摘要:

AbstractA novel convenient method for preparing unsymmetrical 1,1′‐disubstituted ferrocenyl phosphine ligands by using the readily accessible 1,1′‐dibromoferrocene as a precursor is described. The method is of interest for modifying the chelating ferrocenyl phosphine ligands in view of the growing influence of homogeneous catalysis in organic synthesis, manipulation of materials and production of high optica

ISSN:0009-4536    

DOI:10.1002/jccs.199800087

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe development of effective chiral stationary phases (CSPs) and separation strategies for the liquid chromatographic (LC) resolution of enantiomers has been beneficial to many scientific disciplines. Over the last decade the number and type of CSPs has expanded tremendously. Not only have new classes of chiral selectors been introduced, but also many of the first CSPs have been changed and/or improved. The second or third generation of a CSP often can be different from the original. This can be confusing and intimidating to someone just entering the area of LC enantiomeric separations. Fortunately, all CSPs can be categorized in one or another of a few classes. There are generally one or two columns that can accomplish the majority of separations in each class. In this work we look at the different classes of CSPs and how they have expanded and changed over the last decade.

ISSN:0009-4536    

DOI:10.1002/jccs.199800088

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractEnergy dispersive X‐ray diffraction (EDXRD) has been used to perform in‐situ kinetic studies on the intercalation of a range of guest molecules in layered lattices. The kinetics of the intercalation of cations {K+, PyH+(Py = C5H5N), NMe+4} and the long chain ammonium ions C12TMA, C16TMA, C18TMA (C12TMA = dodecyltrimethylammonium, C16TMA = hexadecyltrimethylammonium and C18TMA = octadecyltrimethylammonium) into crystals of MnPS3have been determined. These reactions are very fast and in some cases novel transient phases are observed. The rate of cobaltocene, Co(η‐C5H5)2, intercalation in layered dichalcogenides ZrS2, 2H‐SnS2, 2H‐SnSe2, 2H‐TaS2, 2H‐NbS3, 1T‐TaS2and TiS2has also been investigated. Integrated intensities of the Bragg reflections have been used to determine the extent of reaction, (α), versus time for each of these reactions. A number of kinetic models have been considered, including the Avrami‐Erofeyev (m = 1.5) deceleratory nuclei‐growth model and statistical simulation. The concentration and solvent dependence of the rate of Co(η‐C5H5)2intercalation into 2H‐SnS2has also been determined. Surprisingly we find that the rate of intercalation is invariant to the initial Co(η‐C5H5)2concentration ov

ISSN:0009-4536    

DOI:10.1002/jccs.199800089

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractRecent advances in acid‐base catalysis are summarized. Several examples of solid acid, base, and acid‐base bifunctional catalysis which have brought significant progress of the field or are considered to give strong impacts to industrial application are presented. Selected commercialized processes developed by using solid acid‐base catalysts are demonstrated, their significance being discussed. The future problems in this field are speculated and important fundamental research subjects are pointe

ISSN:0009-4536    

DOI:10.1002/jccs.199800090

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractA β‐glucosidase (EC 3.2.1.21) fromFlavobacterium meningosepticumhas been purified and characterized. Purity was enhanced at least 530‐fold from crude cell extract with 16.6% yield. The estimated molecular mass of the purified enzyme is 150 kDa by gel filtration and 78 kDa by SDS‐PAGE. This dimeric enzyme has a pI= 9.0 and an optimal activity at pH 5.0 and temperature of 50 °C. Divalent metal ions (Hg2+, Cu2+, Ca2+, Mg2+) and EDTA have negligible effect on the enzyme activity. The enzyme exhibited a high specificity on the glycon portion of aryl‐β‐D‐glycosides. NMR spectroscopy revealed the enzyme catalyzed hydrolysis ofp‐nitrophenyl‐β‐D‐glucopyranoside with the retention of anomeric configuration, indicating that a double displacement mechanism was involved. A preliminary study of the Bronsted relationship showed a concave‐downward plot, which is consistent wi

ISSN:0009-4536    

DOI:10.1002/jccs.199800091

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractSalen‐type Ru(III) complexes are found to be capable of reacting with physiologically acceptable oxidants. The water solubility and DNA affinity of these Ru(III)‐salen complexes are enhanced by the utilization of a variety of charged groups through the formation of peptide bonds. In the presence of hydrogen peroxide, modified Ru(III)‐salen complexes are capable of nicking DNA. In addition, the reactivity in DNA cleavage increases along with the total number of positive charges retaining in Ru(III)‐salen complexes and less influence in the electronic effect. Using32P‐end‐labeled oligonucleotides and high resolution polyacrylamide gel electrophoresis, Ru(III)‐salen complexes are found to randomly cleave DNA regardless of the DNA secondary conformation such as bulge, inter‐loop, or double‐stranded regions. The possible reactive species of Ru(III)‐salen complexes in DNA cleavage is considered as the hydroxyl radical and high valent oxoruthenium(IV) species according to the UV titration, quenching studies, and reaction w

