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Isomerization
Kinds of Isomerization Terms modified by Isomerization Selected AbstractsStructural and Electrochemical Studies of Dimerization and Rotational Isomerization in Multi-Iron SilicotungstatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2005Travis M. Anderson Abstract A structural and electrochemical investigation of dimerization and Baker,Figgis (rotational) isomerization in the tri-ferric-substituted silicotungstates has been undertaken because these phenomena are important in a large number of polyoxometalates. A single-crystal X-ray diffraction analysis of K4Na7[(,-SiFe3W9(OH)3O34)2(OH)3] (,1) has been carried out [a = 12.9709(7) Å, b = 38.720(2) Å, c = 21.4221(12) Å, orthorhombic, Pbcm, R1 = 8.48,%, based on 13809 independent reflections]. The complex is isostructural with [(,-SiFe3W9(OH)3O34)2(OH)3]11, (,1) except that the edge-shared W3O13 caps in each [SiFe3W9(OH)3O34]4, unit are rotated by 60°. Electrochemical measurements, performed in a pH 5 acetate buffer, indicate a positive shift in the FeIII -based peak potential (and no change for the WVI -based potential) upon going from ,1 to its monomeric derivative [(,-Si(FeOH2)3W9(OH)3O34)]4, (,2) (,0.484,±,0.005 V and ,0.474,±,0.005 V, respectively). In contrast, the peak potentials of the FeIII - and WVI -based redox processes of ,1 are both found at more negative values than its rotational isomer ,1. The absolute values of the reduction peak potential differences are 0.022 V for FeIII and 0.162 V for WVI. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Reaction of Carboxylic Acids with Isocyanides: A Mechanistic DFT StudyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 28 2008Tommaso Marcelli Abstract We present a computational investigation of the reaction between isocyanides and carboxylic acids. Our results indicate that this reaction begins with a stereoselective concerted ,-addition of the acid to the isocyanide, leading exclusively to a Z -acyl imidate. Isomerization to the E isomer and successive rate-limiting 1,3 O,N acyl migration yields an N -formyl imide. The calculated barriers are in good agreement with the experimental reaction conditions. Our results might provide an explanation for the peculiar reactivity observed when this reaction is carried out in a self-assembled capsule. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Visible-Light Photoresponsivity of a 4-(Dimethylamino)azobenzene Unit Incorporated into Single-Stranded DNA: Demonstration of a Large Spectral Change Accompanying Isomerization in DMSO and Detection of Rapid (Z)-to-(E) Isomerization in Aqueous SolutionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2007Takashi Kamei Abstract We demonstrate significant visible-light photoresponsivity in a synthesized oligonucleotide containing a built-in pseudo-nucleotide possessing a 4-(dimethylamino)azobenzene (4-DMAzo) side chain. In dry DMSO as solvent, two clearly distinguishable spectra corresponding to the (E) and (Z) forms of the 4-DMAzo moiety tethered to the oligonucleotide were recorded with a conventional spectrophotometer before and after irradiation with 420 nm wavelength light, which induced (E)-to-(Z) isomerization. In addition, (Z)-to-(E) isomerization was accelerated by irradiation with either visible (, = 550 nm) or UV (, = 350 nm) light, demonstrating reversible photoresponsivity of the pseudo-oligonucleotide. In aqueous solutions the (Z)-to-(E) thermal isomerization of the photoresponsive pseudo-oligonucleotide was very rapid and was only detectable by laser flash photolysis.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Effect of the Leaving Group on the Rate and Mechanism of the Palladium-Catalyzed Isomerization of Cyclic Allylic Benzoates in Allylic SubstitutionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2006Christian Amatore Abstract In chloroform, the reaction of cis -5-phenylcyclohex-2-enyl 4-Z-benzoate (cis - 1Z, Z = NO2, Cl, H, Me, MeO) with Pd0 complexes ligated to PPh3 is reversible and proceeds with isomerization at the allylic position. The rate of isomerization of cis - 1Z to trans - 1Z depends on the catalytic precursor: Pd0(PPh3)4 > {Pd0(dba)2 + 2PPh3} in agreement with an SN2 mechanism in the rate-determining isomerization of the cationic (,3 -allyl)palladium complexes formed in the oxidative addition. For a given precursor, the rate of isomerization of cis - 1Z to trans - 1Z also depends on the substituent Z, i.e., on the leaving group. The isomerization rate follows the same order as the leaving group properties: 4-NO2,C6H4 -CO2,> 4-Cl,C6H4 -CO2, > C6H5 -CO2, > 4-Me,C6H4 -CO2, > 4-MeO,C6H4 -CO2,. The same tendency is found for the equilibrium constant between the neutral cis - 1Z and the cationic (,3 -allyl)palladium complex in DMF. The higher the concentration of the cationic (,3 -allyl)palladium complex, the faster the isomerization of cis - 1Z to trans - 1Z is. The isomerization of cis - 1Z to trans - 1Z and that of the cationic (,3 -allyl)palladium complexes are at the origin of the lack of stereospecificity observed in catalytic nucleophilic allylic substitutions. These isomerizations are affected by both the leaving groups and the Pd0 precursors, which therefore are not "innocent" but may play an important role in palladium-catalyzed nucleophilic substitutions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] (E/Z)-Isomerization of 3,-EpiluteinHELVETICA CHIMICA ACTA, Issue 8 2004Péter Molnár 3,-Epilutein (=(all- E,3R,3,S,6,R)-4,,5,-didehydro-5,,6,-dihydro- ,,, -carotene-3,3,-diol; 1), isolated from the flowers of Caltha palustris, was submitted to both thermal isomerization and I2 -catalyzed photoisomerization. The structures of the main products (9Z)- 1, (9,Z)- 1, (13Z)- 1, (13,Z)- 1, (15Z)- 1, and (9Z,9,Z)- 1 were determined based on UV/VIS, CD, 1H-NMR, and MS data. [source] Diradical-Promoted Two-Carbon Ring-Expansion Reactions by Thermal Isomerization: Synthesis of Functionalized Macrocyclic KetonesHELVETICA CHIMICA ACTA, Issue 7 2004Georg Rüedi A new method for the smooth and highly efficient preparation of functionalized macrocyclic ketones has been developed. Pyrolysis of medium- and large-ring 3-vinylcycloalkanones by dynamic gas-phase thermo-isomerization (DGPTI) at 600,630° yielded, under insertion of a previously attached vinyl side chain by means of a 1,3-C shift, the corresponding ,,, -unsaturated cycloalkanones. The yield of the two-carbon ring-expanded ketones greatly depended on the relative ring strains of substrate and product (5,87%, cf. Table,5). The formation of minor amounts of one-carbon ring-expanded cycloalkenes (<10%) can be ascribed to a subsequent decarbonylation step. A reaction mechanism involving initial cleavage of the weakest single bond in the molecule has been established (cf. Scheme,6). Recombination within the generated diradical intermediate in terminal vinylogous position led to the observed products, while reclosure gave recovered starting material. Substituents on the vinyl moiety were transferred locospecifically into the ring-expanded products. An isopropenyl group did not significantly affect the isomerization process, whereas substrates bearing a prop-1-enyl group in , -position enabled competing intramolecular H-abstraction reactions, leading to acyclic dienones (cf. Schemes,9,11). DGPTI of the 13-membered analogue directly yielded 4-muscenone, which, upon hydrogenation, led to the valuable musk odorant (±)-muscone. Increasing the steric hindrance on the vinyl moiety gave rise to diminishing amounts of the desired ,,, -unsaturated cycloalkanones. This novel two-carbon ring-expansion protocol was also successfully applied to 3-ethynylcycloalkanones, giving rise to the corresponding ring-expanded cyclic allenes (cf. Scheme,13). [source] Preparation and (E/Z)-Isomerization of the Diastereoisomers of ViolaxanthinHELVETICA CHIMICA ACTA, Issue 1 2004Péter