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141.
Marina DellaGreca Antonio FiorentinoMarina Isidori Lucio PreviteraFabio Temussi Armando Zarrelli 《Tetrahedron》2003,59(26):4821-4825
Investigation of the ethyl acetate extract of Juncus acutus rhizomes revealed seven benzocoumarins, probably derived from oxidation of phenanthrenes already isolated from the plant. The structures were determined by means of spectroscopic methods. The anti-algal activity of the isolated compounds tested on the green alga Pseudokirchneriella subcapitata are reported here. 相似文献
142.
143.
We have studied theoretically the partition equilibrium of a cationic drug between an electrolyte solution and a membrane with pH-dependent fixed charges using an extended Donnan formalism. The aqueous solution within the fixed charge membrane is assumed to be in equilibrium with an external aqueous solution containing six ionic species: the cationic drug (DH(+)), the salt cations (Na(+) and Ca(2+)), the salt anion (Cl(-)), and the hydrogen and hydroxide ions. In addition to these mobile species, the membrane solution may also contain four fixed species attached to the membrane chains: strongly acid sulfonic groups (SO(3)(-)), weakly acid carboxylic groups in dissociated (COO(-)) and neutral (COOH) forms, and positively charged groups (COO...Ca(+)) resulting from Ca(2+) binding to dissociated weakly acid groups. The ionization state of the weak electrolyte groups attached to the membrane chains is analyzed as a function of the local pH, salt concentration, and drug concentration in the membrane solution, and particular attention is paid to the effects of the Ca(2+) binding to the negatively charged membrane fixed groups. The lipophilicity of the drug is simulated by the chemical partition coefficient between the membrane and external solutions giving the tendency of the drug to enter the membrane solution due to hydrophobic interactions. Comparison of the theoretical results with available experimental data allows us to explain qualitatively the effects that the pH, salt concentration, drug concentration, membrane fixed charge concentration, and Ca(2+) binding exert on the ionic drug equilibrium. The role of the interfacial (Donnan) electric potential difference between the membrane and the external solutions on this ionic drug equilibrium is emphasized throughout the paper. 相似文献
144.
Antonio Cnovas Jesús Fonrodona Juan-Julio Bonet Marie Claire Brians Jos Luis Brians 《Helvetica chimica acta》1980,63(8):2380-2389
The UV. irradiation of 17 β-hydroxy-2-aza-4-androsten-3-one (1) , N-methyl-17 β-hydroxy-2-aza-4-androsten-3-one (3) , 17 β-hydroxy-4-aza-5 β-androst-1-en-3-one (2) and N-methyl-17 β-hydroxy-4-aza-5 β-androst-1-en-3-one (4) , gives rise to 1,10-seco (from 1 and 3 ) and 5, 10-seco (from 2 and 4 ) steroids. 相似文献
145.
Molecularly imprinted polymers (MIPs) are tailor-made synthetic polymers with a predetermined selectivity for a given analyte, or group of structurally related compounds, that make them ideal materials for use as stationary phases in affinity chromatography. However, extensive peak broadening and tailing, especially of the more retained compound (normally the template) are often observed. Thus, huge efforts have been made during recent years to use MIPs in capillary electrochromatography, which is inherently a more efficient chromatographic technique than conventional HPLC. Accordingly, this paper gives an overview of the attempts carried out in the recent past to improve the chromatographic performance of MIPs in capillary electrochromatography as well as more recent applications. It is concluded that MIPs are very promising materials for use as selective stationary phases in CEC. 相似文献
146.
Andreoli R Manini P Poli D Bergamaschi E Mutti A Niessen WM 《Analytical and bioanalytical chemistry》2004,378(4):987-994
A new and simple method for the determination of fat-soluble vitamins (retinol, alpha-tocopherol, and beta-carotene) in human serum was developed and validated by using liquid chromatography-tandem mass spectrometry with atmospheric pressure chemical ionization (LC-APCI-MS-MS). Different solvent mixtures were tested to obtain deproteinization and extraction of the analytes from the matrix. As a result, a volume of 240 microL of a 1:1 (v/v) ethanol/ethyl acetate mixture added to 60 microL of serum was found to be suitable for both protein precipitation and antioxidants solubilization, giving the best recovery for all three analytes. Deproteinized samples (20 microL) were injected after dilution, without the need for concentration or evaporation to dryness and reconstruction of the sample. Vitamins were separated on a C-8 column using a 95:5 (v/v) methanol/dichloromethane mixture and ionized in the positive-ion mode; detection was performed in the selected-reaction monitoring mode. Linearity of the LC-APCI-MS-MS method was established over 5 orders of magnitude for retinol and alpha-tocopherol, whereas in the case of beta-carotene it was limited to 4 orders. Lower limits of quantitation were 1.7, 2.3, and 4.1 nM for retinol, alpha-tocopherol, and beta-carotene, respectively. Serum concentrations of retinol, alpha-tocopherol, and alpha+beta-carotene determined in a group of healthy volunteers were 2.48, 38.07, and 0.50 microM, respectively, in samples collected in winter ( n=122) and 2.69, 45.88, and 0.90 microM during summer ( n=66). 相似文献
147.
148.
Let X be a complex projective manifold and AX a non-singular hypersurface which is an ample divisor having characteristic cycles Ai non-singular in every dimension i0. The pairs (X,A) such that g(A1)=h1,0 (X) are characterized. 相似文献
149.
Photolysis of acetonitrile solutions of Cp*Ir(R2dtc)(N3) [Cp* = eta5-C5Me5, R2dtc = S2CNR2; R = Me (1) or Et (1')] at temperatures below 0 degrees C afford five-coordinate complexes Cp*Ir{NSC(NR2)S} (2 or 2'), where a nitrogen atom has been inserted into one of the Ir-S bonds. In solution, complex 2 thermally convert to the azaethene-1,2-dithiolate complex, Cp*Ir[SN=C(NMe2)S] (3), which could be crystallized as the corresponding dimer, {Cp*Ir[mu-SN=C(NMe2)S-kappa3S:S,S']}2 (4). As a result, a nitrogen atom that originated in the azide ligand is transferred into a C-S bond of the dithiocarbamate. 相似文献
150.
Letizia JA Facchetti A Stern CL Ratner MA Marks TJ 《Journal of the American Chemical Society》2005,127(39):13476-13477
New carbonyl-functionalized quaterthiophenes, 5,5' '-diperfluorophenylcarbonyl-2,2':5',2' ':5' ',2' '-quaterthiophene [DFCO-4T], 5,5' '-diphenyl-2,2':5',2' ':5' ',2' '-quaterthiophene [DPCO-4T], and a polymer having the same basic motif as DFCO-4T, poly{1,4-bis[(3'-n-octyl-2,2'-dithiophene)carbonyl]-2,3,5,6-tetrafluorobenzene} [P(COFCO-4T)], have been synthesized, characterized, and the crystal structures of the molecules determined. Field-effect transistors fabricated with vapor-deposited and solution-cast films of DFCO-4T exhibit very high Ion:Ioff current ratios (up to 108) and electron mobilities up to approximately 0.51 and approximately 0.25 cm2.V-1.s-1, respectively. Solution-cast blends of P(COFCO-4T) and DFCO-4T (1:1 weight ratio) exhibit an electron mobility of approximately 0.01 cm2.V-1.s-1 (Ion:Ioff = 104). 相似文献