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61.
Limonoid bitterness is a serious problem in the citrus industry worldwide. Limonoid glucosyltransferase is an enzyme that catalyzes the conversion of bitter limonoid into non-bitter limonoid glucoside while retaining the health benefit of limonoids in the juice. The immobilization of this enzyme in a column can solve the juice bitterness problem. More information about the catalytic residues of the en-zyme is needed in this immobilization process. Glutamate/aspartate, histidine, lysine, tryptophan, serine, and cysteine residues were chemi-cally modified to investigate their roles in the catalytic function of limonoid glucosyltransferase. Inactivation of the enzyme following modi-fication of carboxyl and imidazole moieties was a consequence of a loss in substrate binding and catalysis in the glucosyltransfer reaction. The modification of a single histidine residue completely destroyed the ability of limonoid glucosyltransferase to transfer the D-glucopyranosyl unit. Tryptophan seemed to have some role in maintaining the active conformation of the catalytic site. Lysine also seemed to have some direct or indirect role in this catalysis but the modification of serine and cysteine did not have any effect on catalysis. There-fore, we conclude that the carboxyl and imidazole groups contain amino acids are responsible for the catalytic action of the enzyme. 相似文献
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In carbohydrate systems which contain polar groups such as hydroxyl and carboxylic acid groups, water molecules are adsorbed in a specific way which varies with the type of polar group. Near infrared Spectroscopy (NIR) combined with multivariate statistical analysis was used to study the interactions between water molecules and carboxymethylated cellulose (CMC) with various degrees of substitution of the carboxylic acid groups, in two ionic forms (CMC-Na and CMC-Ca). The adsorbed water molecules were clearly influenced by the counterion; i.e. the nature of the ion-pair. A principle component analysis (PCA) identified variations in the registered spectra related to: the nature of the counter-ion, the degree of substitution (DS), the relative humidity (RH) and the type of polar group to which water was adsorbed. It was, possible furthermore, through the use of partial least square analysis (PLS), to extract spectral information related to the non-freezing bound water adsorbed on hydroxyl and carboxyl groups respectively. Loading spectra indicated that the obtained spectral information indeed correlated to the two kinds of polar groups studied (hydroxyl groups and carboxylic acid groups). The results support the view that, in the humidity range of 0–100%, water molecules are specifically adsorbed to individual polar groups, which characteristics are dependent on the nature of the polar group. 相似文献
64.
Unnatural polar α-aminoxy acid residue with proteingenous hydroxymethyl side chain, a building block of the peptidomimetic foldamer of α-aminoxy peptide, was synthesized starting from natural amino acid L-serine. The starting material, L-serine, undergoes a reaction sequence to produce compound 1 in three steps: (1) the neighboring carboxyl group participates in diazotization/bromination to transform the amino group to a bromo group, (2) the C-terminal carboxyl group is protected, and (3) bromide is SN2-displaced by N-hydroxyl phthalimide to introduce a N?O bond. After several conventional deprotection/coupling reactions, compound 1 is easily transformed to an α-aminoxy diamide, which can be widely used in peptidomimetics design. 相似文献
65.
Emil C. Buruiana Tinca Buruiana Violeta Melinte Mirela Zamfir Aurora Colceriu Marioara Moldovan 《Journal of polymer science. Part A, Polymer chemistry》2007,45(10):1956-1967
Carboxyl urethane dimethacrylate oligomers with poly(ethylene oxide) sequences in the structure were synthesized and examined in photopolymerizable resins that could better adhere to various kinds of materials, including tooth substrates. Aspects of the morphogenesis of dental composites formed through a photochemically initiated radical copolymerization of the carboxylic derivatives, in addition to other partners encountered frequently in such materials, were studied comparatively with the corresponding urethane dimethacrylate monomer. The effect of a small quantity of a carboxylic macromer (ca. 10%) on the formation of a network with a non‐carboxyl urethane dimethacrylate oligomer (90%) as a potential substitute for diglycidyl methacrylate of bisphenol A and a filler (1/1 70% Aerosil/glass) was visualized by fluorescence spectroscopy with a pyrene methanol probe. The results showed the following: (1) the degree of conversion in the formulations into which carboxyl urethane dimethacrylate was incorporated decreased with increasing poly(ethylene oxide) chain length, (2) the formation of excimers was inhibited in the derived composites, and (3) an important quenching of the monomer fluorescence emission with the UV–vis irradiation time was observed in the formulation containing a filler (Aerosil+Zr/Sr glass). Preliminary testing of the resin composites suggested that all urethane oligomers containing carboxylic acid could lead to dental materials with reduced polymerization shrinkage and good mechanical properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1956–1967, 2007 相似文献
66.
Sheng Zhang Jie Qing Chengdong Xiong Yuxing Peng 《Journal of polymer science. Part A, Polymer chemistry》2004,42(14):3527-3536
AB block copolymers composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(amino acid) with a carboxyl group at the end of PEG were synthesized with α‐carboxylic sodium‐ω‐amino‐PEG as a macroinitiator for the ring‐opening polymerization of N‐carboxy anhydride. Characterizations by 1H NMR, IR, and gel permeation chromatography were carried out to confirm that the diblock copolymers were formed. In aqueous media this copolymer formed self‐associated polymer micelles that have a carboxyl group on the surface. The carboxyl groups located at the outer shell of the polymeric micelle were expected to combine with ligands to target specific cell populations. The diameter of the polymer micelles was in the range of 30–80 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3527–3536, 2004 相似文献
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Yan Zhang Jinhong Li Zhengzhen Du Meidong Lang 《Journal of polymer science. Part A, Polymer chemistry》2014,52(2):188-199
pH‐responsive methoxy poly(ethylene glycol)‐b‐poly(ε‐caprolactone) bearing pendant carboxyl groups mPEG‐b‐P(2‐CCL‐co‐6‐CCL) was synthesized based on our newly monomer benzyloxycarbonylmethly functionalized ε‐caprolactone. Their structure was confirmed by 1H NMR, 13C NMR, and Fourier transform infrared spectrum spectra. In addition, SEC results indicated that the copolymers had a relatively narrow polydispersity. WXRD and DSC demonstrated that the introduction of carboxymethyl groups had significant effect on the crystallinity of the copolymers. Furthermore, the solution behavior of mPEG‐b‐P(2‐CCL‐co‐6‐CCL) has been studied by various methods. The results indicated that mPEG‐b‐P(2‐CCL‐co‐6‐CCL) had a rich pH‐responsive behavior and the micelles could be formed by pH induction, and the mPEG‐b‐P(2‐CCL‐co‐6‐CCL) could existed as unimers, micelles or large aggregates in different pH range accordingly. The mechanism of which was supposed to depend on the counteraction between the hydrophobic interaction from PCL and the ionization of the carboxyl groups along the polymer chain. Moreover, the mPEG‐b‐P(2‐CCL‐co‐6‐CCL) copolymers displayed good biocompatibility according to the preliminary cytotoxicity study. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 188–199 相似文献
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