Molnár Violaxanthin A (=(all- E,3S,5S,6R,3,S,5,S,6,R)-5,6,:,5,,6,-diepoxy-5,6,5,,6,-tetrahydro- ,,, -carotene-3,3,-diol =syn,syn- violaxanthin; 5) and violaxanthin B (=(all- E,3S,5S,6R,3,S,5,R,6,S)-5,6,:,5,,6,-diepoxy-5,6,5,,6,-tetrahydro- ,,, -carotene-3,3,-diol=syn,anti- violaxanthin; 6) were prepared by epoxidation of zeaxanthin diacetate (1) with monoperphthalic acid. Violaxanthins 5 and 6 were submitted to thermal isomerization and I2 -catalyzed photoisomerization. The structure of the main products, i.e., (9Z)- 5, (13Z)- 5, (9Z)- 6, (9,Z)- 6, (13Z)- 6, and (13,Z)- 6, was determined by their UV/VIS, CD, 1H-NMR, 13C-NMR, and mass spectra. [source] Highly Active and Selective Semihydrogenation of Alkynes with the Palladium Nanoparticles-Tetrabutylammonium Borohydride Catalyst SystemADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Junichi Hori Abstract Palladium nanoparticles are prepared from palladium(II) acetate and 2 equivalents of potassium tert -butoxide in the presence of 4-octyne. The palladium nanoparticles-tetrabutylammonium borohydride system shows excellent catalytic activity and selectivity in the semihydrogenation of alkynes to the [(Z)-]alkenes. The hydrogenation of 4-octyne is conducted with the catalyst system at a substrate-to-palladium molar ratio of 10,000,200,000 under 8,atm of hydrogen to give (Z)-4-octene in>99% yield. Isomerization and over-reduction of the Z -alkene are very slow even after consumption of the alkyne. [source] Facile Synthesis of Polycyclic Fluorene Derivatives via a Palladium-Catalyzed Coupling, Propargyl-Allenyl Isomerization and Schmittel Cyclization SequenceADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Ruwei Shen Abstract A stepwise process involving Sonogashira coupling, propargyl-allenyl isomerization and Schmittel cyclization has been realized, leading to an efficient synthesis of polycyclic fluorene derivatives from readily available starting materials. The reaction features the formation of three new carbon-carbon bonds to construct the benzene unit together with an efficient assembly of three or four rings in a single operative step. [source] Novel Enantioselective Sequentially Rhodium(I)/BINAP- Catalyzed Cycloisomerization,Hydrogenation,Isomerization, Acetalization (CIHIA)ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Nadine Körber Abstract Linear, easily accessible alkyl and (hetero)aryl-substituted alkynyl allyl alcohols are readily and enantioselectively transformed into 2,7-dioxabicyclo[3.2.1]octanes by a sequential rhodium-catalyzed process. Based on the initial cycloisomerization, the in situ generated rhodium(I)-BINAP complex enables a subsequent reduction with hydrogen and the transformation into bicyclic frameworks. [source] Palladium-Catalyzed Isomerization of exo -Methylenic Allylic AlcoholsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Abstract Treatment of allylic alcohols containing a 1,1-disubstituted alkene with a palladium catalyst and hydrogen gas (1,bar) results in facile isomerization to their corresponding trisubstituted (E)-allylic alcohols, along with small amounts of the corresponding hydrogenated products. [source] Enantioselective Synthesis of Phospholenes via Asymmetric Organocatalytic Alkene IsomerizationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2008Lukas Hintermann Abstract An asymmetric synthesis of the 2,5-diphenylphosphol-2-ene fragment (,95% ee) has been realized via enantioselective Cinchona -alkaloid catalyzed double bond isomerization of a meso -2,5-diphenylphosphol-3-ene amide to a 2,5-diphenylphosphol-2-ene amide (up to 83% ee), followed by enantiomeric enrichment to ,95% ee by crystallization. The 2,5-diphenylphosphol-2-ene amide (a cyclic phosphinic acid amide) was hydrolyzed to the 2,5-diphenylphosphol-2-ene acid (a cyclic phosphinic acid) with retention of configuration at C-5. [source] Water-Soluble Group 8 and 9 Transition Metal Complexes Containing a Trihydrazinophosphaadamantane Ligand: Catalytic Applications in Isomerization of Allylic Alcohols and Cycloisomerization of (Z)-Enynols in Aqueous MediumADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 12-13 2006Abstract An optimized synthesis of the 2,4,10-trimethyl-1,2,4,5,7,10-hexaaza-3-phosphatricyclo[3.3.1.13,7]decane ligand (THPA) is described. It readily reacts with the dimers [{RuCl(,-Cl)(,6 -arene)}2] and [{MCl(,-Cl)(cod)}2] to yield the corresponding mononuclear complexes [RuCl2(THPA)(,6 -arene)] [arene=C6H6 (4a), p -cymene (4b), 1,3,5-C6H3Me3 (4c), C6Me6 (4d)] and [MCl(THPA)(cod)] [M=Rh (7a), Ir (7b)], respectively. Treatment of 4a and b with MeOTf affords the cationic derivatives [RuCl2(THPA-Me)(,6 -arene)][OTf] {arene=C6H6 (5a), p -cymene (5b); THPA-Me=1,2,4,10-tetramethyl-2,4,5,7,10-pentaaza-1-azonia-3-phosphatricyclo[3.3.1.13,7]decane}. The arene-ruthenium(II) complexes 4a,d and 5a and b are efficient catalysts for the redox isomerization of allylic alcohols into carbonyl compounds in both THF and aqueous media. The catalytic systems can be recycled by a simple extraction process and used in up to 4 consecutive runs. All the water-soluble complexes prepared in this work are able to promote the cycloisomerization of (Z)-enynols to afford furans in water, the best performance being obtained with the iridium catalyst 7b. Furthermore, 7b has shown an excellent recyclability (10 runs). This study represents the first example of iridium-catalyzed cycloisomerization of (Z)-enynols. [source] Effects of PTH and Alendronate on Type I Collagen Isomerization in Postmenopausal Women With Osteoporosis: The PaTH Study,,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 9 2008Patrick Garnero Abstract Fracture efficacy of PTH and alendronate (ALN) is only partly explained by changes in BMD, and bone collagen properties have been suggested to play a role. We analyzed the effects of PTH(1,84) and ALN on urinary ,,/,, CTX ratio, a marker of type I collagen isomerization and maturation in postmenopausal women with osteoporosis. In the first year of the previously published PaTH study, postmenopausal women with osteoporosis were assigned to PTH(1,84) (100 ,g/d; n = 119), ALN (10 mg/d; n = 60), or PTH and ALN together (n = 59). We analyzed patients on ALN alone (n = 60) and a similar number of patients assigned to PTH alone (n = 63). During the second year, women on PTH in the first year were reallocated to placebo (n = 31) or ALN (n = 32) and women with ALN continued on ALN. During the first year, there was no significant change in ,,/,, CTX ratio with PTH or ALN. At 24 mo, there was a marked increase of the ,,/,, CTX ratio in women who had received PTH during the first year, followed by a second year of placebo (median: +45.5, p < 0.001) or ALN (+55.2%, p < 0.001). Conversely, the ,,/,, CTX ratio only slightly increased (+16%, p < 0.05) after 2 yr of continued ALN. In conclusion, treatment with PTH(1,84) for 1 yr followed by 1 yr of placebo or ALN may be associated with decreased type I collagen isomerization. The influence of these biochemical changes of type I collagen on bone fracture resistance remains to be studied. [source] Type I Collagen Racemization and Isomerization and the Risk of Fracture in Postmenopausal Women: The OFELY Prospective StudyJOURNAL OF BONE AND MINERAL RESEARCH, Issue 5 2002Patrick Garnero Ph.D. Abstract The Asp1211 residue of the1209AHDGGR1214 sequence of the C-terminal cross-linking telopeptide of type I collagen (CTX) can undergo spontaneous post-translational modifications, namely, racemization and isomerization, which result in the formation of four isomers: the native form (,- L) and three age-related forms, that is, an isomerized form (,- L), a racemized form (,- D), and an isomerized/racemized (,- D) form. Previous studies have suggested that changes in the pattern of type I collagen racemization/isomerization, which can be assessed in vivo by measuring the degradation products of the CTX isoforms, may be associated with alterations of bone structure. The aim of this study was to examine prospectively the value of the different urinary CTX isoforms and their related ratio in the prediction of osteoporotic fractures in 408 healthy untreated postmenopausal women aged 50-89 years (mean, 64 years) who were part of the OFELY cohort. During a median 6.8 years follow-up, 16 incident vertebral fractures and 55 peripheral fractures were recorded in 65 women. The baseline levels of the four CTX isoforms in women who subsequently had a fracture were compared with those of the 343 women who did not fracture. At baseline, women with fractures had increased levels of ratios of native ,- L -CTX to age-related isoforms (,- L, ,- D, and ,- D) compared with controls (p < 0.01). In logistic regression analysis after adjustment for age, prevalent fractures, and physical activity, women with levels of ,- L/,- L, ,- L/,- D, and ,- L/,- D -CTX ratios in the highest quartile had a 1.5- to 2-fold increased risk of fractures compared with women with levels in the three lowest quartiles with relative risk (RR) and 95% CI of 2.0 (1.2-3.5), 1.8 (1.02-2.7), and 1.5 (0.9-2.7), respectively. Adjustment of ,- L/,- L and ,- L/,- D -CTX ratios by the level of bone turnover assessed by serum bone alkaline phosphatase (ALP)- or femoral neck bone mineral density (BMD) decreased slightly the RR, which remained significant for the ,- L/,- L -CTX ratio (RR [95%] CI, 1.8 [1.1-3.2] after adjustment for bone ALP, 1.8 [1.03-3.1] after adjustment for BMD, and 1.7 [0.95-2.9] after adjustment for both bone ALP and BMD). Women with both high ,- L/,- L -CTX ratio and high bone ALP had a 50% higher risk of fracture than women with either one of these two risk factors. Similarly, women with both increased CTX ratio and low femoral neck BMD (T score < ,2.5) had a higher risk of fracture with an RR (95% CI) of 4.5 (2.0-10.1). In conclusion, increased urinary ratio between native and age-related forms of CTX, reflecting decreased degree of type I collagen racemization/isomerization, is associated with increased fracture risk independently of BMD and partly of bone turnover rate. This suggests that alterations of type I collagen isomerization/racemization that can be detected by changes in urinary CTX ratios may be associated with increased skeletal fragility. [source] Isomerization of delta-9-THC to delta-8-THC when tested as trifluoroacetyl-, pentafluoropropionyl-, or heptafluorobutyryl- derivatives,,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2008Justin M. Holler Abstract For GC,MS analysis of delta-9-tetrahydrocannabinol (delta-9-THC), perfluoroacid anhydrides in combination with perfluoroalcohols are commonly used for derivatization. This reagent mixture is preferred because it allows simultaneous derivatization of delta-9-THC and its acid metabolite, 11-nor-delta-9-THC-9-carboxylic acid present in biological samples. When delta-9-THC was derivatized by trifluoroacetic anhydride/hexafluoroisopropanol (TFAA/HFIPOH) and analyzed by GC,MS using full scan mode (50,550 amu), two peaks (P1 and P2) with an identical molecular mass of 410 amu were observed. On the basis of the total ion chromatogram (TIC), P1 with a shorter retention time (RT) was the major peak (TIC 84%). To identify the peaks, delta-8-THC was also tested under the same conditions. The RT and spectra of the major peak (TIC 95%) were identical with that of P1 for delta-9-THC. A minor peak (5%) present also correlated well with the latter peak (P2) for the delta-9-THC derivative. The fragmentation pathway of P1 was primarily demethylation followed by retro Diels-Alder fragmentation (M , 15,68, base peak 100%) indicating P1 as a delta-8-THC-trifluoroacetyl compound. This indicated that delta-9-THC isomerized to delta-8-THC during derivatization with TFAA/HFIPOH. Similar results were also observed when delta-9-THC was derivatized with pentafluoropropionic anhydride/pentafluoropropanol or heptafluorobutyric anhydride/heptafluorobutanol. No isomerization was observed when chloroform was used in derivatization with TFAA. In this reaction, the peaks of delta-8-THC-TFA and delta-9-THC-TFA had retention times and mass spectra matching with P1 and P2, respectively. Because of isomerization, perfluoroacid anhydrides/perfluoroalcohols are not suitable derivatizing agents for analysis of delta-9-THC; whereas the TFAA in chloroform is suitable for the analysis. Published in 2008 by John Wiley & Sons, Ltd. [source] Sub-5-fs Real-time Spectroscopy of Transition States in Bacteriorhodopsin During Retinal Isomerization,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2007Takayoshi Kobayashi By using a sub-5-fs visible laser pulse, we have made the first observation of the vibrational spectra of the transition state during trans-cis isomerization in the retinal chromophore of bacteriorhodopsin (bRS68). No instant isomerization of the retinal occurs in spite of electron promotion from the bonding ,-orbital to the anti-bonding ,*-orbital. The difference between the in-plane and out-of-plane vibrational frequencies (about 1150,1250 and 900,1000 cm,1, respectively) is reduced during the first time period. The vibrational spectra after this period became very broad and weak and are ascribed to a "silent state." The silent state lasts for 700,900 fs until the chromophore isomerizes to the cis -C13=C14 conformation. The frequency of the C=C stretching mode was modulated by the torsion mode of the C13=C14 double bond with a period of 200 fs. The modulation was clearly observed for four to five periods. Using the empirical equation for the relation between bond length and stretching frequency, we determined the transitional C=C bond length with about 0.01 Å accuracy during the torsion motion around the double bond with 1-fs time resolution. [source] Gold(I)-Catalyzed Addition of Diphenyl Phosphate to Alkynes: Isomerization of Kinetic Enol Phosphates to the Thermodynamically Favored Isomers,ANGEWANDTE CHEMIE, Issue 38 2010Prof. Gold, Gold oder , Gold? Der Gold- Katalysator bestimmt, ob bei der im Schema gezeigten Hydrophosphoryloxylierung das Produkt der thermodynamischen oder der kinetischen Steuerung entsteht. Ein dritter Katalysator, [(C6F5)3PAuOTf], erwies sich als enorm effektiv in der bislang unbekannten Isomerisierung kinetischer Enolphosphate in die thermodynamisch begünstigten Isomere. Tf=Trifluormethansulfonyl; R=Alkyl, Cyclohexyl, Ph. [source] Titelbild: Isomerization of Triphenylmethoxyl: The Wieland Free-Radical Rearrangement Revisited a Century Later (Angew. Chem.ANGEWANDTE CHEMIE, Issue 34 201034/2010) Altes Wissen gilt immer noch: 1911 wies Wieland erstmals eine radikalische Umlagerung nach, indem er die Produkte der thermischen Zersetzung von Ph3COOCPh3 studierte. In ihrer Zuschrift auf S.,6118,ff. bestimmen K.,U. Ingold et,al. die Geschwindigkeitskonstante dieser Isomerisierung sowohl experimentell als auch durch DFT-Rechnungen. Im Widerspruch zu früheren photochemischen Befunden untermauern die Ergebnisse Wielands Beobachtungen und geben damit ein warnendes Beispiel für Photochemiker. (Photo mit Genehmigung der Fakultät Chemie und Pharmazie der LMU München.) [source] Isomerization of Triphenylmethoxyl: The Wieland Free-Radical Rearrangement Revisited a Century Later,ANGEWANDTE CHEMIE, Issue 34 2010Altes Wissen gilt immer noch: Die Geschwindigkeitskonstante der Isomerisierung von thermisch erzeugtem Triphenylmethoxyl zu Ph2(PhO)C. (siehe Schema) wurde experimentell und mit DFT-Rechnungen bestimmt. Die Ergebnisse stützen die Beobachtungen und Schlussfolgerungen von Wieland aus dem Jahr 1911 , ganz im Unterschied zu photochemisch erhaltenen Daten. [source] The Catalytic Z to E Isomerization of Stilbenes in a Photosensitizing Porous Coordination Network,ANGEWANDTE CHEMIE, Issue 32 2010Kazuaki Ohara Einbahnreaktion: Die Z,E -Photoisomerisierung von Stilben durch sichtbares Licht geschieht in einem