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Plausible Mechanism (plausible + mechanism)
Selected AbstractsKinetics and mechanism of sodium N -halo- p -toluenesulfonamides oxidation of diclofenac in alkaline mediumAICHE JOURNAL, Issue 12 2009Puttaswamy Abstract Diclofenac belongs to a class of drugs called nonsteroidal antiinflammatory drugs. The kinetics and mechanism of oxidation of diclofenac by sodium N -halo- p -toluenesulfonamides viz., chloramine-T and bromamine-T in NaOH medium have been studied at 293 K. Under comparable experimental conditions, reactions with both the oxidants follow identical kinetics with a first-order dependence on each [oxidant]o and a fractional-order dependence on each [diclofenac]o and [NaOH]. Activation parameters have been computed. N -hydroxyldiclofenac is identified as the oxidation product of diclofenac. Michaelis-Menten type of mechanism has been suggested. The rate of oxidation of diclofenac is about four-fold faster with bromamine-T when compared with chloramine-T. This may be attributed to the difference in electrophilicities of Cl+ and Br+ ions and also the van der Waal's radii of chlorine and bromine. Plausible mechanism and related rate law have been designed for the observed kinetics. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Statistical morphological analysis of hippocampal principal neurons indicates cell-specific repulsion of dendrites from their own cellJOURNAL OF NEUROSCIENCE RESEARCH, Issue 2 2003Alexei V. Samsonovich Abstract Traditionally, the sources of guidance cues for dendritic outgrowth are mainly associated with external bodies (A) rather than with the same neuron from which dendrites originate (B). To quantify the relationship between factors A and B as determinants of the adult dendritic shape, the morphology of 83 intracellularly characterized, stained, completely reconstructed, and digitized principal neurons of the rat hippocampus was statistically analyzed using Bayesian optimization. It was found that the dominant directional preference (tropism) manifested in dendritic turns is to grow away from the soma rather than toward the incoming fibers or in any other fixed direction; therefore, B is predominant. Results are robust and consistent for all examined morphological classes (dentate gyrus granule cells, basal and apical trees of CA3 and CA1 pyramidal cells). In addition, computer remodeling of neurons based on the measured parameters produced virtual structures consistent with real morphologies, as confirmed by measurement of several global emergent parameters. Thus, the simple description of dendritic shape based on dendrites' tendency to grow straight, away from their own soma, and with additional random deflections, proves remarkably accurate and complete. Although based on adult neurons, these results suggest that dendritic guidance during development may be associated primarily with the host cell. This possibility challenges the traditional concept of dendritic guidance: in that hippocampal cells are densely packed and have highly overlapping dendritic fields, the somatodendritic repulsion must be cell specific. Plausible mechanisms involving extracellular effects of spikes are discussed, together with feasible experimental tests and predicted results. © 2002 Wiley-Liss, Inc. [source] Evaluation of tumor affinity of mono-[123I]iodohypericin and mono-[123I]iodoprotohypericin in a mouse model with a RIF-1 tumorCONTRAST MEDIA & MOLECULAR IMAGING, Issue 3 2007Humphrey Fonge Abstract In this study we have compared the tumour-seeking properties of mono-[123I]iodoprotohypericin and mono-[123I]iodohypericin in C3H mice with a subcutaneous radiation-induced fibrosarcoma-1 tumor. After intravenous injection, both tracers were rapidly cleared from all organs and were retained by the tumors. There was no significant difference in tumor uptake of the two tracers at all studied time points (p,>,0.05). To study the plausible mechanism of hypericin and mono-iodohypericin uptake in tumor, their plasma binding profile was investigated. Both agents show high affinity for low-density lipoproteins and to a lesser extent high-density lipoproteins and other heavy proteins. Mono-[123I]iodohypericin appears to be more promising as a tumor diagnostic agent, given its faster clearance from all organs. Copyright © 2007 John Wiley & Sons, Ltd. [source] Forest blowdown impacts of Hurricane Rita on fluvial systemsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2009Jonathan D. Phillips Abstract Hurricane Rita, a category three hurricane which struck the US Gulf Coast near the Louisiana/Texas border in 2005, did not cause extensive river flooding. However, the storm did result in extensive forest damage and tree blowdown. High-resolution post-storm aerial photography allowed an inventory of river bank trees blown into the channel along the lower Neches and Sabine Rivers of southeast Texas and southwest Louisiana. Blowdowns directly into the channel averaged 9·3 per kilometer in the lower Neches and 13·4 in the lower Sabine River, but individual reaches 10 to 20 km in length had rates of 20 to 44 blowdowns per kilometer. Though large woody debris (LWD) from Hurricane Rita was widely perceived to reduce the capacity of channels to convey flow, no strong evidence exists of increased flooding or significant reductions in channel conveyance capacity due to LWD from the storm. The Rita blowdown inventory also allowed an assessment of whether similar blowdown events could account for major logjams and rafts on Red, Atchafalaya, and Colorado Rivers on the Gulf Coast, which blocked navigation from tens to hundreds of kilometers in the 1800s. Results from Hurricane Rita suggest that blowdown into channels alone , not withstanding blowdown elsewhere in the river valleys or along tributaries which could deliver LWD to the river , is sufficient to completely block channels, thus providing a plausible mechanism for initiating such (pre)historic log rafts. Copyright © 2009 John Wiley & Sons, Ltd. [source] Preparation of ZnO Nanowires in a Neutral Aqueous System: Concentration Effect on the Orientation Attachment ProcessEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2006Ming Yang Abstract ZnO nanowires with diameters in the range of 10 to 30 nm and lengths of ca. several micrometers are prepared with the use of ZnO nanoparticles as building blocks. The length and diameter of the ZnO nanowires can be controlled by the variation of the concentration of the nanoparticles in the orientation attachment process. A plausible mechanism for the concentration-controlled orientation attachment process is suggested. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] New Efficient Route to Fused Aryltetrahydroindolizinones via N -Acyliminium IntermediatesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2009Matteo Chiurato Abstract Straightforward routes to fused tetrahydroindolizinones by two routes A and B, starting either from 2-formylbenzoic acid and esters or from ,-hydroxy lactones via acyl iminium ions, are described. A plausible mechanism and limitations are given. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Superacid-Catalyzed Dimerization/Cyclization of Isopropenyl-PAHs , Novel Pathways to PAH Dimers, Phenalenes and Their Stable CarbocationsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2008Cédric Brulé Abstract The isopropenyl derivatives of representative classes of polycyclic aromatic hydrocarbons (PAHs) having four and five fused-ring systems, namely pyrene, chrysene, benzo[c]phenanthrene (BcPh), dibenzo[a,c]anthracene (benzo[f]tetraphene) and perylene, were synthesized by Wittig olefination from the corresponding acetyl-PAHs. Under the influence of triflic acid (TfOH), the isopropenyl derivatives were converted to novel PAH dimers and/or phenalenes in a simple one-pot procedure. A plausible mechanism for this process has been outlined, and the synthetic scope of this chemistry has been explored. Structural features in the PAH dimers were examined by DFT. As representative initial and final carbocation intermediates in the reaction sequence, stable carbocations derived from 3-isopropenylperylene and from 4,6,6-trimethyl-6H -dibenzo[a,kl]anthracene were generated and studied directly by NMR spectroscopy. The NMR characteristics and charge delocalization modes in the resulting benzylic carbocations are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Catalysis by Ionic Liquids: Significant Rate Acceleration with the Use of [pmIm]Br in the Three-Component Synthesis of DithiocarbamatesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2008Brindaban C. Ranu Abstract An easily accessible neutral ionic liquid, 1-methyl-3-pentylimidazolium bromide, promoted a one-pot three-component condensation of an amine, carbon disulfide, and an activated alkene/dichloromethane/epoxide to produce the corresponding dithiocarbamates in high yields at room temperature. The reactions are very fast in ionic liquids relative to those in other reaction media. These reactions do not require any additional catalyst or solvent. The ionic liquid can be recovered and recycled for subsequent reactions. A plausible mechanism is suggested. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Towards a Selective Functionalization of Amino-Terminated DendrimersEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2004Fritz Vögtle Abstract Selective functionalization of the periphery of commercial polypropyleneamine (POPAM) and polyamidoamine (PAMAM) dendrimers has been investigated in preparative scale. The first generation (G1) POPAM dendrimer was for the first time selectively N,N -bis(sulfonylated) with tosyl chloride and the corresponding mono-, di-, tri-, and tetra- N -tosylsulfonamides were isolated and fully characterized. Unexpectedly, similar persulfonylation of G2 POPAM results in splitting of a central C,N bond and only fully and partially sulfonylated halves of the initial dendrimer could be isolated. Higher generations of POPAM are also split during the persulfonylation yielding complex mixtures of persulfonylated dendritic fragments which could hardly be identified. A plausible mechanism of the POPAM decomposition on the basis of the reaction product analysis is proposed. N -Sulfonylation of a peripheral octasulfonamide of G2 POPAM with tosyl chloride also leads to the destruction of the dendrimer, while its N -alkylation with benzyl bromide proved to be not selective yielding a completely alkylated derivative. Unlike POPAM dendrimers, PAMAM dendrimers were shown to be more stable during their sulfonylation and no decomposition of the dendritic backbone was detected. In contrast to the POPAM dendrimers, PAMAM dendrimers were shown to be rather inert with respect to the formation of N -tosylsulfonamides since they could only be N -monosulfonylated at all peripheral amino groups. The combination of MALDI-TOF and ESI-FT-ICR tandem mass spectrometry has been shown to be an effective method for structure assignment and purity check of selectively or fully persulfonylated dendritic oligoamines. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] An Efficient Synthesis of Novel Hexahydropyrido[2,3- d]pyrimidine Derivatives from (Arylmethylidene)pyruvic Acids (=(3E)-4-Aryl-2-oxobut-3-enoic Acids) in Aqueous MediaHELVETICA CHIMICA ACTA, Issue 5 2009Saeed Balalaie Abstract A series of new hexahydropyrido[2,3- d]pyrimidine derivatives 3 were synthesized by the cyclocondensation reaction of (arylmethylidene)pyruvic acids (=(3E)-4-aryl-2-oxobut-3-enoic acids) 1 and 6-aminouracils (=6-aminopyrimidine-2,4(1H,3H)-diones) 2 in H2O under reflux conditions (Scheme,1, Table). This novel protocol has the advantages of facility, of easy workup, of high yields, and of an environmentally benign procedure. The structures of compounds 3a,3f were corroborated spectroscopically (IR, 1H- and 13C-NMR, and EI-MS). A plausible mechanism for the reaction is proposed (Scheme,2). [source] Reaction of diethyl thiocyanatomethylphosphonate with aldehydes as a route to diethyl Z -1-alkenylphosphonatesHETEROATOM CHEMISTRY, Issue 7 2007Roman B, aszczyk Diastereoselective synthesis of diethyl Z-1-alkenylphosphonates from easily available diethyl thiocyanatomethylphosphonate and aromatic aldehydes has been developed. Olefination of the aldehydes occurs under mild conditions and affords the title compounds with moderate yields. A plausible mechanism of the above-mentioned reaction is also discussed. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:732,739, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20371 [source] Reduced risk of prostate cancer in men who are childless as compared to those who have fathered a child: A population based case-control studyINTERNATIONAL JOURNAL OF CANCER, Issue 6 2005Aleksander Giwercman Abstract Androgens are believed to play a major role in the etiology of prostate cancer, but studies of sex-hormone exposure in relation to risk for prostate cancer have been inconclusive. Male fertility may be an indicator of long-term androgen status. To study the role of testicular function in prostate cancer development, we have assessed number of biological children in relation to risk for this malignancy. We carried out a population-based case-control study with retrospective ascertainment of cases occurring in Sweden between 1958,98. In total, 48,850 cases of prostate cancer were identified through the nation-wide Cancer Registry. For each case, one control, matched by year of birth, was randomly selected from the Swedish population. Information on offspring was obtained from the Swedish Multi-Generation Registry. We estimated odds ratios (OR) and 95% confidence intervals (CI) for the association between number of offspring and risk for subsequent prostate cancer. Being childless or having fathered one child only were associated with reduced risks for prostate cancer compared to having fathered 2 or more children (OR = 0.83; 95% CI = 0.81,0.86 and OR = 0.93; 95% CI = 0.90,0.96, respectively). There was no further change in risk associated with fathering of more than 2 children. The risk for prostate cancer is reduced among childless men. A dysfunctioning reproductive apparatus fueling to a lesser extent prostatic growth, could be a plausible mechanism of this association. © 2005 Wiley-Liss, Inc. [source] Copper-Catalyzed Efficient Multicomponent Reaction: Synthesis of Benzoxazoline-Amidine DerivativesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2009Yongjia Shang Abstract We have developed an efficient copper-catalyzed method for the synthesis of the benzoxazoline-amidine derivatives. The protocol uses inexpensive copper(I) iodide as the catalyst, and furnished the expected product in good to excellent yields by a three-component reaction of sulfonyl azides, terminal alkynes and Schiffs' bases in terahydrofuran (THF) at room temperature for 8,h in the presence of triethylamine. This novel synthetic protocol is selective, efficient and general. A plausible mechanism for this process is proposed. [source] Imidazolium-2-Carboxylate as an Efficient, Expeditious and Eco-Friendly Organocatalyst for Glycerol Carbonate SynthesisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Prashant Abstract An improved and greener approach towards the synthesis of glycerol carbonate, via transesterification, using 1- n -butyl-3-methylimidazolium-2-carboxylate as catalyst is described. The catalyst loading as low as 1% was sufficient to yield quantitative conversions. A plausible mechanism is proposed for the catalytic cycle leading to product formation. [source] Hydrogenation of Phenol in Supercritical Carbon Dioxide Catalyzed by Palladium Supported on Al-MCM-41: A Facile Route for One-Pot Cyclohexanone FormationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009M. Chatterjee Abstract The hydrogenation of phenol has been carried out in supercritical carbon dioxide (scCO2) under very mild reaction conditions at the temperature of 50,°C over palladium supported Al-MCM-41 (metal loading ,1%). This palladium catalyst is shown to be highly active and promotes the selective formation of cyclohexanone (,98%), an industrially important compound, in a "one-pot" way. The effects of different variables like carbon dioxide and hydrogen pressure, reaction time and also silica/alumina ratio of the MCM-41 support along with palladium dispersion are presented and discussed. The pressure effect of carbon dioxide is significantly prominent in terms of conversion and cyclohexanone selectivity. Moreover, the silica/alumina ratio was also found to be an important parameter to enhance the effectiveness of the catalyst as it exhibits a remarkable increase in phenol conversion from 20.6% to 98.4% as the support changes from only silica MCM-41 to Al-MCM-41. A plausible mechanism for the hydrogenation of phenol to cyclohexanone over the palladium catalyst has been proposed. The proposition is validated by transition state calculations using density functional theory (DFT), which reveal that cyclohexanone is a favorable product and stabilized by <19,kcal,mol,1 over cyclohexanol in scCO2 medium. Under similar reaction conditions, phenol hydrogenation was also carried out with rhodium, supported on Al-MCM-41. In contrast to the palladium catalyst, a mixture of cyclohexanone (57.8%) and cyclohexanol (42.2%) was formed. Detailed characterization by X-ray diffraction and transmission electron microscopy confirmed the presence of metal nanoparticles (palladium and rhodium) between 10,20,nm. Both the catalysts exhibit strikingly different product distributions in solventless conditions compared to scCO2. This method can also be successfully applied to the other hydroxylated aromatic compounds. [source] A Dramatic Substituent Effect in Silver(I)-Catalyzed Regioselective Cyclization of ortho -Alkynylaryl Aldehyde Oxime DerivativesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Hongyin Gao Abstract A dramatic substituent effect was found in the silver(I)-catalyzed cyclization reaction of ortho -alkynylaryl aldehyde oxime derivatives. When R is an alkyl group, the Ag(I)-catalyzed reaction in dimethylacetamide at 110,°C (conditions A) affords isoquinolines in good to excellent yields, in contrast, isoquinolin-1(2,H)-ones were produced in moderate to high yields under conditions B (dimethylformamide, room temperature) when R is an acetyl group. A plausible mechanism was proposed for this product selectivity control reaction (PSCR) by subtle structure modification. [source] Direct hydroxide attack is a plausible mechanism for amidase antibody 