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171.
Bersani D Antonioli G Lottici PP Casoli A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(10):2409-2417
Micro-Raman spectroscopy, combined with gas chromatography and ultra-violet fluorescence photography, was used to study some wall paintings in the S. Giovanni Evangelista Abbey in Parma, Italy. The restoration of some painted chapels enabled a comparison between two painters of the 16th century: Parmigianino (Girolamo Francesco Maria Mazzola, 1503-1540) and Michelangelo Anselmi (1492?-1556?). Micro-Raman spectroscopy determined the palette used by the artists, leading to the identification of different white, yellow, red, brown, green, blue and black pigments. Some pigments are evidence of later restorations. Gas chromatography combined with mass spectroscopy revealed the presence of organic binding media and enabled to distinguish between fresco and secco paintings. 相似文献
172.
Carlo Costa Antonella Bertazzo Graziella Allegri Ornella Curcuruto Pietro Traldi 《Journal of heterocyclic chemistry》1992,29(6):1641-1647
The extraction and the isolation of some alkaloids from the roots of an African plant (Securidaca Longipedunculata Fres) are reported. The structural characterization was performed by mass spectrometry. Alternative ionization methods (FAB and EI), collisionally-induced decomposition experiments and accurate mass measurements revealed the presence of elymoclavine and dehydroelymoclavine and the presence of a new ergoline alkaloid. 相似文献
173.
Roberto Antonioletti Maurizio DAuria Antonella De Mico Giovanni Piancatelli Arrigo Scettri 《Tetrahedron》1984,40(19):3805-3808
5-methylene-2(5H)-furanone derivatives are easily obtained by treatment of tertiary 2-furylcarbinols with pyridinium dichromate in dimethylformamide solution. Through this procedure, a natural product, the thiophene lactone isolated from Chamaemelum Nobile L., has been synthesized. 相似文献
174.
Franco Frau Antonella Rossi Carla Ardau Riccardo Biddau Stefania Da Pelo Davide Atzei Cristina Licheri Carla Cannas GianCarlo Capitani 《Mikrochimica acta》2005,151(3-4):189-201
Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS) have been used to refine the solid-state
speciation of As in mine waste materials and stream-bed sediments from the Baccu Locci mine area in Sardinia, Italy. The combined
use of TEM and XPS confirmed previous studies and pointed out that: (i) As is contained in plumbojarosite in substitution
of S, (ii) As-bearing Fe(III) hydroxides are represented by arsenical 2-line ferrihydrites with most Fe/As molar ratios in
the range of 1.6–3.2, (iii) scorodite often lacks long range order. Arsenatian plumbojarosite will tend to dissolve incongruently
in ferrihydrite, releasing Pb and As into water. However, Pb is fated to precipitate as Pb(OH)2 or to be adsorbed onto ferrihydrite, whereas As mobility is favoured since the adsorptive capacity of ferrihydrite for As(V)
is notably reduced under the neutral to alkaline pH conditions occurring in the Baccu Locci stream water. Arsenical ferrihydrites
will tend to be converted into goethite or hematite with time, releasing As into the water as a consequence of the notably
lower density of the adsorption sites of the crystalline Fe(III) phases. Also scorodite is relatively unstable under the Baccu
Locci system conditions, and its stability is further decreased owing to the higher solubility of the amorphous form compared
to the crystalline one. 相似文献
175.
Hydroxylamine-mediated syntheses of stereodefined acyclic polyfunctionalized δ-azido-nitriles and 5-substituted isoxazoles, bearing a differentially protected glycerol moiety, from 2-deoxysugars and glycals are described. 相似文献
176.
