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Irreversible
Terms modified by Irreversible Selected AbstractsCharacterization of Bordetella pertussis clinical isolates that do not express the tracheal colonization factorFEMS IMMUNOLOGY & MEDICAL MICROBIOLOGY, Issue 1 2007Marjolein Van Gent Abstract Bordetella pertussis, the causative agent of whooping cough, has remained endemic and there is a resurgence in some countries despite vaccination. Bordetella pertussis produces a wide range of virulence factors which are assumed to play an important role in infection and transmission, including tracheal colonization factor (TcfA). Here we show that clinical isolates belonging to distinct lineages may lose their ability to produce TcfA. Irreversible and reversible loss occurred, respectively, by recombination between repeats leading to deletion of the tcfA gene and by mutations in a polymorphic G-track. These phenomena may reflect adaptation to distinct niches. [source] NMR in photo-induced chemical exchange systems.CONCEPTS IN MAGNETIC RESONANCE, Issue 5 2006-dipyridyl)ethene photoisomerization kinetics, Double-resonance inverse fractional population transfer application for investigation of Abstract The analytical expression describing the dynamics of nuclear magnetization with the use of double-resonance NMR by the procedure of inverse fractional population transfer in requirements of photo-induced chemical exchange (PICE) is obtained in this article. Laser-induced (, = 308 nm) photoisomerization of 1,2-(2,2,-dipyridyl)ethene was studied by NMR and UV absorption spectroscopy under irreversible and photostationary conditions. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 337,346, 2006 [source] Differential physiologic responses of ,7 nicotinic acetylcholine receptors to ,-amyloid1,40 and ,-amyloid1,42DEVELOPMENTAL NEUROBIOLOGY, Issue 1 2003Daniel H.S. Lee Abstract The ,-amyloid peptides (A,), A,1,40 and A,1,42, have been implicated in Alzheimer's disease (AD) pathology. Although A,1,42 is generally considered to be the pathological peptide in AD, both A,1,40 and A,1,42 have been used in a variety of experimental models without discrimination. Here we show that monomeric or oligomeric forms of the two A, peptides, when interact with the neuronal cation channel, ,7 nicotinic acetylcholine receptors (,7nAChR), would result in distinct physiologic responses as measured by acetylcholine release and calcium influx experiments. While A,1,42 effectively attenuated these ,7nAChR-dependent physiology to an extent that was apparently irreversible, A,1,40 showed a lower inhibitory activity that could be restored upon washings with physiologic buffers or treatment with ,7nAChR antagonists. Our data suggest a clear pharmacological distinction between A,1,40 and A,1,42. © 2003 Wiley Periodicals, Inc. J Neurobiol 55: 25,30, 2003 [source] Cognitive impairment in schizophrenia:its impact on social functioningACTA PSYCHIATRICA SCANDINAVICA, Issue 400 2000P. F. Liddle Objective: To examine cognitive impairment in schizophrenia and its impact on social functioning. Method: Cohort studies recording cognitive and social development, studies of predictors of poor community outcome, and evidence from brain imaging studies are reviewed. Results: Executive function deficits, and poor performance in verbal memory, vigilance, and working memory tests are strong predictors of poor community outcome and impairment in skills learning. PET scans of regional cerebral blood flow suggest a dynamic imbalance between different cerebral areas rather than overall loss of brain function. Conclusion: Chronic cognitive impairment is the strongest predictor of social disability. Results suggest that the impairment of brain function associated with executive deficits is not necessarily irreversible and may therefore be treatable with appropriate drug therapy. [source] Long-term succession in a Danish temperate deciduous forestECOGRAPHY, Issue 2 2005Richard H. W. Bradshaw Forest successional trajectories covering the last 2000 yr from a mixed deciduous forest in Denmark show a gradual shift in dominance from Tilia cordata to Fagus sylvatica and a recent increase in total forest basal area since direct management ceased in 1948. The successions are reconstructed by combining a fifty-year record of direct tree observations with local pollen diagrams from Draved Forest, Denmark. Five of the seven successions record a heathland phase of Viking Age dating from 830 AD. The anthropogenic influence is considerable throughout the period of study even though Draved contains some of the most pristine forest stands in Denmark. Anthropogenic influence including felling masks the underlying natural dynamics, with the least disturbed sites showing the smallest compositional change. Some effects of former management, such as loss of Tilia cordata dominance, are irreversible. Artificial disturbance, particularly drainage, has accelerated and amplified the shift towards Fagus dominance that would have occurred on a smaller scale and at a slower rate in the absence of human intervention. [source] Species loss leads to community closureECOLOGY LETTERS, Issue 6 2000P. Lundberg Global extinction of a species is sadly irreversible. At a local scale, however, extinctions may be followed by re-invasion. We here show that this is not necessarily the case and that an ecological community may close its doors for re-invasion of species lost from it. Previous studies