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Exchange Mechanism (exchange + mechanism)
Selected AbstractsChemInform Abstract: Cu(II)-Azide Polymers of Cu3 and Cu6 Building Units: Synthesis, Structures and Magnetic Exchange Mechanism.CHEMINFORM, Issue 20 2010Sandip Mukherjee Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Activation of a calcium entry pathway by sodium pyrithione in the bag cell neurons of AplysiaDEVELOPMENTAL NEUROBIOLOGY, Issue 4 2004Ronald J. Knox Abstract The ability of sodium pyrithione (NaP), an agent that produces delayed neuropathy in some species, to alter neuronal physiology was accessed using ratiometric imaging of cytosolic free Ca2+ concentration ([Ca2+]i) in fura PE-filled cultured Aplysia bag cell neurons. Bath-application of NaP evoked a [Ca2+]i elevation in both somata and neurites with an EC50 of ,300 nM and a Hill coefficient of ,1. The response required the presence of external Ca2+, had an onset of 3,5 min, and generally reached a maximum within 30 min. 2-Methyl-sulfonylpyridine, a metabolite and close structural analog of NaP, did not elevate [Ca2+]i. Under whole-cell current-clamp recording, NaP produced a ,14 mV depolarization of resting membrane potential that was dependent on external Ca2+. These data suggested that NaP stimulates Ca2+ entry across the plasma membrane. To minimize the possibility that a change in cytosolic pH was the basis for NaP-induced Ca2+ entry, bag cell neuron intracellular pH was estimated with the dye 2,,7,-bis(carboxyethyl-5(6)-carboxy-fluorescein acetoxy methylester. Exposure of the neurons to NaP did not alter intracellular pH. The slow onset and sustained nature of the NaP response suggested that a cation exchange mechanism coupled either directly or indirectly to Ca2+ entry could underlie the phenomenon. However, neither ouabain, a Na+/K+ ATPase inhibitor, nor removal of extracellular Na+, which eliminates Na+/Ca2+ exchanger activity, altered the NaP-induced [Ca2+]i elevation. Finally, the possibility that NaP gates a Ca2+ -permeable ion channel in the plasma membrane was examined. NaP did not appear to activate two major forms of bag cell neuron Ca2+ -permeable ion channels, as Ca2+ entry was unaffected by inhibition of voltage-gated Ca2+ channels using nifedipine or by inhibition of a voltage-dependent, nonselective cation channel using a high concentration of tetrodotoxin. In contrast, two potential store-operated Ca2+ entry current inhibitors, SKF-96365 and Ni2+, attenuated NaP-induced Ca2+ entry. We conclude that NaP activates a slow, persistent Ca2+ influx in Aplysia bag cell neurons. © 2004 Wiley Periodicals, Inc. J Neurobiol 411,423, 2004 [source] Biphasic Resorbable Calcium Phosphate Ceramic for Bone Implants and Local Alendronate Delivery,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Shashwat S. Banerjee A novel biphasic calcium phosphate ceramic composed of tricalcium phosphate (TCP) and calcium pyrophosphate (CP) is synthesized in order to tailor the biodegradation behavior of the ceramic. The results show that biphasic TCP/CP ceramic has a strength of 62.2,±,2.1 MPa, which is superior to single-phase TCP and CP ceramics, which show strengths of 44.3,±,3.0 and 53.0,±,4.8 MPa, respectively. In addition, biphasic TCP/CP ceramic displays a controlled strength degradation from 62.2,±,2.1 to 40.5,±,1.0 MPa in stimulated body fluid over a period of 28 d. An in vitro cell materials interaction study using human fetal osteoblast cells indicates that TCP/CP ceramic is cytocompatible. TCP/CP ceramic also show a good loading capacity for alendronate. Adsorption of alendronate (AD) on the TCP/CP surface is found to proceed via ligand exchange mechanism and the in vitro release profile of AD from TCP/CP surface is characterized by an initial fast release followed by a slow and sustained release. Strong electrostatic interactions between AD groups and surface Ca2+ ions enable the slow and sustained release of AD. These results demonstrate that the newly developed biphasic ceramic, with its controlled strength degradation and drug release, shows promise for use in orthopedic and tissue engineering applications. [source] Solvent-Free Ionic Liquid Electrolytes for Mesoscopic Dye-Sensitized Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Shaik M. Zakeeruddin Abstract Ionic liquids have been identified as a new class of solvent that offers opportunities to move away from the traditional solvents. The physical-chemical properties of ionic liquids can be tuned and controlled by tailoring their structures. The typical properties of ionic liquids, such