porösen Koordinationsnetzwerk (siehe Bild). Die Reaktion verläuft in einer Pore über die Photoanregung des Ladungstransfer-Komplexes zwischen einem elektronenarmen Liganden und dem Stilben. Das in,situ gebildete E -Isomer wird schnell gegen nicht umgesetztes Z -Isomer aus der Lösung ausgetauscht, daher genügt eine katalytische Menge des Netzwerkes, um die Reaktion voranzutreiben. [source] Reversible 100,% Linkage Isomerization in a Single-Crystal to Single-Crystal Transformation: Photocrystallographic Identification of the Metastable [Ni(dppe)(,1 -ONO)Cl] Isomer,ANGEWANDTE CHEMIE, Issue 31 2009Mal N, mal O: Raman-spektroskopische und photokristallographische Studien an Einkristallen identifizierten den Komplex [Ni(dppe)(,1 -NO2)Cl] als das erste System, das im Festkörper eine reversible und vollständige Umwandlung in ein metastabiles Isomer, in diesem Fall [Ni(dppe)(,1 -ONO)Cl], eingeht. [source] Structures of mannose-6-phosphate isomerase from Salmonella typhimurium bound to metal atoms and substrate: implications for catalytic mechanismACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2009S. R. Sagurthi Mannose-6-phosphate isomerase (MPI) catalyzes the interconversion of mannose 6-phosphate and fructose 6-phosphate. X-ray crystal structures of MPI from Salmonella typhimurium in the apo form (with no metal bound) and in the holo form (with bound Zn2+) and two other structures with yttrium bound at an inhibitory site and complexed with Zn2+ and fructose 6-phosphate (F6P) were determined in order to gain insights into the structure and the isomerization mechanism. Isomerization involves acid/base catalysis with proton transfer between the C1 and C2 atoms of the substrate. His99, Lys132, His131 and Asp270 are close to the substrate and are likely to be the residues involved in proton transfer. The interactions observed at the active site suggest that the ring-opening step is probably catalyzed by His99 and Asp270. An active-site loop consisting of residues 130,133 undergoes conformational changes upon substrate binding. Zn2+ binding induces structural order in the loop consisting of residues 50,54. The metal atom appears to play a role in substrate binding and is probably also important for maintaining the architecture of the active site. Isomerization probably follows the previously suggested cis -enediol mechanism. [source] Discovering New Water Soluble Catalysts for the Liquid/Liquid Isomerization of Allylic Alcohols Using MicrodevicesCHEMIE-INGENIEUR-TECHNIK (CIT), Issue 5 2004C. de Bellefon Abstract No abstracts. [source] ChemInform Abstract: Unusual Regioselectivity in Pd(0)-Catalyzed Coupling of Allylic Monoacetates and Nitroalkenes: One-Pot Isomerization,Alkylation.CHEMINFORM, Issue 26 2010Pasha M. Khan Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Tandem Ir-Catalyzed Allylic Substitution Reaction of Allyl Sulfinates and Isomerization.CHEMINFORM, Issue 25 2010Qing-Long Xu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Mild and Efficient Palladium-Catalyzed Isomerization of Baylis,Hillman Acetates.CHEMINFORM, Issue 39 2009Jinhyung Park Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Encapsulated Molecular Catalysts in Polysiloxane Gels: Ruthenium Cluster-Catalyzed Isomerization of Alkenes.CHEMINFORM, Issue 12 2009Yukihiro Motoyama Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: A Novel Synthesis of 2-Functionalized Benzofurans by Palladium-Catalyzed Cycloisomerization of 2-(1-Hydroxyprop-2-ynyl)phenols Followed by Acid-Catalyzed Allylic Isomerization or Allylic Nucleophilic Substitution.CHEMINFORM, Issue 5 2009Bartolo Gabriele Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Unexpected Solvent-Induced cis/trans Isomerization and Catalytic Application of a Bis-bidentate Nickel(II) Complex with N-Heterocyclic Carbene and Amido Functionalities.CHEMINFORM, Issue 13 2008Chuang-Yi Liao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] | |||||||||||||||||||||||||||||||||||||||||||