43C9,JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2003Lillian T. Chong Abstract Direct hydroxide attack on the scissile carbonyl of the substrate has been suggested as a likely mechanism for esterase antibodies elicited by phosphonate haptens, which mimic the transition states for the alkaline hydrolysis of esters.1 The unique amidase activity of esterase antibody 43C9 has been attributed to nucleophilic attack by an active-site histidine residue.2 Yet, the active site of 43C9 is strikingly similar to those of other esterase antibodies, particularly 17E8. We have carried out quantum mechanical calculations, molecular dynamics simulations, and free energy calculations to assess the mechanism involving direct hydroxide attack for 43C9. Results support this mechanism and suggest that the mechanism is plausible for other antiphosphonate antibodies that catalyze the hydrolysis of (p -nitro)phenyl esters. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1371,1377, 2003 [source] The experimental evolution of specialists, generalists, and the maintenance of diversityJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2002R. Kassen Environmental heterogeneity may be a general explanation for both the quantity of genetic variation in populations and the ecological niche width of individuals. To evaluate this hypothesis, I review the literature on selection experiments in heterogeneous environments. The niche width usually , but not invariably , evolves to match the amount of environmental variation, specialists evolving in homogeneous environments and generalists evolving in heterogeneous environments. The genetics of niche width are more complex than has previously been recognized, particularly with respect to the magnitude of costs of adaptation and the putative constraints on the evolution of generalists. Genetic variation in fitness is more readily maintained in heterogeneous environments than in homogeneous environments and this diversity is often stably maintained through negative frequency-dependent selection. Moreover environmental heterogeneity appears to be a plausible mechanism for at least two well-known patterns of species diversity at the landscape scale. I conclude that environmental heterogeneity is a plausible and possibly very general explanation for diversity across the range of scales from individuals to landscapes. [source] Systematic review: Heliocobacter pylori infection and impaired drug absorptionALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 4 2009E. LAHNER Summary Background, Impaired acid secretion may affect drug absorption and may be consequent to corporal Heliocobacter pylori- gastritis, which may affect the absorption of orally administered drugs. Aim, To focus on the evidence of impaired drug absorption associated with H. pylori infection. Methods, Data sources were the systematic search of MEDLINE/EMBASE/SCOPUS databases (1980,April 2008) for English articles using the keywords: drug malabsorption/absorption, stomach, Helicobacter pylori, gastritis, gastric acid, gastric pH, hypochlorhydria, gastric hypoacidity. Study selection was made from 2099 retrieved articles, five studies were identified. Data were extracted from selected papers, investigated drugs, study type, main features of subjects, study design, intervention type and results were extracted. Results, In all, five studies investigated impaired absorption of l -dopa, thyroxine and delavirdine in H. pylori infection. Eradication treatment led to 21,54% increase in l -dopa in Parkinon's disease. Thyroxine requirement was higher in hypochlorhydric goitre with H. pylori- gastritis and thyrotropin levels decreased by 94% after treatment. In H. pylori- and HIV-positive hypochlorhydric subjects, delavirdine absorption increased by 57% with orange juice administration and by 150% after eradication. Conclusions, A plausible mechanism of impaired drug absorption is decreased acid secretion in H. pylori -gastritis patients. Helicobacter pylori infection and hypochlorhydria should be considered in prescribing drugs the absorption of which is potentially affected by intragastric pH. [source] Synthesis, Characterization, and Mechanism of Polymerization of Poly(but-2-ene sulfide),MACROMOLECULAR RAPID COMMUNICATIONS, Issue 15 2004Subramanian Sundarrajan Abstract Summary: The effect of structural factors on polymer formation versus cyclization is reported. The reaction of sodium sulfide with either 1,4-dibromobut-2-ene 1 or 1,4-dibromobutane 2 has been carried out in presence of a phase transfer catalyst and it was observed that the former yields polymer, whereas the latter gives cyclic and linear products. Interestingly, trans/cis