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451.
Anastasia?Ruzmaikina Zoran?Gruji?Email author 《Communications in Mathematical Physics》2004,247(3):601-611
Certain new cancellation properties in the vortex-stretching term are detected leading to new geometric criteria for preventing finite-time blow-up in the 3D Navier-Stokes equations. 相似文献
452.
[reaction: see text] The Pd-catalyzed alkynylation of various alkenyl halides and triflates with alkynylzincs proceeds well even with alkynyl derivatives containing electron-withdrawing groups. The reaction appears to be highly general. Noteworthy is that the corresponding Sonogashira reactions under various reported conditions are significantly less satisfactory in all cases performed in this study. 相似文献
453.
Phosphodiesterase production in an aqueous two-phase system by Nicotiana tabacum 1507 总被引:1,自引:0,他引:1
Studies were conducted on the production of phosphodiesterases by Nicotiana tabacum 1507 cell suspension in an aqueous two-phase system formed by adding 4% polyethylene glycol (mol wt 20,000) and 7.5% dextran
(mol wt 70,000) to the medium. The time course of growth, biosynthesis, secretion, and partitioning of phosphodiesterases
was followed in comparison with N. tabacum 1507 cultivation as a free suspension. Partitioning of phosphodiesterases took place mainly in the bottom dextran phase,
and a possibility was revealed for obtaining an enzyme preparation with high phosphodiesterase activity. 相似文献
454.
Anastasia Winkler 《Annals of Operations Research》2013,202(1):197-210
We analyze the non-preemptive assignment of a single server to two infinite-capacity retrial queues. Customers arrive at both queues according to Poisson processes. They are served on first-come-first-served basis following a cost-optimal routing policy. The customer at the head of a queue generates a Poisson stream of repeated requests for service, that is, we have a constant retrial policy. All service times are exponential, with rates depending on the queues. The costs to be minimized consist of costs per unit time that a customer spends in the system. In case of a scheduling problem that arise when no new customers arrive an explicit condition for server allocation to the first or the second queue is given. The condition presented covers all possible parameter choices. For scheduling that also considers new arrivals, we present the conditions under which server assignment to either queue 1 or queue 2 is cost-optimal. 相似文献
455.
Karioti A Skaltsa H Linden A Perozzo R Brun R Tasdemir D 《The Journal of organic chemistry》2007,72(21):8103-8106
Anthecularin (1), a minor sesquiterpene lactone with a novel ring system was isolated from Greek Anthemis auriculata (Asteraceae). Its structure was elucidated by means of NMR, HRMS, and X-ray crystallography. Anthecularin showed antitrypanosomal (IC50=10.1 microg/mL) and antiplasmodial activity (IC50=23.3 microg/mL) and inhibited two key enzymes of the plasmodial type II fatty acid biosynthesis pathway, PfFabI and PfFabG (IC50 values=14 and 28.3 microg/mL, respectively). A probable biogenesis of 1 is also proposed and discussed. 相似文献
456.
A simple and sensitive HPLC method was developed and validated for the determination of four frequently prescribed 1,4-benzodiazepines: alprazolam (ALP), bromazepam (BRZ), diazepam (DZP), and flunitrazepam (FNZ). Separation was achieved on an Inertsil C8 analytical (250 mm x 4 mm, 5 microm) column, after selective extraction of benzodiazepine drugs from biological matrices by means of SPE. Isocratic elution was performed with a mobile phase consisting of CH3COONH4, 0.05 M CH3OH, and CH3CN (33:57:10 by volume). Quantification was performed at 240 nm with mefenamic acid (6 ng/microL) as the internal standard. DSC-18 Supelco cartridges provided high absolute recoveries (81-115%). The developed method was fully validated in terms of selectivity, linearity, accuracy, precision, stability, and sensitivity. Repeatability (n = 8) and between-day precision (n = 8) revealed RSD <12%. Recoveries from biological samples ranged from 81.2 to 115%. The detection limit of the method was calculated as 3.3-10.2 ng in blood plasma and 2.6-12.6 ng in urine for 20 microL injection volume. The method was applied to spiked biological matrices. Moreover, the method was applied to real samples of urine after an oral administration. 相似文献
457.
The occurrence of pharmaceuticals and their metabolites and transformation products in the environment is becoming a matter
of concern, because these compounds, which may have adverse effects on living organisms, are extensively and increasingly
used in human and veterinary medicine and are released continuously into the environment. A variety of pharmaceuticals have
been detected in many environmental samples worldwide. Their occurrence has been reported in sewage-treatment-plant effluents,
surface water, seawater, groundwater, soil, sediment and fish. This paper provides an overview of recent scientific research
on the sources, occurrence, and fate of pharmaceuticals in water and wastewater. 相似文献
458.
Gros CP Brisach F Meristoudi A Espinosa E Guilard R Harvey PD 《Inorganic chemistry》2007,46(1):125-135
A new series of relatively flexible cofacial donor-acceptor dyads for singlet-singlet energy transfer with the corrole or etio-porphyrin free base and zinc porphyrin as the acceptor and donor, respectively, were synthesized and characterized (represented as (PMes2COx)ZnH3 (13), (PMes2CO)ZnH3 (14), and (PMes2CX)ZnH3 (15)) where (PMes2COx = [2-[5-(5,15-dimesitylcorrol-10-yl)-diphenylether-2'-yl]-13,17-diethyl-2,3,7,8,12,18-hexamethylporphyrin]), (PMes2CO = [5-[5-(5,15-dimesitylcorrol-10-yl)-dibenzofuran-4-yl]-13,17-diethyl-2,3,7,8,12,18-hexamethylporphyrin]), and (PMes2CX = [5-[5-(5,15-dimesitylcorrol-10-yl)-9,9-dimethylxanthen-4-yl)]-13,17-diethyl-2,3,7,8,12,18-hexamethylporphyrin]), respectively) along with the homobismacrocycles (DPOx)ZnH2 (17) and (DPOx)Zn2 (18) (where (DPOx = 2,2'-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]diphenylether) as comparison standards. The rate for energy transfer (kET) extracted by the measurements of fluorescence lifetimes are of the same order of magnitude as those recently reported for the rigidly held face-to-face dyads ((DPB)ZnH2 (1), (DPX)ZnH2 (2), (DPA)ZnH2 (3), (DPO)ZnH2 (4), and (DPS)ZnH2 (5) where (DPB = 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]biphenylene), (DPX = 4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene), (DPA = 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]anthracene), (DPO = 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzofuran), and (DPS = 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzothiophene), respectively), but for the first time, it is shown that the presence of a bulky group located between the acceptor and the donor moiety influences the transfer rate. The presence of perpendicular mesityl groups on the acceptor macrocycle prevents the two macrorings from interacting strongly; therefore, kET is slower. On the other hand, by rendering the rigid spacer flexible (i.e., changing the dibenzofuran rigid spacer to the flexible diphenylether assembling fragment), kET increases due to stronger intermacrocycle interactions. This study is complemented by DFT computations (B3LYP/3-21G*) as a molecular modeling tool where subtle structural features explain the changes in kET. During the course of this study, X-ray structures of 17 and 18 were investigated and exhibit a linear stacking of the bismacrocycles where intermolecular porphyrin-porphyrin interactions are observed (dinter(Zn...Zn) = 4.66 and 4.57 A, for 17 and 18, respectively). 相似文献
459.
Dimitra Kovala-Demertzi Anastasia Galani Nikolaos KourkoumelisMavroudis A. Demertzis 《Polyhedron》2007
New platinum complexes have been synthesized by the reaction of Na2PtCl4 with 2-acetylpyridine-4-cyclohexyl-thiosemicarbazone, HAc4CyclHexyl (1). The new complexes [Pt(Ac4CyclHexyl)Cl] (2) and [Pt(Ac4CyclHexyl)2] (3) have been characterized by elemental analyses and spectroscopic studies. The crystal structure of the complex [Pt(Ac4CyclHexyl)Cl] · DMF has been solved by single-crystal X-ray diffraction. The anion of Ac4CyclHexyl coordinates in a planar conformation to the central platinum(II) through the pyridyl N, azomethine N and thiolato S atoms. The crystal packing is determined by double intermolecular hydrogen interactions, π–π, Pt–C and Pt–π contacts. The cytotoxic activities of 1–3 have been evaluated for antiproliferative activity in vitro against the cells of three human cancer cell lines: MCF-7 (human breast cancer cell line), T24 (bladder cancer cell line), A-549 (non-small cell lung carcinoma) and a mouse L-929 (a fibroblast-like cell line cloned from strain L). The compounds 1–3 display IC50 values in a μM range better than that of the antitumor drug cisplatin and are considered as agents with potential antitumor activity candidates for further stages of screening in vitro and/or in vivo. 相似文献
460.
Yucelen GI Choudhury RP Vyalikh A Scheler U Beckham HW Nair S 《Journal of the American Chemical Society》2011,133(14):5397-5412
We report the identification and elucidation of the mechanistic role of molecular precursors and nanoscale (1-3 nm) intermediates with intrinsic curvature in the formation of single-walled aluminosilicate nanotubes. We characterize the structural and compositional evolution of molecular and nanoscale species over a length scale of 0.1-100 nm by electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy ((27)Al liquid-state, (27)Al and (29)Si solid-state MAS), and dynamic light scattering. Together with structural optimization of key experimentally identified species by solvated density functional theory calculations, this study reveals the existence of intermediates with bonding environments, as well as intrinsic curvature, similar to the structure of the final nanotube product. We show that "proto-nanotube-like" intermediates with inherent curvature form in aqueous synthesis solutions immediately after initial hydrolysis of reactants, disappear from the solution upon heating to 95 °C due to condensation accompanied by an abrupt pH decrease, and finally form ordered single-walled aluminosilicate nanotubes. Detailed quantitative analysis of NMR and ESI-MS spectra from the relevant aluminosilicate, aluminate, and silicate solutions reveals the presence of a variety of monomeric and polymeric aluminate and aluminosilicate species (Al(1)Si(x)-Al(13)Si(x)), such as Keggin ions [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+) and polynuclear species with a six-membered Al oxide ring unit. Our study also directly reveals the complexation of aluminate and aluminosilicate species with perchlorate species that most likely inhibit the formation of larger condensates or nontubular structures. Integration of all of our results leads to the construction of the first molecular-level mechanism of single-walled metal oxide nanotube formation, incorporating the role of monomeric and polymeric aluminosilicate species as well as larger nanoparticles. 相似文献