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101.
Xiaojuan Hao Luca Albertin L. John R. Foster Thomas P. Davis Christopher Barner‐Kowollik 《Macromolecular bioscience》2003,3(11):675-683
A novel synthetic method combining chemo and enzymatic synthesis strategies was employed to prepare a vinyl acetate type monomer, 6‐(4‐methoxybiphenyl‐4′‐oxy)hexyl vinyl hexanedioate (VA‐LC). Homo‐ and copolymers of VA‐LC with maleic anhydride (MAn) were prepared by conventional free radical polymerization using 2,2′‐azobisisobutyronitrile (AIBN) and 1,1′‐azobis (cyclohexane carbonitrile) (AHCN) as an initiator at 95 and 60 °C, respectively. The thermal properties of the generated polymeric material were investigated by differential scanning calorimetry (DSC), and the optical texture was inspected by polarizing optical microscopy (POM). While the monomer VA‐LC does not exhibit liquid‐crystalline properties, poly(VA‐LC), and the alternating copolymer of VA‐LC with maleic anhydride both displayed such properties.
102.
A non ionic surfactant with a rigid rod-like hydrophobic group has been synthesized. Owing to the molecular geometry of the surfactant only lamellar micelles are formed in aqueous solution.This system exhibits a lyotropic nematic phase (N
L), which for the first time has been found for a binary non ionic surfactant/water system.Herrn Professor Dr. H.-G. Kilian mit herzlichen Glückwünschen zum 60. Geburtstag gewidmet. 相似文献
103.
Summary An improved method of alanine-amino transferase determination is proposed. The reaction is carried out with alanine and 2-oxoglutarate as substrates and analysis is by HPLC on a reversed-phase chromatographic system using a C18 column and tetrabutylammonium phosphate in phosphate buffer (pH 7.0)-acetonitrile as mobile phase. The enzyme activity was determined by directly following the formation of pyruvic acid without employing any secondary reaction, which is necessary in the spectrophotometric method. The detection limit of pyruvic acid is 10 pmole l–1 and the standard deviation for the enzymatic activity of standard solutions is 5.4%. Furthermore under the chromatographic conditions selected it is possible to detect the presence of some intermediate species.Work supported by National Research Council of Italy. Presented in part at the First International Symposium on Applications of HPLC in Enzyme Chemistry, Verona, September 1990. 相似文献
104.
《Arabian Journal of Chemistry》2022,15(12):104368
Protein hydrolysates have the potential to be natural and safer sources of bioactive peptides. In this study, two proteases were used to hydrolyze Chinese sturgeon (Acipenser sinensis) protein, and the hydrolysates were then purified to yield antioxidant peptides. The degree of hydrolysis of 23.56 % and 18.14 % was obtained using papain and alcalase 2.4L, respectivly, and hydrolysates had 96.80 % and 87.24 % total amino acid content, respectivly. The papain hydrolysate (PH) and alcalase 2.4L hydrolysate (AH) showed good antioxidant activity against DPPH? (IC50 of 3.64 and 3.15 mg/mL) and ABTS?+ (IC50 of 1.92 and 1.58 mg/mL), respectively. The low-molecular-weight (<1000 Da) fraction of both hydrolysates demonstrated the highest antiradical activity (IC50 of 2.59 and 2.31 mg/mL, DPPH) and (IC50 of 1.54 and 1.36 mg/mL, ABTS), respectively. Nine peptides were separated from both hydrolysates using reverse phase high performance liquid chromatography (RP-HPLC). The IC50 for ABTS?+ scavenging activity of peptide P5 with valine, glycine and asparagine (MW of 282.13 Da) from PH, and peptide P3 with histidine, glycine and alanine (MW of 302.74 Da) from AH was 0.89 and 0.72 mg/mL, respectively. The fractions and purified peptides obtained from Chinese sturgeon hydrolysates could be utilized as natural antioxidant substitutes in pharmaceuticals and food products. 相似文献
105.
Summary The effect of silica gel pretreatment and of different bonding techniques, on the chromatographic properties of octadecyl
bonded phases is described. The experiments show that a monomeric octadecyl bonded phase, prepared from silica gel that has
not been treated before bonding, has a poor selectivity towards polycyclic aromatic hydrocarbons (PAHs) and shows high adsorption
of basic components. Silica gel treatment before the bonding of the monofunctional silane does not give a substantial improvement.
Polymeric phases on the other hand show a much better PAH selectivity and a lower adsorptivity towards basic components. Further
improvement can be achieved with the polymeric modification if silica gel treatment is carried out before bonding. 相似文献
106.
