Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Coupling

  • Copper-Catalyze coupling
  • Palladium-Catalyze coupling
  • aldol coupling
  • antiferromagnetic coupling
  • aryl coupling
  • c coupling
  • chemical coupling
  • contraction coupling
  • covalent coupling
  • cross coupling
  • dehydrogenative coupling
  • dipolar coupling
  • dipole coupling
  • direct coupling
  • dye coupling
  • dynamic coupling
  • efficient coupling
  • efficient three-component coupling
  • electrical coupling
  • electromagnetic coupling
  • electromechanical coupling
  • electronic coupling
  • electrotonic coupling
  • exchange coupling
  • exciton coupling
  • ferromagnetic coupling
  • full coupling
  • functional coupling
  • gap junctional coupling
  • heck coupling
  • hyperfine coupling
  • inductive coupling
  • intercellular coupling
  • intermolecular coupling
  • intramolecular coupling
  • junctional coupling
  • ligand coupling
  • loose coupling
  • magnetic coupling
  • mechanical coupling
  • miyaura coupling
  • mode coupling
  • mutual coupling
  • negishi coupling
  • neurovascular coupling
  • nonlinear coupling
  • on-line coupling
  • orbit coupling
  • oxidative coupling
  • phonon coupling
  • pinacol coupling
  • plasmon coupling
  • protein coupling
  • quadrupolar coupling
  • radical coupling
  • reductive coupling
  • residual dipolar coupling
  • scalar coupling
  • sonogashira coupling
  • spatial coupling
  • spin coupling
  • spin-orbit coupling
  • stille coupling
  • strong coupling
  • suzuki coupling
  • temporal coupling
  • three-component coupling
  • tight coupling
  • ullmann coupling
  • weak coupling
  • weak ferromagnetic coupling

  • Terms modified by Coupling

  • coupling agent
  • coupling apparatus
  • coupling approach
  • coupling characteristic
  • coupling chemistry
  • coupling coefficient
  • coupling condition
  • coupling constant
  • coupling device
  • coupling effect
  • coupling effects
  • coupling efficiency
  • coupling factor
  • coupling interaction
  • coupling interval
  • coupling loss
  • coupling matrix
  • coupling matrix element
  • coupling mechanism
  • coupling method
  • coupling methods
  • coupling model
  • coupling parameter
  • coupling partner
  • coupling pathway
  • coupling polymerization
  • coupling procedure
  • coupling process
  • coupling product
  • coupling products
  • coupling protein
  • coupling reaction
  • coupling reagent
  • coupling regime
  • coupling scheme
  • coupling sequence
  • coupling strategy
  • coupling strength
  • coupling technique
  • coupling techniques
  • coupling term
  • coupling value

  • Selected Abstracts


    While total undergraduate enrolments at Australian universities are increasing, enrolments in Economics are falling,a source of alarm for economists. By appealing to females, economics could effectively tap into the largest sector (58%) of the undergraduate student population. This study suggests that gender is contributing to the falling enrolments. Males need the prospect of money to entice them to study more economics but females require a connection between studying economics and employment opportunities. Providing visible role models may be a practical step to encouraging more females to read economics. More concentration on ,feminising economics' in the undergraduate curricula could help women to believe that they have a contribution to make to the discipline. [source]

    Changing patterns of ganglion cell coupling and connexin expression during chick retinal development

    David L. Becker
    Abstract We have used dye injection and immunolabeling to investigate the relationship between connexin (Cx) expression and dye coupling between ganglion cells (GCs) and other cells of the embryonic chick retina between embryonic days 5 and 14 (E5,14). At E5, GCs were usually coupled, via soma-somatic or dendro-somatic contacts, to only one or two other cells. Coupling increased with time until E11 when GCs were often coupled to more than a dozen other cells with somata in the ganglion cell layer (GCL) or inner nuclear layer (INL). These coupled clusters occupied large areas of the retina and coupling was via dendro-dendritic contacts. By E14, after the onset of synaptogenesis and at a time of marked cell death, dye coupling was markedly decreased with GCs coupled to three or four partners. At this time, coupling was usually to cells of the same morphology, whereas earlier coupling was heterogeneous. Between E5 and E11, GCs were sometimes coupled to cells of neuroepithelial morphology that spanned the thickness of the retina. The expression of Cx 26, 32, and 43 differed and their distribution changed during the period studied, showing correlation with events such as proliferation, migration, and synaptogenesis. These results suggest specific roles for gap junctions and Cx's during retinal development. © 2002 Wiley Periodicals, Inc. J Neurobiol 52: 280,293, 2002 [source]

    Evidence of Robust Coupling of Atrioventricular Mechanical Function of the Right Side of the Heart: Insights from M-Mode Analysis of Annular Motion

    ECHOCARDIOGRAPHY, Issue 6 2008
    Raveen Bazaz M.D.
    Background: Extensive data exist regarding annular descent and ventricular function. We have already demonstrated significant differences in amplitude and timing of events between maximal mitral (MAPSE) and tricuspid (TAPSE) annular plane systolic excursion as well as described quantitative temporal differences in annular ascent (AA) between the right and left sides of the heart. However, whether any relationship exists between annular ascent and descent components remains uninvestigated. Methods: Left ventricular ejection fraction (LVEF), right ventricular fractional area change (RVFAC), MAPSE, TAPSE, MV, and TV AA as well as pulsed tissue Doppler of the lateral MV and TV annuli were recorded from 53 patients. Results: In this population (age 55 ± 17 years) mean LVEF was 55 ± 19%, mean RVFAC was 47 ± 20%, mean MAPSE was 2.11 ± 0.72 cm, mean TAPSE was 1.48 ± 0.44 cm, mean MV AA was 0.52 ± 0.17 cm, TV AA was 0.96 ± 0.47, MV A-wave 0.10 ± 0.04 cm/s, and TV A-wave was 0.13 ± 0.05 cm/s. A more robust correlation was seen between TV AA and RVFAC than between MV AA and LVEF and also between TV AA and pulsed TDI TV A-wave velocity than between MV AA and pulsed TDI MV A-wave. Conclusion: Our data reveal that mechanical systolic functions of the atria and the ventricles are more closely coupled on the right than on the left side of the heart. Whether this is a result of anatomic linking or chamber geometry will require further study. [source]

    Determination of gaseous and particulate carbonyls in air by gradient-elution micellar electrokinetic capillary chromatography

    ELECTROPHORESIS, Issue 19 2008
    Hui Sun
    Abstract A new continuous-flow gradient-elution micellar electrokinetic capillary chromatography method is developed for the determination of airborne carbonyls after derivatization with 2,4-dinitrophenylhydrazine. A total of 16 carbonyls can be determined with detection limits ranging from 0.94 to 8.50,mg/L, working range from 4.72 to 346,mg/L, and repeatabilities (relative standard deviation, n=5) from 1.23 to 4.6% or 3.93 to 7.6% for migration time and peak area, respectively. Coupling with denuder-filter sampling, a preliminary survey has been conducted to determine gaseous and particulate carbonyls from air sampled at a roadside station. The method is shown to have sufficient sensitivity for 1-h sampling of ambient carbonyls with detection limits ranging from 0.045 to 1.2,,g/m3 and working range from 0.11 to 43.3,,g/m3 at a flow rate of 10,Lpm. The method requires minimal modification of commercially available capillary electrophoresis equipment and can differentiate gaseous and particulate carbonyls to provide essential information and objective data for adopting effective measures to combat the discharge of carbonyl compounds to the atmosphere. [source]

    Coupling of solid-phase microextraction continuous bed (monolithic) capillaries with capillary zone electrophoresis for direct analysis of drugs in biological fluids,

    ELECTROPHORESIS, Issue 8 2008
    Reda Jarmalavi
    Abstract Hyperlink robust biocompatible solid-phase microextraction (SPME) devices were prepared using continuous bed (monolithic) restricted-access media (RAM) as the SPME capillary insert. The RAM-based SPME approach was able to simultaneously separate proteins from a biological sample, while directly extracting the active components of caffeine, paracetamol and acetylsalicylic acid from the drug NeoCitramonum. The devices were interfaced with a CZE system and fully automated analysis for sample preconcentration, desorption, separation and quantification of analytes was evaluated. Comparative study of in-line coupled SPME,CZE using RAM and RP capillary inserts was carried out. Using an SPME (RAM) insert, the calculated caffeine, paracetamol and acetylsalicylic acid LODs in a bovine plasma sample were 0.3, 0.8 and 1.9,ng/mL, respectively. [source]

    Fluoride-Free Hiyama and Copper- and Amine-Free Sonogashira Coupling in Air in a Mixed Aqueous Medium by a Series of PEPPSI-Themed Precatalysts,

    Chandrakanta Dash
    Abstract A new series of robust, user-friendly, and highly active PEPPSI-themed (pyridine-enhanced precatalyst preparation, stabilization and initiation) (NHC)PdX2(pyridine)-type (X = Cl, Br) precatalysts of C4,C5 saturated imidazole- (1,4) and triazole-based (5 and 6) N-heterocyclic carbenes for the Hiyama and Sonogashira couplings under amenable conditions are reported. Specifically 1,6 efficiently catalyze the fluoride-free Hiyama coupling of aryl halides with PhSi(OMe)3 and CH2=CHSi(OMe)3 in air in the presence of NaOH as a base in a mixed aqueous medium (dioxane/H2O, 2:1 v/v). Along the same lines, these 1,6 precatalysts also promote the Cu-free and amine-free Sonogashira coupling of aryl bromides and iodides with phenylacetylene in air and in a mixed aqueous medium (DMF/H2O, 3/1 v/v). The complexes 1,6 were synthesized by the direct reaction of the respective imidazolinium and triazolium halide salts with PdCl2 in pyridine in the presence of K2CO3 as a base. DFT studies on the catalytically relevant palladium(0) (NHC)Pd(pyridine) precursors 1a,6a reveal significant donation from the N-heterocyclic carbene lone pair onto the unfilled ,* orbital of the trans Pd,pyridine bond. This weakens the Pd-bound "throwaway" pyridine ligand, and its dissociation marks the initiation of the catalytic cycle.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Coordination Chemistry of 3-Mercapto-2-(mercaptomethyl)propanoic Acid (Dihydroasparagusic Acid) with Iron and Nickel

    Phillip I. Volkers
    Abstract The first transition-metal complexes bearing the natural product dihydroasparagusic acid, (HSCH2)2CHCO2H, as a ligand are reported. Various coordination modes and nuclearities are demonstrated for the chelating ligand by a series of iron and nickel complexes. Fe2[(SCH2)2CHCO2H](CO)6 retains carbonyl substitution reactivity typical of Fe2(SR)2(CO)6 complexes, yet carboxy coordination to FeI was unobserved. Coupling of the carboxylic acid with amines yields the corresponding amides Fe2[(SCH2)2CHC(O)NHR](CO)6 (R = Et, gly,O,tBu). Fe2[(SCH2)2CHCO2H](CO)4(PMe3)2 catalyzes H2 production, but no better than unfunctionalized alkyl dithiolate analogs. Reactions of the ligand with NiCl2(dppe) afforded mono-, di-, and trinuclear complexes. Noteworthy is Ni3[(SCH2)2CHCO2]2(dppe)2, which features an octahedrally coordinated NiII center linked to a pair of square-planar NiII centers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Reactions of K2[Fe(CO)3(PPh3)]: Reductive Sb,Sb Coupling with Ph2SbCl To Form trans -[Fe(CO)3(PPh3)(Sb2Ph4)] and Salt Metathesis with Me3SbCl2 To Yield trans -[Fe(CO)3(PPh3)(SbMe3)]

    Ingo-Peter Lorenz
    Abstract In contrast to the ferrate K2[Fe(CO)4], the phosphane-substituted ferrate K2[Fe(CO)3(PPh3)] (1) reacts with the stibane derivative Ph2SbCl by metal-assisted reductive Sb,Sb coupling to give the distibane complex trans -[Fe(CO)3(PPh3)(Sb2Ph4)] (3). The distibane ligand in 3 is terminally ,1 -coordinated trans to the phosphane ligand. However, the stiborane derivative Me3SbCl2 reacts with 1 in a metathetical substitution reaction to form the monostibane complex trans -[Fe(CO)3(PPh3)(SbMe3)] (5). Both compounds have been characterized by spectroscopic (IR, NMR, MS), analytical (C, H) and X-ray diffraction analyses. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    A New Trinuclear Linear Copper(II) Complex: Unusual Crystal Structure with Semi-Coordinated Thiophene Moieties and Weak Antiferromagnetic Coupling Through the Bridging Imidazolate Rings

    Yufei F. Song
    Abstract A trinuclear copper(II) complex, [Cu3(imthio)2(NO3)4(MeOH)2] [where Himthio is 1,1-bis(imidazol-2-yl)-3-(thiophen-2-yl)-2-azapropane], has been synthesized by the reaction of Himthio with Cu(NO3)2·3H2O in MeOH. The structure of the copper complex is centrosymmetric and contains a linear trinuclear array of copper atoms. The central copper(II) ion, Cu1, which lies on an inversion centre, is equatorially coordinated by four nitrogen atoms from two anionic imthio ligands and axially by two semicoordinated thiophene sulfur atoms to give an octahedral environment (Cu1,S1 3.136 Ĺ). The Himthio ligand bridges Cu1 and the terminal copper(II) ions through imidazole nitrogen atoms. The coordination around the external ions is completed by the oxygen atoms from two nitrate groups and by a methanol molecule in a distorted square-pyramidal geometry. The two terminal copper(II) complexes can be considered to be chelating ligands for the central CuII ion. The EPR spectrum of the complex in MeOH at 77 K shows two mononuclear species, as is fully confirmed by EPR simulation. Magnetic susceptibility of the complex shows weak antiferromagnetic behaviour (J = ,71.37 cm,1) caused by the overlapping of the magnetic orbitals of the copper atoms and the bridging imidazolate rings. (© Wiley-VCH Verlag GmbH & Co.. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Tuning the Magnetic Properties of a Dinuclear Copper Complex: From Ferromagnetic to Antiferromagnetic Coupling

    Simon P. Foxon
    Abstract A novel structural motif in oxalate bridged copper(II) complexes has been prepared namely a metallamacrocyclic compound of the dinucleating ligand 1,3-bis[bis(2-pyridylmethyl)amino]benzene (= 1,3-tpbd). It could be demonstrated that the magnetic properties of copper(II) complexes of the 1,3-tpbd ligand can be adjusted from weakly ferromagnetic (J = +9.3 cm,1) to strongly antiferromagnetic [J = ,366(9) cm,1] by variation of the additional ligands (e.g. perchlorate, azide, oxalate etc.). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    A Theoretical Study of the Exchange Coupling in Hydroxo- and Alkoxo-Bridged Dinuclear Oxovanadium(IV) Compounds

    Antonio Rodríguez-Fortea
    Abstract A density functional study of exchange coupling in hydroxo- and alkoxo-bridged dinuclear oxovanadium(IV) compounds is presented. Coupling constants calculated for full unmodeled structures are in good agreement with experimentally reported values, confirming the ability of the computational strategy used in this work to predict the exchange coupling in dinuclear VIV compounds. The influence of the configuration of the [VO(,-OR)2VO]2+ core in compounds with two edge-sharing octahedrally coordinated oxovanadium(IV) centers, of the nature of the terminal ligands and of structural distortions on the coupling constant have been analyzed through model calculations. The results indicate that the coupling constant is less affected by these factors than for hydroxo- and alkoxo-bridged CuII compounds. The calculations support the orbital models usually employed in qualitative interpretations of magneto-structural correlations, showing good correlations between the calculated coupling constants and the overlap between the two magnetic orbitals or the square of the orbital gap. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Divalent Samarium Triflate Mediated Stereoselective Pinacol Coupling of Planar Chiral Phosphanyl and Phosphoryl Ferrocenecarbaldehyde

    Shin-ichi Fukuzawa
    Abstract The pinacol coupling reaction of (Rp)-2-diphenylphosphanyl ferrocenecarbaldehyde (1) was smoothly mediated by divalent samarium triflate to give (R,R)-diol 2a predominantly, whereas the use of samarium(II) iodide resulted in low selectivity as described in the previous literature. In contrast, the coupling reaction of (Rp)-2-diphenylphosphoryl ferrocenecarbaldehyde (3) with Sm(OTf)2 gave the (S,S)-diol as the major isomer, which was the opposite stereochemistry of that obtained in the reaction with 1. The rhodium complexes of diphosphanes 2a were good catalysts for the asymmetric hydrogenation of ,-acetamidocinnamic acid, and the product was obtained quantitatively with up to 92,%,ee. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    First Total Synthesis of the Potent Anticancer Natural Product Dideoxypetrosynol A: Preparation of the "Skipped" (Z)-Enediyne Moiety by Oxidative Coupling of Homopropargylphosphonium Ylide

    Benjamin W. Gung
    Abstract Dideoxypetrosynol A is a C30 polyacetylenic alcohol with C2 symmetry. The first total synthesis of both enantiomers of the potent anti-cancer natural product (+)- and (,)-dideoxypetrosynol A is reported. The key step is an oxidative coupling of a homopropargylphosphonium ylide to prepare the "skipped" (Z)-enediyne moiety. The natural dideoxypetrosynol A was isolated as a racemic mixture as shown in structure 1. The absolute configurations of the chiral centers are established for the (+)- and (,)-enantiomers using Burgess' enzymatic resolution procedure with Pseudomonas AK lipase. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Three Phase Microemulsion/Sol,Gel System for Aqueous C,C Coupling of Hydrophobic Substrates

    Dmitry Tsvelikhovsky
    Abstract Heck, Stille, Suzuki and three-component coupling reactions with hydrophobic substrates have been carried out in water. The substrates are initially transformed by a general procedure into a microemulsion, which consists of nearly 90,% water with the aid of sodium dodecyl sulfate and either PrOH or BuOH. The surfactant carries the molecules of the substrates to Pd(OAc)2 entrapped within a hydrophobicitized silica sol,gel matrix where the coupling between the substrates is assumed to take place. The products are then returned by the surfactant into the microemulsion from which it can be released. The immobilized palladium catalyst is leach proof and recyclable. It can be used in various coupling processes at least six times without loss of activity. Experiments with D2O have revealed that the water does not take part in the coupling process, but it has an effect on the pore size of the sol,gel matrix, which hosts the palladium catalyst. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Silica-Immobilized NHC,CuI Complex: An Efficient and Reusable Catalyst for A3 -Coupling (Aldehyde,Alkyne,Amine) under Solventless Reaction Conditions

    Min Wang
    Abstract A novel silica-immobilized NHC,CuI complex was developed and used as a highly efficient catalyst in the three-component coupling reactions of aldehydes, alkynes and amines (A3 -coupling). The reactions were applicable to aromatic and aliphatic aldehydes, alkynes and amines, and generated the corresponding propargylamines in good yields only in the presence of SiO2,NHC,CuI (2 mol-%) at room temp. under solvent-free reaction conditions. Moreover, the catalyst was quantitatively recovered from the reaction mixture by a simple filtration and reused for ten cycles with almost consistent activity.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Preparation of Chiral Homoannularly Bridged N,P-Ferrocenyl Ligands by Intramolecular Coupling of 1,5-Dilithioferrocenes and Their Application in Asymmetric Allylic Substitution Reactions,

    Shin-ichi Fukuzawa
    Abstract Homoannularly bridged ferrocene 6b was prepared by intramolecular coupling of 1,5-dilithioferrocene 5b mediated by Fe(acac)3. Dilithioferrocene 5b was prepared by lithium,halogen exchange of the corresponding diiodide, which was prepared by 1,5-dilithiation of the o -TMS-blocked ferrocene and followed by trapping with iodine and removal of the TMS group. Alternatively, 5b could be readily prepared by the reaction of o -bromophenylferrocene 8 with nBuLi (>2 equiv.). The benzene ring of 6b underwent ortho lithiation with tBuLi, and the resulting lithiated species was trapped with Ph2PCl to produce corresponding aminophosphane 7d. Aminophosphane 13, which has the phosphanyl group on the cyclopentadienyl ring, was prepared by intramolecular coupling of 1,5-dilithiated PhPPFA 11 mediated by Fe(acac)3. New N,P ligands 7d and 13 were used in the palladium-catalyzed allylic alkylation and amination of 1,3-diphenyl-2-propenyl acetate (14), and ligand 7d was found to give good yields with enantioselectivities as high as 96,% ee. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Reductive Coupling of Aromatic Aldehydes Promoted by an Aqueous TiCl3/tBuOOH System in Alcoholic Cosolvents

    Angelo Clerici
    Abstract The tert -butoxyl radical, generated by the aqueous TiIII/TBHP system, abstracts an H atom from alcoholic cosolvents (EtOH, iPrOH), leading to ,-hydroxyalkyl radicals thatreduce aromatic aldehydes to the corresponding 1,2-diols. The reactivities observed are explained by resonance stabilization of the ,-hydroxybenzyl radicals formed in the electron-transfer (ET) process. Good Hammett-type correlations are obtained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Simultaneous Regio- and Enantiodifferentiation in Carbohydrate Coupling,

    M. Belén Cid
    Abstract The glycosylation of 1,2- trans -diequatorial diols derived from tetrabenzoylated and tetrabenzylated D - and L - chiro -inositol with several glycosyl donors has been investigated. An unprecedented dependence of the regioselectivity on the absolute configuration of the acceptor has been found. However this trend is also modulated by the nature of the protecting groups on both the donor and acceptor, with benzoylated acceptors affording higher levels of regioselectivity. Most of the results have been rationalized by DFT calculations which indicate that stereoelectronic factors and hydrogen bonding between the donor and acceptor govern their relative orientation and determine the regiochemical outcome of the process. These studies also highlight the role of the acyl group adjacent to the OH to be glycosylated in facilitating the glycosylation reaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Coupling of Forming Process and Fatigue Design Computations: A Local Approach

    Matteo Luca Facchinetti
    The fatigue design of stamped parts is supposed to take into account for the forming process. In this paper, stamping of steel sheets is addressed by basic rules coming from elementary solid mechanics and plasticity. As an effective alternative to complex FE computations, such a pragmatic approach highlights how the forming process affects fatigue design and allows direct application in an industrial framework. [source]

    Formation of Pyridazinium Salts by Azo Coupling of N -Substituted 3-Amino-1-phenylbut-2-en-1-ones and Diazonium Salts


    Abstract Treatment of 3-(2,4-dimethoxyphenylamino)- and 3-methylamino-1-phenylbut-2-en-1-ones with some benzenediazonium tetrafluoroborates gives, besides the usual azo coupling products [i.e., 3-(substituted imino)-1-phenylbutane-1,2-diones 2-(4-substituted phenylhydrazones) and 2-(4-methoxyphenyldiazenyl)-3-methylamino-1-phenylbut-2-en-1-one, respectively], the previously unreported 1,4,5,6-tetrasubstituted pyridazinium tetrafluoroborates. The pyridazinium salts have been identified by X-ray analysis and by their 1H, 13C, 15N, 11B and 19F NMR spectra. Their formation is most probably the result of nucleophilic attack on the carbonyl carbon by the nitrogen of the hydrazone group and subsequent dehydration. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Lithium Perchlorate-Catalyzed Three-Component Coupling: A Facile and General Method for the Synthesis of ,-Aminophosphonates under Solvent-Free Conditions

    Najmedin Azizi
    Abstract A simple, efficient, and general method has been developed for the synthesis of ,-aminophosphonates in the presence of solid lithium perchlorate under solvent-free conditions. Thus secondary and tertiary ,-aminophosphonates were synthesized relatively quickly in good yields at room temperature. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


    EVOLUTION, Issue 3 2000
    David C. Krakauer
    Abstract., When the same sequence of nucleotides codes for regions of more than one functional polypeptide, this sequence contains overlapping genes. Overlap is most common in rapidly evolving genomes with high mutation rates such as viruses, bacteria, and mitochondria. Overlap is thought to be important as: (1) a means of compressing a maximum amount of information into short sequences of structural genes; and (2) as a mechanism for regulating gene expression through translational coupling of functionally related polypeptides. The stability of overlapping codes is examined in relation to the information cost of overlap and the mutation rate of the genome. The degree of overlap in a given population will tend to become monomorphic. Evolution toward partial overlap of genes is shown to depend on a convex cost function of overlap. Overlap does not evolve when expression of overlapping genes is mutually exclusive and produced by rare mutations to the wild-type genome. Assuming overlap increases coupling between functionally related genes, the conditions favoring overlap are explored in relation to the kinetics of gene activation and decay. Coupling is most effective for genes in which the gene overlapping at its 5'end (leading gene) decays rapidly, while the gene overlapping at the 3'end (induced gene) decays slowly. If gene expression can feedback on itself (autocatalysis), then high rates of activation favor overlap. [source]

    Cardioventilatory Coupling in Resting Human Subjects

    Y. C. Tzeng
    In 48 conscious resting subjects we examined the temporal coupling of heart beat timing and the onset of inspiration (cardioventilatory coupling), and the relationship between coupling and spectral indices of autonomic function. Using the proportional Shannon entropy (SH,) of the RI -1 interval (interval between inspiration and the preceding ECG R wave) as a measure of coupling we detected statistically significant coupling in 32 of the 48 subjects. This was confirmed by visual inspection of time series plots of RI intervals, in which coupling was evident as horizontal banding. Coupling resulted in a significant preference for whole number heart rate/respiratory frequency ratios. The strongest coupling was associated with low ventilatory frequency and high heart rate variability in the high (0.15-0.40 Hz) and low (0.04-0.15 Hz) frequency ranges, but was not related to blood pressure variability, or to a spectral measure of baroreflex sensitivity (,-index, low frequency range). There was no difference in coupling strength between males and females. We have previously described cardioventilatory coupling in spontaneously breathing anaesthetised subjects. The current study extends those observations by demonstrating that the qualitative features of coupling seen during anaesthesia are also observed in the conscious state. We conclude that the role of coupling in normal physiological respiratory control needs to be more widely explored. [source]

    Coupling of endothelin receptors to the ERK/MAP kinase pathway,

    FEBS JOURNAL, Issue 20 2001
    Roles of palmitoylation
    Endothelins are potent mitogens that stimulate extracellular signal-regulated kinases (ERK/MAP kinases) through their cognate G-protein-coupled receptors, ETA and ETB. To address the role of post-translational ET receptor modifications such as acylation on ERK activation and to identify relevant downstream effectors coupling the ET receptor to the ERK signaling cascades we have constructed a panel of palmitoylation-deficient ET receptor mutants with differential G, protein binding capacity. Endothelin-1 stimulation of wild-type ETA or ETB induced a fivefold to sixfold increase in ERK in COS-7 and CHO cells whereas full-length nonpalmitoylated ETA and ETB mutants failed to stimulate ERK. A truncated ETB lacking the C-terminal tail domain including putative phosphorylation and arrestin binding site(s) but retaining the critical palmitoylation site(s) was still able to fully stimulate ERK activation. Using mutated ET receptors with selective G-protein-coupling we found that endothelin-induced stimulation of G,q, but not of G,i or G,s, is essential for endothelin-mediated ERK activation. Inhibition of protein kinases A and C or epidermal growth factor receptor kinase failed to prevent ETA - and ETB -mediated ERK activation whereas blockage of phospholipase C-, completely abrogated endothelin-promoted ERK activation through ETA and ETB in recombinant COS-7 and native C6 cells. Complex formation of Ca2+ or inhibition of Src family tyrosine kinases prevented ET-1-induced ERK-2 activation in C6-cells. Our results indicate that endothelin-promoted ERK/MAPK activation criticially depends on palmitoylation but not on phosphorylation of ET receptors, and that the G,q/phospholipase C-,/Ca2+/Src signaling cascade is necessary for efficient coupling of ET receptors to the ERK/MAPK pathway. [source]

    Bioelectronics: Induced SER-Activity in Nanostructured Ag,Silica,Au Supports via Long-Range Plasmon Coupling (Adv. Funct.

    The picture shows a nanostructured layered silver-silica-gold electrode developed by J.-J. Feng, I. M. Weidinger, et al. on page 1954 where the underlying silver surface can be excited by laser light. The resulting surface plasmon resonance is transferred over a distance of up to 20 nm to the outer gold layer where attached proteins can be detected by surfaceenhanced Raman spectroscopy. [source]

    Induced SER-Activity in Nanostructured Ag,Silica,Au Supports via Long-Range Plasmon Coupling

    Jiu-Ju Feng
    Abstract A novel Ag,silica,Au hybrid device is developed that displays a long-range plasmon transfer of Ag to Au leading to enhanced Raman scattering of molecules largely separated from the optically excited Ag surface. A nanoscopically rough Ag surface is coated by a silica spacer of variable thickness from ,1 to 21,nm and a thin Au film of ,25,nm thickness. The outer Au surface is further functionalized by a self-assembled monolayer (SAM) for electrostatic binding of the heme protein cytochrome c (Cyt c) that serves as a Raman probe and model enzyme. High-quality surface-enhanced resonance Raman (SERR) spectra are obtained with 413,nm excitation, demonstrating that the enhancement results exclusively from excitation of Ag surface plasmons. The enhancement factor is estimated to be 2,×,104,8,×,103 for a separation of Cyt c from the Ag surface by 28,47,nm, corresponding to an attenuation of the enhancement by a factor of only 2,6 compared to Cyt c adsorbed directly on a SAM-coated Ag electrode. Upon immobilization of Cyt c on the functionalized Ag,silica,Au device, the native structure and redox properties are preserved as demonstrated by time- and potential-dependent SERR spectroscopy. [source]

    Customized Electronic Coupling in Self-Assembled Donor,Acceptor Nanostructures

    Dimas G. de Oteyza
    Abstract Charge transfer processes between donor,acceptor complexes and metallic electrodes are at the heart of novel organic optoelectronic devices such as solar cells. Here, a combined approach of surface-sensitive microscopy, synchrotron radiation spectroscopy, and state-of-the-art ab initio calculations is used to demonstrate the delicate balance that exists between intermolecular and molecule,substrate interactions, hybridization, and charge transfer in model donor,acceptor assemblies at metal-organic interfaces. It is shown that charge transfer and chemical properties of interfaces based on single component layers cannot be naively extrapolated to binary donor,acceptor assemblies. In particular, studying the self-assembly of supramolecular nanostructures on Cu(111), composed of fluorinated copper-phthalocyanines (F16CuPc) and diindenoperylene (DIP), it is found that, in reference to the associated single component layers, the donor (DIP) decouples electronically from the metal surface, while the acceptor (F16CuPc) suffers strong hybridization with the substrate. [source]

    A Novel Coupling 1,3-Dipolar Cycloaddition Sequence as a Three-Component Approach to Highly Fluorescent Indolizines

    Indolizines 4 and biindolizines 6 can be synthesized in moderate yields in a consecutive one-pot three-component process by a coupling/1,3-dipolar cycloaddition sequence of a (hetero)arenecarbonyl chloride 1, a terminal alkyne 2, and a suitable 1-(2-oxoethyl) pyridinium bromide 3 or 5, respectively (Schemes,1 and 2). After the Sonogashira coupling, a [2+3] cycloaddition of the in situ formed pyridinium ylide, an allyl-type 1,3-dipole, furnishes a cycloadduct that is instantaneously oxidatively aromatized to give the highly fluorescent indolizine derivatives that were unambiguously characterized by an X-ray-structure analysis of compound 4d (Fig.,1). Additionally, fluorescence studies with pyridinyl-substituted representatives reveal not only that indolizines and biindolizines are highly interesting fluorescence dyes but that their fluorescence color can also be reversibly switched upon altering the pH of the medium. [source]

    Synthesis of Substituted , -(Hydroxymethyl)- , -iodoacrylates via MgI2 -Promoted Stereoselective Aldol Coupling

    Han-Xun Wei
    The efficient and highly stereoselective syntheses of a variety of (Z)-configured, substituted , -(hydroxymethyl) - , -iodo-acrylates from prop-2-ynoate and various aldehydes was achieved. The synthetic protocol involves a simple one-pot coupling reaction under mild conditions, promoted by MgI2, which serves both as a Lewis acid and iodine source for a BaylisHillman -type reaction. All adducts were generated in good-to-excellent yields, the (Z)-isomers being formed in high selectivity (>98%). The conversion of methyl prop-2-ynoate into an active ,, -iodo allenolate' intermediate, which then nucleophilically attacks an aldehyde, is proposed as a plausible reaction mechanism. [source]

    A Theoretical Study of Correlation between Hydrogen-Bond Stability and J -Coupling through a Hydrogen Bond

    Shun-ichi Kawahara
    trans -Hydrogen-bond hyperfine splitting via magnetic interaction, which is observed as J -coupling in NMR experiments, was theoretically studied. trans -Hydrogen-bond hyperfine splitting should be closely related to the orbital interaction between the lone-pair orbital of the H-bond acceptor and the antibond orbital of the H-bond donor. A linear relationship was observed between magnetic interaction hyperfine splitting through a H-bond and the H-bond strength. The relationship was dependent on the type of the nucleus forming the H-bond; linear correlation was observed in NH,,,O/N type or OH,,,N type H-bonded complexes, but not in OH,,,O type H-bonded complexes. [source]