摘要:

AbstractIn this review of the properties and applications of mesophases, after a general description of the states of aggregation of matter, the types of liquid crystals are distinguished. The thermotropic liquid crystals are classified on the basis of their structural properties. A comparison of sets of chemically related molecules indicates how details of molecular structure (topology and conformation) affect the existence and sequence of mesophases for the lath‐like thermotropic mesogen

ISSN:0009-4536    

DOI:10.1002/jccs.198900053

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractChelating resins, the polymeric complexing compounds, are specific and selective ion exchange resins. A chelating ion exchange resin consists essentially of two components,i.e. a chelating group and a polymeric matrix. The properties of both components affect the selectivity of the synthesized resin. Methods used to synthesize chelating resins are reviewed. The analytical and physical techniques used to characterize the dissociation constant, metal capacity and distribution coefficient of the newly synthesized resin as well as the coordination site, the composition and the formation constant of the metal‐resin complexes are discussed. Chelating resins could be used in various forms. Some important features of the analytical application of chelating resins, including selective concentration and separation both in inorganic analysis and organic analysis are also discussed. The techniques by which sorption or separation with the help of chelating resins achieved can be static, dynamic, or chromatographic. After sorptive concentration or separation, the elements can be determined either directly in the sorbent phase, its decomposition residue, the eluent solution after desorption, or the effluent after the solution has been passed through the sorbent. Various objects such as natural waters, geological objects, industrial materials, foodstuffs, coal, fuel oil. shale oil, transuranium elements and biological materials could be analyzed with the help of chelating resin

ISSN:0009-4536    

DOI:10.1002/jccs.198900054

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe substitution reaction of benzal chloride (PhCHCl2) and sodium iodide in acetone needs a metal‐ion catalyst. Without considering the effects of solubility and the dissociation of salt, salts of Cr(III), Mn(II), Fe(II, III), Co(II), Ni(II), Cu(II)m Zn(II), Cd(II), Hg(I, II), and Sb(III) ions are used to study their catalytic reactivities. It is found that the Fe(II) ion exhibits acceptable catalytic effect. The overall Fe(II)‐catalyzed PhCHCl2‐NaI reaction can be described by the following competitive consecutive scheme: PhCHCl2→ PhCHCII → PhCHI2. Under suitable conditions, coupling products such as PhCH=CHPh and PhCHClCHClPh are also found. The rate of the first‐stage substitution of the PhCHCl2‐NaI reaction increases linearly with the PhCHCl2concentration. It increases asymptotically with the FeCl2concentration. However, there is an optimum concentration for Nal. The apparent activation energies are 104 ± 4 kJ/mol and 133 ± 4 kJ/mol for the Fe(II)‐catalyzed PhCHCl2‐NaI and PhCHCH‐NaI re

ISSN:0009-4536    

DOI:10.1002/jccs.198900055

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe secondary dissociation constants of α‐phthalic and phosphoric acids have been determined in 50% w/w methanol‐water mixture from the e.m.f measurements of the cell of the type: Pt; H2(1 atm), M2A(m), MHA(m), MCl, AgCl; Ag at different temperatures (288.15–308.15 K) and at different ionic strengths.The thermodynamic values ΔG°, ΔH°, ΔS° for the respective equilibria are estimated. The possibility of using these acids as basis for some buffer solutions in 50% methanol – water mixtur

ISSN:0009-4536    

DOI:10.1002/jccs.198900056

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe pulse sequence for generating coherence transfer (or polarization transfer) is invoked to enhance the signal of heteronuclear two spin order (e.g. 2IZSZ) in a spin system with CH moiety. This allows the observation of selective conversion of Zeeman order, in a sample with natural abundant13C nuclei, into two spin order for measuring cross‐correlation of chemical shift anisotropy and dipole‐dipole interactions. The molecular reorientational correlation time and the orientation of the C–H axis with respect to the principal axes of carboxyl CSA tensor may be determined simultaneously in the relaxation profile of two spin

