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921.
Polymorphism of paracetamol 总被引:1,自引:0,他引:1
G. L. Perlovich Tatyana V. Volkova Annette Bauer-Brandl 《Journal of Thermal Analysis and Calorimetry》2007,89(3):767-774
The thermodynamic relationship between crystal modifications of paracetamol was studied by alternative methods. Temperature
dependence of saturated vapor pressure for polymorphic modifications of the drug paracetamol (acetaminophen) was mea sured
and thermodynamic functions of the sublimation process calculated. Solution calorimetry was carried out for the two modifications
in the same solvent. Thermodynamic parameters for sublimation for form I (monoclinic) were found: ΔG
sub298=60.0 kJ mol−1; ΔH
sub298=117.9±0.7 kJ mol−1; ΔS
sub298=190±2 J mol−1 K−1. For the orthorhombic modification (form II), the saturated vapor pressure could only be studied at 391 K. Phase transition
enthalpy at 298 K, ΔH
tr298(I→II)=2.0±0.4 kJ mol−1, was derived as the difference between the solution enthalpies of the noted polymorphs in the same solution (methanol). Based
on ΔH
tr298 (I→II), differences between temperature dependencies of heat capacities of both modifications and the vapor pressure value
of form II at 391 K, the temperature dependence of saturated vapor pressure and thermodynamic sublimation parameters for modification
II were also estimated (ΔG
sub298=56.1 kJ mol−1; ΔH
sub298=115.9±0.9 kJ mol−1; ΔS
sub298=200±3 J mol−1 K−1). The results indicate that the modifications are monotropically related, which is in contrast to findings recently reported
found by classical thermochemical methods. 相似文献
922.
Reversed-phase liquid chromatography and argentation chromatography of the minor capsaicinoids 总被引:1,自引:0,他引:1
Thompson RQ Phinney KW Sander LC Welch MJ 《Analytical and bioanalytical chemistry》2005,381(7):1432-1440
An investigation of the liquid chromatography of the minor capsaicinoids in a commercial capsaicinoid mixture is reported. Twelve stationary phases including C8, C18, C30, phenyl, and cation-exchange chemistries were examined in combination with isocratic aqueous methanol and aqueous acetonitrile mobile phases. A phenyl stationary phase and aqueous acetonitrile mobile phase baseline-resolved 7 of 11 capsaicinoids, and selected ion chromatograms (LC–ESI-MS) demonstrated this was the most effective reversed-phase separation. Argentation chromatography with an alkyl or phenyl column and aqueous silver nitrate–methanol mobile phase revealed the presence of the 6-ene-8-methyl and 6-ene-9-methyl homocapsaicin isomers and the absence of 7-ene-9-methyl homocapsaicin. A mixed phenyl–cation-exchange stationary phase (charged with silver ion) enabled unique and useful separations of the capsaicinoids. 相似文献
923.
The synthesis of aldehyde intermediates suitable for the preparation of indole alkaloids of the tacamine ( 1 ) type is described. The four possible aldehydes 4–7 were prepared from methyl 5-ethylnicotinate ( 8 ) in a few simple steps using a base-catalyzed epimerization as the final step (Schemes 1 and 2). The key aldehyde 4 , which is an analogue of the important vincamine intermediate 3 (‘Oppolzer's aldehyde’), was finally converted into the indole alkaloid (±)-apotacamine ( 21 ). 相似文献
924.
Nano-sized phosphine and pyridine ligands having tetraphenylphenyl-, m-terphenyl-, poly(benzylether) moieties were synthesized. These ligands showed a remarkable effect on homogeneous transition
metal catalyzed reactions. Pd(II) complexes with tetraphenylphenyl substituted pyridine ligands show high catalytic activities
for oxidation of ketones suppressing Pd black formation and maintains the catalytic activity for a long time. Rh(I) complex
catalysts with m-terphenyl substituted phosphine ligands showed remarkable rate acceleration in the hydrosilylation of ketones. In addition,
several phosphinocalixarene ligands were synthesized and their coordination studies with Pd(II), Pt(II), Ru(II), Ir(I), and
Rh(I) metals were documented. Ir(I) and Rh(I) cationic complexes with a 1,3,5-triphosphinocalix[6]arene ligand showed dynamic
behavior with size-selective molecular recognition. 相似文献
925.
