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Dynamic Equilibrium (dynamic + equilibrium)
Terms modified by Dynamic Equilibrium Selected AbstractsDynamic Equilibria in Solvent-Mediated Anion, Cation and Ligand Exchange in Transition-Metal Coordination Polymers: Solid-State Transfer or Recrystallisation?CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2009Xianjin Cui Abstract The solution properties of a series of transition-metal,ligand coordination polymers [ML(X)n], [M=AgI, ZnII, HgII and CdII; L=4,4,-bipyridine (4,4,-bipy), pyrazine (pyz), 3,4,-bipyridine (3,4,-bipy), 4-(10-(pyridin-4-yl)anthracen-9-yl)pyridine (anbp); X=NO3,, CH3COO,, CF3SO3,, Cl,, BF4,; n=1 or 2] in the presence of competing anions, metal cations and ligands have been investigated systematically. Providing that the solubility of the starting complex is sufficiently high, all the components of the coordination polymer, namely the anion, the cation and the ligand, can be exchanged on contact with a solution phase of a competing component. The solubility of coordination polymers is a key factor in the analysis of their reactivity and this solubility depends strongly on the physical properties of the solvent and on its ability to bind metal cations constituting the backbone of the coordination polymer. The degree of reversibility of these solvent-induced anion-exchange transformations is determined by the ratio of the solubility product constants for the starting and resultant complexes, which in turn depend upon the choice of solvent and the temperature. The extent of anion exchange is controlled effectively by the ratio of the concentrations of incoming ions to outgoing ions in the liquid phase and the solvation of various constituent components comprising the coordination polymer. These observations can be rationalised in terms of a dynamic equilibrium of ion exchange reactions coupled with Ostwald ripening of crystalline products. The single-crystal X-ray structures of [Ag(pyz)ClO4], (1), {[Ag(4,4,-bipy)(CF3SO3)],CH3CN}, (2), {[Ag(4,4,-bipy)(CH3CN)]ClO4, 0.5,CH3CN}, (3), metal-free anbp (4), [Ag(anbp)NO3(H2O)], (5), {[Cd(4,4,-bipy)2(H2O)2](NO3)2,4,H2O}, (6) and {[Zn(4,4,-bipy)SO4(H2O)3] ,2,H2O}, (7) are reported. [source] Disulfides, Imines, and Metal Coordination within a Single System: Interplay between Three Dynamic EquilibriaCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2007Rupam Abstract We report a system in which three distinct dynamic linkages, disulfide (SS), imine (CN), and coordinative (N,metal) bonds were shown to be capable of simultaneous reversible exchange. The "disulfide layer" of the system under study consists of two homo-disulfides, bis(4-aminophenyl) disulfide 1 and bis(4-methoxyphenyl) disulfide 2 that equilibrate in the presence of catalytic amount of triethylamine to favor the formation of a hetero-disulfide product, 4-aminophenyl-4,-methoxyphenyl disulfide 3. The addition of 2-formylpyridine and a metal salt strongly perturbed this 1+2,3 equilibrium through the formation of metal complexes incorporating disulfide 1 as a subcomponent. CuI perturbed the equilibrium by a factor of 3.3, and FeII by a factor of 179, in both cases in favor of the homo-disulfides. The disulfide equilibrium could be further modified, following metal-complex formation, by coordinative (transmetallation: substitution of FeII for CuI) or covalent (imine exchange: the substitution of one amine residue for another) exchange. Thus, although the three kinds of dynamic linkages were demonstrated to be mutually compatible, changes at one kind of linkage could be used to predictably perturb an equilibrium involving another. [source] Memory Effects in Palladium-Catalyzed Allylic Alkylations of 2-Cyclohexen-1-yl AcetateADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17-18 2007Nina Svensen Abstract The objective of this work was to characterize the enantiospecificity of the allylic alkylation of enantioenriched 2-cyclohexen-1-yl acetate with the enolate ion of dimethyl malonate catalyzed by unsymmetrical palladium catalysts. The precatalysts employed were (,3 -allyl)PdLCl, where L is a monophosphine ligand [PPh3, PCy3, P(2-BiPh)Cy2, or P(t- Bu)3], all of which afforded enantiospecificity to some extent (5,47,%). Quantum mechanical calculations show that, theoretically, the enantiospecificity should be high due to a preference for the "trans to P" transition state in both formation of the ,3 -allyl intermediate and nucleophilic attack. However, the observed enantiospecificity is relatively low due to isomerization of the ,3 -allyl intermediate and/or dynamic equilibria between the catalytically active (,3 -allyl)PdLCl species and [(,3 -allyl)PdL2]+ or [(,3 -allyl)PdCl]2. It was also observed experimentally that increasing the bulk of the phosphine inhibits formation of the [(,3 -allyl)PdL2]+ complexes, significantly increasing the observed enantiospecificity for some of the ligands. [source] FROM EXOGENOUS TO ENDOGENOUS ECONOMIC NETWORKS: INTERNET APPLICATIONSJOURNAL OF ECONOMIC SURVEYS, Issue 5 2006Alessio D'Ignazio Abstract Economic agents' behaviour is affected by their position in a network, either exogenous or endogenous, in which they interact with a sub-set of neighbours only. The network's links, which may be generated by vertical and/or horizontal relations, or by more complex morphologies, may explain the transition between dynamic equilibria and the instability of economic aggregates. Moreover, networks shape strategic interaction among agents by determining their strategies; the problem of access and interconnection, particularly relevant in the Internet, is perhaps the best example. A two-way feedback between strategies and network structures arises instead when links are endogenous: those features are clearly shown in the mechanism underlying the formation of peering links and R & D networks. [source] Novel Molecular Building Blocks Based on the Boradiazaindacene Chromophore: Applications in Fluorescent Metallosupramolecular Coordination PolymersCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2009Ö. Altan Bozdemir Dr. Abstract Bright polymers: Fluorescent coordination polymers made up of versatile functionalized bodipy (boron-dipyrrin) chromophore building blocks, such as that depicted, are described. Polymerization is signaled by changes in fluorescence emission intensity and shifts in peak emission wavelengths. We designed and synthesized novel boradiazaindacene (Bodipy) derivatives that are appropriately functionalized for metal-ion-mediated supramolecular polymerization. Thus, ligands for 2-terpyridyl-, 2,6-terpyridyl-, and bipyridyl-functionalized Bodipy dyes were synthesized through Sonogashira couplings. These fluorescent building blocks are responsive to metal ions in a stoichiometry-dependent manner. Octahedral coordinating metal ions such as ZnII result in polymerization at a stoichiometry corresponding to two terpyridyl ligands to one ZnII ion. However, at increased metal ion concentrations, the dynamic equilibria are re-established in such a way that the monomeric metal complex dominates. The position of equilibria can easily be monitored by 1H,NMR and fluorescence spectroscopies. As expected, although open-shell FeII ions form similar complex structures, these cations quench the fluorescence emission of all four functionalized Bodipy ligands. Bu çal,,mada, metal iyonlar, arac,l,,,yla supramoleküler polimerizasyon için uygun ,ekilde fonksiyonland,r,lm,, yeni boradiazaindasen (Bodipy) türevleri tasarlanm,, ve sentezlenmi,tir. Bu amaçla, ligand olarak Sonogashira reaksiyonu ile 2- ve 2,6-terpiridil ve bipiridil gruplar,n, içeren Bodipy boyarmaddeleri sentezlenmi,tir. Bu floresan yap, bloklar, stokiyometriye ba,l, bir biçimde metal iyonlar,na duyarl,l,k gösterirler. ZnIIgibi oktahedral koordinasyon e,ilimi olan metal iyonlar,, iki terpiridil ligand,na bir ZnIIiyonu tekabül edecek bir stokiyometride polimerizasyona yol açmaktad,rlar. Bununla beraber, yüksek metal iyonu deri,imlerinde monomerik metal kompleksinin bask,n olaca,, bir biçimde, dinamik dengeler yeniden kurulmaktad,r. Bu dengelerin pozisyonu1H,NMR ve fluoresans spektroskopileriyle kolayl,kla izlenebilmektedir. Beklenildi,i gibi, benzer kompleks yap,lar olu,turmas,na ra,men FeIIiyonu, sentezlenen tüm fonksiyonalize Bodipy ligandlar,n,n emisyonlar,n, sönümlendirmektedir. [source] Long-term landscape evolution: linking tectonics and surface processesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2007Paul Bishop Abstract Research in landscape evolution over millions to tens of millions of years slowed considerably in the mid-20th century, when Davisian and other approaches to geomorphology were replaced by functional, morphometric and ultimately process-based approaches. Hack's scheme of dynamic equilibrium in landscape evolution was perhaps the major theoretical contribution to long-term landscape evolution between the 1950s and about 1990, but it essentially ,looked back' to Davis for its springboard to a viewpoint contrary to that of Davis, as did less widely known schemes, such as Crickmay's hypothesis of unequal activity. Since about 1990, the field of long-term landscape evolution has blossomed again, stimulated by the plate tectonics revolution and its re-forging of the link between tectonics and topography, and by the development of numerical models that explore the links between tectonic processes and surface processes. This numerical modelling of landscape evolution has been built around formulation of bedrock river processes and slope processes, and has mostly focused on high-elevation passive continental margins and convergent zones; these models now routinely include flexural and denudational isostasy. Major breakthroughs in analytical and geochronological techniques have been of profound relevance to all of the above. Low-temperature thermochronology, and in particular apatite fission track analysis and (U,Th)/He analysis in apatite, have enabled rates of rock uplift and denudational exhumation from relatively shallow crustal depths (up to about 4 km) to be determined directly from, in effect, rock hand specimens. In a few situations, (U,Th)/He analysis has been used to determine the antiquity of major, long-wavelength topography. Cosmogenic isotope analysis has enabled the determination of the ,ages' of bedrock and sedimentary surfaces, and/or the rates of denudation of these surfaces. These latter advances represent in some ways a ,holy grail' in geomorphology in that they enable determination of ,dates and rates' of geomorphological processes directly from rock surfaces. The increasing availability of analytical techniques such as cosmogenic isotope analysis should mean that much larger data sets become possible and lead to more sophisticated analyses, such as probability density functions (PDFs) of cosmogenic ages and even of cosmogenic isotope concentrations (CICs). PDFs of isotope concentrations must be a function of catchment area geomorphology (including tectonics) and it is at least theoretically possible to infer aspects of source area geomorphology and geomorphological processes from PDFs of CICs in sediments (,detrital CICs'). Thus it may be possible to use PDFs of detrital CICs in basin sediments as a tool to infer aspects of the sediments' source area geomorphology and tectonics, complementing the standard sedimentological textural and compositional approaches to such issues. One of the most stimulating of recent conceptual advances has followed the considerations of the relationships between tectonics, climate and surface processes and especially the recognition of the importance of denudational isostasy in driving rock uplift (i.e. in driving tectonics and crustal processes). Attention has been focused very directly on surface processes and on the ways in which they may ,drive' rock uplift and thus even influence sub-surface crustal conditions, such as pressure and temperature. Consequently, the broader geoscience communities are looking to geomorphologists to provide more detailed information on rates and processes of bedrock channel incision, as well as on catchment responses to such bedrock channel processes. More sophisticated numerical models of processes in bedrock channels and on their flanking hillslopes are required. In current numerical models of long-term evolution of hillslopes and interfluves, for example, the simple dependency on slope of both the fluvial and hillslope components of these models means that a Davisian-type of landscape evolution characterized by slope lowering is inevitably ,confirmed' by the models. In numerical modelling, the next advances will require better parameterized algorithms for hillslope processes, and more sophisticated formulations of bedrock channel incision processes, incorporating, for example, the effects of sediment shielding of the bed. Such increasing sophistication must be matched by careful assessment and testing of model outputs using pre-established criteria and tests. Confirmation by these more sophisticated Davisian-type numerical models of slope lowering under conditions of tectonic stability (no active rock uplift), and of constant slope angle and steady-state landscape under conditions of ongoing rock uplift, will indicate that the Davis and Hack models are not mutually exclusive. A Hack-type model (or a variant of it, incorporating slope adjustment to rock strength rather than to regolith strength) will apply to active settings where there is sufficient stream power and/or sediment flux for channels to incise at the rate of rock uplift. Post-orogenic settings of decreased (or zero) active rock uplift would be characterized by a Davisian scheme of declining slope angles and non-steady-state (or transient) landscapes. Such post-orogenic landscapes deserve much more attention than they have received of late, not least because the intriguing questions they pose about the preservation of ancient landscapes were hinted at in passing in the 1960s and have recently re-surfaced. As we begin to ask again some of the grand questions that lay at the heart of geomorphology in its earliest days, large-scale geomorphology is on the threshold of another ,golden' era to match that of the first half of the 20th century, when cyclical approaches underpinned virtually all geomorphological work. Copyright © 2007 John Wiley & Sons, Ltd. [source] Synthesis, Structure and Reactivity of Homo- and Heterobimetallic Complexes of the General Formula [Cp*Ru(,-Cl)3ML] [LM = (arene)Ru, Cp*Rh, Cp*Ir]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2006Laurent Quebatte Abstract The homo- and heterobimetallic complexes [Cp*Ru(,-Cl)3ML] [LM = (C6H6)Ru, (cymene)Ru, (1,3,5-C6H3iPr3)Ru, Cp*Rh, Cp*Ir] were prepared by reaction of [Cp*Ru(,-OMe)]2 with Me3SiCl and subsequent addition of [LMCl2]2. The complexes [Cp*Ru(,-Cl)3Ru(cymene)] and [Cp*Ru(,-Cl)3IrCp*] were characterized by single-crystal X-ray analyses. In crossover experiments with [Cp*Rh(,-Cl)3RuCl(PPh3)2] and [Cp*Ru(,-Cl)3Ru(1,3,5-C6H3iPr3)] in CD2Cl2, a dynamic equilibrium with the complexes [Cp*Rh(,-Cl)3RuCp*] and [(1,3,5-C6H3iPr3)Ru(,-Cl)3RuCl(PPh3)2] was rapidly established, demonstrating the kinetic lability of the triple chloro bridge. Upon reaction of [Cp*Rh(,-Cl)3RuCp*] with benzene, the ionic complex [Cp*Ru(C6H6)][Cp*RhCl3] was formed, which was characterized by X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Characterization of 1H NMR detectable mobile lipids in cells from human adenocarcinomasFEBS JOURNAL, Issue 5 2009Anna Maria Luciani Magnetic resonance spectroscopy studies are often carried out to provide metabolic information on tumour cell metabolism, aiming for increased knowledge for use in anti-cancer treatments. Accordingly, the presence of intense lipid signals in tumour cells has been the subject of many studies aiming to obtain further insight on the reaction of cancer cells to external agents that eventually cause cell death. The present study explored the relationship between changes in neutral lipid signals during cell growth and after irradiation with gamma rays to provide arrest in cell cycle and cell death. Two cell lines from human tumours were used that were differently prone to apoptosis following irradiation. A sub-G1 peak was present only in the radiosensitive HeLa cells. Different patterns of neutral lipids changes were observed in spectra from intact cells, either during unperturbed cell growth in culture or after radiation-induced growth arrest. The intensities of triglyceride signals in the spectra from extracted total lipids changed concurrently. The increase in lipid peak intensities did not correlate with the apoptotic fate. Modelling to fit the experimental data revealed a dynamic equilibrium between the production and depletion of neutral lipids. This is observed for the first time in cells that are different from adipocytes. [source] Fire, flow and dynamic equilibrium in stream macroinvertebrate communitiesFRESHWATER BIOLOGY, Issue 2 2010ROBERT S. ARKLE Summary 1. The complex effects of disturbances on ecological communities can be further complicated by subsequent perturbations within an ecosystem. We investigated how wildfire interacts with annual variations in peak streamflow to affect the stability of stream macroinvertebrate communities in a central Idaho wilderness, USA. We conducted a 4-year retrospective analysis of unburned (n = 7) and burned (n = 6) catchments, using changes in reflectance values (,NBR) from satellite imagery to quantify the percentage of each catchment's riparian and upland vegetation that burned at high and low severity. 2. For this wildland fire complex, increasing riparian burn severity and extent were associated with greater year-to-year variation, rather than a perennial increase, in sediment loads, organic debris, large woody debris (LWD) and undercut bank structure. Temporal changes in these variables were correlated with yearly peak flow in burned catchments but not in unburned reference catchments, indicating that an interaction between fire and flow can result in decreased habitat stability in burned catchments. 3. Streams in more severely burned catchments exhibited increasingly dynamic macroinvertebrate communities and did not show increased similarity to reference streams over time. Annual variability in macroinvertebrates was attributed, predominantly, to the changing influence of sediment, LWD, riparian cover and organic debris, as quantities of these habitat components fluctuated annually depending on burn severity and annual peak streamflows. 4. These analyses suggest that interactions among fire, flow and stream habitat may increase inter-annual habitat variability and macroinvertebrate community dynamics for a duration approaching the length of the historic fire return interval of the study area. [source] Quantifying carbon sequestration as a result of soil erosion and deposition: retrospective assessment using caesium-137 and carbon inventoriesGLOBAL CHANGE BIOLOGY, Issue 12 2007TIMOTHY ANDREW QUINE Abstract The role of soil erosion in the global carbon cycle remains a contested subject. A new approach to the retrospective derivation of erosion-induced quantitative fluxes of carbon between soil and atmosphere is presented and applied. The approach is based on the premise that soil redistribution perturbs the carbon cycle by driving disequilibrium between soil carbon content and input. This perturbation is examined by establishing the difference between measured carbon inventories and the inventories that would be found if input and content were in dynamic equilibrium. The carbon inventory of a profile in dynamic equilibrium is simulated by allowing lateral and vertical redistribution of carbon but treating all other profile inputs as equal to outputs. Caesium-137 is used to derive rates of vertical and lateral soil redistribution. Both point and field-scale estimates of carbon exchange with the atmosphere are derived using the approach for a field subject to mechanized agricultural in the United Kingdom. Sensitivity analysis is undertaken and demonstrates that the approach is robust. The results indicate that, despite a 15% decline in the carbon content of the cultivation layer of the eroded part of the field, this area has acted as a net sink of 11 ± 2 g C m,2 yr,1 over the last half century and that in the field as a whole, soil redistribution has driven a sink of 7 ± 2 g C m,2 yr,1 (6 ± 2 g C m,2 yr,1 if all eroded carbon transported beyond the field boundary is lost to the atmosphere) over the same period. This is the first empirical evidence for, and quantification of, dynamic replacement of eroded carbon. The relatively modest field-scale net sink is more consistent with the identification of erosion and deposition as a carbon sink than a carbon source. There is a clear need to assemble larger databases with which to evaluate critically the carbon sequestration potential of erosion and deposition in a variety of conditions of agricultural management, climate, relief, and soil type. In any case, this study demonstrated that the operation of erosion and deposition processes within the boundaries of agricultural fields must be understood as a key driver of the net carbon cycle consequences of cultivating land. [source] The Planck,Benzinger thermal work function in the condensation of water vaporINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2006Paul W. Chun Abstract Based on the Planck,Benzinger thermal work function using Chun's method, the innate temperature-invariant enthalpy at 0 K, ,H0(T0), for the condensation of water vapor as well as the dimer, trimer, tetramer, and pentamer form in the vapor phase, was determined to be 0.447 kcal mol,1 for vapor, 1.127 for the dimer, 0.555 for the trimer, 0.236 for the tetramer, and 0.079 kcal mol,1 for the pentamer using ,G(T) data reported by Kell et al. in 1968 and Kell and McLaurin in 1969. These results suggest that the predominant dimeric form is the most stable of these n -mers. Using Nemethy and Scheraga's 1962 data for the Helmholtz free energy of liquid water, the value of ,H0(T0) was determined to be 1.21 kcal mol,1. This is very close to the value for the energy of the hydrogen bond EH of 1.32 kcal mol,1 reported by Nemethy and Scheraga, using statistical thermodynamics. It seems clear that very little energy is required for interconversion between the hypothetical supercooled water vapor and glassy water at 0 K. A hypothetical supercooled water vapor at 0 K is apparently almost as highly associated as glassy water at that temperature, suggesting a dynamic equilibrium between vapor and liquid. This water vapor condensation is highly similar in its thermodynamic behavior to that of sequence-specific pairwise (dipeptide) hydrophobic interaction, except that the negative Gibbs free energy change minimum at ,Ts,, the thermal setpoint for vapor condensation, where T,S = 0, occurs at a considerably lower temperature, 270 K (below 0°C) compared with ,350 K. The temperature of condensation ,Tcond, at which ,G(T) = 0, where water vapor begins to condense, was found to be 383 K. In the case of a sequence-specific pairwise hydrophobic interaction, the melting temperature, ,Tm,, where ,G(Tm) = 0 was found to be 460 K. Only between two temperature limits, ,Th, = 99 K and ,Tcond, = 383 K, where ,G(Tcond) = 0, is the net chemical driving force favorable for polymorphism of glassy water and hypothetical supercooled water vapor. Analysis of the water vapor condensation process based on the Planck,Benzinger thermal work function confirms that a thermodynamic molecular switch occurs at 10 K, wherein a change of sign in [,Cp(T)]cond leads to a true negative minimum in the Gibbs free energy of vapor condensation, and hence a maximum in the related equilibrium constant, Kcond. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] G-protein coupled receptors: SAR analyses of neurotransmitters and antagonistsJOURNAL OF CLINICAL PHARMACY & THERAPEUTICS, Issue 3 2004C. L. Kuo MS Summary Background:, From the deductive point of view, neurotransmitter receptors can be divided into categories such as cholinergic (muscarinic, nicotinic), adrenergic (, - and , -), dopaminergic, serotoninergic (5-HT1,5-HT5), and histaminergic (H1 and H2). Selective agonists and antagonists of each receptor subtype can have specific useful therapeutic applications. For understanding the molecular mechanisms of action, an inductive method of analysis is useful. Objective:, The aim of the present study is to examine the structure,activity relationships of agents acting on G-protein coupled receptors. Method:, Representative sets of G-PCR agonists and antagonists were identified from the literature and Medline [P.M. Walsh (2003) Physicians' desk reference; M.J. O'Neil (2001) The Merck index]. The molecular weight (MW), calculated logarithm of octanol/water partition coefficient (C log P) and molar refraction (CMR), dipole moment (DM), Elumo (the energy of the lowest unoccupied molecular orbital, a measure of the electron affinity of a molecule and its reactivity as an electrophile), Ehomo (the energy of the highest occupied molecular orbital, related to the ionization potential of a molecule, and its reactivity as a nucleophile), and the total number of hydrogen bonds (Hb) (donors and receptors), were chosen as molecular descriptors for SAR analyses. Results:, The data suggest that not only do neurotransmitters share common structural features but their receptors belong to the same ensemble of G-protein coupled receptor with seven to eight transmembrane domains with their resultant dipoles in an antiparallel configuration. Moreover, the analysis indicates that the receptor exists in a dynamic equilibrium between the closed state and the open state. The energy needed to open the closed state is provided by the hydrolysis of GTP. A composite 3-D parameter frame setting of all the neurotransmitter agonists and antagonists are presented using MW, Hb and , as independent variables. Conclusion:, It appears that all neurotransmitters examined in this study operate by a similar mechanism with the G-protein coupled receptors. [source] Alternative parasite development in transmission strategies: how time flies!JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 10 2010M. BADETS Abstract Among parasitic platyhelminths with complex life cycles, it has been well documented that transmission opportunities are the main forces shaping the diversity of life-history traits and parasite developmental strategies. While deviations in the development pathway usually involve shortening of life cycles, their extension may also occur following perception of remaining time by parasites. Polystoma gallieni, the monogenean parasite of Hyla meridionalis, is able to trigger two alternative developmental strategies depending on the physiological stage of the tadpoles upon which larvae attach. The distribution and reproductive outputs of both resulting phenotypes were surveyed to address questions about the dynamics of transmission in natural environments. Because modifications in the completion of life cycles can have drawbacks which may perturb the dynamic equilibrium of the resulting host,parasite systems, experimental infestations were also performed to assess parasite,parasite interactions. Our results suggest that the bladder adult phenotype, which involves transmission between frogs and tadpoles, is supplied secondarily by the branchial phenotype which involves transmission between tadpoles and metamorphs. They also support the occurrence of finely tuned trade-offs between hosts and parasites and highlight positive trends behind the extension of direct life cycles, in which host-derived signals account for the remaining time to achieve parasitic transmission. [source] Synthesis of ethyl 6-aryl-4-oxo-4,6-dihydro-1(12)(13)h -pyrimido-[2,,1,:4,5][1,3,5]triazino[1,2- a]benzimidazole-3-carboxylates,JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2006Anton V. Dolzhenko The synthesis of ethyl 6-aryl-4-oxo-4,6-dihdro-1(12)(13)H -pyrimido[2,,1,:4,5][1,3,5]triazino[1,2- a]-benzimidazole-3-carboxylates (4a-p) was described via pyrimidine ring annulation to 4-aryl-3,4-dihydro[1,3,5]triazino[1,2- a]benzimidazole-2-amines (2a-p) which were obtained from 2-guanidinobenzimidazole (1). Tautomerism in the prepared compounds was investigated using nmr spectroscopy. Compounds 2a-p were found to be present in dimethyl sulfoxide solution predominantly as 3,4-dihyhydro tautomeric form. Compounds 4a-p existed in dynamic equilibrium of 1-, 12- and 13H -forms. It was found that methylation of 4a-d led to 13-methyl substituted derivatives 9a-d exclusively. [source] Synthesis of functionalized cyclic enamines from lithium alkylphenyl sulfones and N -carbo- tert -butoxy lactamsJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2001Luis A. Arias Alkylphenyl sulfones 3 are appropriate synthons for the synthesis of 2-phenylsulfonyl alkylidene pyrro-lidine or piperidine derivatives 1 in good to moderate yields. The lithium alkyl sulfones 4 are first reacted with the desired protected lactams and then subjected to acidic methanolysis to afford the unusual enam-ines 1a-e. NMR studies (COSY 1H- 1H, COSY 1H- 13C, NOE) showed the Z enamines to exist in a dynamic equilibrium with the corresponding imines 2. The stereochemistry of the described compounds was confirmed by molecular calculations. [source] Reversible inhibitors of TAFIa can both promote and inhibit fibrinolysisJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 1 2003M. Schneider Summary., The plasma carboxypeptidase activated thrombin-activable fibrinolysis inhibitor (TAFIa), is thermally unstable at 37 °C, with a half-life of 8 or 15 min depending on the isoform. The arginine analog, 2-guanidinoethylmercaptosuccinate (GEMSA), not only inhibits TAFIa but also slows the spontaneous inactivation of the enzyme, thereby reducing the activity of TAFIa, while extending its apparent half-life. Because, as shown in previous work, the ability of TAFIa to prolong clot lysis can be more dependent on its half-life than its concentration, in this study we determined whether reversible inhibitors of TAFIa could paradoxically prolong clot lysis. Potato tuber carboxypeptidase inhibitor (PTCI) or GEMSA were titrated into normal pooled human plasma, in the presence of soluble thrombomodulin. Both inhibitors mediate a biphasic antifibrinolytic effect, prolonging clot lysis at lower concentrations and enhancing clot lysis at higher concentrations. The antifibrinolytic effect of GEMSA is maximized at 1 mmol L,1, increasing clot lysis time from 100 min to 350 min. The antifibrinolytic effect of PTCI is maximized at 100 nmol L,1, increasing clot lysis time from 100 min to 240 min. To further characterize the nature of this biphasic effect, TAFI at various concentrations was added to TAFI-immunodepleted human plasma in the presence of PTCI or GEMSA. The magnitude of the effect depends on the concentration of TAFIa, the concentration of inhibitor, and the potency of the inhibitor. We propose that the biphasic antifibrinolytic effect is mediated by the dynamic equilibrium of free TAFIa that inactivates quickly, and TAFIa bound to inhibitor that inactivates slowly. TAFIa inhibitors used as therapeutic agents might not only enhance lysis at higher concentrations, but also stabilize fibrin clots at intermediate concentrations. [source] ON THE SUSTAINABILITY OF GOVERNMENT BORROWING IN A DYNAMIC GENERAL EQUILIBRIUMPACIFIC ECONOMIC REVIEW, Issue 5 2007Article first published online: 1 NOV 200, Atsumasa Kondo The limitation level of the government borrowing for which a dynamic equilibrium and the no Ponzi Game condition are compatible with each other is explicitly derived. The critical level depends on the long-run interest rate, primary balance, money supply etc. [source] Critical Elections and Political Realignments in the USA: 1860,2000POLITICAL STUDIES, Issue 2 2003Norman Schofield The sequence of US presidential elections from 1964 to 1972 is generally regarded as heralding a fundamental political realignment, during which time civil rights became as important a cleavage as economic rights. In certain respects, this realignment mirrored the transformation of politics that occurred in the period before the Civil War. Formal models of voting (based on assumptions of rational voters, and plurality-maximizing candidates) have typically been unable to provide an account of such realignments. In this paper, we propose that US politics necessarily involves two dimensions of policy. Whatever positions US presidential candidates adopt, there will always be two groups of disaffected voters. Such voters may be mobilized by third party candidates, and may eventually be absorbed into one or other of the two dominant party coalitions. The policy compromise, or change, required of the successful presidential candidate then triggers the political realignment. A formal activist-voter model is presented, as a first step in understanding such a dynamic equilibrium between parties and voters. [source] Detecting equilibrium cytochrome c folding intermediates by electrospray ionisation mass spectrometry: Two partially folded forms populate the molten-globule statePROTEIN SCIENCE, Issue 3 2002Rita Grandori Abstract Nanoelectrospray ionization mass spectrometry (nano-ESI-MS) is applied to the characterization of ferric cytochromec (cytc) conformational states under different solvent conditions. The methanol-induced molten-globule state in the pH range 2.6,3.0 is found to be populated by two distinct, partially folded conformers IA and IB. The more compact intermediate IB resembles that induced by glycerol in acid-unfolded cytc. The less compact one, IA, also can be induced by destabilization of the native