects of coating load, concentration of proteins and flow rate of liquid chromatographic eluent were also inv

ISSN:0009-4536    

DOI:10.1002/jccs.200100029

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractA new method of indirect determination of ascorbic acid with ammonium sulfate and ethanol by extraction and flotation of copper in the presence of thiocyanate has been studied in this paper. The study shows that a small amount of Cu(II) is reduced to Cu(I) by ascorbic acid, then Cu(I) precipitates with SCN−. In the course of phase separation of ethanol from water, the precipitated CuSCN is extracted and stays in the interface of ethanol and water. A good linear relationship is observed between the extraction yield of Cu(II) and the amount of ascorbic acid. The detection limit for ascorbic acid is 1 10−5M. Every parameter has been optimized and the reaction mechanism has been studied. The method is simple, rapid (5 min) and suffers from few interferences of common anions and cations. It has been successfully applied for the determination of ascorbic acid in pharmaceuticals and fru

ISSN:0009-4536    

DOI:10.1002/jccs.200100030

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractMillipore hydrophobic polyvinylidene fluoride (PVDF) microfiltration membranes were used for whey processing. Fouled membranes were cleaned with acid (HCl), alkaline (NaOH) and surfactant (Triton‐X100). The latter resulted in maximum flux recovery and resistance removal. Hydrochloric acid had a moderate effect and sodium hydroxide was the weakest cleaning agent. This is due to the cleaning strength of emulsifiers compared to acid or alkali. However acids are more efficient than alkaline solutions for removal of mineral compounds which remain on the membrane surface.Cleaning efficiency depends on the concentration of cleaning agent being higher for higher surfactant concentration. For acids and alkali, the efficiency increases with increasing the concentration of the reagent reaches a maximum (optimum concentration) and then decreases. This can be explained by changes in permeability of the deposit layer with the concentration of the cleaning agent. Another explanation is the breakage of proteins by acid or alkali which produces more fouling materials and causes less cleaning efficiency.Operating conditions affect the cleaning process. At higher stirring speeds (turbulent flow) or longer cleaning time better removal of deposits and higher cleaning efficiency were observed. The sequential cleaning process may or may not improve the cleaning efficiency. When acidic cleaning was followed by washing with a surfactant an improvement was achieved. This can be attributed to the incomplete removal of deposits by acid. However further cleaning with acid can not improve the cleaning efficiency.During whey processing fouling occurs by deposition of foulants of mostly proteins and macromolecules on the membrane surface or in the membrane matrix. Large substances (compared to the membrane pores) settle on the membrane surface and the small species penetrate and are adsorbed in the membrane pores. Cleaning dissolves and removes the adsorbed foulants from the membran

ISSN:0009-4536    

DOI:10.1002/jccs.200100031

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractCyclohexane‐1,3,5‐tricarbonitrile reached equilibrium having 1,3‐cis‐1,5‐cisand 1,3‐cis‐1,5‐trans isomers in a ratio of 3:7. Thecis, cis‐isomer preferred the conformation with three equatorial cyano groups, where as thecis, trans‐isomer displayed two cyano groups on equatorial positions and another cyano group on axial position. Condensation ofcis, cis‐cyclohexane‐1,3,5‐tricarbonitrile with L‐(S)‐valinol by the catalysis of ZnCl2in refluxing 1,2‐dichlorobenzene afforded two isomeric cyclohexane‐1,3,5‐trioxazolines in favor of the 1,3‐cis‐1,5‐trans isomer. Metalation ofcis, cis‐cyclohexane‐1,3,5‐tricarbonitrile, followed by alkylations with dimethyl sulfate, benzyl bromide or allyl bromide, gave the cor responding trialkylation products with predominance of 1,3‐cis‐1,5‐trans isomers. Thecis, trans‐isomer showed two cyano groups on axial positions and another cyano group on equatorial position, where as thecis, cis‐isomer exhibited three axial cyano groups. Treatment of trimethylcis, cis‐cyclohexane‐1,3,5‐tricarboxylate with lithium diisopropylamide and dimethyl sulfate afforded mainly the trimethyl ester of Kemp's triacid, which showed three axial carboxylate groups. Two competitive factors, i.e. the steric effect of in coming electrophiles and the dipole‐dipole inter actions of the cyano or carboxylate groups, might inter pla

ISSN:0009-4536    

DOI:10.1002/jccs.200100032

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY