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1.
The binding properties of metal ions to a pectic polysaccharide, rhamnogalacturonan II (RG-II), from plant cell walls were analyzed by size-exclusion HPLC/ICP-MS. The dimeric RG-II borate complex (dRG-II-B) from sugar beet and red wine contained 0.8 - 1.1 mol/mol of B, 0.8 - 1.1 mol/mol of Ca, 0.1 - 0.3 mol/mol of Sr, and 0.03 - 0.07 mol/mol of Ba. The treatment of dRG-II-B with Sr2+, Ba2+, Pb2+ or La3+ exchanged the originally present Ca, Sr and Ba. In contrast, monomeric RG-II (mRG-II), which contained approximately 0.1 mol/mol of Ca, formed complexes with La3+, Eu3+, and Lu3+ added to the solution, but did not do so with Ca2+, Sr2+, Ba2+ and Pb2+. The HPLC/ICP-MS and HPLC/RI (refractive index detector) analysis of the partially hydrolyzed mRG-II that was treated with La3+ indicated that the side chains and backbone of mRG-II together form a lanthanoid binding site. 相似文献
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Homologous series of 2-alkoxycarbonyl-4-(4-ethoxyphenylazo)phenyl 4-methoxybenzoates (L) and their orthopalladated μ-chloro dimers (Pd2Cl2L2) have been synthesized and their thermotropic phase transition behaviour has been characterized. The ligands, L, are three-ring nematogens with their central rings substituted in the 2-position by n-alkyl chains of varied length. The thermal stability of the nematic phases decreases rapidly with increasing side chain length and then levels off as the series is ascended. In every case the mesomorphic phase appears only over a small temperature range (less than 20° C). The orthopalladated species also proved to be nematogenic. Melting and clearing points rise on the average by 87° C and 126° C, respectively, and thus the temperature ranges of the nematic phases are enlarged considerably upon metallation. In relation to the observed stabilization of the nematic phases, particularly of higher homologues, a lath-like molecular structure, in which the side chains of the ligands fill up the clefts of the core part, has been deduced for a Pd2Cl2L2 homologue from its solution 1H-NMR spectrum. 相似文献
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Yamamoto A Akiba N Kodama S Matsunaga A Kato K Nakazawa H 《Journal of chromatography. A》2001,928(2):139-144
A multi-beam circular dichroism (CD) detector which is easily constructed by inserting inexpensive optics into a conventional photo-diode array detector has an advantage of simultaneous detection of the absorbance and CD. The enantiomeric purity determination of malic acid in beverages was performed by this detection system. Malic acid when complexed with Cu(II) was found to have an absorbance maximum at around 750 nm. The L-malic acid-Cu(II) complex showed a positive Cotton effect in its absorbance band and its anisotropy factor (delta epsilon/epsilon) was relatively large at about 1/170. This complex was retained on a reversed-phase column with the addition of racemic 2-hydroxy-3-methylbutyric acid to the mobile phase as the ligand. A plot of the relative peak areas between the CD and the absorption (delta abs/abs) versus optical purity showed good linearity with a correlation coefficient of 0.999, and the precision expressed as the relative standard deviation of the errors from the regression line was +/-2.7% (2sigma). The accuracy of the proposed method was assessed by capillary electrophoresis. Eight commercially available juice products were analyzed using this method. Five of them were thought to be adulterated with synthetic malic acid. 相似文献
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Abstract— As a model for studies involving biologic systems, rates of hematoporphyrin and protopor-phyrin-sensitized photooxidation of tryptophan were measured in water-methanol mixtures. Absorption and fluorescence-emission spectra associated with solutions of porphyrins in different water-methano! mixtures were also examined. The optimal rate of photooxidation by hematoporphyrin occurred in 30% methanol; by protoporphyrin, in 60% methanol. Absorption spectra were examined to characterize dispersion of hematoporphyrin into monomeric form in 90% methanol, and the dimer formation which predominates in 30% methanol. With the more hydrophobic protoporphyrin, an absorption spectrum characteristic of drug monomer was seen in 100% methanol, a dimer spectrum was observed in 60% methanol. At methanol concentrations < 60%, we observed impaired photooxidation and another alteration in the absorption pattern apparently reflecting drug aggregation beyond the dimer stage. Fluorescence emission maxima of both porphyrins were blue-shifted with increasing solvent dielectric constant, but an additional blue shift was detected in an aqueous environment which was apparently related to porphyrin aggregation. Absorption and fluorescence-emission spectra appear helpful for characterizing environmental determinants of porphyrin-sensitized photooxidation. 相似文献
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A sensitive assay for acyl CoA-cholesterol acyltransferase (EC 2.3.1.26) in rat liver microsomal and mitochondrial preparations is described. The lowered cholesterol concentration in the enzyme reaction with oleoyl CoA is determined spectrofluorimetrically by using the cholesterol oxidase/peroxidase/p-hydroxyphenylpropionic acid system. The assay requires as little as 20 μg of protein in the enzyme preparation. 相似文献
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Kozo Arai Atsushi Matsunaga Masaru Yoneyama Shoji Takigami Yoshio Nakamura Haydn E. Edwards Glyn O. Phillips 《Journal of polymer science. Part A, Polymer chemistry》1993,31(1):249-258
The reactions of heparin with 2,4,6-trinitrobenzenesulfonic acid (TNBS) were studied spectrometrically. Seven different commercial heparins were used in this study. The amino groups react with TNBS to form equimolar amounts of trinitrophenylated (TNP) amino groups and bisulfite ions. The TNP-amino groups further react with bisulfite ions to form the monosubstituted anionic sigma complex. The absorption spectrum with two maxima at approximately 350 nm and approximately 420 nm, characteristic of either the TNP-amino groups or the complex, was analyzed for the reaction of TNBS with heparin. It was shown that the reactivities of TNBS with amino groups from α-amino acid and hexosamine residues are greatly different. By combining the results of the reaction kinetics and the reaction of heparin with Sanger's reagent, the number of the α-amino groups and the free amino groups in hexosamine residues were determined. These data have been performed with a range of heparins from different commercial sources, of different activities and physical characteristics. No correlation was found between the free amino contents of these heparins and biological potency. © 1993 John Wiley & Sons, Inc. 相似文献