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951.
952.
Lucia Caporaso 《Transactions of the American Mathematical Society》2003,355(9):3475-3484
We prove certain uniform versions of the Mordell Conjecture and of the Shafarevich Conjecture for curves over function fields and their rational points.
953.
Zakharova LY Semenov VE Voronin MA Valeeva FG Ibragimova AR Giniatullin RKh Chernova AV Kharlamov SV Kudryavtseva LA Latypov SK Reznik VS Konovalov AI 《The journal of physical chemistry. B》2007,111(51):14152-14162
New amphiphilic pyrimidinic macrocycles (APMs) with two (APM-1) and three (APM-2) decyl tails have been synthesized by quaternization of the bridged N. Complex examination of the APM-based systems with the help of tensiometry, conductometry, dynamic light scattering, and UV and NMR spectroscopy provides evidence for their aggregation. Calculations based on surface tension isotherms and on packing parameter considerations make it possible to assume a lamellar packing of macrocycles when aggregating. Marked differences in the aggregation behavior of APM-1 and APM-2 have been found. The additives of polyethylenimine (PEI) exert little influence on the critical micelle concentration (cmc) of APM-1, while in the APM-2/PEI systems there occurs a pronounced decrease in the cmc and also a ca. 2-fold decrease in the surface area per molecule. The APM-based assemblies are explored as nanoreactors for the hydrolysis of O-alkyl O-p-nitrophenyl (chloromethyl)phosphonates (alkyl = ethyl, hexyl). The kinetic study reveals a minor rate effect of the APM-1-based systems. In the APM-2-based systems an acceleration of the hydrolysis of both phosphonates occurs as compared to the uncatalyzed process. Within the APM-2 --> APM-2/PEI --> APM-2/PEI/La(III) series, due to the cooperative contributions of the supramolecular, polymer, and homogeneous catalysis, an increase in the catalytic effect is observed from 30 times to 3 orders of magnitude as compared to that of the basic hydrolysis of the substrates. 相似文献
954.
Giordano L Coletta W Rapisarda P Donati MB Rotilio D 《Journal of separation science》2007,30(18):3127-3136
Blood orange juice has a high content in anthocyanins, especially represented by delphinidin-3-glucoside (D3G), cyanidin-3-glucoside (C3G) and cyanidin-3-(6-malonylglucoside) (CMG). An LC-MS/MS method for the simultaneous determination of D3G and C3G in human plasma and urine was developed and validated. After sample preparation by SPE, chromatographic separation was performed with an RP-C(18) column, using a water/methanol linear gradient. The quantitation of target compounds was determined by multiple reaction monitoring (MRM) mode, using ESI. The method showed good selectivity, sensitivity (LOD = 0.05 and 0.10 ng/mL for C3G in plasma and urine, respectively; LOD = 0.10 ng/mL for D3G in plasma and urine), linearity (0.20-200 ng/mL; r >or= 0.998), intra- and interday precision and accuracy (相似文献
955.
Saggioro D Rigobello MP Paloschi L Folda A Moggach SA Parsons S Ronconi L Fregona D Bindoli A 《Chemistry & biology》2007,14(10):1128-1139
Although gold compounds are now recognized as promising anticancer agents, so far only gold(I) derivatives have been investigated for this purpose, whereas the use of gold(III) complexes has been hampered by their poor stability under physiological conditions. We have therefore carried out studies on selected gold(III) anticancer agents, showing enhanced stability due to the presence of chelating dithiocarbamato ligands. We found that they induce cancer cell death through both apoptotic and nonapoptotic mechanisms. They also inhibit thioredoxin reductase activity, generate free radicals, modify some mitochondrial functions, and increase ERK1/2 phosphorylation. Based on our results, we propose and discuss a working model suggesting that deregulation of the thioredoxin reductase/thioredoxin redox system is a major mechanism involved in the anticancer activity of the investigated gold(III)-dithiocarbamato complexes. 相似文献
956.
A series of rodlike ruthenium(II)-rhodium(III) polypyridine dyads based on modular oligo-p-phenylene bridges, of the general formula [(Me2phen)2Ru-bpy-(ph)n-bpy-Rh(Me2bpy)]5+ (Me2phen=4,7-dimethyl-1,10-phenanthroline; bpy=2,2'-bipyridine; ph=1,4-phenylene; n=1-3), have been synthesized and their photophysical properties investigated. The dyad [(Me2bpy)2Ru-bpy-(ph)3'-bpy-Rh(Me2bpy)]5+ with the central phenylene unit bearing two hexyl chains has also been studied. The metal-to-metal distance reaches 24 A for the longest (n=3) spacer in the series. For all of the dyads in a room-temperature CH3CN solution, quenching of the typical metal-to-ligand charge-transfer luminescence of the Ru-based chromophoric unit is observed, indicating that an efficient intramolecular photoinduced electron transfer from the excited Ru moiety to the Rh-based unit takes place. The rate constants for the electron-transfer process have been determined by time-resolved emission and absorption spectroscopy in the nanosecond and picosecond time scale. An exponential dependence of experimental transfer rates on the bridge length is observed, consistent with a superexchange mechanism. An attenuation factor beta of 0.65 A(-1) is determined, in line with the behavior of other systems containing oligo-p-phenylene spacers. Interestingly, for n=3, the presence/absence of hexyl substituents in the central p-phenylene ring causes a 10-fold difference in the rates between otherwise identical dyads. This comparison highlights the importance of the twist angle between adjacent spacers on the overall through-bond donor-acceptor coupling. 相似文献
957.
Baraldi A Vesselli E Bianchettin L Comelli G Lizzit S Petaccia L de Gironcoli S Locatelli A Mentes TO Aballe L Weissenrieder J Andersen JN 《The Journal of chemical physics》2007,127(16):164702
The (1 X 1) --> quasihexagonal (HEX) phase transition on a clean Pt(100) surface was investigated by monitoring the time evolution of the Pt4f(72) core level photoemission spectra. The spectral component originating from the atoms forming the (1x1) metastable unreconstructed surface was found at -570+/-20 meV with respect to the bulk peak. Ab initio calculations based on density functional theory confirmed the experimental assignment. At temperatures above 370 K, the (1 X 1) phase irreversibly reverts to the more stable HEX phase, characterized by a surface core level shifted component at -185 +/ -40 meV. By analyzing the intensity evolution of the core level components, measured at different temperatures in the range of 393 - 475 K, we determined the activation energy of the phase transformation, E = 0.76 +/- 0.04 eV. This value is considerably lower than the one previously determined by means of low energy electron diffraction. Possible reasons for this discrepancy are discussed. 相似文献
958.
Clare E. Gutteridge Marshall M. Hoffman Apurba K. Bhattacharjee Lucia Gerena 《Journal of heterocyclic chemistry》2007,44(3):633-637
959.
Zanardi F Sartori A Curti C Battistini L Rassu G Nicastro G Casiraghi G 《The Journal of organic chemistry》2007,72(5):1814-1817
A short, practical synthesis of novel, unsymmetrical 4,5'-bis-proline compounds has been achieved, highlighted by the application of an unprecedented samarium diiodide-driven regio- and diastereocontrolled reductive dimerization of N-acyloxyiminium ions generated from readily available 2-methoxy-5-silyloxymethyl-N-Boc pyrrolidines. The title proline dimers proved to be pertinent metal-free catalysts in aldol and Mannich reactions. 相似文献
960.
Lucia Mutihac Radu Mutihac 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(1-2):177-181
The extractability together with the transport through liquid membrane of some amino acid methylesters by using p-tert-butylcalix[4]arene as extractant or carrier was studied. In this context, p-tert-butylcalix[n]arenes (n = 6, 8) were found to act as useful carriers or extractant reagents for l-tryptophan methylester and l-tyrosine methylester. The calix[n]arene derivatives used in experiments extracted amino acids methylesters from the aqueous phase into chloroformic phase in
the presence of tropaeolin 00 ([4(4′-anilinophenylazo)benzenesulphonic acid]) as counterion at
. The extraction and the transport depend on the structure of calixarenes, the structure of amino acids, the pH, and the nature
of anion used as ion pair for cation-receptor complexes. The properties of solvent involved in liquid membrane play an important
role in membrane stability and also in selecting membrane systems. The results demonstrated that the inclusion properties
of the investigated hosts are correlated with their structural properties and also they suggest further possibilities for
optimal separation of amino acids derivatives. 相似文献