structure by trifluoroethanol. IA and IB can be detected, in the absence of additives, around the midpoint of the acid-induced unfolding transition, providing direct evidence for involvement of equilibrium folding intermediates in cytc conformational transitions at low pH. This study shows that mass spectrometry can contribute to the characterization of molten-globule states of proteins by detection of distinct, although poorly populated, conformations involved in a dynamic equilibrium. [source] Structures of and interactions between domains of trigger factor from Thermotoga maritimaACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2007Erik Martinez-Hackert Trigger factor (TF) is a eubacterial chaperone that associates with ribosomes at the peptide-exit tunnel and also occurs in excess free in the cytosol. TF is a three-domain protein that appears to exist in a dynamic equilibrium of oligomerization states and interdomain conformations. X-ray crystallography and chemical cross-linking were used to study the roles of the N- and C-terminal domains of Thermotoga maritima TF in TF oligomerization and chaperone activity. The structural conservation of both the N- and C-terminal TF domains was unambiguously established. The biochemical and crystallographic data reveal a tendency for these domains to partake in diverse and apparently nonspecific protein,protein interactions. It is found that the T. maritima and Escherichia coli TF surfaces lack evident exposed hydrophobic patches. Taken together, these data suggest that TF chaperones could interact with nascent proteins via hydrophilic surfaces. [source] How does alluvial sedimentation at range fronts modify the erosional dynamics of mountain catchments?BASIN RESEARCH, Issue 3 2005S. Carretier At the geological time scale, the way in which the erosion of drainage catchments responds to tectonic uplift and climate changes depends on boundary conditions. In particular, sediment accumulation and erosion occurring at the edge of mountain ranges should influence the base level of mountain catchments, as well as sediment and water discharges. In this paper, we use a landform evolution model (LEM) to investigate how the presence of alluvial sedimentation at range fronts affects catchment responses to climatic or tectonic changes. This approach is applied to a 25 km × 50 km domain, in which the central part is uplifted progressively to simulate the growth of a small mountain range. The LEM includes different slope and river processes that can compete with each other. This competition leads to ,transport-limited', ,detachment-limited' or ,mixed' transport conditions in mountains at dynamic equilibrium. In addition, two end-member algorithms (the channellized-flow and the sheet-flow regimes) have been included for the alluvial fan-flow regime. The three transport conditions and the two flow algorithms represent six different models for which the responses to increase of rock uplift rate and/or cyclic variation of the precipitation rate are investigated. Our results indicate that addition of an alluvial apron increases the long-term mountain denudation. In response to uplift, mountain rivers adapt their profile in two successive stages; first by propagation of an erosion wave and then by slowly increasing their channel gradients. During the second stage, the erosion rate is almost uniform across the catchment area at any one time, which suggests that dynamic equilibrium has been reached, although the balance between erosion and rock uplift rates has not yet been achieved. This second stage is initiated by the uplift of the mountain river outlets because of sedimentation aggradation at the mountain front. The response time depends on the type of water flow imposed on the alluvial fans domains (× by 1.5 for channelized flow regime and by 10 for the sheet flow one). Cyclic variations of precipitation rate generate cyclic incisions in the alluvial apron. These incision pulses create knick-points in the river profile in the case of ,detachment-limited' and ,mixed' river conditions, which could be mistaken for tectonically induced knick-points. ,Transport-limited' conditions do not create such knick-points, but nevertheless trigger erosion in catchments. The feedbacks linked to sedimentation and erosion at range front can therefore control catchment incision or aggradation. In addition, random river captures in the range front trigger auto-cyclic erosion pulses in the catchment, capable of generating incision,aggradation cycles. [source] Higher Soluble Amyloid , Concentration in Frontal Cortex of Young Adults than in Normal Elderly or Alzheimer's DiseaseBRAIN PATHOLOGY, Issue 4 2010Zoë Van Helmond Abstract Little is known about the relationship between soluble amyloid , (A,) and age. We have measured soluble and insoluble A, by enzyme-linked immunosorbent assay (ELISA) in post-mortem frontal cortex in normal brains (16,95 years) and AD. Insoluble A, increased with age, and was significantly higher in Alzheimer's disease (AD) than age-matched controls. However, levels of soluble A, declined with age and were significantly greater in younger adults than older adults with or without AD. In AD, insoluble : soluble A, ratio was much higher than in age-matched controls. The high levels of soluble A, in young adults included oligomeric species of A,1-42. These observations do not preclude A, oligomers as neurotoxic mediators of AD but suggest that if they are, the toxicity may be restricted to certain species (eg, ,-pleated protofibrillar species not detected by our assay) or takes decades to manifest. The dramatically increased insoluble : soluble A, in AD points to an altered dynamic equilibrium of A, in AD, reflecting both enhanced aggregation and continued overproduction or impaired removal of the soluble peptide in older age, when the concentration of this peptide should be declining. [source] Modification of epithelial cell barrier permeability and intercellular junctions by Clostridium sordellii lethal toxinsCELLULAR MICROBIOLOGY, Issue 7 2006Catherine Boehm Summary Clostridium sordellii lethal toxin (LT) is a glucosyltransferase which inactivates small GTPases from the Rho and Ras families. In the present work, we studied the effects of two variants, LT82 and LT9048, on the integrity of epithelial cell barrier using polarized MCCD (Mouse Cortical Collecting Duct) and MDCK (Madin-Darby Canine Kidney) cells. Our results demonstrate for the first time that LTs have very limited effects on tight junctions. In contrast, we show that both toxins modified the paracellular permeability within 2,4 h. Concomitantly LT82 and LT9048 induced a disorganization of basolateral actin filaments, without modifying apical actin. Both toxins mainly altered adherens junctions by removing E-cadherin-catenin complexes from the membrane to the cytosol. Similar effects on adherens junctions have been observed with other toxins, which directly or indirectly depolymerize actin. Thereby, Rac, a common substrate of both LTs, might play a central role in LT-dependent adherens junction alteration. Here, we show that adherens junction perturbation induced by LTs results neither from a direct effect of toxins on adherens junction proteins nor from an actin-independent Rac pathway, but rather from a Rac-dependent disorganization of basolateral actin cytoskeleton. This further supports that a dynamic equilibrium of cortical actin filaments is essential for functional E-cadherin organization in epithelia. [source] Dynamic Equilibria in Solvent-Mediated Anion, Cation and Ligand Exchange in Transition-Metal Coordination Polymers: Solid-State Transfer or Recrystallisation?CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2009Xianjin Cui Abstract The solution properties of a series of transition-metal,ligand coordination polymers [ML(X)n], [M=AgI, ZnII, HgII and CdII; L=4,4,-bipyridine (4,4,-bipy), pyrazine (pyz), 3,4,-bipyridine (3,4,-bipy), 4-(10-(pyridin-4-yl)anthracen-9-yl)pyridine (anbp); X=NO3,, CH3COO,, CF3SO3,, Cl,, BF4,; n=1 or 2] in the presence of competing anions, metal cations and ligands have been investigated systematically. Providing that the solubility of the starting complex is sufficiently high, all the components of the coordination polymer, namely the anion, the cation and the ligand, can be exchanged on contact with a solution phase of a competing component. The solubility of coordination polymers is a key factor in the analysis of their reactivity and this solubility depends strongly on the physical properties of the solvent and on its ability to bind metal cations constituting the backbone of the coordination polymer. The degree of reversibility of these solvent-induced anion-exchange transformations is determined by the ratio of the solubility product constants for the starting and resultant complexes, which in turn depend upon the choice of solvent and the temperature. The extent of anion exchange is controlled effectively by the ratio of the concentrations of incoming ions to outgoing ions in the liquid phase and the solvation of various constituent components comprising the coordination polymer. These observations can be rationalised in terms of a dynamic equilibrium of ion exchange reactions coupled with Ostwald ripening of crystalline products. The single-crystal X-ray structures of [Ag(pyz)ClO4], (1), {[Ag(4,4,-bipy)(CF3SO3)],CH3CN}, (2), {[Ag(4,4,-bipy)(CH3CN)]ClO4, 0.5,CH3CN}, (3), metal-free anbp (4), [Ag(anbp)NO3(H2O)], (5), {[Cd(4,4,-bipy)2(H2O)2](NO3)2,4,H2O}, (6) and {[Zn(4,4,-bipy)SO4(H2O)3] ,2,H2O}, (7) are reported. [source] Selection of a Pentameric Host in the Host,Guest Complexes {[{[P(,-NtBu)]2(,-NH)}5],I},[Li(thf)4]+ and [{[P(,-NtBu)]2(,-NH)}5],HBr,THFCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2004Felipe García Abstract The structures of the host,guest complexes {[{[P(,-NtBu)]2(,-NH)}5]I},,[Li(thf)4]+ [2,I{Li(thf)4}] and [{[P(,-NtBu)]2(,-NH)}5],HBr,THF (2,HBr,THF) show that increased distortion of the framework of the pentameric macrocycle [{[P(,-NtBu)]2(,-NH)}5] (2) occurs with the larger halide ions. Theoretical studies show that the thermodynamic stabilities of the model host,guest anions [2,X], (X=Cl, Br, I) are in the order Cl,,Br,>I,, that is, the reverse of the templating trend observed experimentally. These studies support the view that the selection of the pentamer 2 over the tetramer [{[P(,-NtBu)]2(,-NH)}4] (1) is kinetically controlled, a conclusion which is also consistent with the previous observation that the frameworks of 1 and 2 are not in dynamic equilibrium with each other. [source] Synthesis and conformation of cis -1,2-disubstituted cyclododeceneCHINESE JOURNAL OF CHEMISTRY, Issue 6 2004Xiang-Yu Han Abstract Eight 1,2-disubstituted cyclododecenes were synthesized from ,-alkoxycarbonyl-cyclododecanone and alkyl chloroformate. Their configuration and conformation determined by IR, NMR spectroscopy and X-ray diffraction analysis showed that the carbon-carbon double bond of all of the synthesized compounds has cis -configuration. and the ring skeleton of their preferred conformation is [lene2333] in solid, and they may adopt two different [lene2333] conformations, which exist in a dynamic equilibrium in solution. [source] | ||||||||||||||||||||||||||||||||||