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991.
Domingos H. U. Marchetti Abel Klein J. Fernando Perez 《Journal of statistical physics》1990,60(1-2):137-166
We give a rigorous proof of power-law falloff in the Kosterlitz-Thouless phase of a two-dimensional Coulomb gas in the sense that there exists a critical inverse temperaturegb and a constant >0 such that for all> and all external charges R we have
, whereG
(x) is the two-point external charges correlation function,=dist(, Z), and
for
0$$
" align="middle" border="0">
. In the case of a hard-core or standard Coulomb gas with activityz, we may choose=(z) such that(z)24 asz0. 相似文献
992.
993.
Gustavo Von Poelhsitz André Luiz Bogado Márcio Peres de Araujo Heloisa S. Selistre-de-Araújo Javier Ellena Eduardo E. Castellano Alzir Azevedo Batista 《Polyhedron》2007
The reaction of RuCl3NO · 2H2O with stoichiometric amount of dppf, 1,1′-bis(diphenylphosphino)ferrocene, afforded the new neutral nitrosyl complex fac-[RuCl3(NO)(dppf)] which was characterized by spectroscopical, electrochemical and X-ray crystallography techniques as well as elemental analysis. The νNO band in the IR spectrum is at 1860 cm−1 (CH2Cl2 solution) and in the cyclic voltammogram an irreversible wave was observed at −1.35 V, both are characteristics of a nitrosonium (NO+) character for the coordinated NO. Additionally, preliminary in vitro antitumor activity against the MDA-MB-231 breast tumor cell line was carried out for the new complex. The initial results indicated an important activity for fac-[RuCl3(NO)(dppf)] (IC50 = 10 ± 3 μM ). The complex has a higher cytotoxicity than the precursor complex RuCl3NO · 2H2O, the free dppf ligand as well as the reference metallodrug cisplatin. 相似文献
994.
Enantiopure 2,5-dihydrofuran derivatives were prepared from (S)-glycidol through a new reaction sequence involving epoxide opening with a vinylcuprate, selenium-induced cyclization to give exclusively the 5-endo product, and regioselective selenoxide elimination. Unsaturated acyclonucleosides of Z configuration were obtained in a straightforward manner by treating 2,5-dihydrofuran with iodotrimethylsilane in the presence of silylated purinic or pyrimidinic bases. This synthetic process involves opening of the dihydrofuran ring by trimethylsilyl iodide and substitution of iodine by the nucleic base in a single reaction step. 相似文献
995.
Natalia de la Figuera Pilar Forns Sandra Fiol Fernando Albericio 《Tetrahedron letters》2005,46(42):7271-7274
Palladium acetate catalyzed C-glycosidation of peracetylated glycals with arylboronic acids in acetonitrile (CH3CN) yields the desired 1-substituted 2,3-unsaturated glycal as well as a byproduct corresponding to the ring-opened pyran, present in varying proportions depending on the reaction conditions used. The byproduct is not formed when toluene/EtOH is used as reaction solvent. 相似文献
996.
Zoltan Dekan Thomas Kremsmayr Peter Keov Mathilde Godin Ngari Teakle Leopold Dürrauer Huang Xiang Dalia Gharib Christian Bergmayr Roland Hellinger Marina Gay Marta Vilaseca Dennis Kurzbach Fernando Albericio Paul F. Alewood Christian W. Gruber Markus Muttenthaler 《Chemical science》2021,12(11):4057
Vasopressin (VP) and oxytocin (OT) are cyclic neuropeptides that regulate fundamental physiological functions via four G protein-coupled receptors, V1aR, V1bR, V2R, and OTR. Ligand development remains challenging for these receptors due to complex structure–activity relationships. Here, we investigated dimerization as a strategy for developing ligands with novel pharmacology. We regioselectively synthesised and systematically studied parallel, antiparallel and N- to C-terminal cyclized homo- and heterodimer constructs of VP, OT and dVDAVP (1-deamino-4-valine-8-d-arginine-VP). All disulfide-linked dimers, except for the head-to-tail cyclized constructs, retained nanomolar potency despite the structural implications of dimerization. Our results support a single chain interaction for receptor activation. Dimer orientation had little impact on activity, except for the dVDAVP homodimers, where an antagonist to agonist switch was observed at the V1aR. This study provides novel insights into the structural requirements of VP/OT receptor activation and spotlights dimerization as a strategy to modulate pharmacology, a concept also frequently observed in nature.Structural and pharmacological study of parallel, antiparallel and N- to C-terminal cyclized homo- and heterodimers of vasopressin and oxytocin. This study spotlights dimerization as a strategy to modulate the pharmacology of neuropeptides. 相似文献
997.
Rubin Gulaboski Carlos M. Pereira M. Natalia D. S. Cordeiro Ivan Bogeski Fernando Silva 《Journal of Solid State Electrochemistry》2005,9(6):469-474
An electrochemical method for the detection of enzymatically created anions is described that uses a thin-film electrode with decamethylferrocene as an electroactive redox probe. The enzymatic oxidation of glucose with enzyme glucose oxidase produces gluconic acid as a final product. The oxidation of decamethylferrocene dissolved in the thin-nitrobenzene film, that is spread on the working graphite electrode and submerged in the aqueous solution containing glucose and glucose oxidase, is followed by the up-take of gluconate anions from the aqueous phase to nitrobenzene. The peak currents of the square-wave voltammetric responses of that system are a linear function of the glucose concentration in the milimolar range from 0.1 mmol/L to 0.7 mmol/L (R2=0.994). 相似文献
998.
Semipermanent side-chain protection of Orn and Lys with p-nitrobenzyloxycarbonyl (pNZ) for Fmoc/tBu chemistry does not result in the unwanted removal of α-Fmoc that occurs when groups such as Alloc are used for the same application. Furthermore, pNZ can be used in conjuction with p-nitrobenzyl ester (pNB) to prepare cyclic peptides. 相似文献
999.
Urzua MD Mendizábal FJ Cabrera WJ Ríos HE 《Journal of colloid and interface science》2005,281(1):93-100
The interfacial properties of poly(maleic acid-alt-1-alkene) disodium salts at hydrocarbon/water interfaces are determined. In all the studied systems, the interfacial tension decreases markedly with the polyelectrolyte concentration as the side-chain length increases. The results of the standard free energy of adsorption, DeltaG(ads)(0), are a linear function of the number of carbon atoms in the polyelectrolyte side chain. The contribution to DeltaG(ads)(0) per mol of methylene group varies from -0.64 to -0.52 kJ/mol for the n-octane/water to n-dodecane/water interfaces. DeltaG(ads)(0) data also reveal that the adsorption process is mainly determined by adsorption efficiency. Comparatively, the adsorption effectiveness seems to play a less important role. The theoretical interaction energies calculated for the insertion of one hydrocarbon molecule into the space formed by two neighboring polyelectrolyte side chains are in good agreement with the experimental results. The latter results are consistent with van der Waals-type interactions between the hydrocarbon molecules and the polyelectrolyte side chains. 相似文献
1000.
In this work, a flow analysis-hydride generation-gas phase derivative molecular absorption-(UV) spectrophotometric method has been developed for the direct determination of antimony in aqueous and hydro-alcoholic samples. Antimony (III) from undiluted samples is directly transformed into the gaseous stibine (SbH3) form by on-line reaction with sodium tetrahydroborate (NaBH4) in acidic medium (HCl). The gaseous phase generated is separated from the liquid phase using a commercial gas-liquid separator, and swept - with the help of a carrier gas (N2) stream - into a quartz gas cell (10 cm pathlength); where the corresponding absorption spectrum is acquired in a continuous mode over the 190-300 nm wavelength range, using a conventional spectrophotometer. A derivative strategy was selected in order to avoid the strong spectral interference of the ethanol vapor on the gaseous SbH3 absorption spectrum. In this way, the peak height at 223 nm of the second order derivative spectrum appears as a clear, clean and interference free analytical signal, which allows the direct determination of antimony. The recovery values obtained from homeopathic formulations (prepared in alcoholic medium) spiked with know amounts of antimony ranged between 97.5 and 103%. The method provides a dynamic range from 0.20 to 30 mg Sb l−1. The precision (RDS), evaluated by replicate analysis (n = 5) of samples and standard solution containing between 2.5 and 15 mg Sb l−1 was in all cases lower than 1.2%. The proposed method was applied to the determination of antimony in commercial homeopathic products (“Antimonium Tartaricum”) prepared in hydro-alcoholic medium; and showed to be simple, precise, and accurate. 相似文献