Leopoldo Ceraulo Paolo De Maria Antonella Fontana Sara Frascari Domenico Spinelli 《Journal of heterocyclic chemistry》1992,29(6):1657-1662
The study of the electron ionization mass spectra of 5-nitro-3-thiophenecarboxanilides 1-24 has shown peculiar effects induced by the 5-nitro group on the fragmentation of molecular ions M and the thenoyl cation a (Scheme 1). A comparison of the abundances of the important fragment ions for 5-nitro-3-thiophene-carboxanilides with those of the corresponding 3-thiophenecarboxanilides shows that the extent of C-N amide bond cleavage decreases in the former series as a consequence of the increased bond strength. The produced ion a does not eliminate carbon monoxide as 2- and 3-thenoyl cations usually do. Again this behaviour depends on the electronic effects of the nitro group which strongly destabilizes the 5-nitro-3-thienyl cation and consequently strengthens the carbon-3 carbonyl carbon bond. Recalling the behavior of the previously studied 2- and 3-thiophenecarboxanilides most of the 2′-substituted 5-nitro-3-thiophenecarboxanilides give loss of the ‘ortho’ substituent of the phenyl ring furnishing the cyclic ion g(Scheme 2). In the instance of 2′-alkyl substituted derivatives the formation of abundant ions h' by loss of 5-nitrothenoyl radical from M (Scheme 3) was observed, thus confirming the occurrence of a cryptic ‘ortho’ effect. The results are also discussed in relation to those obtained on some related benzoylanilides. 相似文献
177.
The first diastereoisomeric mixture of an inherently chiral uranyl-salophen complex was prepared using (S)-naproxen as a chiral derivatizing agent. Slow crystallization from diisopropyl ether-chloroform afforded one pure diastereoisomer in 45% yield. Kinetic studies allowed the determination of the epimerization rate. [reaction--see text] 相似文献
178.
Andrea M. Gasco Clara Cena Antonella Di Stilo Giuseppe Ermondi Claudio Medana Alberto Gasco 《Helvetica chimica acta》1996,79(7):1803-1817
The synthesis, structural characterization, and NO donor properties of a series of terfuroxan (= terfurazan trioxide) derivatives 1a–h and 2a–j are reported (Schemes 1 and 2). Structural assignments were confirmed principally by mass and 13C- and 1H-NMR spectroscopy. The extent and the initial rate of NO release in the presence of thiol cofactor was evaluated for each derivative. Vasodilator effects of all the terfuroxan derivatives were evaluated on endothelium-denuded strips of rat aorta precontracted with noradrenaline. Concentration-response curves were also evaluated in the presence of 10 m?M oxyhemoglobin (HbO2), a well known NO scavenger. The whole series displays high vasodilating potency; the most active terfuroxans ( 1a, b, g and 2i ) are 5–10 times as potent as glyceryl trinitrate taken as reference (see Table 3). The potency decrease observed in the presence of HbO2 agrees with the involvement of NO in the vasorelaxing action. The 4,3′:4′,4″ connection (series 1 ; furoxan numbering) gives rise to the most potent compounds. The conformational factors seem to play important roles in the activity. No clear relationship between physico-chemical properties of the substituents and potencies of derivative emerges. 相似文献
179.
Alunni S Del Giacco T De Maria P Fontana A Gasbarri C Ottavi L 《The Journal of organic chemistry》2004,69(18):6121-6123
Second-order rate constants have been determined for the title reactions in OH(-)/H(2)O and in OH(-)/ (CH(3)CN/H(2)O) [30/70, 60/40, and 85/15 (v/v) mixtures]. A relatively small increase in reactivity is observed for the four substrates upon increasing the percentage of CH(3)CN in the solvent mixture. The methyl activating factors (/) are also slightly affected by the solvent composition. On the other hand, the high acceleration of the reaction by methylation of the pyridine ring amounts to 10(4)-10(6) according to an E1cb mechanism. 相似文献
180.
V. Vitagliano G. Borriello C. Della Volpe O. Ortona 《Journal of solution chemistry》1986,15(10):811-826
The four diffusion coefficients for the system sucrose (0.097M)-NaCl-(0.291M)-water at 25°C have been measured by the Gouy interferometric technique. The cross terms D12 and D21 are small However, if sucrose or NaCl are chosen as component 3 instead of water, one of the cross terms becomes very large. Several runs were used to test the McDougall analysis of gravitational instability in diffusion boundaries for three component systems. Growth of convective motions at the center and at the edges of the boundary have been observed that confirm the McDougall model. 相似文献