ISSN:0009-4536    

DOI:10.1002/jccs.199800092

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractHigh mobility group protein (HMG) is known to be involved in the formation of high order structure of chromatin. HMGs with minor‐groove binding ability in the AT‐rich DNA region play a vital role in controlling gene transcription activity. In this report, a 18‐residue HMG‐I/DAT1chimeric peptide,PRGRPKGKTLREPRGRPY, was designed and synthesized containing two repetitive PRGRP units and a linking peptide, KGKTLRE, as a targeted DNA‐binding peptide. The segment PRGRP is derived from HMG‐I while KGKTLRE is from theDAT1peptide. Using gel‐mobility shift assay and32P‐end labeled 27 bp AT‐rich DNA, the dissociation constant of this chimeric peptide was found to be 4.7 × 10−6M, that is, 104times stronger than that of the PRGRP segment stand alone (>10−2M). In addition, the binding constant was found to increase with the length of AT‐rich DNA. The possible DNA binding site of theHMG−1/DAT1chimeric peptide is determined by footprinting experiments using a minor‐groove cleaving agent ruthenium(III)‐Schiff base complex and a 135‐bp32P‐5′‐end‐labeled DNA restriction fragment ofHind III/Rsa Ifrom plasmid pBR322 DNA. The major pattern protected by the HMG‐I/DAT1chimeric peptide exhibits a preference for 5′‐AAAT‐3′ of the AT‐rich region. Therefore, this novel design HMG‐1/DAT1chimeric peptide possesses not only a high affinity to AT‐rich DNA but also the sequence‐specific binding in the minor groove of DNA, which may further lead to the desig

ISSN:0009-4536    

DOI:10.1002/jccs.199800093

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractPummerer‐type reaction intermediate2of 1‐[(2‐methylthio)ethanoyl]pyrrolidine(1)has been found to react with 1‐alkenes to afford ene adducts3. Trichonine4was synthesized from the a

ISSN:0009-4536    

DOI:10.1002/jccs.199800094

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractFour lignans and six kauranes, (+)‐epi‐syringaresinol (1), annocherin A (16β‐hydroxy‐17,19‐diacetoxy‐ent‐kaurane) (2), (+)‐syringaresinol (3), (+)‐dia‐syringaresinol (4), liriodendrin[(+)‐syringaresinol‐di‐O‐β‐D‐glucopyranoside] (5), 16α‐hydro‐17‐acetoxy‐ent‐kauran‐19‐oic acid (6), 16β‐hydro‐17‐hydroxy‐ent‐kauran‐19‐al (7), 16α‐hydro‐17‐hydroxy‐ent‐kauran‐19‐al (8), 16β‐hydro‐17‐hydroxy‐ent‐kauran‐19‐oic acid (9) and 16α‐hydro‐17‐hydroxy‐ent‐kauran‐19‐oic acid (10) were isolated from the stems ofAnnona cherimola.Among them,1is obtained for the first time from natural sources and 2

ISSN:0009-4536    

DOI:10.1002/jccs.199800095

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractDiazepam (1) is a frequently prescribed hypnotic/anxiolytic drug worldwide. 7‐Chloro‐1,3‐dihydro‐l‐methyl‐5‐phenyl‐2H‐1,4‐benzodiazepin‐2,2‐dioxide (2) is an initial alkaline hydrolysis product of 1. The mechanisms in the conversion of2to 2‐methylamino‐5‐chloro‐α‐(phenylbenzylidene)glycinate (3), 2‐methylamino‐5‐chlorobenzophenone (4), and1in aqueous solutions with pH ranging from 0 to 12.2 is the subject of this report. Results of temperature‐dependent hydrolysis kinetics and product identification indicated that: (1) in solutions with pH between 7 and 12.2,2underwent a ring‐opening reaction to form 3; the rate decreased with increasing pH. (2) In solutions with pH between 2 and 7,2was rapidly converted to 3, followed by a pH‐dependent conversion to4; the rate increased with decreasing pH and became less sentitive to pH at pH ≤ 4.5. (3) In solutions with pH between 0 and 2,2was rapidly converted to 4 and 1; the percentage of 1 increased with decreasing pH. (4) A2containing one oxygen‐18 atom lost 50% of its oxygen‐18 following conversion to1in 1 M HCl. In addition to understanding the mechanism in the transformations of2in various pH solutions, this study established a simple and efficient method in the quantitative conversion of 1 to 4 and in the p

ISSN:0009-4536    

DOI:10.1002/jccs.199800096

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY