Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Substrate

  • GaA substrate
  • InA substrate
  • SER substrate
  • acceptor substrate
  • al2o3 substrate
  • alcohol substrate
  • aldehyde substrate
  • alloy substrate
  • allylic substrate
  • alternative substrate
  • alumina substrate
  • aluminum substrate
  • anatomical substrate
  • appropriate substrate
  • arboreal substrate
  • aromatic substrate
  • arrhythmogenic substrate
  • artificial substrate
  • atrial substrate
  • available substrate
  • b substrate
  • bare substrate
  • best substrate
  • biological substrate
  • bound substrate
  • bulk gan substrate
  • c substrate
  • calcareous substrate
  • calpain substrate
  • candidate substrate
  • carbon substrate
  • cellular substrate
  • cellulosic substrate
  • ceramic substrate
  • chiral substrate
  • chromogenic substrate
  • coarse substrate
  • common substrate
  • complex substrate
  • composite substrate
  • conducting substrate
  • copper substrate
  • crystalline substrate
  • culture substrate
  • cyclic substrate
  • diamond substrate
  • dielectric substrate
  • different substrate
  • dna substrate
  • donor substrate
  • electroanatomic substrate
  • electrophysiological substrate
  • endogenous substrate
  • energy substrate
  • enzyme substrate
  • exogenous substrate
  • ferrite substrate
  • film substrate
  • first substrate
  • flat substrate
  • flexible polymer substrate
  • flexible substrate
  • fluorescent substrate
  • fluorogenic substrate
  • food substrate
  • fused silica substrate
  • gan substrate
  • glass substrate
  • gold substrate
  • good substrate
  • gravel substrate
  • growth substrate
  • hard substrate
  • homogeneous substrate
  • hydrophobic substrate
  • imine substrate
  • important substrate
  • inp substrate
  • insulin receptor substrate
  • kinase c substrate
  • kinase substrate
  • limiting substrate
  • ltcc substrate
  • main substrate
  • major substrate
  • metabolic substrate
  • metal substrate
  • metallic substrate
  • mgo substrate
  • mica substrate
  • model substrate
  • morphological substrate
  • multiple substrate
  • native substrate
  • natural substrate
  • nesting substrate
  • neural substrate
  • neuroanatomical substrate
  • neurobiological substrate
  • neuronal substrate
  • new substrate
  • novel substrate
  • of substrate
  • olefin substrate
  • organic substrate
  • other substrate
  • oviposition substrate
  • oxide substrate
  • p-glycoprotein substrate
  • p-gp substrate
  • paper substrate
  • particle substrate
  • pc substrate
  • peptide substrate
  • phenolic substrate
  • physiological substrate
  • piezoelectric substrate
  • planar substrate
  • plane sapphire substrate
  • plant substrate
  • plastic substrate
  • polar substrate
  • polyimide substrate
  • polymer substrate
  • polymeric substrate
  • poor substrate
  • porous substrate
  • potential substrate
  • prefer substrate
  • preferential substrate
  • probe substrate
  • protein kinase c substrate
  • protein substrate
  • putative substrate
  • quartz substrate
  • racemic substrate
  • receptor substrate
  • rigid substrate
  • rna substrate
  • rock substrate
  • rocky substrate
  • same substrate
  • sandy substrate
  • sapphire substrate
  • second substrate
  • secretion substrate
  • selective substrate
  • several substrate
  • sic substrate
  • silica substrate
  • silicon substrate
  • single substrate
  • sio2 substrate
  • soft substrate
  • sole substrate
  • solid substrate
  • soluble substrate
  • specific substrate
  • srtio3 substrate
  • stainless steel substrate
  • steel substrate
  • straw substrate
  • sugar substrate
  • suitable substrate
  • synthetic substrate
  • target substrate
  • test substrate
  • tested substrate
  • titanium substrate
  • transparent substrate
  • transport substrate
  • transporter substrate
  • underlying substrate
  • useful substrate
  • variety of substrate
  • various substrate
  • vicinal substrate
  • vitro substrate
  • zno substrate

  • Terms modified by Substrate

  • substrate acceptance
  • substrate access
  • substrate activation
  • substrate addition
  • substrate adhesion
  • substrate affinity
  • substrate analog
  • substrate analogue
  • substrate availability
  • substrate binding
  • substrate binding site
  • substrate characteristic
  • substrate cleavage
  • substrate complex
  • substrate composition
  • substrate concentration
  • substrate configuration
  • substrate conversion
  • substrate d
  • substrate diameter
  • substrate drug
  • substrate effects
  • substrate electrode
  • substrate flux
  • substrate geometry
  • substrate hydrolysis
  • substrate inhibition
  • substrate inhibitor
  • substrate integrate waveguide
  • substrate interaction
  • substrate interface
  • substrate loss
  • substrate material
  • substrate metabolism
  • substrate molecule
  • substrate orientation
  • substrate oxidation
  • substrate p
  • substrate peptide
  • substrate ph
  • substrate pool
  • substrate preference
  • substrate profile
  • substrate property
  • substrate protein
  • substrate quality
  • substrate ratio
  • substrate recognition
  • substrate scope
  • substrate selection
  • substrate selectivity
  • substrate solution
  • substrate specificity
  • substrate spectrum
  • substrate stiffness
  • substrate structure
  • substrate supply
  • substrate surface
  • substrate temperature
  • substrate thickness
  • substrate tolerance
  • substrate topography
  • substrate transport
  • substrate type
  • substrate underlying
  • substrate uptake
  • substrate used
  • substrate utilization

  • Selected Abstracts

    Dispersion relation of the optical phonon frequencies in AlN/GaN superlattices

    S.K. Medeiros
    Abstract In this work we study the dispersion relation of the phonon frequencies in heterojunctions composed by III-V nitride materials (GaN and AlN). We are concerned with the superlattice structure, namely /substrate /AlN /AlxGa1,xN/GaN/AlxGa1,xN/,, where the substrate is here considered to be a transparent dielectric medium like sapphire. We make use of a model based on the Fröhlich Hamiltonian, taking into account the macroscopic theory known as the continuum dielectric model. The optical phonon modes are modelled considering only the electromagnetic boundary conditions, in the absence of charge transfer between ions. Numerical results of the confined optical phonon dispersion are presented, characterizing three distinct optical phonon classes designated as interface (IF), half-space (HS) and propagating (PR) modes. Furthermore, due to the dielectric anisotropy presented in the nitride, some additional peculiarities will be presented, like dispersive confined modes. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    B. Han
    First page of article [source]


    ABSTRACT Postharvest browning of litchi fruit results in short shelf life and reduced commercial value. Experiments were conducted to separate, purify and identify polyphenol oxidase (PPO ) substrates that cause litchi fruit to brown. PPO and its substrate were extracted from the pericarp tissues of litchi fruit. The litchi PPO substrate was purified using polyamide column, silica gel column and Sephadex LH-20 column chromatography. The browning substrate was selected by a 0.5% FeCl3 solution and then identified using a partially purified litchi PPO. Analyses of ultraviolet spectrometry, nuclear magnetic resonance and electrospray ionization mass spectrometry indicated that the PPO substrate was procyanidin A2. The substrate can be oxidized to , -quinones by litchi PPO and then form brown-colored by-products, resulting in pericarp browning of harvested litchi fruit. [source]

    Fast Simultaneous Adsorptive Stripping Voltammetric Determination of Ni(II) and Co(II) at Lead Film Electrode Plated on Gold Substrate

    ELECTROANALYSIS, Issue 14 2007
    Katarzyna Tyszczuk
    Abstract A fast adsorptive stripping voltammetric procedure for simultaneous determination of Ni(II) and Co(II) in the presence of nioxime as a complexing agent at an in situ plated lead film electrode was described. The time of determination of these ions was shortened due to the application of gold as a substrate for lead film. At gold substrate lead film formation and accumulation of Ni(II) and Co(II) complexes with nioxime proceeds simultaneously. To obtain a stable signals for both ions a simple procedure of activation of the electrode was proposed. Calibration graphs for an accumulation time of 20,s were linear from 5×10,9 to 1×10,7 mol L,1 and from 5×10,10 to 1×10,8 mol L,1 for Ni(II) and Co(II), respectively. The procedure with the application of a lead film electrode on a gold substrate was validated in the course of Ni(II) and Co(II) determination in certified reference materials. [source]

    Towards Higher Laccase Activities Produced by Aquatic Ascomycetous Fungi Through Combination of Elicitors and an Alternative Substrate