Mark P Scott 《European Polymer Journal》2003,39(10):1947-1953
Room temperature ionic liquids (ILs) based on imidazolium salts, were found to be excellent plasticizers for poly(methyl methacrylate), with improved thermal stability, and the ability to reduce glass transition temperatures to near 0 °C. Because ILs have environmentally benign properties, they can be used in place of traditional chemicals in numerous products and processes. In this work, PMMA was formulated using dioctyl phthalate, DOP, as a traditional plasticizer, and properties were compared to PMMA plasticized with two ILs: butyl methylimidazolium/hexafluorophosphate, [bmim+][PF6−], and hexyl methylimidazolium/hexafluorophosphate, [hmim+][PF6−]. Formulations incorporated up to 30 vol.% DOP and 50 vol.% ILs. Bulk and plasticized polymers were characterized for glass transition temperature, elastic modulus, and the thermal stability of the plasticizers. 相似文献
107.
The partial molal volumes of Li+, Na+, K+, Rb+, Cs+, Cl–, Br–, I–, and NO
3
-
in DMSO at 25°C have been determined from ultrasonic vibration potential data and density data for solutions of uni-univalent electrolytes. Hepler's semiemprirical equation has been used to split ionic partial molal volumes into geometric and electrostrictive contributions. The results obtained in this work confirm the conclusion of our previous studies, namely, that the contribution of electrostriction is essentially determined by the properties of that layer of atoms, 0.3 to 0.4 nm thick, in contact with the ion and by the degree of steric hindrance of the poles of the dipole of the solvent molecule. On the other hand, the geometric contribution depends on the size of the solvent molecule and also on the arrangement of the solvent molecules about the ions. It is shown that the geometric contribution to the partial molal volume of ions is largely increased when ions cannot come close enough to the poles of the solvent-molecule dipole, owing to steric hindrance. 相似文献
108.
B. Kaufmann S. Souverain S. Cherkaoui P. Christen J. -L. Veuthey 《Chromatographia》2002,56(3-4):137-141
Summary A rapid analytical method has been developed for the mutual resolution of three steroidal compounds, withaferin A, iochromolide,
and withacnistin. Liquid chromatography was performed on a Chromolith analytical column (4.6 mm i.d.×50 mm), made from a cylindrical
silica rod, operated at a flow rate of 4 mL min−1 with a simple linear gradient prepared from 0.1% aqueous formic acid and 0.1% formic acid in acetonitrile. Under optimum
conditions simultaneous separation of the compounds was achieved in less than 7 min, one eighth the time required for conventional
LC separation. The overall analysis time was reduced without sacrificing chromatographic performance—essential for the resolution
of positional isomers such as iochromolide and withacnistin. The column was coupled to a single-quadrupole mass spectrometer
and the method was characterized by good performance in terms of repeatability, selectivity, linearity, and sensitivity. Detection
limits in the single-ion-monitoring mode were 0.15 μg mL−1 or below. Finally, the developed method was successfully applied to the determination of withanolides in extracts fromlochroma gesnerioides obtained by three different processes—traditional Soxhlet extraction and two faster methods, microwave-assisted extraction
and pressurized solvent extraction. 相似文献
109.
Possible use of room temperature ionic liquids (RTILs) as chelate extraction solvent was evaluated by using 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF6]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF6]). These RTILs showed high extraction performance for divalent metal cations with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (Htta). The extracted metals were back-extracted into 1 mol dm−3 nitric acid quantitatively. Furthermore, the extracted species were estimated as neutral hydrated complexes M(tta)2(H2O)n (n= 1 or 2) for M = Ni, Cu and Pb and anionic complexes M(tta)3− for M = Mn, Co, Zn and Cd. 相似文献
110.
Julie L. S. Bell David J. Wesolowski Donald A. Palmer 《Journal of solution chemistry》1993,22(2):125-136
The dissociation quotients of formic acid were measured potentiometrically from 25 to 200°C in NaCl solutions at ionic strengths of 0.1, 0.3 1.0, 3.0, and 5.0 mol-kg–1. The experiments were carried out in a concentration cell with hydrogen electrodes. The resulting molal acid dissociation quotients for formic acid, as well as a set of infinite dilution literature values and a calorimetrically-determined enthalpy of reaction, were fitted by an empirical equation involving an extended Debye Hückel term and seven adjustable parameters involving functions of temperature and ionic strength. This regressional analysis yielded the following thermodynamic quantities for 25°C: logK=–3.755±0.002, Ho=–0.09±0.15 kJ-mol–1, So=–72.2±0.5 J-K–1-mol–1, and C
p
o
=–147±4 J-K–1-mol–1. The isocoulombic form of the equilibrium constant is recommended for extrapolation to higher temperatures. 相似文献