isomerization takes place during the polymer formation from 1 and a plausible mechanism has also been discussed. The reaction mechanism for unsaturated compound 1 and saturated compound 2 is discussed here. [source] PHYSIOLOGICAL AND BEHAVIORAL DEVELOPMENT IN DELPHINID CALVES: IMPLICATIONS FOR CALF SEPARATION AND MORTALITY DUE TO TUNA PURSE-SEINE SETSMARINE MAMMAL SCIENCE, Issue 1 2007Shawn R. Noren Abstract Tuna purse-seiners in the eastern tropical Pacific (ETP) capture yellowfin tuna by chasing and encircling herds of associated dolphins. This fishery has caused mortality in 14 dolphin species (20 stocks) and has led to significant depletions of at least three stocks. Although observed dolphin mortality is currently low, set frequency remains high and dolphin stocks are not recovering at expected rates. Mortality of nursing calves permanently separated from their mothers during fishery operations may be an important factor in the lack of population recovery, based on the recent discovery that calves do not accompany 75%,95% of lactating females killed in the purse-seine nets. We assessed age-specific potential for mother,calf separations and subsequent mortality of calves by reviewing and synthesizing published data on physiological and behavioral development in delphinids from birth through 3 yr postpartum. Results indicate that evasive behavior of mothers, coupled with the developmental state of calves, provides a plausible mechanism for set-related mother,calf separations and subsequent mortality of calves. Potential for set-related separation and subsequent mortality is highest for 0,12-mo-old dolphins and becomes progressively lower with age as immature dolphins approach adult stamina and attain independence. [source] Soluble nickel inhibits HIF-prolyl-hydroxylases creating persistent hypoxic signaling in A549 cellsMOLECULAR CARCINOGENESIS, Issue 7 2006Todd L. Davidson Abstract Soluble nickel compounds are carcinogenic to humans although the mechanism by which they cause cancer remains unclear. One major consequence of exposure to nickel is the stabilization of hypoxia inducible factor-1, (HIF-1,), a protein known to be overexpressed in a variety of cancers. In this study, we report a persistent stabilization of HIF-1, by nickel chloride up to 72 h after the removal of nickel from the culture media. In addition, we show that the HIF-prolyl hydroxylases (PHD's) are inhibited when cells are exposed to nickel and that they remain repressed for up to 72 h after nickel is removed. We then show that nickel can inhibit purified HIF-PHD's 2 in vitro, through direct interference with the enzyme. Through theoretical calculations, we also demonstrate that nickel may be able to replace the iron in the active site of this enzyme, providing a plausible mechanism for the persistent inhibition of HIF-PHD's by nickel. The data presented suggest that nickel can interfere with HIF-PHD directly and does not inhibit the enzyme by simply depleting cellular factors, such as iron or ascorbic acid. Understanding the mechanisms by which nickel can inhibit HIF-PHD's and stabilize HIF-1, may be important in the treatment of cancer and ischemic diseases. © 2006 Wiley-Liss, Inc. [source] Positioning of the MinE binding site on the MinD surface suggests a plausible mechanism for activation of the Escherichia coli MinD ATPase during division site selectionMOLECULAR MICROBIOLOGY, Issue 1 2004Luyan Ma Summary Division site selection in Escherichia coli requires that the MinD protein interact with itself and with MinC and MinE. MinD is a member of the NifH-ArsA-Par-MinD subgroup of ATPases. The MinE,MinD interaction results in activation of MinD ATPase activity in the presence of membrane vesicles. The sites within MinD responsible for its interaction with MinC and MinE were studied by site-directed mutagenesis and yeast two-hybrid analysis, guided by the known three-dimensional structure of MinD proteins. This provided evidence that MinC and MinE bind to overlapping sites on the MinD surface. The results also suggested that MinE and the invariant Lys11 residue in the ATPase P-loop of MinD compete for binding to a common site within the MinD structure, thereby providing a plausible structural basis for the ability of MinE to activate the ATPase activity of MinD. [source] Interfacial polymerization of morphologically modified polyaniline: from hollow microspheres to nanowiresPOLYMER INTERNATIONAL, Issue 2 2008Jinbo Li Abstract BACKGROUND: Polyaniline (PANI) has attracted much attention in many fields due to its chemical and physical properties, and different nanostructures of PANI changing from one-dimensional to three-dimensional have been obtained. By changing the concentration of cetyltrimethylammonium bromide (CTAB), the morphology of hydrochloric acid-doped polyaniline could be changed from one-dimensional nanoneedles or nanowires with a network structure (50,100 nm in diameter) to three-dimensional hollow microspheres (ca 400 nm in outer diameter) via combining interfacial polymerization and self-assembly process. RESULTS These different nanostructures of PANI were proved using scanning electron and transmission electron microscopies. A plausible mechanism of the formation of the changeable nanostructures of PANI may be different from that of interfacial polymerization without surfactant or a traditional homogenous reaction system using CTAB as surfactant. CONCLUSION The results obtained from Fourier transform infrared spectrometry, X-ray diffraction and the four-probe method showed that the molecular structure of PANI does not change with increasing CTAB concentration, but crystallinity and conductivity of PANI increase with surfactant concentration. Copyright © 2007 Society of Chemical Industry [source] Is There a Stabilizing Selection Around Average Fertility in Modern Human Populations?POPULATION AND DEVELOPMENT REVIEW, Issue 3 2001Ulrich Mueller Possibly the greatest challenge for an evolutionary explanation of demographic transition is the fact that fertility levels universally start to fall first among the well-to-do, well-educated, healthy classes, which can be explained only by some voluntary or at least adaptive action. The problem of how restraints on fertility could have evolved by natural selection has been tackled with group selection models as well as with stabilizing selection models. The latter model, which is critically discussed in this article, posits that some intermediate (rather than maximal) level of fertility is optimal for long-term reproductive success. Tests of stabilizing selection in human populations are rare, their results inconclusive. Here four sets of data are analyzed: they are samples drawn from the 'class of 1950 of the US Military Academy at West Point (cohorts 1923,29), retired US noncommissioned officers (cohorts 1913,37), and western German and eastern German physicians (cohorts 1930,35), all containing fertility data over two generations, and from European royalty (cohorts 1790,1939) containing fertility data over four generations. Deterministic as well as stochastic fitness measures are used. It is found that maximal, not average, fertility in the first generation leads to maximal long-term reproductive success. Also against prediction, no decreasing marginal fitness gains by increasing fertility can be observed. The findings leave little space for considering stabilizing selection as a plausible mechanism explaining the course of demographic transition but indicate instead that biological evolution today is as fast and vigorous as ever in human history. Even in large populations, all people living today may be the descendants of just some few percents,a much smaller proportion than generally believed, of the people living some generations ago. [source] p -Phenylenediamine and its dihydrate: two-dimensional isomorphism and mechanism of the dehydration process, and N,H...N and N,H..., interactionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2010Agnieszka Czapik p -Phenylenediamine can be obtained as the dihydrate, C6H8N2·2H2O, (I), and in its anhydrous form, C6H8N2, (II). The asymmetric unit of (I) contains one half of the p -phenylenediamine molecule lying about an inversion centre and two halves of water molecules, one lying on a mirror plane and the other lying across a mirror plane. In (II), the asymmetric unit consists of one molecule in a general position and two half molecules located around inversion centres. In both structures, the p -phenylenediamine molecules are arranged in layers stabilized by N,H..., interactions. The diamine layers in (I) are isostructural with half of the layers in (II). On dehydration, crystals of (I) transform to (II). Comparison of their crystal structures suggests the most plausible mechanism of the transformation process which requires, in addition to translational motion of the diamine molecules, in-plane rotation of every fourth p -phenylenediamine molecule by ca 60°. A search of the Cambridge Structural Database shows that the formation of hydrates by aromatic amines should be considered exceptional. [source] Abnormal B-cell cytokine responses a trigger of T-cell,mediated disease in MS?ANNALS OF NEUROLOGY, Issue 4 2010Amit Bar-Or MD, FRCP Objective To study antibody-independent contributions of B cells to