Krisztián Bogár 《Central European Journal of Chemistry》2005,3(1):63-71
(R, R)-(−)-N, N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminocobalt(II) was encapsulated into MCM-22 using the zeolite synthesis method. The
encapsulated catalyst proved to be active in the oxidation of α-methylstyrene with NaOCl with higher specific activity than
the homogeneous catalyst. At the same time, this encapsulated catalyst was completely inactive in the hydrolytic kinetic resolution
of racemic styrene oxide. This observation is in a good correlation with the assumption of the cooperative bimetallic mechanism
proposed by Annis and Jacobsen. 相似文献
926.
A simplified approach was developed to estimate the vapor pressure of pure compounds from experimental data obtained by isothermal
thermogravimetric (TG) analysis. A numerical procedure was developed to estimate the Antoine parameters of the substance by
the analysis of isothermal TG data. The results of the experimental validations carried out evidenced that at least a preliminary
estimation of vapour pressures of pure substances by the analysis of TG data is possible. The limited time and the reduced
amounts of sample required for the experimental runs make the technique attractive with respect to the conventional and more
accurate techniques for vapor pressure assessment. 相似文献
927.
A biosensor for the specific determination of hydrogen peroxide was developed using catalase (EC 1.11.1.6) in combination with a dissolved oxygen probe. Catalase was immobilized with gelatin by means of glutaraldehyde and fixed on a pretreated teflon membrane served as enzyme electrode. The electrode response was maximum when 50 mM phosphate buffer was used at pH 7.0 and at 35 degrees C. The biosensor response depends linearly on hydrogen peroxide concentration between 1.0x10(-5) and 3.0x10(-3) M with a response time of 30 s. The sensor is stable for >3 months so in this period >400 assays can be performed. 相似文献
928.
Rhodium trichloride supported on Ti-hexagonal mesoporous silica (Ti-HMS), via a bipyridyl group, is an efficient catalyst for the hydroformylation of olefins at 120 °C and 40.8 atm of CO/H2 (CO/H2=2/1). The catalyst is selective leading to high ratios of linear or branched aldehydes from functionalized olefins, and high activity in the case of propene which gave a turnover frequency of 6209 mol/mol(Rh)/h. 相似文献
929.
Ethylene diamine (EDA)/salt solvent systems can dissolve cellulose without any pretreatment. A comparison of the electrical
conductivity of different salts in EDA was made at 25 °C, and conductivity decreased in the order of KSCN>KI>NaSCN at the
same molar concentration. Among the salts tested, potassium thiocyanate (KSCN) was capable of dissolving both high molecular
weight (DP>1000) and low molecular weight (DP = 210) cellulose, and this was confirmed by polarized light microscopy. 39K and 14N NMR experiments were conducted at 70 °C as a function of cellobiose concentration with EDA/KSCN as the solvent. The results
showed that the K+ ion interacts with cellobiose more than the SCN− ion does. Recovered cellulose was studied by infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). Changes
in the FTIR absorption bands at 1,430 and 1,317 cm−1 were associated with a change in the conformation of the C-6CH2OH group. The changes in positions and/or intensities of absorption bands at 2,900, 1,163, and 8,97cm−1 were related to the breaking of hydrogen bonds in cellulose. X-ray diffraction studies revealed that cellulose, recovered
by precipitating cellulose solutions with water, underwent a polymorphic transformation from cellulose I to cellulose II. 相似文献
930.
A versatile nonaqueous emulsion polyaddition process for the one-step fabrication of spherical polyurethane nanoparticles
is presented. Three different emulsion systems were used consisting of N,N′-dimethylformamide (DMF) dispersed in n-hexane, acetonitrile dispersed in cyclohexane, and acetonitrile dispersed in tetradecane. After successful stabilization
of the emulsion systems by using a poly(isoprene)-poly(methylmethacrylate) block copolymer, the fabrication of the polyurethanes
was carried out within the dispersed polar phase. The polyurethane particles showed average diameters as small as 35 nm. Additionally,
infrared (IR) characterization revealed that the formation of any urea, which decreases the mechanical properties of the polyurethanes,
was prevented during the polyaddition. This was attributed to the anhydrous reaction conditions. Gel permeation chromatography
(GPC) analysis demonstrated the average molecular weights (M
n) of the polyurethanes to be as high as 16,500 g/mol, corresponding to conversions of 0.98. Comparable molecular weights and
conversions have not previously been achieved without the formation of urea. 相似文献