ISSN:0009-4536    

DOI:10.1002/jccs.198900057

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractA tetrapeptide has been studied by means of NMR of13C in natural abundance. By the combined application of various two‐dimensional1H/1H and13C/1H correlation techniques, the primary structure of the peptides could be unambiguously determine

ISSN:0009-4536    

DOI:10.1002/jccs.198900058

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe chromatographic behavior of 8 lanostanoid triterpenes including 4 pairs of C‐3 epimers and 2 pairs of C‐3/C‐15 positional isomers was studied by reversed phase HPLC. A consistent elution sequence of these paired isomers in all combination of three distinct solvent systems was observed. The mobile phase selectivity to separate specific, paired isomers was mainly dependent on the polarity difference contributed by C‐3/C‐15 hydroxyl and acetoxyl groups. The stereochemistry at C‐3 played more profound role in guiding the hydrophobic interaction with C18stationary phase in the separation of C‐3/C‐15 pos

ISSN:0009-4536    

DOI:10.1002/jccs.198900059

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractA rapid peptide‐bond hydrolysis by means of microwave irradiation is introduced for the facile preparation of protein hydrolysates used for amino acid analysis. The optimal hydrolysis condition has been determined using several enzymes with known amino acid compositions. The effects of hydrolysis time on the recovery of various labile and hydrophobic amino acids are also exemplified in the microwave heating of standard amino acids. The method has been applied to the complete amino acid analysis with a single nonvolatile solvent of methanesulfonic acid with good recovery of tryptophan and half‐cystine. It provides a radical expedition of protein and peptide hydrolysis via commercial microwave ovens and specially‐designed Teflon‐Pyrex tubes, circumventing the tedious procedures using vacuum‐sealed pyrex lubes heating at 110°C for more than 24 h. This novel type of microwave chemistry associated with rapid peptide‐bond cleavage is of great potential in the automation of the complete process of amino acid analysis starting from the preparation of protein

ISSN:0009-4536    

DOI:10.1002/jccs.198900060

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractIncubation of various cultured mammalian cells under growth‐stimulatory condition with [3H]putrescine or [3H]spermidine results in a labeling of an 18, 000‐dalton protein (Cell,1982,29, 791; BBA,1983,756, 395). The labeling is due to post‐translational conversion of a lysine residue to hypusine residue, using the butylamino moiety derived from spermidine. In order to search for an abundant source for the purification of this protein, we have examined possible existence of this hypusine‐containing 18, 000‐dalton protein (hyp‐18k) in chick embryos by the metabolic labeling method. Metabolic labeling of chick embryo fibroblasts, prepared from the Day 11 embryos, by [3H]putrescine resulted in two prominently labeled protein bands.Mr=18, 000 and 20, 000, as shown by sodiun dodecyl sulfate‐polyacrylamide gel electrophoresis and fluorography. Two‐dimensional gel analysis indicated that the labeled 20, 000‐dalton protein had a pI value of 5.5 and the labeled 18, 000‐dalton protein exhibited isoform structures with pI values ranging from 4.6 to 5.1. Peptide map analysis showed that these two proteins are similar but not identical. Both labeled proteins contained radioactive hypusine residue and exhibited strong binding to Cibacron Blue dye. The time course of the metabolic labeling of these two proteins, however, differed dramatically. The labeling of the 18, 000‐dalton protein appeared early and continued to increase 24 h after serum stimulation. In contrast, the labeling of the 20, 000‐dalton protein became prominent only after much long

ISSN:0009-4536    

DOI:10.1002/jccs.198900061

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractOptically active 3‐benzylthio‐2‐methylpropionic acid and 3‐benzoylthio‐2‐methylpropionic acid have been prepared via protease‐catalyzed hydrolysis of their corresponding ester and thioester. Subtilisin catalyzed the hydrolysis of the thioester of methyl 3‐benzoylthio‐2‐methylpropionate twice as fast as that of the methyl ester derivative. The stability of the enzyme in organic cosolvents was studied. Immobilization of subtilisin on the solid support XAD‐8 improved the stability of the enzyme. A practical preparative resolution of the title

ISSN:0009-4536    

DOI:10.1002/jccs.198900062

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY