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RCM
Terms modified by RCM Selected AbstractsBenzylideneruthenium Complexes Bearing Pyridine-Based Ligands and Their Influence on the Formation of Mono- or Bis(pyridine) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 34 2007Wen-Zhen Zhang Abstract Benzylideneruthenium complexes bearing the N-heterocyclic carbene (NHC) ligand 1,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene (H2IMe) and one or two pyridine-based ligands have been prepared by treating [RuCl2(=CHPh)(H2IMe)(PPh3)] with the corresponding pyridine derivative. X-ray crystallographic and mass spectrometric evidence is used to investigate the interconversion between mono- and bis(pyridine) complexes and the influence of the pyridine ligand on the formation of these complexes. The catalytic activity of these complexes has been tested in the ring-closing metathesis (RCM) reaction of diallylmalononitrile and the cross metathesis (CM) reaction of acrylonitrile with terminal olefins.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Phenylphosphoric Acid as a New Additive to Inhibit Olefin Isomerisation in Ruthenium-Catalysed Metathesis ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2007Nélida Gimeno Abstract A systematic study of the ruthenium-catalysed metathesis of alkenes containing hydrogen-bonding substituents (namely urea and thiourea groups) is presented. Under standard metathesis conditions, several of the substrates under study undergo alkene isomerisation instead of the targeted metathesis. However, in the course of these investigations it has been established that this unwanted isomerisation process can be suppressed by addition of phenylphosphoric acid to the reaction mixture. Some other potential isomerisation inhibitors (e.g. benzoic acid and salts of phosphoric acid) have been studied and their performance compared to that of phenylphosphoric acid. To extend the scope of phenylphosphoric acid, we also studied the metathesis of 1,3-diallylurea. Interestingly, not only did we observe the complete suppression of the isomerisation process, but also that it is possible to obtain instead of the ring-closing metathesis (RCM) product,ADMET oligomers resulting from the cross-metathesis of diallylurea at higher concentrations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] New Solutions to the C-12,13 Stereoproblem of Epothilones B and D; Synthesis of a 12,13-Diol-Acetonide Epothilone B AnalogEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2006Tanja Gaich Abstract New approaches are described to the synthesis of epothilone B and a 12,13-diol-acetonide derivative. Specifically the (12Z) double bond is formed quantitatively by a silicon-tethered ring-closing metathesis (RCM) reaction with 85,% selectivity. Alternatively, a direct route to the 12,13-epoxide by cyclization of a 12,13-diol has been developed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Efficient Synthesis of Doubly Connected Primary Face-to-Face Cyclodextrin Homo-DimersEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2003Thomas Lecourt Abstract "Head-to-head" type ,- and ,-cyclodextrin homo-dimers in which the two primary rims are doubly ligated through alkyl chains have been synthesised in high yield by acyclic diene metathesis (ADM), followed by ring-closing metathesis (RCM). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Straightforward Synthesis of Labeled and Unlabeled Pyrimidine d4Ns via 2,,3, - Diyne seco Analogues through Olefin Metathesis ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2003Isabelle Gillaizeau Abstract The synthesis of dideoxynucleosides (ddNs) or didehydro-dideoxynucleosides (d4Ns) from nucleosides has been extensively reviewed. While previously described methods are based on the modification of the 2,- and/or 3,-OH group of the intact ribose moiety, the use of a ring-closing metathesis (RCM) for the formation of the unsaturated cyclic system of nucleosides could be a straightforward approach to the d4Ns. Thus, as part of our drug labeling program, this paper reports a straightforward synthesis of 2,,3,-didehydro-2,,3,-dideoxyuridine (d4U) and [1,,2,,3,,4,,5,- 13C5,6- 13C,1,3- 15N2]d4T using the RCM protocol. This paper discusses the preparation of nucleoside dienes and the activity of ruthenium-based metathesis catalysts. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Regional Climate Models for Hydrological Impact Studies at the Catchment Scale: A Review of Recent Modeling StrategiesGEOGRAPHY COMPASS (ELECTRONIC), Issue 7 2010Claudia Teutschbein This article reviews recent applications of regional climate model (RCM) output for hydrological impact studies. Traditionally, simulations of global climate models (GCMs) have been the basis of impact studies in hydrology. Progress in regional climate modeling has recently made the use of RCM data more attractive, although the application of RCM simulations is challenging due to often considerable biases. The main modeling strategies used in recent studies can be classified into (i) very simple constructed modeling chains with a single RCM (S-RCM approach) and (ii) highly complex and computing-power intensive model systems based on RCM ensembles (E-RCM approach). In the literature many examples for S-RCM can be found, while comprehensive E-RCM studies with consideration of several sources of uncertainties such as different greenhouse gas emission scenarios, GCMs, RCMs and hydrological models are less common. Based on a case study using control-run simulations of fourteen different RCMs for five Swedish catchments, the biases of and the variability between different RCMs are demonstrated. We provide a short overview of possible bias-correction methods and show that inter-RCM variability also has substantial consequences for hydrological impact studies in addition to other sources of uncertainties in the modeling chain. We propose that due to model bias and inter-model variability, the S-RCM approach is not advised and ensembles of RCM simulations (E-RCM) should be used. The application of bias-correction methods is recommended, although one should also be aware that the need for bias corrections adds significantly to uncertainties in modeling climate change impacts. [source] Assessment of climate-change impacts on alpine discharge regimes with climate model uncertaintyHYDROLOGICAL PROCESSES, Issue 10 2006Pascal Horton Abstract This study analyses the uncertainty induced by the use of different state-of-the-art climate models on the prediction of climate-change impacts on the runoff regimes of 11 mountainous catchments in the Swiss Alps having current proportions of glacier cover between 0 and 50%. The climate-change scenarios analysed are the result of 19 regional climate model (RCM) runs obtained for the period 2070,2099 based on two different greenhouse-gas emission scenarios (the A2 and B2 scenarios defined by the Intergovernmental Panel on Climate Change) and on three different coupled atmosphere-ocean general circulation models (AOGCMs), namely HadCM3, ECHAM4/OPYC3 and ARPEGE/OPA. The hydrological response of the study catchments to the climate scenarios is simulated through a conceptual reservoir-based precipitation-runoff transformation model called GSM-SOCONT. For the glacierized catchments, the glacier surface corresponding to these future scenarios is updated through a conceptual glacier surface evolution model. The results obtained show that all climate-change scenarios induce, in all catchments, an earlier start of the snowmelt period, leading to a shift of the hydrological regimes and of the maximum monthly discharges. The mean annual runoff decreases significantly in most cases. For the glacierized catchments, the simulated regime modifications are mainly due to an increase of the mean temperature and the corresponding impacts on the snow accumulation and melting processes. The hydrological regime of the catchments located at lower altitudes is more strongly affected by the changes of the seasonal precipitation. For a given emission scenario, the simulated regime modifications of all catchments are highly variable for the different RCM runs. This variability is induced by the driving AOGCM, but also in large part by the inter-RCM variability. The differences between the different RCM runs are so important that the predicted climate-change impacts for the two emission scenarios A2 and B2 are overlapping. Copyright © 2006 John Wiley & Sons, Ltd. [source] Performance comparison of some dynamical and empirical downscaling methods for South Africa from a seasonal climate modelling perspectiveINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2009Willem A. Landman Abstract The ability of advanced state-of-the-art methods of downscaling large-scale climate predictions to regional and local scale as seasonal rainfall forecasting tools for South Africa is assessed. Various downscaling techniques and raw general circulation model (GCM) output are compared to one another over 10 December-January-February (DJF) seasons from 1991/1992 to 2000/2001 and also to a baseline prediction technique that uses only global sea-surface temperature (SST) anomalies as predictors. The various downscaling techniques described in this study include both an empirical technique called model output statistics (MOS) and a dynamical technique where a finer resolution regional climate model (RCM) is nested into the large-scale fields of a coarser GCM. The study addresses the performance of a number of simulation systems (no forecast lead-time) of varying complexity. These systems' performance is tested for both homogeneous regions and for 963 stations over South Africa, and compared with each other over the 10-year test period. For the most part, the simulations method outscores the baseline method that uses SST anomalies to simulate rainfall, therefore providing evidence that current approaches in seasonal forecasting are outscoring earlier ones. Current operational forecasting approaches involve the use of GCMs, which are considered to be the main tool whereby seasonal forecasting efforts will improve in the future. Advantages in statistically post-processing output from GCMs as well as output from RCMs are demonstrated. Evidence is provided that skill should further improve with an increased number of ensemble members. The demonstrated importance of statistical models in operation capacities is a major contribution to the science of seasonal forecasting. Although RCMs are preferable due to physical consistency, statistical models are still providing similar or even better skill and should still be applied. Copyright © 2008 Royal Meteorological Society [source] Simulation of New Zealand's climate using a high-resolution nested regional climate modelINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2007Frank Drost Abstract A regional climate model (RCM) for New Zealand has been developed. The RCM is embedded within a GCM and both models are run under pre-industrial conditions. Seasonal mean output of the RCM is compared against NCEP data and the New Zealand national climate database. Regional and seasonal aspects of modelled surface temperature and precipitation are to a large extent simulated correctly. The main anomalies are related to the difficulty of incorporating New Zealand's orography appropriately and to the initial and lateral boundary conditions, which were supplied by the GCM. The largest anomalies occur over the Southern Alps, where the modelled temperatures are too low and where the amount of precipitation is too high. Many parts of the east coasts in both the North and South Island are too warm and too dry. Correlation patterns of temperature and precipitation with mean sea-level pressure differ considerably from the equivalent patterns constructed from NCEP data, but do show in general the dominant relationships between wind direction and temperature and precipitation. Copyright © 2006 Royal Meteorological Society [source] Canadian RCM projected climate-change signal and its sensitivity to model errorsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2006L. Sushama Abstract Climate change is commonly evaluated as the difference between simulated climates under future and current forcings, based on the assumption that systematic errors in the current-climate simulation do not affect the climate-change signal. In this paper, we investigate the Canadian Regional Climate Model (CRCM) projected climate changes in the climatological means and extremes of selected basin-scale surface fields and its sensitivity to model errors for Fraser, Mackenzie, Yukon, Nelson, Churchill and Mississippi basins, covering the major climate regions in North America, using current (1961,1990) and future climate simulations (2041,2070; A2 and IS92a scenarios) performed with two versions of CRCM. Assessment of errors in both model versions suggests the presence of nonnegligible biases in the surface fields, due primarily to the internal dynamics and physics of the regional model and to the errors in the driving data at the boundaries. In general, results demonstrate that, in spite of the errors in the two model versions, the simulated climate-change signals associated with the long-term monthly climatology of various surface water balance components (such as precipitation, evaporation, snow water equivalent (SWE), runoff and soil moisture) are consistent in sign, but differ in magnitude. The same is found for projected changes to the low-flow characteristics (frequency, timing and return levels) studied here. High-flow characteristics, particularly the seasonal distribution and return levels, appear to be more sensitive to the model version. CRCM climate-change projections indicate an increase in the average annual precipitation for all basins except Mississippi, while annual runoff increases in Fraser, Mackenzie and Yukon basins. A decrease in runoff is projected for Mississippi. A significant decrease in snow cover is projected for all basins, with maximum decrease in Fraser. Significant changes are also noted in the frequency, timing and return levels for low flows. Copyright © 2006 Royal Meteorological Society. [source] Ten-year climatology of summer monsoon over South China and its surroundings simulated from a regional climate modelINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2006Yiming Liu Abstract In a previous study by the authors, a regional climate model (hereafter the RCM) developed to study the summer monsoon over South China (SC) and the South China Sea (SCS) has been tested and found to be able to simulate to a large extent the precipitation over this region for the months of May and June. To examine the interannual variability of the summer monsoon here, it is necessary to establish a model climatology to serve as a comparison and to reduce or even remove any systematic model biases. This paper presents the analyses of such a 10-year climatology (1991,2000). The model was initialized on 1 April and integrated up to the end of June for the ten years. The initial atmospheric conditions and lateral boundary data used in this study are from the European Centre for Medium-range Weather Forecasts ,40-year' reanalyses. The RCM can reproduce well the main features of the monsoon circulation and vertical structure of the atmosphere. The RCM can simulate the intensification and northwestward displacement of the south Asian upper anticyclones from May to June, as well as the low-level moisture transport from the Bay of Bengal to SC. In the simulation, the average SCS summer monsoon onset occurs in the fourth pentad of May, which is consistent with the results from previous observational research. In addition, the RCM can reproduce the main characteristics of the onset such as the change of the low-level zonal flow from easterly to westerly as well as the rapid increase in daily precipitation. The SC and SCS precipitation anomalies have the correct sign in almost all the years. The shortcomings of the model simulation include an under-prediction of the strength of the subtropical high over the Northwest Pacific and the moisture transport from the Bay of Bengal to the Indochina Peninsula (IC) and SCS. A cold bias in surface air temperature is also observed, with the 10-year mean biases of the simulated surface air temperature over SC, SCS and IC in May and June being about ,2.1 °C, ,2.4 °C and ,1.4 °C respectively. The 10-year mean biases of the simulated daily precipitation rate over SC, SCS and IC are about 2.0, ,3.8 and 3.5 mm d,1 respectively. Copyright © 2005 Royal Meteorological Society. [source] Mixed Isobutylphobane/N-Heterocyclic Carbene Ruthenium- Indenylidene Complexes: Synthesis and Catalytic Evaluation in Olefin Metathesis ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Xavier Sauvage Abstract Two new second generation ruthenium(II) dichloride-indenylidene complexes [RuCl2(9-isobutylphosphabicyclo[3.3.1]nonane)(NHC)(3-phenyl-1-indenylidene)], where NHC=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) or its unsaturated imidazol-2-ylidene analogue (IMes), were isolated in high yields upon heating a tetrahydrofuran (THF) solution of the diphosphane complex [RuCl2(isobutylphobane)2(3-phenyl-1-indenylidene)] with a two-fold excess of the corresponding imidazol(in)ium-2-carboxylate zwitterions. Both products were characterized by 1H, 13C, and 31P,NMR spectroscopy, and the molecular structure of [RuCl2(isobutylphobane)(SIMes)(3-phenyl-1-indenylidene)] was determined by X-ray diffraction analysis. A close inspection of the packing structure revealed the presence of different types of intra- and intermolecular interactions that enhanced the global stability of the crystals, while low temperature NMR experiments showed the existence of two distinct rotational isomers due to the unsymmetrical nature of the phobane ligand. The catalytic activity of both compounds was assessed in olefin metathesis using benchmark ring-opening metathesis polymerization, ring-closing metathesis (RCM), and cross-metathesis reactions, and compared with those of related first and second generation ruthenium-benzylidene and indenylidene catalyst precursors. Kinetic studies confirmed the high thermal stability of the mixed isobutylphobane/N-heterocyclic carbene complexes, which suffered from a slow initiation efficiency compared to other catalytic systems based on the tricyclohexylphosphane ligand. However, the remarkable robustness of [RuCl2(isobutylphobane)(SIMes)(3-phenyl-1-indenylidene)] was beneficial for performing the RCM of diethyl 2,2-bis(2-methylallyl)malonate. Monitoring the formation of the ruthenium-methylidene active species [RuCl2(isobutylphobane)(SIMes)(CH2)] derived from this precursor further demonstrated its ability to sustain long reaction times and high temperatures required to carry out the RCM of tetrasubstituted olefins. [source] New Indenylidene-Schiff Base-Ruthenium Complexes for Cross-Metathesis and Ring-Closing MetathesisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2009Abstract We here report on the stability and catalytic activity of new indenylidene-Schiff base-ruthenium complexes 3a,f through representative cross-metathesis (CM) and ring-closing metathesis (RCM) reactions. Excellent activity of the new complexes was found for the two selected RCM reactions; prominent conversion was obtained compared to the commercial Hoveyda,Grubbs catalyst 2. Moreover, excellent results were obtained for a standard CM reaction. Higher conversions were achieved with one of the indenylidene catalysts compared with Hoveyda,Grubbs catalyst. Unexpectedly, an isomerization reaction was observed during the CM reaction of allylbenzene. To the best of our knowledge, isomerization reactions in this model CM reaction in closed systems have never been described using first generation catalysts, including the Hoveyda,Grubbs catalyst. The first model CM reactions as well as the RCM reactions have been monitored using 1H,NMR. The course of the CM reaction of 3-phenylprop-1-ene (8) and cis -1,4-diacetoxybut-2-ene (9) was monitored by GC. The isomerization reaction was studied by means of GC-mass spectrometry and in situ IR spectroscopy. All catalysts were structurally characterized by means of 1H, 13C, and 31P,NMR spectroscopy. [source] Stability of Second Generation Grubbs' Alkylidenes to Primary Amines: Formation of Novel Ruthenium-Amine ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Gerald Abstract The stability of second generation Grubbs' alkylidenes to primary amines relative to the first generation derivatives is investigated. For both Grubbs' alkylidene derivatives, the tricyclohexylphosphine (PCy3) ligand is displaced by n -butylamine and diethylenetriamine. However, while displacement of PCy3 in first generation Grubbs' alkylidene derivatives results in decomposition of the catalyst, the N-heterocyclic carbene (NHC) ligand in second generation derivatives is not displaced by primary amines present in up to 100 equivalents. The result is the formation of new stable ruthenium-amine complexes. These complexes are characterized and their catalytic activity is evaluated in ring-closing metathesis (RCM) and ring-opening metathesis (ROMP) reactions. While the amine complexes evaluated were minimally active in RCM reactions, the ruthenium-butylamine complex was significantly active in ROMP and exhibited an initiation rate constant that was at least an order of magnitude greater than that of the second generation Grubbs' alkylidene from which it was synthesized. [source] Ferrocene Redox Controlled Reversible Immobilization of Ruthenium Carbene in Ionic Liquid: A Versatile Catalyst for Ring-Closing MetathesisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Guiyan Liu Abstract A ferrocene-tagged ruthenium carbene 15 that can be reversibly immobilized in an ionic liquid (IL) via the controlled oxidation and reduction of a ferrocene tag was prepared. This offers a new strategy which uses redox chemistry to control immobilization and to recycle both the catalyst and the IL. In this experiment, 11 recycles were performed for the ring-closing metathesis (RCM) of a substrate using 16 as the catalyst in an ionic liquid (IL). More importantly, after the reaction was completed, the ruthenium catalyst was easily separated from the supporting IL by just adding decamethylferrocene (DMFc) to reduce the cationic ferrocene and then extracting it with benzene. Thus, this recycle system offers an easy way to recycle both the ruthenium catalyst and the IL. [source] Palladium(II)-Catalyzed Domino Reaction of 2-(1-Alkynyl)-2-alken-1-ones with Nucleophiles: Scope, Mechanism and Synthetic Application in the Synthesis of 3,4-Fused Bicyclic Tetrasubstituted FuransADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009Yuanjing Xiao Abstract Described herein is the development of a palladium(II)-catalyzed two- or three-component reaction of 2-(1-alkynyl)-2-alken-1-ones with nucleophiles and allylic chlorides. Various types of nucleophiles such as O- , N- , C -based nucleophiles and olefin-tethered O- , N- , C -based nucleophiles were investigated. The scope, mechanism and application of this Pd(II)-catalyzed domino reaction were studied. In these transformations, the palladium catalyst exhibits a dual role, serving simultaneously as a Lewis acid and a transition metal. Two possible reaction pathways (cross-coupling reaction vs. Heck reaction) from the same intermediate furanylpalladium species were observed. The reaction pathway is dependent on the property of the nucleophile and the length of the tethered chain as well. When olefin-tethered O -based nucleophiles were used, only the cross-coupling reaction pathway was observed, in contrast, both reaction pathways were observed when olefin-tethered C -based nucleophiles were employed. The product ratio is dependent on the length of the tethered chain. Furthermore, ring-closing metathesis (RCM) of corresponding furans with CC bonds provides an easy method for the preparation of functionalized oxygen-heterocycles , 3,4-fused bicyclic furans. It is also noteworthy that allylic chloride can be as an oxidant besides its well known function as an alkylating reagent. [source] Homobimetallic Ruthenium Vinylidene, Allenylidene, and Indenylidene Complexes: Synthesis, Characterization, and Catalytic StudiesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2009Xavier Sauvage Abstract Four homobimetallic ruthenium-(p -cymene) complexes bearing a tricyclohexylphosphine ligand and polyunsaturated carbon-rich fragments were obtained via a vinylidene-allenylidene-indenylidene cascade pathway from the ethylene complex [(p -cymene)Ru(,-Cl)3RuCl(PCy3)(,2 -C2H4)] (7a). All the products were isolated and fully characterized by IR and NMR spectroscopies. The molecular structure of the indenylidene complex 11 was determined by X-ray crystallographic analysis. The catalytic activity of the four complexes was probed in various types of olefin metathesis reactions and compared with those of a related homobimetallic ruthenium-benzylidene complex, as well as first, second, and third generation monometallic Grubbs catalysts. In the ring-closing metathesis (RCM) of diethyl diallylmalonate, the homobimetallic ruthenium-indenylidene complex 11 outperformed all the ruthenium-benzylidene complexes under investigation and was only slightly less efficient than its monometallic parent. Cross-metathesis experiments with ethylene showed that deactivation of ruthenium-benzylidene or indenylidene complexes was due to the rapid bimolecular decomposition of methylidene active species into ethylene complex 7a. Vinylidene and allenylidene complexes were far less efficient catalyst precursors for ring-opening metathesis polymerization (ROMP) or RCM and remained inert under an ethylene atmosphere. Their catalytic activity was, however, substantially enhanced upon addition of an acidic co-catalyst that most likely promoted their in situ transformation into indenylidene species. Due to its straightforward synthesis and high metathetical activity, homobimetallic ruthenium-indenylidene complex 11 is a valuable intermediate for the preparation of the Hoveyda,Grubbs catalyst [Cl2Ru(PCy3)(CH- o -O- i- PrC6H4)] via stoichiometric cross-metathesis with 2-isopropoxystyrene. The procedure did not require any sacrificial phosphine and the transition metal not incorporated into the final product was easily recovered and recycled at the end of the process. [source] Synthesis of Schiff Base-Ruthenium Complexes and Their Applications in Catalytic ProcessesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14 2005Renata Drozdzak Abstract The synthesis of various Schiff base mononuclear and binuclear ruthenium complexes, whose additional ligands around the metal core have been selected from an array of motifs, is described. These types of ruthenium complexes, conveniently prepared from commonly available ruthenium sources, are rather stable, display good tolerance towards diverse organic functionalities and also to air and moisture. Remarkably, they exhibit a high activity and chemoselectivity in a variety of catalytic processes such as ring-closing metathesis (RCM), Kharasch addition, alkyne dimerization, enol ester synthesis, ring-opening metathesis polymerization (ROMP) and atom-transfer radical polymerization (ATRP). This review covers both homogeneous and heterogeneous hybrid Schiff base-ruthenium complexes. [source] Thin Layer Chromatography for the Detection of Unexpected Reactions in Organometallic Combinatorial CatalysisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 8 2003Olivier Lavastre Abstract Thin layer chromatography (TLC) represents a fast and inexpensive alternative to NMR spectroscopy or analytical methods based on chromatography for the detection of unexpected products in organometallic combinatorial catalysis. This screening test led to the detection of the catalytic system [Ir(COD)Cl]2/PPh3 for isomerisation of diolefinic substrates instead the expected ring closing metathesis (RCM) reaction. [source] Is a long-term ranitidine-based triple therapy against Helicobacter pylori only a heritage of the past?ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 4 2005A prospective, randomized clinicopharmacological study Summary Background:, Acid suppression plus two antibiotics is currently considered the gold standard anti- Helicobacter pylori treatment, but the effective role of gastric antisecretory drugs is still poorly understood. Aims:, To compare a 14-day ranitidine-based triple regimen against Helicobacter pylori with one based on omeprazole, and to study the influence of antisecretory drugs on metronidazole pharmacokinetics in human plasma. Methods:, A total of 150 dyspeptic H. pylori -infected patients were randomized for ranitidine 300 mg b.d. (RCM group) or omeprazole 20 mg b.d. (OCM group) 14-day triple therapy, with clarithromycin 500 mg b.d. and metronidazole 500 mg b.d. On the eighth day of therapy, metronidazole pharmacokinetics was studied in plasma by high-performance liquid chromatography. The pharmacokinetic parameters (terminal half-life, area under the curve, peak-plasma level, peak time) of metronidazole were computed using standard non-compartmental methods. H. pylori status was monitored before and 4 weeks after the end of therapy by histology, serology and rapid urease test. Results:, On an intention-to-treat basis, eradication rates were 91 and 76% for the RCM and OCM groups respectively (P < 0.02). Significantly different pharmacokinetic parameters of metronidazole were found between the groups: peak-plasma level (P < 0.01) and area under the curve (P < 0.02). Conclusion:, Our results show that the RCM regimen was more effective than that based on OCM and that the antisecretory drugs affected metronidazole availability, increasing the efficacy of ranitidine-based regimens. [source] Heterogenization of a Modified Grubbs,Hoveyda Catalyst on a ROMP-Derived Monolithic SupportMACROMOLECULAR RAPID COMMUNICATIONS, Issue 15 2003Jens O. Krause Abstract A ring-opening metathesis polymerization- (ROMP-) based monolith was synthesized using a Grubbs' first generation catalyst. The living termini were used for surface grafting of norborn-5-ene-2-ylmethyl hexafluoroglutarate. The free carboxylic acid groups of the graft polymer were converted into the corresponding silver salt and reacted with the Grubbs,Hoveyda catalyst [RuCl2(CH(2- iPrO)C6H4)(IMesH2)] (IMesH2,=,1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) to yield a stable heterogeneous version of this catalyst for use in ring-closing metathesis (RCM) under continuous flow conditions. The monolith-supported Grubbs,Hoveyda catalyst. [source] Three-dimensional ultrasound image-guided robotic system for accurate microwave coagulation of malignant liver tumoursTHE INTERNATIONAL JOURNAL OF MEDICAL ROBOTICS AND COMPUTER ASSISTED SURGERY, Issue 3 2010Jing Xu Abstract Background The further application of conventional ultrasound (US) image-guided microwave (MW) ablation of liver cancer is often limited by two-dimensional (2D) imaging, inaccurate needle placement and the resulting skill requirement. The three-dimensional (3D) image-guided robotic-assisted system provides an appealing alternative option, enabling the physician to perform consistent, accurate therapy with improved treatment effectiveness. Methods Our robotic system is constructed by integrating an imaging module, a needle-driven robot, a MW thermal field simulation module, and surgical navigation software in a practical and user-friendly manner. The robot executes precise needle placement based on the 3D model reconstructed from freehand-tracked 2D B-scans. A qualitative slice guidance method for fine registration is introduced to reduce the placement error caused by target motion. By incorporating the 3D MW specific absorption rate (SAR) model into the heat transfer equation, the MW thermal field simulation module determines the MW power level and the coagulation time for improved ablation therapy. Two types of wrists are developed for the robot: a ,remote centre of motion' (RCM) wrist and a non-RCM wrist, which is preferred in real applications. Results The needle placement accuracies were < 3 mm for both wrists in the mechanical phantom experiment. The target accuracy for the robot with the RCM wrist was improved to 1.6 ± 1.0 mm when real-time 2D US feedback was used in the artificial-tissue phantom experiment. By using the slice guidance method, the robot with the non-RCM wrist achieved accuracy of 1.8 ± 0.9 mm in the ex vivo experiment; even target motion was introduced. In the thermal field experiment, a 5.6% relative mean error was observed between the experimental coagulated neurosis volume and the simulation result. Conclusion The proposed robotic system holds promise to enhance the clinical performance of percutaneous MW ablation of malignant liver tumours. Copyright © 2010 John Wiley & Sons, Ltd. [source] Twenty-Year Experience With Heart Transplantation for Infants and Children With Restrictive Cardiomyopathy: 1986,2006AMERICAN JOURNAL OF TRANSPLANTATION, Issue 1 2008A. J. Bograd Idiopathic restrictive cardiomyopathy (RCM) is a rare cardiomyopathy in children notable for severe diastolic dysfunction and progressive elevation of pulmonary vascular resistance (PVR). Traditionally, those with pulmonary vascular resistance indices (PVRI) >6 W.U. × m2 have been precluded from heart transplantation (HTX). The clinical course of all patients transplanted for RCM between 1986 and 2006 were reviewed. Preoperative, intraoperative and postoperative variables were evaluated. A total of 23 patients underwent HTX for RCM, with a mean age of 8.8 ± 5.6 years and a mean time from listing to HTX of 43 ± 60 days. Preoperative and postoperative (114 ± 40 days) PVRI were 5.9 ± 4.4 and 2.9 ± 1.5 W.U. × m2, respectively. At time of most recent follow-up (mean = 5.7 ± 4.6 years), the mean PVRI was 2.0 ± 1.0 W.U. × m2. Increasing preoperative mean pulmonary artery pressure (PA) pressure (p = 0.04) and PVRI > 6 W.U. × m2 (,2= 7.4, p < 0.01) were associated with the requirement of ECMO postoperatively. Neither PVRI nor mean PA pressure was associated with posttransplant mortality; 30-day and 1-year actuarial survivals were 96% and 86%, respectively. Five of the seven patients with preoperative PVRI > 6 W.U. × m2 survived the first postoperative year. We report excellent survival for patients undergoing HTX for RCM despite the high proportion of high-risk patients. [source] Synthese und biologische Evaluierung von Iriomoteolid-3a und seinen Analoga,ANGEWANDTE CHEMIE, Issue 46 2009Riccardo Cribiú Dr. Metathese hoch zwei: Eine Kreuzmetathese(CM)-Ringschlussmetathese(RCM)-Strategie ermöglichte die stereokontrollierte Synthese der Titelverbindung, eines zytotoxischen Verwandten der Amphidinolide. Die chemische Bearbeitung des Moleküls führte zu nichtnatürlichen Analoga mit einer zum Naturstoff vergleichbaren zytostatischen Wirkung, die als Testmoleküle in der chemischen Biologie eingesetzt werden könnten. [source] Totalsynthese des Antibiotikums Kendomycin durch Photo-Fries-Umlagerung und Ringschlussmetathese,ANGEWANDTE CHEMIE, Issue 33 2009Thomas Magauer Mag. Große Ringe bieten viele Möglichkeiten: Zwei neue Wege zum Antibiotikum Kendomycin werden beschrieben. Charakteristische Merkmale sind komplexe Claisen-Ireland-Umlagerungen und Makrocyclisierungen über Ringschlussmetathese (RCM) oder Photo-Fries-Umlagerung (siehe Retrosyntheseschema). [source] Behavior of Cardiomyocytes and Skeletal Muscle Cells on Different Extracellular Matrix Components,Relevance for Cardiac Tissue EngineeringARTIFICIAL ORGANS, Issue 1 2007Karin Macfelda Abstract:, Myocardial cell transplantation in patients with heart failure is emerging as a potential therapeutic option to augment the function of remaining myocytes. Nevertheless, further investigations on basic issues such as ideal cell type continue to be evaluated. Therefore, the aim of our studies was to compare the performance of skeletal muscle cells and cardiomyocytes with respect to their proliferation rate and viability on different extracellular matrix components (EMCs). Rat cardiomyocytes (RCM) and rat skeletal muscle cells (RSMC) were cultured on EMCs such as collagen type I, type IV, laminin, and fibronectin. The components were used as "single coating" as well as "double coating." Proliferation rates were determined by proliferation assays on days 1, 2, 4, and 8 after inoculation of the cells. The most essential result is that collagen type I enhances the proliferation rate of RSMC but decreases the proliferation of RCM significantly. This effect is independent of the second EMC used for the double-coating studies. Other EMCs also influence cellular behavior, whereas the sequence of the EMCs is essential. Results obtained in our studies reveal the significant different proliferation behavior of RCM and RSMC under identical conditions. As skeletal muscle cells are also used in heart tissue engineering models, these results are essential and should be investigated in further studies to prove the applicability of skeletal muscle cells for heart tissue engineering purposes. [source] Noninvasive diagnostic tools for nonmelanoma skin cancerBRITISH JOURNAL OF DERMATOLOGY, Issue 2007M. Ulrich Summary Minimally invasive diagnostic tools have received increased attention for diagnosis, screening and management of nonmelanoma skin cancer (NMSC). Several modalities are commercially available, including high frequency ultrasound, optical coherence tomography and confocal microscopy. While systematic clinical analyses are often lacking, recent reports have shown promising results for reflectance confocal microscopy (RCM) for diagnosis of actinic keratoses and basal cell carcinoma. [source] Preliminary evaluation of in vivo reflectance confocal microscopy features of discoid lupus erythematosusBRITISH JOURNAL OF DERMATOLOGY, Issue 6 2007M. Ardigò Summary Background, Discoid lupus erythematosus (DLE) can simulate other inflammatory diseases both clinically and histologically. In vivo reflectance confocal microscopy (RCM) is a noninvasive, reproducible imaging technique already reported to be useful in the evaluation of several inflammatory skin conditions such as contact dermatitis, psoriasis and Darier disease. Objectives, The aims of our study were to define RCM features of DLE and to evaluate its feasibility in biopsy site selection. Methods, Discoid lesions were selected for RCM evaluation from 10 patients with an established diagnosis of DLE. Subsequently, a 4-mm punch biopsy of the same areas evaluated with RCM was rendered for histopathological examination. Results, A series of RCM features of DLE was identified and shown to correlate well with histopathological evaluation. Interface changes, as well as epidermal, dermal and adnexal inflammatory cell infiltration, were identified with RCM in a high percentage of the lesions. A limitation of RCM examination besides imaging depth was the inability to distinguish lymphocytes from other white blood cells. Conclusions, The utility of RCM as a diagnostic tool for DLE awaits further evaluation, although it appears to be promising for biopsy site selection. [source] Recessive congenital methaemoglobinaemia: functional characterization of the novel D239G mutation in the NADH-binding lobe of cytochrome b5 reductaseBRITISH JOURNAL OF HAEMATOLOGY, Issue 6 2005M. J. Percy Summary Type I recessive congenital methaemoglobinaemia (RCM), caused by the reduced form of nicotinamide adenine dinucleotide (NADH)-cytochrome b5 reductase (cytb5r) deficiency, manifests clinically as cyanosis without neurological dysfunction. Two mutations, E255- and G291D, have been identified in the NADH-binding lobe of cytb5r in previously reported patients, and we have detected a further novel mutation, D239G, in this lobe in two unrelated Irish families. Although one family belongs to the genetically isolated Traveller Community, which separated from the general Irish population during the 1845,48 famine, the D239G mutation was present on the same haplotype in both families. Three known cytb5r mutations were also identified, including the R159- mutation, which causes loss of the entire NADH-binding lobe and had previously been reported in an individual with type II RCM. Characterization of the three NADH-binding lobe mutants using a heterologous expression system revealed that all three variants retained stoichiometric levels of flavin adenine dinucleotide with spectroscopic and thermodynamic properties comparable with those of native cytb5r. In contrast to the E255- and G291D variants, the novel D239G mutation had no adverse impact on protein thermostability. The D239G mutation perturbed substrate binding, causing both decreased specificity for NADH and increased specificity for NADPH. Thus cytb5r deficient patients who are heterozygous for an NADH-binding lobe mutation can exhibit the clinically less severe type I phenotype, even in association with heterozygous deletion of the NADH-binding lobe. [source] Conformationally Constrained Mimics of the Membrane-Proximal Domain of Fc,RI,CHEMBIOCHEM, Issue 15 2007Carsten Peters Dr. Spitting image. The peptide fragment KAPREKYWL is part of the high-affinity IgE receptor and is critical in mast cell signaling. By applying ring-closing metathesis (RCM), conformationally constraint cyclic peptides were prepared that mimicked the 3D structure of KAPREKYWL. Peptide 1 (illustrated in the scheme) showed strong binding to a monoclonal anti-KAPREKYWL antibody; this was predicted by molecular modeling. [source] | |||||||||||||||||||||||||||||||