as non-volatility, electrochemical stability and high conductivity, render them attractive as electrolytes for dye-sensitized solar cells. However, the high viscosity of ionic liquids leads to mass transport limitations on the photocurrents in the solar cells at full sunlight intensity, but the contribution of a Grotthous-type exchange mechanism in these viscous electrolytes helps to alleviate these diffusion problems. This article discusses recent developments in the field of high-performance dye-sensitized solar cells with ionic liquid-based electrolytes and their characterization by electrochemical impedance analysis. [source] Hydrogen/deuterium exchange kinetics of cytochrome C: An electrospray ionization fast flow experimentISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2003Orit Geller New experiments are described in which the gas phase hydrogen/deuterium (H/D) exchange kinetics is studied for multiply-protonated cytochrome c ions with +10 to +17 charges. The experimental technique involves electrospray ionization (ESI) combined with a fast-flow method. Experimental results are presented including (1) average rate constants for H/D exchange, (2) overall decay kinetics of the reactant ion, and (3) sets of profiles for consecutive deuterium exchanges as a function of the flow rate of ND3 as the deuterating agent. The maximum number of exchanged hydrogen atoms and the exchange rate are observed to increase with increasing charge. The +13 state demonstrates special reactivity with a reactant ion decay constant of 2.5 × 10,9 cc/molecule's. Further insight into the H/D exchange mechanism is anticipated upon analysis of the data with a newly developed algorithm for extracting site-specific rate constants from profiles for H/D exchange in gas phase protonated amino acids, their clusters, and peptides. The algorithm minimizes the mutual entropy or the Kullback-Leibler information divergence between the observed concentrations and a chosen model. [source] Glutamate receptors modulate sodium-dependent and calcium-independent vitamin C bidirectional transport in cultured avian retinal cellsJOURNAL OF NEUROCHEMISTRY, Issue 2 2009Camila Cabral Portugal Abstract Vitamin C is transported in the brain by sodium vitamin C co-transporter 2 (SVCT-2) for ascorbate and glucose transporters for dehydroascorbate. Here we have studied the expression of SVCT-2 and the uptake and release of [14C] ascorbate in chick retinal cells. SVCT-2 immunoreactivity was detected in rat and chick retina, specially in amacrine cells and in cells in the ganglion cell layer. Accordingly, SVCT-2 was expressed in cultured retinal neurons, but not in glial cells. [14C] ascorbate uptake was saturable and inhibited by sulfinpyrazone or sodium-free medium, but not by treatments that inhibit dehydroascorbate transport. Glutamate-stimulated vitamin C release was not inhibited by the glutamate transport inhibitor l -,-threo-benzylaspartate, indicating that vitamin C release was not mediated by glutamate uptake. Also, ascorbate had no effect on [3H] d -aspartate release, ruling out a glutamate/ascorbate exchange mechanism. 2-Carboxy-3-carboxymethyl-4-isopropenylpyrrolidine (Kainate) or NMDA stimulated the release, effects blocked by their respective antagonists 6,7-initroquinoxaline-2,3-dione (DNQX) or (5R,2S)-(1)-5-methyl-10,11-dihydro-5H -dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801). However, DNQX, but not MK-801 or 2-amino-5-phosphonopentanoic acid (APV), blocked the stimulation by glutamate. Interestingly, DNQX prevented the stimulation by NMDA, suggesting that the effect of NMDA was mediated by glutamate release and stimulation of non-NMDA receptors. The effect of glutamate was neither dependent on external calcium nor inhibited by 1,2-bis (2-aminophenoxy) ethane-N,,N,,N,,N,,-tetraacetic acid tetrakis (acetoxy-methyl ester) (BAPTA-AM), an internal calcium chelator, but was inhibited by sulfinpyrazone or by the absence of sodium. In conclusion, retinal cells take up and release vitamin C, probably through SVCT-2, and the release can be stimulated by NMDA or non-NMDA glutamate receptors. [source] Simplified heat exchange model for semiconductor laser diodes thermal parameters extractionLASER PHYSICS LETTERS, Issue 11 2005P. S. André Abstract By investigating the heat flow mechanism in a semiconductor laser diode, we demonstrate a comprehensive technique for optical device thermal parameters extraction to be used in the prediction of the laser performance This accurate and precise heat exchange model takes into account the relevant heat exchange mechanism and