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31.
Sabbioni C Mandrioli R Ferranti A Bugamelli F Saracino MA Forti GC Fanali S Raggi MA 《Journal of chromatography. A》2005,1081(1):65-71
Glycyrrhizin is the main active compound of Glycyrrhiza glabra root extracts; according to recent studies, glycyrrhizin and its aglycon, glycyrrhetic acid, have interesting therapeutic properties. A new capillary electrophoretic method has been developed for the separation and quantification of glycyrrhizin, beta-glycyrrhetic acid and its isomer a-glycyrrhetic acid. Separation of the analytes was achieved in less than 3 min on a fused silica capillary, by injecting the samples at the short end of the capillary (effective length: 8.5 cm). The background electrolyte was composed of pH 10.0 carbonate buffer, methanol and ethylene glycol (80/10/10) and contained 0.4% beta-cyclodextrin; indomethacin was used as the internal standard. Diode array detection was used, with quantitative assays carried out at 254 nm. Linearity was found over the 5-200 and 2.5-100 microg mL(-1) concentration ranges for glycyrrhizin and glycyrrhetic acid, respectively. This method has been applied to the determination of the analytes in different matrices (liquorice roots and commercial confectionery products), and to the purity control of beta-glycyrrhetic acid obtained from the hydrolysis of glycyrrhizin. When analysing beta-glycyrrhetic acid and its epimer in roots, the samples were purified by means of a suitable solid-phase extraction (SPE) procedure with Oasis HLB cartridges, which granted good selectivity, eliminating matrix interference. 相似文献
32.
Giorgio Roma Aldo Ermili Alessandro Balbi Elda Massa Mario Di Braccio 《Journal of heterocyclic chemistry》1981,18(8):1619-1623
The reaction of 3-(dimethylamino)-1-oxo-1H-naphtho[2,1-b]pyran-2-carbaldehyde (Ia) with o-phenylenediamines or N-monosubstituted o-phenylenediamines in refluxing glacial acetic acid afforded the corresponding naphtho[1′,2′:5,6]pyrano[2,3-b][1,5]benzodiazepin-15-(8H)ones V in very good yields. A similar result was achieved when the reaction was carried out in refluxing pyridine, using N-monosubstituted o-phenylenediamine hydrochlorides. The isolation of a significant intermediate as well as the synthesis through a different univocal pathway confirmed the structure of the compounds V. Moreover the reaction of Ia with N-monosubstituted o-phenylenediamines in refluxing pyridine generally afforded only low yields of compounds V, sometimes together with naphtho[1′,2′:5,6]pyrano[2,3-b][1,5]benzodiazepin-15-(13H)ones VII, isomers of V. 相似文献
33.
Giorgio Parisi 《Journal of statistical physics》1980,23(1):49-82
We review the physical principles which are at the basis of recent field-theoretic computations of the critical exponents in two- and three-dimensional systems. We concentrate on those points that do not show up explicitly in the more standard-expansion: they must be discussed with care if one uses a perturbative approach at fixed space dimensions (the loop expansion). We present in detail simple computations of the critical exponents, while we summarize the results of longer and more accurate computations. 相似文献
34.
S-Adenosyl-L-homocysteine hydrolase (SAHh) inhibitors have long been used as broad-range antivirals and have been recently evaluated as an experimental therapy of filovirus infections. In response to the need for a rapid laboratory testing method that could assess antiviral potency in vivo, our group developed a capillary electrophoresis (CE) method for the determination of the S-adenosyl-L-homocysteine (SAH) to S-adenosyl-L-methionine (SAM) ratio. After chloroacetaldehyde derivatization, SAH and SAM were detected using laser-induced fluorescence detection with a HeCd laser. Separation and quantitation of both SAH and SAM in human plasma were achieved in less than 1 min. The proposed method is rapid and reliable, and could be easily applied to routine monitoring of clinical and preclinical trials subjects. 相似文献
35.
Lorenzo MalavasiPaolo Ghigna Gaetano ChiodelliGiorgio Maggi Giorgio Flor 《Journal of solid state chemistry》2002,166(1):171-176
The synthesis and structural properties of Mg1−xMn2+xO4, for 0≤x≤1 are described. Complete miscibility in the solid state exists for this system. For the material with the correct stoichiometry, i.e. MgMn2O4, the effect of temperature on the cation distribution was investigated= above 600°C the inversion degree (m) starts increasing. The electrical conductivity shows a small dependence on P(O2) which is consistent with the small oxygen non-stoichiometry determined by means of thermogravimetry. The main contribution to the transport properties arises from the inversion equilibrium. Two distinct conductivity regimes, below and above the inversion threshold, can be assumed to explain the electrical conductivity and thermoelectric power results. 相似文献
36.
Alberto Ballistreri Domenico Garozzo Mario Giuffrida Pietro Maravigna Giorgio Montaudo 《Journal of polymer science. Part A, Polymer chemistry》1986,24(2):331-346
The thermal fragmentation processes in poly-Schiff bases have been investigated by direct pyrolysis–mass spectrometry. The mass spectral data show that the thermal fragmentation occurring in the polymers under investigation is characterized by hydrogen transfer reactions. In the case of a totally aromatic poly-Schiff base (polymer I ), the thermal fragmentation process involves hydrogen transfer irom the methyne group with formation of fragments bearing nitrile and/or phenyl end groups. In the case of aromatic-aliphatic poly-Schiff bases (polymers II–IV ), the hydrogen transfer process occurs from the aliphatic methylene groups. The latter process involves a lower energy and therefore occurs at lower temperatures with respect to the totally aromatic polymer I , with formation of thermal fragments bearing olefin and/or imine end groups. Beside these fragments, several thermal fragmentation compounds are also evolved by multiple hydrogen transfer reactions. 相似文献
37.