of how communities are assembled have shown that there may be rules for that process and that limitations are set to the order by which species are introduced and put together. Instead of focusing on the assembly process we randomly generated simple competitive model communities that were stable and allowed for two to 10 coexisting species. When a randomly selected single species was removed from the community, the cascading species loss was recorded and frequently the resulting community was more than halved. Cascading extinctions have previously been recorded, but we here show that the relative magnitude of the cascade is dependent on community size (and not only trophic structure) and that the reintroduction of the original species lost often is impossible. Hence, species loss does not simply leave a void potentially refilled, but permanently alters the entire community structure and consequently the adaptive landscape for potential re-invaders. [source] Social Learning in One-Arm Bandit ProblemsECONOMETRICA, Issue 6 2007Dinah Rosenberg We study a two-player one-arm bandit problem in discrete time, in which the risky arm can have two possible types, high and low, the decision to stop experimenting is irreversible, and players observe each other's actions but not each other's payoffs. We prove that all equilibria are in cutoff strategies and provide several qualitative results on the sequence of cutoffs. [source] Electrochemical Investigation of Heavy Metal Ion Transfer Across the Water/1,2-Dichloroethane Interface Assisted by 9-Ethyl-3-Carbazolecarboxaldehyde-ThiosemicarbazoneELECTROANALYSIS, Issue 12 2007Haluk Bingol Abstract The transfer of heavy metal ions across the polarized water/1,2-dichloroethane (1,2-DCE) interface assisted by 9-ethyl-3-carbazolecarboxaldehyde-thiosemicarbazone (ECCAT) in the 1,2-DCE phase has been studied by cyclic voltammetry. Voltammetric waves of Pb(II) and Cd(II) ions were reversible and quasi-reversible, respectively, whereas that of Hg(II) and Zn(II) ion were irreversible. The voltammogram of Cu(II) ion showed a two-step wave, however the nature of the transfer could not be satisfactorily evaluated by analyzing the cyclic voltammetric data. When Ni(II) and Co(II) was used no peak was visible under the experimental conditions used in this study. The dependence of the half-wave potentials of Pb(II) and Cd(II) ions on the ligand concentration reveals that their ion-transfer is assisted by the formation of 1:3 metal-ECCAT complex in 1,2-DCE. The over-all association constants of [Pb(ECCAT)3]2+ and [Cd(ECCAT)3]2+ complexes in DCE-phase have been determined to be log ,=14.03 and log ,=15.44, respectively. [source] Microwave Activation of Electrochemical Processes at Glassy Carbon and Boron-Doped Diamond ElectrodesELECTROANALYSIS, Issue 5-6 2005Kumar Sur, Ujjal Abstract Voltammetric experiments under intense microwave field conditions have been carried out at a carbon microfiber electrode, an array of carbon microfiber electrodes, and at a boron-doped diamond electrode. For the reversible one electron redox systems Fe(CN) and Ru(NH3) in aqueous KCl solution increased currents (up to 16 fold at a 33,,m diameter carbon microelectrode) and superheating (up to ca. 400,K at all types of electrodes) are observed. Electrodes with smaller diameter allow better signal enhancements to be achieved. From the missing effect of the supporting electrolyte concentration on the microwave enhanced currents, it can be concluded that effects observed at carbon electrodes (microwave absorbers) are due to the interaction of microwaves with the electrode material whereas for metal electrodes (microwave conductors) effects are dominated by the interaction of the microwaves with the aqueous dielectric. Short heat pulses can be applied by pulsing the microwave field and relatively fast temperature transients are observed for small electrodes. For the irreversible two electron oxidation of L -dopa in aqueous phosphate buffer, different types of effects are observed at glassy carbon and at boron-doped diamond. Arrays of carbon microfibers give the most reproducible and analytically useful current signal enhancements in the presence of microwaves. [source] Fast immobilization of probe beads by dielectrophoresis-controlled adhesion in a versatile microfluidic platform for affinity assayELECTROPHORESIS, Issue 19 2005Janko Auerswald Dr. Abstract The use of probe beads for lab-on-chip affinity assays is very interesting from a practical point of view. It is easier to handle and trap beads than molecules in microfluidic systems. We present a method for the immobilization of probe beads at defined areas on a chip using dielectrophoresis (DEP)-controlled adhesion. The method is fast, i.e., it takes between 10 and 120,s , depending on the protocol , to functionalize a chip surface at defined areas. The method is versatile, i.e., it works for beads with different types of probe molecule coatings. The immobilization is irreversible, i.e., the retained beads are able to withstand high flow velocities in a flow-through device even after the DEP voltage is turned off, thus allowing the use of conventional high-conductivity analyte buffers in the following assay procedure. We demonstrate the on-chip immobilization of fluorescent beads coated with biotin, protein,A, and goat,antimouse immunoglobulin G (IgG). The number of immobilized beads at an electrode array can be determined from their fluorescence signal. Further, we use this method to demonstrate the detection of streptavidin and mouse IgG. Finally, we demonstrate the feasibility of the parallel detection of different analyte molecules on the same chip. [source] Use of a site-specific recombination-based biosensor for detecting bioavailable toluene and related compounds on rootsENVIRONMENTAL MICROBIOLOGY, Issue 4 2003N. Carol Casavant Summary We constructed and characterized a plasmid-based genetic system that reports the expression of a toluene-responsive promoter (PtbuA1) by effecting an irreversible, heritable change in the biosensor cell. Expression of the reporter gene gfp is strongly repressed in the absence of expression from the PtbuA1 promoter, and high level gfp expression in the original cell and its progeny is mediated by the site-specific recombination machinery of bacteriophage P22 to initiate removal of a repressor cassette. The reporter plasmid pTolLHB was functional in two soil saprophytes, Pseudomonas fluorescens A506 and Enterobacter cloacae JL1157, with the efficiency and sensitivity to low toluene concentrations being optimal in P. fluorescens A506. In culture, 80,100% of the A506 (pTolLHB) population expressed gfp following exposure to 0.2 µm toluene for one to three hours. Compared to the response of A506 containing a plasmid-borne PtbuA1 - gfp fusion, the recombination-based biosensor was more sensitive at detecting low toluene and trichloroethylene concentrations. An A506 (pTolLHB) inoculum, which had a background of 2.5% of the cells expressing gfp, was introduced onto barley roots in soil microcosms. If toluene was introduced into the microcosms, after 24 h, 72% of the A506 (pTolLHB) cells recovered from roots expressed gfp, indicating bioavailable toluene to rhizosphere bacteria. When toluene was not introduced, 16.5% of the A506 (pTolLHB) cells recovered from the roots expressed gfp, indicating that natural inducers of the PtbuA1 promoter were present in the barley rhizosphere. When introduced into rhizotrons containing barley plants and toluene vapours, the biosensor allowed localization of the availability of toluene along the seminal roots. In rhizotrons that were not exposed to toluene vapours, the biosensor exhibited high PtbuA1 -promoter activity in distinct regions along the seminal roots, indicating spatial heterogeneity plant- or rhizosphere microbial community-derived inducers of the PtbuA1 promoter. This recombination-based toluene biosensor thus was useful in identifying bacterial exposure to transient or low levels of toluene, or related compounds, directly in the environment. [source] Differential inhibition in vivo of ammonia monooxygenase, soluble methane monooxygenase and membrane-associated methane monooxygenase by phenylacetyleneENVIRONMENTAL MICROBIOLOGY, Issue 5 2000Sonny Lontoh Phenylacetylene was investigated as a differential inhibitor of ammonia monooxygenase (AMO), soluble methane monooxygenase (sMMO) and membrane-associated or particulate methane monooxygenase (pMMO) in vivo. At phenylacetylene concentrations >,1 µM, whole-cell AMO activity in Nitrosomonas europaea was completely inhibited. Phenylacetylene concentrations above 100 µM inhibited more than 90% of sMMO activity in Methylococcus capsulatus Bath and Methylosinus trichosporium OB3b. In contrast, activity of pMMO in M. trichosporium OB3b, M. capsulatus Bath, Methylomicrobium album BG8, Methylobacter marinus A45 and Methylomonas strain MN was still measurable at phenylacetylene concentrations up to 1000 µM. AMO of Nitrosococcus oceanus has more sequence similarity to pMMO than to AMO of N. europaea. Correspondingly, AMO in N. oceanus was also measurable in the presence of 1000 µM phenylacetylene. Measurement of oxygen uptake indicated that phenylacetylene acted as a specific and mechanistic-based inhibitor of whole-cell sMMO activity; inactivation of sMMO was irreversible, time dependent, first order and required catalytic turnover. Corresponding measurement of oxygen uptake in whole cells of methanotrophs expressing pMMO showed that pMMO activity was inhibited by phenylacetylene, but only if methane was already being oxidized, and then only at much higher concentrations of phenylacetylene and at lower rates compared with sMMO. As phenylacetylene has a high solubility and low volatility, it may prove to be useful for monitoring methanotrophic and nitrifying activity as well as identifying the form of MMO predominantly expressed in situ. [source] Sorption irreversibility of 1,4-dichlorobenzene in two natural organic matter,rich geosorbentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2009Michael Sander Abstract Hysteresis, a frequently observed phenomenon in sorption studies, is inconsistent with the key assumption of sorption reversibility in most fate and bioavailability models. Therefore, a study of the underlying causes of hysteresis is essential. Carbon-radiolabeled 1,4-dichlorobenzene (DCB) isotope tracer exchange was carried out at select points along the isotherms of DCB in a brown coal and a peat soil, holding total DCB concentration constant. Tracer exchange was performed both in the forward (sorption) and reverse (desorption) directions at the bulk sorption points and in the desorption direction at the corresponding bulk desorption points. Bulk DCB isotherms showed concentration-dependent hysteresis. However, tracer reequilibration in all cases was consistent with free exchange between sorbed and aqueous-phase molecules. These results rule out common experimental artifacts and demonstrate that sorption of bulk DCB is truly hysteretic (i.e., irreversible). The differences in rates between bulk and tracer sorption and desorption are consistent with the coupling of bulk DCB diffusion to other processes that retard equilibration, which we assign to matrix swelling or shrinking. Hysteresis is attributed to matrix deformation,specifically, to inelastic expansion and creation of voids accommodating sorbate molecules in the matrix, which leads to enhanced affinity in the desorption step. Comparing the results to previous results for naphthalene in the coal, we find that irreversible effects are similar for DCB and naphthalene in the coal but differ for DCB between the two sorbents. An explanation based on the different physical properties of these sorbents is provided. Solid-phase extraction of equilibrated DCB with Tenax® revealed a highly desorption-resistant fraction. While too small to account for the observed hysteresis, this fraction may represent molecules that become trapped as the matrix collapses and simultaneously stiffens during abrupt desorption. [source] Two clinical manifestations of desmopathy of the accessory ligament of the deep digital flexor tendon in the hindlimb of 23 horsesEQUINE VETERINARY JOURNAL, Issue 6 2005E. ELIASHAR Summary Reasons for performing study: Desmopathy of the accessory ligament of the deep digital flexor tendon (ALDDFT) in the hindlimb is an unusual cause of lameness in horses, and reports of the condition are sparse. Objectives: To describe the clinical and ultrasonographic findings, therapy and outcome of 23 horses treated for desmopathy of the ALDDFT in the hindlimb. Methods: Records of 23 horses with ultrasonographic evidence of desmopathy of the ALDDFT in one or both hindlimbs from 3 referral centres were reviewed retrospectively. Age, breed, sex, duration and nature of clinical signs, results of clinical and lameness examinations, treatment and outcome were recorded. Results: In 13 horses (Group A), there was an acute onset of unilateral lameness. Ten horses (Group B) had an insidious or sudden onset of postural abnormality. There were 10 cobs, 5 British native-breed ponies and 8 horses of various larger breeds. Twenty horses were used for general purposes, and mean age was 12 years. Enlargement of the ALDDFT in the affected hindlimb(s) was identified in all horses. In 44% of horses, ultrasonographic abnormalities were localised to part of the ALDDFT. Treatment included box-rest and controlled exercise, and 10 horses were subjected to desmotomy or desmectomy of the ALDDFT. Seventy-three percent of horses in Group A returned to full function, while 90% of those in Group B remained lame. Conclusions: Two distinct clinical conditions are associated with the ALDDFT of the hindlimb. Traumatically induced injury resulting in acute onset lameness appears to have a favourable prognosis, with most horses returning to previous work. However, postural changes, once present, are irreversible and indicate a poor prognosis. Potential relevance: Desmopathy of the ALDDFT should be recognised as a potential cause of hindlimb lameness and this study provides clinical and prognostic information. Knuckling and/or semiflexion of the metatarsophalangeal joint may accompany the condition; therefore, if a horse is presented with a flexural deformity of this joint, desmopathy of the ALDDFT should be considered as a primary differential diagnosis. [source] Bulk Nanostructured Materials: Non-Mechanical Synthesis,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Yulia Ivanisenko An overview of the synthesis and processing techniques for bulk nanostructured materials that are based on "bottom-up" approaches is presented. Typically, these processes use nanoparticles, which can be produced by a variety of methods in the gas, liquid or solid state, as the basic building blocks. Their assembly into bulk nanostructured materials requires at least one more processing step, such as compaction or the formation of thick films. For certain nanostructures, film deposition techniques can also be employed. A wide range of nanostructures , from thick films with theoretical density to bulk nanocrystalline materials with nanoporosity , exhibiting novel structural and functional properties useful in many fields of applications are presented. Additionally, the properties of these bulk nanostructured materials can be categorized as either tailored, i.e., microstructure-dependent and inherently irreversible, or tunable, i.e., reversible by the application of an external field. Examples of both categories of properties are presented and the special role of the synthesis and processing routes to achieve the necessary nanostructures is emphasized. [source] ,-Conotoxin CVIB differentially inhibits native and recombinant N- and P/Q-type calcium channelsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2007Leonid Motin Abstract ,-Conotoxins are routinely used as selective inhibitors of different classes of voltage-gated calcium channels (VGCCs) in excitable cells. In the present study, we examined the potent N-type VGCC antagonist ,-conotoxin CVID and non-selective N- and P/Q-type antagonist CVIB for their ability to block native VGCCs in rat dorsal root ganglion (DRG) neurons and recombinant VGCCs expressed in Xenopus oocytes. ,-Conotoxins CVID and CVIB inhibited depolarization-activated whole-cell VGCC currents in DRG neurons with pIC50 values of 8.12 ± 0.05 and 7.64 ± 0.08, respectively. Inhibition of Ba2+ currents in DRG neurons by CVID (, 66% of total) appeared to be irreversible for >,30 min washout, whereas Ba2+ currents exhibited rapid recovery from block by CVIB (, 80% within 3 min). The recoverable component of the Ba2+ current inhibited by CVIB was mediated by the N-type VGCC, whereas the irreversibly blocked current (, 22% of total) was attributable to P/Q-type VGCCs. ,-Conotoxin CVIB reversibly inhibited Ba2+ currents mediated by N- (CaV2.2) and P/Q- (CaV2.1), but not R- (CaV2.3) type VGCCs expressed in Xenopus oocytes. The ,2,1 auxiliary subunit co-expressed with CaV2.2 and CaV2.1 reduced the sensitivity of VGCCs to CVIB but had no effect on reversibility of block. Determination of the NMR structure of CVIB identified structural differences to CVID that may underlie differences in selectivity of these closely related conotoxins. ,-Conotoxins CVIB and CVID may be useful as antagonists of N- and P/Q-type VGCCs, particularly in sensory neurons involved in processing primary nociceptive information. [source] Accession's Democracy Dividend: The Impact of the EU Enlargement upon Democracy in the New Member States of Central and Eastern EuropeEUROPEAN LAW JOURNAL, Issue 4 2004Wojciech Sadurski The purpose of this article is to examine this claim, that accession will provide a ,democracy dividend' in this fashion. To this end, the article begins by examining the political conditionality of the accession process, and the extent to which the process of democratisation can be understood as a result of ,external' pressures. It also discusses the extent to which the effectiveness of political conditionality is likely to survive after the accession takes place. The article then moves on to consider the effects of accession upon democracy in the states of the region by looking in detail at three areas that have been particularly important: the role of national parliaments, the new constitutional courts, and the tendency towards decentralisation and regionalism. The article concludes by noting that, although not all of the developments discussed are necessarily good for democracy in the region, the real dividend coming from the accession process lies in the fact that, on a macro-level, membership in the EU will make the democratic transition in Central and Eastern Europe practically irreversible. [source] 7,8-Diaminoperlargonic acid aminotransferase from Mycobacterium tuberculosis, a potential therapeutic targetFEBS JOURNAL, Issue 20 2006Characterization, inhibition studies Diaminopelargonic acid aminotransferase (DAPA AT), which is involved in biotin biosynthesis, catalyzes the transamination of 8-amino-7-oxononanoic acid (KAPA) using S -adenosyl- l -methionine (AdoMet) as amino donor. Mycobacterium tuberculosis DAPA AT, a potential therapeutic target, has been overproduced in Escherichia coli and purified to homogeneity using a single efficient step on a nickel-affinity column. The enzyme shows an electronic absorption spectrum typical of pyridoxal 5,-phosphate-dependent enzymes and behaves as a homotetramer in solution. The pH profile of the activity at saturation shows a single ionization group with a pKa of 8.0, which was attributed to the active-site lysine residue. The enzyme shows a Ping Pong Bi Bi kinetic mechanism with strong substrate inhibition with the following parameters: KmAdoMet = 0.78 ± 0.20 mm, KmKAPA = 3.8 ± 1.0 µm, kcat = 1.0 ± 0.2 min,1, KiKAPA = 14 ± 2 µm. Amiclenomycin and a new analogue, 4-(4c -aminocyclohexa-2,5-dien-1r -yl)propanol (referred to as compound 1), were shown to be suicide substrates of this enzyme, with the following inactivation parameters: Ki = 12 ± 2 µm, kinact = 0.35 ± 0.05 min,1, and Ki = 20 ± 2 µm, kinact = 0.56 ± 0.05 min,1, for amiclenomycin and compound 1, respectively. The inactivation was irreversible, and the partition ratios were 1.0 and 1.1 for amiclenomycin and compound 1, respectively, which make these inactivators particularly efficient. compound 1 (100 µg·mL,1) completely inhibited the growth of an E. coli C268bioA mutant strain transformed with a plasmid expressing the M. tuberculosis bioA gene, coding for DAPA AT. Reversal of the antibiotic effect was observed on the addition of biotin or DAPA. Thus, compound 1 specifically targets DAPA AT in vivo. [source] The Effects of Moisture in Low-Voltage Organic Field-Effect Transistors Gated with a Hydrous Solid ElectrolyteADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Nikolai Kaihovirta Abstract The concept of using ion conducting membranes (50,150 ,m thick) for gating low-voltage (1 V) organic field-effect transistors (OFETs) is attractive due to its low-cost and large-area manufacturing capabilities. Furthermore, the membranes can be tailor-made to be ion conducting in any desired way or pattern. For the electrolyte gated OFETs in general, the key to low-voltage operation is the electrolyte "insulator" (the membrane) that provides a high effective capacitance due to ionic polarization within the insulator. Hydrous ion conducting membranes are easy to process and readily available. However, the role of the water in combination with the polymeric semiconductor has not yet been fully clarified. In this work electrical and optical techniques are utilized to carefully monitor the electrolyte/semiconductor interface in an ion conducting membrane based OFET. The main findings are that 1) moisture plays a major part in the transistor operation and careful control of both the ambient atmosphere and the potential differences between the electrodes are required for stable and consistent device behavior, 2) the obtained maximum effective capacitance (5 ,F cm,2) of the membrane suggests that the electric double layer is distributed over a broad region within the polyelectrolyte, and 3) electromodulation spectroscopy combined with current,voltage characteristics provide a method to determine the threshold gate voltage from an electrostatic field-effect doping to a region of (irreversible) electrochemical perturbation of the polymeric semiconductor. [source] The Influence of Surface Chemistry and Pore Size on the Adsorption of Proteins on Nanostructured Carbon MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Munusami Vijayaraj Abstract Carbon films are synthesized by templating of anodic aluminum oxide films. These carbon materials exhibit nanochannels with controlled diameter and length. Selected chemical treatments are done to tailor the surface chemistry. The adsorption capacities of bovine serum albumin and cytochrome c are measured by temperature-programmed desorption with mass spectrometry (TPD-MS) analysis and with conventional biological assays. The first method allows quantification of the proteins that exhibit strong interactions with the surface, while the second one is used to obtain the total adsorption capacity. Moreover, the TPD-MS profiles, which are related to the structural modifications of the proteins during the adsorption, show that strong interactions take place with hydrophobic surfaces. When oxygenated functions are present, the adsorption capacity increases and the nature of the interactions is modified. The ratio of irreversible to reversible adsorption is significantly different for the two proteins, and is slightly related to the surface chemistry. The influence of nanochannel size is studied: below 50 nm, the coverage ratio shows that access to the porosity is limited by diffusion in the channel and by pore plugging, in agreement with the strong interactions of proteins with the carbon surface. [source] Thermally induced conformational changes in horseradish peroxidaseFEBS JOURNAL, Issue 1 2001David G. Pina Detailed differential scanning calorimetry (DSC), steady-state tryptophan fluorescence and far-UV and visible CD studies, together with enzymatic assays, were carried out to monitor the thermal denaturation of horseradish peroxidase isoenzyme c (HRPc) at pH 3.0. The spectral parameters were complementary to the highly sensitive but integral method of DSC. Thus, changes in far-UV CD corresponded to changes in the overall secondary structure of the enzyme, while that in the Soret region, as well as changes in intrinsic tryptophan fluorescence emission, corresponded to changes in the tertiary structure of the enzyme. The results, supported by data about changes in enzymatic activity with temperature, show that thermally induced transitions for peroxidase are irreversible and strongly dependent upon the scan rate, suggesting that denaturation is under kinetic control. It is shown that the process of HRPc denaturation can be interpreted with sufficient accuracy in terms of the simple kinetic scheme where k is a first-order kinetic constant that changes with temperature, as given by the Arrhenius equation; N is the native state, and D is the denatured state. On the basis of this model, the parameters of the Arrhenius equation were calculated. [source] New Organic Nonlinear Optical Polyene Crystals and Their Unusual Phase Transitions,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2007O-P. Kwon Abstract A series of new nonlinear optical chromophores based on configurationally locked polyenes (CLPs) with chiral pyrrolidine donors are synthesized. All CLP derivatives exhibit high thermal stability with decomposition temperatures Td at least > ,270,°C. Acentric single crystals of enantiopure D - and L -prolinol-based chromophores with a monoclinic space group P21 exhibit a macroscopic second-order nonlinearity that is twice as large than that of analogous dimethylamino-based crystal. This is attributed to a strong hydrogen-bonded polar polymer-like chain built by these molecules, which is aligned along the polar crystallographic b -axis. Five ,-phase CLP crystals with different donors grown from solution exhibit a reversible or irreversible thermally induced structural phase transition to a ,-phase. These phase transitions are unusual, changing the crystal symmetry from higher to lower at increasing temperatures, for example, from centrosymmetric to non-centrosymmetric, enhancing their macroscopic second-order nonlinear optical properties. [source] Histologic and biochemical changes during the evolution of chronic rejection of liver allograftsHEPATOLOGY, Issue 3 2002Desley A. H. Neil Criteria for histologic diagnosis of chronic rejection (CR) are based on changes seen late in the disease process that are likely to be irreversible and unresponsive to treatment. Changes occurring during the evolution of CR are less clearly defined. The serial biopsy specimens, failed allografts, and biochemical profiles of 28 patients who underwent retransplantation for CR were examined with the aim of identifying histologic and biochemical features that were present during the early stages of CR. For each case, a point of acute deterioration in liver function tests (LFTs) was identified ("start time" [ST]) that subsequently progressed to graft failure. Biopsy specimens before, at the time of ("start biopsy" [SB]), and after the ST were assessed histologically, and findings were correlated with the biochemical changes. CR resulted from acute rejection (AR) that did not resolve. Centrilobular necroinflammation (CLNI) associated with an elevated aspartate transaminase (AST) level and portal tract features of AR were present at the start. Portal AR features resolved, CLNI persisted, AST level remained elevated, and bilirubin and alkaline phosphatase levels progressively increased throughout the evolution of CR. Portal tracts also showed a loss of small arterial and bile duct branches, with arterial loss occurring early and bile duct loss as a later progressive lesion. Foam cell arteriopathy was rarely seen in needle biopsy specimens. In conclusion, findings from this study may help identify patients at risk of progressing to graft loss from CR at a stage when the disease process is potentially reversible and amenable to treatment. [source] Efficacy of citalopram and moclobemide in patients with social phobia: some preliminary findingsHUMAN PSYCHOPHARMACOLOGY: CLINICAL AND EXPERIMENTAL, Issue 8 2002Murad Atmaca Abstract The efficacy of irreversible and reversible monoamine oxidase inhibitors (MAOIs) in the treatment of social phobia (SP) is well established. Recently, selective serotonin reuptake inhibitors (SSRIs) have been used more frequently. In the present study, the efficacy and side-effect profile of citalopram, an SSRI, and moclobemide, the only MAOI used in Turkey, were compared. The 71 patients diagnosed with SP according to DSM-III-R were randomly assigned to two subgroups; citalopram (n,=,36) or moclobemide (n,=,35). The study was an 8-week, randomized, open-label, rater-blinded, parallel-group trial. All patients were assessed by Hamilton anxiety rating (HAM-A), Liebowitz social anxiety (LSAS), clinical global impression-severity of illness (CGI-SI) and clinical global impression-improvement (CGI-I) scales. There was a similar percentage of responders (citalopram 75%, n,=,27 and moclobemide 74.3%, n,=,26), with a >50% or greater reduction in LSAS total score and ratings of ,very much' or ,much improved' on the CGI-I. None of the patients withdrew from the study. The results of the present study suggest that citalopram has shown promising results in patients with SP. Copyright © 2002 John Wiley & Sons, Ltd. [source] Tuning the Amphiphilicity of Building Blocks: Controlled Self-Assembly and Disassembly for Functional Supramolecular Materials,ADVANCED MATERIALS, Issue 28 2009Yapei Wang Abstract Amphiphilicity is one of the molecular bases for self-assembly. By tuning the amphiphilicity of building blocks, controllable self-assembly can be realized. This article reviews different routes for tuning amphiphilicity and discusses different possibilities for self-assembly and disassembly in a controlled manner. In general, this includes irreversible and reversible routes. The irreversible routes concern irreversible reactions taking place on the building blocks and changing their molecular amphiphilicity. The building blocks are then able to self-assemble to form different supramolecular structures, but cannot remain stable upon loss of amphiphilicity. Compared to the irreversible routes, the reversible routes are more attractive due to the good control over the assembly and disassembly of the supramolecular structure formed via tuning of the amphiphilicity. These routes involve reversible chemical reactions and supramolecular approaches, and different external stimuli can be used to trigger reversible changes of amphiphilicity, including light, redox, pH, and enzymes. It is anticipated that this line of research can lead to the fabrication of new functional supramolecular assemblies and materials. [source] A numerical model for the cyclic deterioration of railway tracksINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2003Akke S. J. Suiker Abstract An elasto-plastic material model is proposed that can be used to simulate the cyclic deterioration of railway tracks. The model describes the envelope of the irreversible, plastic material response generated during a cyclic loading process, thereby distinguishing the mechanisms of frictional sliding and volumetric compaction. The reversible response is represented by a pressure-dependent, hypo-elastic material law. After the numerical integration of the model is specified, the model is calibrated on laboratory experiments and employed in a finite-element case study of the long-term settlement behaviour of a railway track. The main features of the model are illustrated by comparing the computed response with the response obtained by in situ track measurements. Copyright © 2003 John Wiley & Sons, Ltd. [source] The reactive Riemann problem for thermally perfect gases at all combustion regimesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2010A. Beccantini Abstract In this work we analyze the reactive Riemann problem for thermally perfect gases in the deflagration or detonation regimes. We restrict our attention to the case of one irreversible infinitely fast chemical reaction; we also suppose that, in the initial condition, one state (for instance the left one) is burnt and the other one is unburnt. The indeterminacy of the deflagration regime is removed by imposing a (constant) value for the fundamental flame speed of the reactive shock. An iterative algorithm is proposed for the solution of the reactive Riemann problem. Then the reactive Riemann problem and the proposed algorithm are investigated from a numerical point of view in the case in which the unburnt state consists of a stoichiometric mixture of hydrogen and air at almost atmospheric condition. In particular, we revisit the problem of 1D plane-symmetric steady flames in a semi-infinite domain and we verify that the transition from one combustion regime to another occurs continuously with respect to the fundamental flame speed and the so-called piston velocity. Finally, we use the ,all shock' solution of the reactive Riemann problem to design an approximate (,all shock') Riemann solver. 1D and 2D flows at different combustion regimes are computed, which shows that the approximate Riemann solver, and thus the algorithm we use for the solution of the reactive Riemann problem, is robust in both the deflagration and detonation regimes. Copyright © 2009 John Wiley & Sons, Ltd. [source] Differential effect of hyperthyroidism on rat epididymal glycosidasesINTERNATIONAL JOURNAL OF ANDROLOGY, Issue 4 2001R. R. M. Maran The impact of hyperthyroidism on epididymal glycosidases was studied in albino rats. Hyperthyroidism was induced in Wistar rats aged 30 days by daily injection of T4 (25 ,g/100 g body weight/day intramuscularly) for 30 or 60 days; control rats were injected with vehicle (alkaline saline, pH 7.8). One set of hyperthyroid rats was reverted to euthyroid status by withdrawing T4 treatment after 30 days of hyperthyroidism. To asses the direct effect of thyroid hormone on epididymal hexosaminidases, caput, corpus and cauda tissues were stimulated with 25, 50 or 100 ng/mL T3 for 24 h, after an initial culture of 24 h. The activity of ,-glucosidase decreased in caput, corpus and cauda epididymis of hyperthyroid rats. ,-Galactosidase activity increased in the caput epididymis irrespective of the duration of hyperthyroidism. While a similar decrease occurred in the corpus and cauda epididymis in the 30 day hyperthyroid group, an opposite trend was observed in 60 day hyperthyroid rats. Caput ,- N -acetylglucosaminidase activities increased at both time points, whereas activity decreased in the corpus and cauda in 30 day, but increased in 60 day hyperthyroid rats. Hyperthyroidism consistently increased caput and corpus ,- N -acetylgalactosaminidase activity irrespective of the duration. Cauda epididymal ,- N -acetylgalactosaminidase activity was decreased in 30 day and increased in 60 day hyperthyroid rats. Hyperthyroidism induced changes in caput ,-galactosidase, ,- N -acetylgalactosaminidases, corpus ,-N-acetylglucosaminidase and cauda ,- N -acetylgalactosaminidase which were irreversible while the remaining actvities were brought back to normal when T4 treatment was withdrawn. In vitro studies showed that T3 stimulates epididymal hexosaminidases (,- N -acetylglucosaminidase and ,- N -acetylgalactosaminidase) irrespective of the dose. These data suggest that thyroid hormones have a specific and direct influence on glycosidases in specific regions of the epididymis. [source] Rasagiline: defining the role of a novel therapy in the treatment of Parkinson's diseaseINTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 2 2006F. Stocchi Summary Parkinson's disease (PD) is a therapy area with considerable unmet needs. The current key targets for PD treatment include the slowing of disease progression, improved control of motor fluctuations in advanced disease and the treatment of nonmotor symptoms. In view of such major requirements, it is important to consider how new drug treatments fit into the context of PD therapy, and the practical advantages that they may offer in the management of PD in clinical practice. Rasagiline is a novel, second-generation, irreversible, selective monoamine oxidase type B inhibitor that is indicated for the treatment of idiopathic PD, either as initial monotherapy or as adjunct therapy (with levodopa) for patients experiencing end-of-dose motor fluctuations. This review assesses the outcome from several large-scale clinical studies that have investigated the use of rasagiline in early and advanced PD patient populations and discusses the role of rasagiline within the current scope of PD therapy. [source] ESR detection of irradiated broad bean (Vicia faba L.) and kinetics of the radiation induced free radical and Mn2+ signalsINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 6 2003Mustafa Polat Summary An ESR (Electron Spin Resonance) investigation on irradiated dry broad bean gave a spectrum which was composed of an equally spaced sextet and a single resonance line. These lines appeared at g = 2.0045 (±0.0005) and originated from Mn2+ ions and radiation induced radicals, respectively. Ground broad bean was used throughout the work to avoid any artefacts arising from a microwave cavity filling factor. Free radical signal intensity was observed to increase exponentially in relation to the increase in absorbed dose over the dose range 1.25,15 kGy. Although the Mn2+ signal increases below room temperature, the signal due to the natural and radiation induced radicals decreases. Above room temperature, they both decreased and these decreases were irreversible. The kinetics of these decreases were studied in detail over a temperature range of 308,373 K by annealing samples at different temperatures for various times. [source] | ||||||||||||||||||||||||||||||||||||||||||||||