inflammatory disease activity, and the immune consequences of B-cell depletion with rituximab, in patients with multiple sclerosis (MS). Methods B-Cell effector-cytokine responses were compared between MS patients and matched controls using a 3-signal model of activation. The effects of B-cell depletion on Th1/Th17 CD4 and CD8 T-cell responses in MS patients were assessed both ex vivo and in vivo, together with pharmacokinetic/pharmacodynamic studies as part of 2 rituximab clinical trials in relapsing,remitting MS. Results B Cells of MS patients exhibited aberrant proinflammatory cytokine responses, including increased lymphotoxin (LT):interleukin-10 ratios and exaggerated LT and tumor necrosis factor (TNF)-, secretion, when activated in the context of the pathogen-associated TLR9-ligand CpG-DNA, or the Th1 cytokine interferon-,, respectively. B-Cell depletion, both ex vivo and in vivo, resulted in significantly diminished proinflammatory (Th1 and Th17) responses of both CD4 and CD8 T cells. Soluble products from activated B cells of untreated MS patients reconstituted the diminished T-cell responses observed following in vivo B-cell depletion in the same patients, and this effect appeared to be largely mediated by B-cell LT and TNF,. Interpretation We propose that episodic triggering of abnormal B-cell cytokine responses mediates ,bystander activation' of disease-relevant proinflammatory T cells, resulting in new relapsing MS disease activity. Our findings point to a plausible mechanism for the long-recognized association between infections and new MS relapses, and provide novel insights into B-cell roles in both health and disease, and into mechanisms contributing to therapeutic effects of B-cell depletion in human autoimmune diseases, including MS. ANN NEUROL 2010;67:452,461 [source] Comment: A biological guide for electromagnetic safety: the stress responseBIOELECTROMAGNETICS, Issue 8 2004Martin Blank Abstract Questions of safety of electromagnetic (EM) fields should be based on relevant biological properties, i.e., specific cellular reactions to potentially harmful stimuli. The stress response is a well documented protective reaction of plant and animal cells to a variety of environmental threats, and it is stimulated by both extremely low frequency (ELF) and radio frequency (RF) EM fields. It involves activation of DNA to initiate synthesis of stress proteins. Thermal and non-thermal stimuli affect different segments of DNA and utilize different biochemical pathways. However, both ELF and RF stimulate the same non-thermal pathway. Since the same biochemical reactions are stimulated in different frequency ranges with very different specific absorption rates (SARs), SAR level is not a valid basis for safety standards. Studies of EM field interactions with DNA and with model systems provide insight into a plausible mechanism that can be effective in ELF and RF ranges. Bioelectromagnetics 25:642,646, 2004. © 2004 Wiley-Liss, Inc. [source] A role for genetic accommodation in evolution?BIOESSAYS, Issue 9 2006Christian Braendle Whether evolutionary change can occur by genetic assimilation, or more generally by genetic accommodation, remains controversial. Here we examine some of the experimental evidence for both phenomena. Several experiments in Drosophila suggest that assimilation is possible, and a new paper1 shows that a color polyphenism in the tobacco hornworm, Manduca sexta, can evolve by genetic accommodation. We argue that genetic accommodation, including assimilation, is a plausible mechanism in evolution; however, more work is required to test how this mechanism acts and how often it is involved in evolutionary change. BioEssays 28: 868,873, 2006. © 2006 Wiley periodicals, Inc. [source] Synthesis of Substituted 1,3-Diene Synthetic Equivalents by a Ru-Catalyzed Diyne Hydrative CyclizationCHEMISTRY - AN ASIAN JOURNAL, Issue 3 2006Barry Abstract Catalyzed by [CpRu(CH3CN)3]PF6, the hydrative cyclization of dipropargylic sulfone substrates provides an effective way to synthesize highly functionalized substituted 3-sulfolenes. The amount of water is crucial for the reactivity of this cycloisomerization reaction. The scope and limitations of the Ru-catalyzed cycloisomerization are discussed. A marked ketone-directing effect was observed for the first time in ruthenium-catalyzed cyclizations. A plausible mechanism for the ketone-directed cycloisomerization is also rationalized. The utility of this method was demonstrated by both sulfur dioxide extrusion of the 3-sulfolenes to afford 1,3-dienes and subsequent inter- or intramolecular Diels,Alder reactions. [source] | ||||||||||||||||||||||||||||||||||