mechanical considerations of the laser diode mounting. We measured the thermal response of a semiconductor laser diode attach to a substrate, deriving from those the device thermal parameters such as heat capacity and thermal conductance for the device and subtract. From the estimated values a prediction of the real laser temperature response is obtained directly from the measurements realized in the substrate. (© 2005 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Double exchange model in cubic vanadatesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006Krzysztof Wohlfeld Abstract We investigate the role of the double exchange mechanism for stability of the metallic C-type antiferromagnetic (C-AF) phase, which was observed experimentally in hole doped La1,xSrx VO3. The double exchange model treats localized electrons in xy orbitals as classical S = 1/2 spins, which interact by Hund's exchange JH with yz /zx electrons in partly filled t2g orbitals. Including strong on-site Coulomb repulsion U between t2g electrons, and using slave boson method we demonstrate that C -AF and metallic phase can be stabilized due to the specific features of the hopping in degenerate and partly filled t2g orbitals. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Peritoneal Microcirculation in Peritoneal DialysisMICROCIRCULATION, Issue 5 2001BENGT RIPPE ABSTRACT This paper deals with the peritoneal microcirculation and with peritoneal exchange occurring in peritoneal dialysis (PD). The capillary wall is a major barrier to solute and water exchange across the peritoneal membrane. There is a bimodal size-selectivity of solute transport between blood and the peritoneal cavity, through pores of radius ,40,50 Ĺ as well as through a very low number of large pores of radius ,250 Ĺ. Furthermore, during glucose-induced osmosis during PD, nearly 40% of the total osmotic water flow occurs through molecular water channels, termed "aquaporin-1." This causes an inequality between 1,, and the sieving coefficient for small solutes, which is a key feature of the "threepore model" of peritoneal transport. The peritoneal interstitium, coupled in series with the capillary walls, markedly modifies small-solute transport and makes large-solute transport asymmetric. Thus, although severely restricted in the blood-to-peritoneal direction, the absorption of large solutes from the peritoneal cavity occurs at a high clearance rate (,1 mL/min), largely independent of molecular radius. True absorption of macromolecules to the blood via lymphatics, however, seems to be occurring at a rate of ,0.2 mL/min. Several controversial issues regarding transcapillary and transperitoneal exchange mechanisms are discussed in this paper. [source] Scion genotype controls biomass allocation and root development in grafted grapevineAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 2 2010J.-P. TANDONNET Abstract Background and Aims:, Grafting is used in viticulture worldwide. Rootstocks are known to alter scion development or ,confer vigour' to varying degrees. This work examines scion/rootstock interactions in young grafted grapevines. Its aim was to determine the effects of scion and rootstock genotypes on biomass allocation within the plant. Methods and Results:, Five months after grafting, biomass allocation between the root and the shoot was measured for all the scion/rootstock combinations made between three Vitis genotypes. The scion genotype explained the highest percentage of the non-random variance for biomass allocation within the plant, including biomass allocation to the roots, i.e. it conferred differences in root vigour. In addition, we developed a double-grafted system, in which a single scion was grafted onto two rootstocks, to analyse further scion (or carbon source) effects on root development. Conclusions:, This work provides evidence of conferred root vigour by the scion which does not appear to be related to carbon supply from the shoot. The genotypes studied display varying levels of plasticity in their response to different grafting partners. Significance of the Study:, This work presents detailed analysis of biomass allocation within young grafted vines. In young grafted grapevines, the scion genotype has a major effect on most parameters of development, especially in the root. This aspect of rootstock/scion interactions should be taken into account when selecting rootstocks. A double-grafting system was developed for future research on signalling pathways and exchange mechanisms between scion and rootstock in grafted grapevine. [source] | |||||||||||||||||||