An enantioselective addition of titanium phenylacetylide to ketones, promoted by BINOL, is described; this new enantioselective protocol gives high enantiomeric excess (up to 90% ee) with aromatic ketones using a simple procedure without pyrophoric or expensive reagents. 相似文献
38.
Pier Giorgio Righetti Barbara Barzaghi Edoardo Sarubbi Adolfo Soffientini Giovanni Cassani 《Journal of chromatography. A》1989,470(2):337-350
When analysing homogeneous preparations of recombinant pro-urokinase and urinary urokinase by isoelectric focusing (IEF) in immobilized pH gradients, an extreme charge heterogeneity was detected (at least ten major and ten minor bands in the pH range 7–10). This extensive polydispersity was not caused by different degrees of glycosylation, or by IEF artefacts, such as binding to carrier ampholytes or carbamylation by urea. A great part of this heterogeneity could be traced back to the existence of a multitude of protein molecules containing Cys residues at different oxidation levels (-SH, -S-S-, even cysteic acid). Owing to the very large number of Cys residues in pro-urokinase (24 out of a total of 411 amino acids) and to the relatively high pI of its native forms (pI 9.5–9.8; the native form is believed to contain all Cys residues as -S-S- bridges), the presence of SH or cysteic acid residues would increase the negative surface charge, as even SH groups would be extensively ionized. In pro-urokinase, part of the heterogeneity was also due to spontaneous degradation to urokinase and possibly also to cleavage into lower-molecular-mass fragments. When all these causes of heterogeneity were removed, the pI spectrum was reduced to only four, about equally intense, bands. The cause of this residual heterogeneity is unknown. 相似文献
39.
Giorgio Montaudo Concetto Puglisi Filippo Samperi 《Journal of polymer science. Part A, Polymer chemistry》1994,32(1):15-31
The chemical reactions occurring in the melt mixing of nylon6/polycarbonate (Ny6/PC) at 240°C were investigated. The reaction of equimolar Ny6/PC blends can be reconciled within the overall scheme of an exchange reaction occurring with the attack of active amino terminals on the inner carbonate groups. We have performed the synthesis of low molecular weight amino-terminated nylon 6 and the effect of the active amino terminal groups on the exchange kinetics was investigated. The exchange reaction yields sizeable amounts of copolymer, in fact after 75 min of melt mixing the (initially equimolar) blend contains 30 mol of unreacted PC and 70 mol of Ny6/PC copolymer (all the Ny6 was therefore incorporated in the copolymer). Trifluoroacetylation of nylon 6 was used to produce CHCl3-soluble Ny6/PC copolymers, that could be analyzed by NMR. The NMR analysis yielded, beside the copolymer composition, evidence of the presence of urethane units interconnecting the Ny6 and PC blocks. The amount of urethane units increased with the reaction time, indicating a reduction of the block size as a function of the extent of exchange. Our study established the structure of the products formed, provided the materials balance of the process, and investigated some salient kinetic aspects. A thermal degradation study was also performed by thermogravimetry and direct pyrolysis mass spectrometry, to identify the products formed in the thermal treatment of the blends and to investigate the possible role of the inner amide groups in the intermolecular exchange reactions occurring between Ny6 and PC. Our results prove that these reactions occur above 300°C, and that only the cleavage of carbonate groups, by means of Ny6 amino end groups, is actually occurring at 240°C. © 1994 John Wiley & Sons, Inc. 相似文献
40.
The coil/helix transition of a synthetic, branched-chain polymeric polypeptide (poly (Lys(Glu(1)-DL-Ala(3))EAK), 50-Lys residues long in the backbone, as a function of increasing molarities of methanol in solution, is here studied by both, circular dichroism (CD) and capillary zone electrophoresis. CD spectra showed that, at 75% v/v methanol, the transition from random coil to fully helical structure was obtained, in a pH 1.1 HCI solution in the presence of 20 mM NaCI. CZE studies, run in parallel, exhibited the classical unfolding to folding sigmoidal transition, with mid-point at 60% v/v methanol concentration, plateauing at ca. 80% v/v organic solvent. Surprisingly, though, such unfolding to folding transition was accompanied by an expansion, rather than a contraction, of the resulting ordered polypeptide. As the charge of the polypeptide (a pure polycation at a pH of 2.1 in CZE) was kept rigorously constant, a plot of the radius of the polymer along the sigmoidal transition clearly showed that the radius of gyration of the helical, structured polypeptide was in fact larger than that of the random coil. Such results were confirmed by molecular dynamics simulations, which indicated that the dimensions of such polypeptide, in alpha-helix configuration, were 8.5 nm (in length) and 3.2 nm (in diameter), whereas those of the corresponding random coil were 7.2 nm (in length) and 5.1 nm (length of shorter axis). It would thus appear that the randomized structure assumes the shape of a more compact object, roughly resembling a "rugby ball". 相似文献