    C. Junghanns
    Abstract Laccases are versatile biocatalysts with various potential biotechnological applications, e.g. the treatment of industrial waste waters, the detoxification of environmental pollutants, or the functionalization of renewable polymeric materials. Central composition experimental design and response surface methodology was applied to optimize the production of laccase by the aquatic ascomycetous fungi, Phoma sp. UHH 5-1-03 and Coniothyrium sp.,Kl-S5, in shake flasks. A complex plant-based medium (tomato juice) and two elicitors (Remazol Brilliant Blue R [RBBR] and CuSO4) were tested in combination at three concentrations. The highest laccase activity of 6322,±,403,U/L was achieved on day,9 for Phoma sp. Coniothyrium sp. exerted a maximum laccase activity of 3035,±,111 U/L on day,4. Optimal conditions were 30,% tomato juice and 450,mg/L RBBR for both strains. A concentration of 250,,M CuSO4 led to highest laccase activities in cultures of Coniothyrium sp., and 50,,M CuSO4 was most effective for Phoma sp. A remarkable synergistic effect of tomato juice and RBBR on laccase production was observed for both strains. The upscaling potential of the optimal induction conditions was demonstrated in a lab-scale fermenter which resulted in maximum activities of 11030,±,177,U/L on day,6 for Phoma sp. and 11530,±,161,U/L on day,9 for Coniothyrium sp. This study therefore presents a promising alternative for laccase production in ascomycetes based on a cheap complex substrate in combination with two elicitors. [source]

    Seasonal and substrate preferences of fungi colonizing leaves in streams: traditional versus molecular evidence

    Liliya G. Nikolcheva
    Summary Aquatic hyphomycetes are the main fungal decomposers of plant litter in streams. We compared the importance of substrate (three leaf species, wood) and season on fungal colonization. Substrates were exposed for 12 4-week periods. After recovery, mass loss, fungal biomass and release of conidia by aquatic hyphomycetes were measured. Fungal communities were characterized by counting and identifying released conidia and by extracting and amplifying fungal DNA (ITS2), which was subdivided into phylotypes by denaturing gradient gel electrophoresis (DGGE) and terminal-restriction fragment length polymorphism (T-RFLP). Mass loss, fungal biomass and reproduction were positively correlated with stream temperature. Conidial diversity was highest between May and September. Numbers of different phylotypes were more stable. Principal coordinate analyses (PCO) and canonical analyses of principal coordinates (CAP) of presence/absence data (DGGE bands, T-RFLP peaks and conidial species) showed a clear seasonal trend (P, 0.002) but no substrate effect (P, 0.88). Season was also a significant factor when proportional similarities of conidial communities or relative intensities of DGGE bands were evaluated (P, 0.003). Substrate was a significant factor determining DGGE band intensities (P = 0.002), but did not significantly affect conidial communities (P = 0.50). Both traditional and molecular techniques suggest that strict exclusion of fungi by substrate type is rare, and that presence of different species or phylotypes is governed by season. Biomasses of the various taxa (based on DGGE band intensities) were related to substrate type. [source]

    Elaboration of Monophasic and Biphasic Calcium Phosphate Coatings on Ti6Al4V Substrate by Pulsed Electrodeposition Current

    Hicham Benhayoune
    Calcium phosphate coatings on Ti6Al4V substrates are elaborated by pulsed electrodeposition. The surface morphology and chemical composition of the coatings are characterized by SEM,EDS. The obtained results are systematically confirmed at the nanometre scale using TEM. Moreover, XRD is performed in order to identify the coatings phases. The results show that pulsed electrodeposition allows uniform coatings to be obtained without the holes and craters usually observed with classical electrodeposition. After appropriate heat treatment, these coatings have a biphasic composition of stoichiometric hydroxyapatite and , -tricalcium phosphate. Moreover, the addition of 9% H2O2 to the electrolyte leads to monophasic coatings made of stoichiometric hydroxyapatite. As an indication of the passive nature of the electrodeposited coating, electrochemical potentiodynamic tests are performed in physiological solution in order to determine the corrosion behaviour of these coatings. [source]

    2,3-Di- n -undecylanthracene and 2,3-Di- n -decyloxyanthracene (DDOA) , on the Connecting Link between the Aromatic Substrate and the Aliphatic Chain in Self-Assembling Systems

    Henning Hopf
    Abstract In contrast to its bis(oxa) analog 1 (DDOA), the hydrocarbon 11 was not found to form organogels with linear alcohols, alkanes, toluene, acetonitrile and other solvents. Whereas the photoreactivity of 1 did not follow the usual behaviour of anthracene derivatives, compound 11, irradiated in cyclohexane, produced the two expected [4+4]cycloadducts 12 and 13 (anti and syn photodimers, respectively). These facts point to the role of the connecting link between the rigid core and the flexible chain for some self-assembled systems.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Sequential Stereoselective Catalysis: Two Single-Flask Reactions of a Substrate in the Presence of a Bifunctional Chiral Ligand and Different Transition Metals

    Rita Annunziata
    Abstract A new bifunctional ligand capable of promoting different stereoselective catalytic transformations in combination with different transition metals has been prepared by connecting with a spacer a bis(oxazoline) to dihydroquinidine; this ligand was employed in a one-flask procedure in which methyl (E)-3-(4-vinylphenyl)propenoate underwent first cyclopropanation at the electron-rich double bond and then dihydroxylation at the electron-poor alkene to afford a product containing four stereocenters with complete regiocontrol and high stereoselectivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Substrate and inhibitor specificity of Mycobacterium avium dihydrofolate reductase

    FEBS JOURNAL, Issue 13 2007
    Ronnie A. Böck
    Dihydrofolate reductase (EC is a key enzyme in the folate biosynthetic pathway. Information regarding key residues in the dihydrofolate-binding site of Mycobacterium avium dihydrofolate reductase is lacking. On the basis of previous information, Asp31 and Leu32 were selected as residues that are potentially important in interactions with dihydrofolate and antifolates (e.g. trimethoprim), respectively. Asp31 and Leu32 were modified by site-directed mutagenesis, giving the mutants D31A, D31E, D31Q, D31N and D31L, and L32A, L32F and L32D. Mutated proteins were expressed in Escherichia coli BL21(DE3)pLysS and purified using His-Bind resin; functionality was assessed in comparison with the recombinant wild type by a standard enzyme assay, and growth complementation and kinetic parameters were evaluated. All Asp31 substitutions affected enzyme function; D31E, D31Q and D31N reduced activity by 80,90%, and D31A and D31L by >,90%. All D31 mutants had modified kinetics, ranging from three-fold (D31N) to 283-fold (D31L) increases in Km for dihydrofolate, and 12-fold (D31N) to 223 077-fold (D31L) decreases in kcat/Km. Of the Leu32 substitutions, only L32D caused reduced enzyme activity (67%) and kinetic differences from the wild type (seven-fold increase in Km; 21-fold decrease in kcat/Km). Only minor variations in the Km for NADPH were observed for all substitutions. Whereas the L32F mutant retained similar trimethoprim affinity as the wild type, the L32A mutation resulted in a 12-fold decrease in affinity and the L32D mutation resulted in a seven-fold increase in affinity for trimethoprim. These findings support the hypotheses that Asp31 plays a functional role in binding of the substrate and Leu32 plays a functional role in binding of trimethoprim. [source]

    Simple Patterning via Adhesion between a Buffered-Oxide Etchant-Treated PDMS Stamp and a SiO2 Substrate,

    Y.-K. Kim
    Abstract A very simple polydimethylsiloxane (PDMS) pattern-transfer method is devised, called buffered-oxide etchant (BOE) printing. The mechanism of pattern transfer is investigated, by considering the strong adhesion between the BOE-treated PDMS and the SiO2 substrate. PDMS patterns from a few micrometers to sub-micrometer size are transferred to the SiO2 substrate by just pressing a stamp that has been immersed in BOE solution for a few minutes. The patterned PDMS layers work as perfect physical and chemical passivation layers in the fabrication of metal electrodes and V2O5 nanowire channels, respectively. Interestingly, a second stamping of the BOE-treated PDMS on the SiO2 substrate pre-patterned with metal as well as PDMS results in a selective transfer of the PDMS patterns only to the bare SiO2. In this way, the fabrication of a device structure consisting of two Au electrodes and V2O5 nanowire network channels is possible; non-ohmic semiconducting I,V characteristics, which can be modeled by serially connected percolation, are observed. [source]

    Real-Time Observation and Control of Pentacene Film Growth on an Artificially Structured Substrate

    ADVANCED MATERIALS, Issue 48 2009
    Yuki Tsuruma
    Suppression of nucleation around a gold electrode during pentacene growth on a SiO2 channel is found by photoemission electron microscopy. Mass flow is driven by the difference between the molecular orientations on SiO2 and gold. The poor connectivity at the channel/electrode boundary causes degradation in the performance of a field-effect transistor, which is found to be improved by self-assembled monolayer treatment on the electrode (see figure; thickness in monolayers (ML)). [source]

    Nanowire-Induced Wurtzite InAs Thin Film on Zinc-Blende InAs Substrate

    ADVANCED MATERIALS, Issue 36 2009
    Jiming Bao
    InAs pyramids and platelets on a zinc-blende InAs substrate are found to exhibit a wurtzite crystal structure. Induced by wurtzite InAs nanowires, wurtzite InAs thin film and its associated zinc-blende/wurtzite heterocrystalline heterostructures may open up new opportunities in band-gap engineering and related device applications. [source]

    Synthesis of Large-Area Graphene Layers on Poly-Nickel Substrate by Chemical Vapor Deposition: Wrinkle Formation

    ADVANCED MATERIALS, Issue 22 2009
    Seung Jin Chae
    Large-area, few-layer graphene is grown on a poly-nickel substrate using optimized CVD conditions. High temperature, short growth time, and an optimal gas mixing ratio (C2H2/H2,=,2/45) are found to be necessary to synthesize highly crystalline few-layer grapheme, which may find applications in electronic devices. The wrinkles that are observed under all growth conditions are proposed to be formed by two processes. [source]

    Wafer-Level Patterned and Aligned Polymer Nanowire/Micro- and Nanotube Arrays on any Substrate

    ADVANCED MATERIALS, Issue 20 2009
    Jenny Ruth Morber
    A novel technique for fabrication of patterned and aligned polymer-nanowire/micro-and nanotube (PNW/PNT) arrays on a wafer-level substrate of any material is reported. By creating a designed pattern on a spin-coated polymer film using techniques, such as stamping or micro-tip writing, plasma etching results in the formation of aligned PNW arrays distributed according to the pattern. [source]

    Nanotopographic Carbon Nanotube Thin-Film Substrate Freezes Lateral Motion of Secretory Vesicles

    ADVANCED MATERIALS, Issue 7 2009
    Jing Zhang
    Thin-film carbon-nanotube networks can interface with living neuroendocrine PC12 cells and support their growth and proliferation. Interestingly, as revealed by total-internal-reflection fluorescence microscopy, the nanoroughness created by the carbon-nanotube net physically deforms the 5,nm thick cell membrane with high local curvature, and significantly impedes the lateral motion of subplasmalemmal secretory vesicles. [source]

    Achieving Perpendicular Alignment of Rigid Polythiophene Backbones to the Substrate by Using Solvent-Vapor Treatment,

    ADVANCED MATERIALS, Issue 21 2007
    H. Lu
    The rigid backbone of the poly(3-butylthiophene) molecule adopts a perpendicular orientation with respect to the substrate by using a solvent-vapor treatment (see figure). Small and closely contacting spherulites instead of conventional whisker-like crystals are achieved. This could be utilized to improve charge-carrier mobility particularly in the direction normal to the film plane by designing and constructing thick crystalline domains in the functional layer. [source]

    Flow-Through-Type DNA Array Based on Ideally Ordered Anodic Porous Alumina Substrate ,

    ADVANCED MATERIALS, Issue 23-24 2004
    F. Matsumoto
    A flow-through-type DNA array fabricated from an ideally ordered anodic porous alumina substrate is reported. Single-stranded probe DNA was affixed to the walls of the sub-micrometer-diameter holes, and fluorescently labelled target DNA was passed through the holes in the substrate. Fluorescence microscopy revealed an ordered array of fluorescent spots after the hybridization (see Figure), demonstrating the applicability of these porous alumina substrates to fabrication of high-density DNA arrays. [source]

    Fabrication of Super-Site-Selective TiO2 Micropattern on a Flexible Polymer Substrate Using a Barrier-Effect Self-Assembly Process,

    ADVANCED MATERIALS, Issue 16 2004
    J. Xiang
    A super-site-selective micropattern of TiO2 on a flexible polymer substrate (see Figure) has been achieved by utilizing a barrier-effect self-assembly process. The TiO2 micropattern is useful as a UV filter for nanodevices in integrated electronic and optical circuits. [source]

    Semiconductor Nanorod Liquid Crystals and Their Assembly on a Substrate,

    ADVANCED MATERIALS, Issue 5 2003
    L.-S. Li
    The macroscopic alignment and superlattice structures of CdSe nanorods in a nematic liquid-crystalline (LC) phase are determined by the phases that form prior to complete solvent evaporation (e.g., vortex structures in linear arrays, see Figure). By controlling the phase of the LC solution and its orientation using pretreated surfaces or external fields, it may be possible to achieve fine control of order in deposited nanorod films. [source]

    Regioselective Reactions on a Chiral Substrate Controlled by the Configuration of a Chiral Catalyst

    Raju Ranjith Kumar
    Abstract A racemic mixture may be partially transformed in the presence of a chiral catalyst by kinetic resolution and formation of products with new structural features. If the starting material is fully consumed the products may still be enantiomerically enriched. The situation is summarized in the Introduction. A brief discussion on the regioselective transformations occurring on a racemic mixture under the influence of a chiral catalyst is presented in Section 2. Often stereo-differences occur, each enantiomer of the starting material resulting in a different product. It allows one to predict what the behaviour of some enantiopure substrates should be in presence of each of the enantiomers of a chiral catalyst. Many examples are presented in Section 3. The chiral substrates under consideration have two different reacting sites, usually of the same nature (OH, CC, allylic positions, CH for carbene insertion, epoxide fragment, etc.). In some cases the absolute configuration of the catalyst allows an excellent control of the regioselectivity. This approach is promising for the selective transformation of chiral molecules. [source]

    Multicomponent Reactions of 1,3-Cyclohexanediones and Formaldehyde in Glycerol: Stabilization of Paraformaldehyde in Glycerol Resulted from using Dimedone as Substrate

    Minghao Li
    Abstract Glycerol has proved to be an effective promoting medium for many multicomponent reactions of 1,3-cyclohexanediones and formaldehyde. Styrenes, amines, 2-naphthol, 4-hydroxy-6-methyl-2-pyrone and 4-hydroxy-1-methyl-2-quinolone could easily react with 1,3-cyclohexanediones and paraformaldehyde in glycerol under catalyst-free conditions to afford a variety of complex skeletons in fair to excellent yields. In these reactions, glycerol not only showed a significant promoting effect on the reaction yields but also endowed the reaction system with many typical properties of green chemistry, such as cheap, renewable, recyclable and biodegradable solvent, good safety and easy separation of product. The promoting effect of glycerol for the three-component reaction of styrene, dimedone and paraformaldehyde could be attributed to a restricted formation of the methylene intermediate in glycerol. During the reaction, a physical shell, which is mainly composed of a by-product generated in the beginning of the reaction, might be formed in the surface of paraformaldehyde and plays a key role in controlling the formation of the intermediate by means of restricting the decomposition of paraformaldehyde. [source]

    Activated ,,,-Unsaturated Aldehydes as Substrate of Dihydroxyacetone Phosphate (DHAP)-Dependent Aldolases in the Context of a Multienzyme System

    Israel Sánchez-Moreno
    Abstract The utility for carbon-carbon bond formation of a multienzyme system composed of recombinant dihydroxyacetone kinase (DHAK) from Citrobacter freundii, the fructose bisphosphate aldolase from rabbit muscle (RAMA) and acetate kinase (AK) for adenosine triphosphate (ATP) regeneration has been studied. Several aldehydes with great structural diversity, including three ,,,-unsaturated aldehydes, have been analysed as acceptor substrates. It was found that ,,,-unsaturated aldehydes bearing an electron-withdrawing group in the , position to the double bond with a trans configuration are good acceptors for RAMA in this multienzyme system. The aldol reaction proceeds with excellent D - threo enantioselectivity and the aldol adduct is obtained in good overall yield. The L - threo and D - erythro enantiomers are also accessible from rhamnulose 1-phosphate aldolase (Rha-1PA) and fuculose 1-phosphate aldolase (Fuc-1PA) catalysed reactions, respectively. [source]

    Can We Improve the Identification of Ventricular Scar to Guide Substrate-Based Ventricular Tachycardia Ablation?

    No abstract is available for this article. [source]

    Acute Effect of Circumferential Pulmonary Vein Isolation on Left Atrial Substrate

    Introduction: The left atrial (LA) substrate plays an important role in the maintenance of atrial fibrillation (AF). However, little is known about the acute effect of circumferential pulmonary vein isolation (CPVI). This study was to investigate the acute change of LA activation, voltage and P wave in surface electrocardiogram (ECG) after CPVI. Methods and Results: Electroanatomic mapping (NavX) was performed in 50 patients with AF (mean age = 54 ± 10 years, 36 males) who underwent only CPVI. The mean peak-to-peak bipolar voltage and total activation time of LA were obtained during sinus rhythm before and immediately after CPVI. The average duration and amplitude of P waves in 12-lead ECG were also analyzed before and after CPVI. Change in the earliest LA breakthrough sites could cause decreased LA total activation time. Downward shift in the breakthrough site was inversely proportional to the proximity of the breakthrough site to the radiofrequency lesions. A shortening of P-wave duration and decrease in voltage after CPVI were observed after CPVI. Patients with recurrent AF had less voltage reduction in the atrial wall 1 cm from the circumferential PV lesions compared with those without recurrent AF (60.1 ± 11.7% vs 74.1 ± 6.6%, P = 0.002). Reduction of voltage ,64.4% in this area after CPVI is related with recurrent AF. Conclusion: CPVI could result in acute change of LA substrate, involving LA activation and voltage. Less reduction of voltage in the atrial wall adjacent to the circumferential PV lesions after CPVI may be associated to the recurrence of AF. [source]

    Substrate and Procedural Predictors of Outcomes After Catheter Ablation for Atrial Fibrillation in Patients with Hypertrophic Cardiomyopathy

    Background: Hypertrophic cardiomyopathy (HCM) is often accompanied by atrial fibrillation (AF) due to diastolic dysfunction, elevated left atrial pressure, and enlargement. Although catheter ablation for drug-refractory AF is an effective treatment, the efficacy in HCM remains to be established. Methods: Thirty-three consecutive patients (25 male, age 51 ± 11 years) with HCM underwent pulmonary vein (PV) isolation (n = 8) or wide area circumferential ablation with additional linear ablation (n = 25) for drug-refractory AF. Twelve-lead and 24-hour ambulating ECGs, echocardiograms, event monitor strips, and SF 36 quality of life (QOL) surveys were obtained before ablation and for routine follow-up. Results: Twenty-one (64%) patients had paroxysmal AF and 12 (36%) had persistent/permanent AF for 6.2 ± 5.2 years. The average ejection fraction was 0.63 ± 0.12. The average left atrial volume index was 70 ± 24 mL/m2. Over a follow-up of 1.5 ± 1.2 years, 1-year survival with AF elimination was 62%(Confidence Interval [CI]: 66-84) and with AF control was 75%(CI: 66-84). AF control was less likely in patients with a persistent/chronic AF, larger left atrial volumes, and more advanced diastolic disease. Additional linear ablation may improve outcomes in patient with severe left atrial enlargement and more advanced diastolic dysfunction. Two patients had a periprocedureal TIA, one PV stenosis, and one died after mitral valve replacement from prosthetic valve thrombosis. QOL scores improved from baseline at 3 and 12 months. Conclusion: Outcomes after AF ablation in patients with HCM are favorable. Diastolic dysfunction, left atrial enlargement, and AF subtype influence outcomes. Future studies of rhythm management approaches in HCM patients are required to clarify the optimal clinical approach. [source]

    A Peek at AF Myocardial Substrate Through the Signal-Averaged ECG?

    No abstract is available for this article. [source]

    Characterization of the Electroanatomical Substrate in Human Atrial Fibrillation: The Relationship between Changes in Atrial Volume, Refractoriness, Wavefront Propagation Velocities, and AF Burden

    Introduction: Progressive remodeling occurs in experimental models of AF whereby slowing of conduction, shortening of refractoriness, and atrial dilatation are associated with an increased vulnerability to atrial fibrillation (AF). This study investigates the relative changes in atrial geometry and electrophysiology with increasing AF burden in humans. Methods and Results: Patients undergoing ablation of AF or left-sided accessory pathways were recruited. Atrial volumes were determined by echocardiography. Wavefront propagation velocities (WPV), specifically in the direction of activation, were calculated from pre-ablation activation (CartoÔ) maps of both atria. Dispersion, adaptation of, and effective refractoriness (ERP) were measured at 3 sites. A composite arrhythmogenic index (Atrial Volume/WPV × ERP) was derived to compare the degree of electroanatomical remodeling with AF burden. Fifty-nine patients (22 paroxysmal AF, 19 recurrent persistent AF, and 18 controls) were recruited. AF subjects had slower right atrial WPV (P = 0.01), but no difference in left atrial WPV compared with controls. ERP was reduced globally (P < 0.05), with increased dispersion (P < 0.05). WPV and ERP did not distinguish between patients with paroxysmal or persistent AF. Biatrial volumes were greater only in patients with persistent AF (P < 0.01). There was a stepwise increase in the AI with increasing AF burden (P < 0.0001). Conclusion: An arrhythmogenic substrate exists in human AF, characterized by globally decreased refractoriness with greater dispersion, slower right atrial conduction, and atrial dilatation. Persistence of AF is not accompanied by any further electrical remodeling, but only atrial dilatation. The degree of electroanatomical remodeling is associated with the clinical pattern of AF. [source]

    A Single Pulmonary Vein as Electrophysiological Substrate of Paroxysmal Atrial Fibrillation

    Introduction: It has been demonstrated that pulmonary veins (PVs) play an important role in initiation and maintenance of paroxysmal atrial fibrillation (AF). However, it is not clearly known whether a single PV acts as electrophysiological substrate for paroxysmal AF. Methods and Results: This study included five patients with paroxysmal AF. All patients underwent complete PV isolation with continuous circular lesions (CCLs) around the ipsilateral PVs guided by a three-dimensional mapping system. Irrigated radiofrequency (RF) delivery was performed during AF on the right-sided CCLs in two patients and on the left-sided CCLs in three patients. The incomplete CCLs resulted in a change from AF to atrial tachycardia (AT), which presented with an identical atrial activation sequence and P wave morphology. Complete CCLs resulted in AF termination with persistent PV tachyarrhythmias within the isolated PV in all five patients. PV tachyarrhythmia within the isolated PV was PV fibrillation from the left common PV (LCPV) in two patients, PV tachycardia from the right superior PV (RSPV) in two patients, and from the left superior PV in one patient. All sustained PV tachyarrhythmias persisted for more than 30 minutes, needed external cardioversion for termination in four patients and a focal ablation in one patient. After the initial procedure, an AT from the RSPV occurred in a patient with PV fibrillation within the LCPV, and was successfully ablated. Conclusion: In patients with paroxysmal AF, sustained PV tachyarrhythmias from a single PV can perpetuate AF. Complete isolation of all PV may provide good clinical outcome during long-term follow-up. [source]

    Sex Modulates the Arrhythmogenic Substrate in Prepubertal Rabbit Hearts with Long QT 2

    Ph.D., TONG LIU M.D.
    Females have a greater susceptibility to Torsade de Pointes in congenital and drug-induced long QT syndrome (LQTS) that has been attributed to the modulation of ion channel expression by sex hormones. However, little is known regarding sex differences in pre-puberty, that is, before the surge of sexual hormones. In patients with congenital LQTS types 1 and 2, male children tend to have a greater occurrence of adverse events, especially in 10,15 year olds, than their female counterpart. To evaluate whether the rabbit model of drug-acquired LQTS exhibits similar age dependences, hearts of prepubertal rabbits were perfused, mapped optically to record action potentials (APs) and treated with an IKr blocker, E4031 to elicit LQTS2. As expected, AP durations (APD) were significantly longer in female (n = 18) than male hearts (n = 10), at long cycle length. Surprisingly, E4031 (50,250 nM) induced a greater prolongation of APDs in male than in female hearts, and in both genders reversed the direction of repolarization (apex , base to base , apex), enhancing dispersions of repolarization. Furthermore, in male hearts, E4031 (0.5 ,M) elicited early afterdepolarizations (EADs) that progressed to polymorphic ventricular tachycardia (PVT) (n = 7/10) and were interrupted by isoproterenol (40 nM) and prevented by propranolol (0.5,2.5 ,M). In female hearts, E4031 (0.5 ,M) produced marked prolongations of APDs yet few EADs with no progression to PVT (n = 16/18). Thus, sex differences are opposite in prepubertal versus adult rabbits with respect to E4031-induced APD prolongation, EADs and PVT, underscoring the fact that APD prolongation alone is insufficient to predict arrhythmia susceptibility. [source]