Home  About us  Contact
 

Trans Isomers (trans + isomer)

Distribution by Scientific Domains
Chemistry81%
Life Sciences15%
Distribution within Chemistry
Crystallography14%

Selected Abstracts

G,G Base-Pairing in Nucleobase Adducts of the Anticancer Drug cis -[PtCl2(NH3)(2-picoline)] and Its trans Isomer

CHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2005
Geraldine McGowan
Abstract cis -[PtCl2(NH3)(2-picoline)] (AMD473) is a sterically-hindered anticancer complex with a profile of chemical and biological activity that differs significantly from that of cisplatin. Adducts of AMD473 with neutral 9-ethylguanine (9-EtGH) and anionic (N1-deprotonated) 9-ethylguanine (9-EtG) as perchlorate and nitrate salts, and also a nitrate salt of the trans isomer (AMD443), were prepared and their structures determined by X-ray crystallography: cis -[Pt(NH3)(2-pic)(9-EtGH)2](ClO4)2 (1),2,H2O,Me2CO, cis -[Pt(NH3)(2-pic)(9-EtGH)2](NO3)2 (2),2,H2O, cis -[Pt(NH3)(2-pic)(9-EtGH)(9-EtG)]NO3 (3),3.5,H2O, trans -[Pt(NH3)(2-pic)(9-EtGH)(9-EtG)]NO3 (4),8,H2O. In all cases, platinum coordination is through N7 of neutral (1, 2) and anionic (3, 4) guanine. In each complex, the guanine bases are arranged in the head-to-tail conformation. In complex 1, there is an infinite array of six-molecule cycles, based on both hydrogen bonding and ,,, stacking of the 2-picoline and guanine rings. Platinum(II) coordinated at N7 acidifies the N1 proton of neutral 9-ethylguanine (pKa=9.57) to give pKa1=8.40 and pKa2=8.75 for complex 2, and pKa1=7.77 and pKa2=9.00 for complex 4. In complexes 3 and 4, three intermolecular hydrogen bonds are formed between neutral and deprotonated guanine ligands involving O6, N1 and N2 sites. Unusually, both of the platinated guanine bases of complexes 3 and 4 participate in this triple GG hydrogen bonding. This is the first report of X-ray crystal structures of nucleobase adducts of the promising anticancer drug AMD473. [source]

Syntheses and Fluxional Processes of Diphenyl(2-thienyl)phosphane Derivatives of Triosmium Clusters

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2006
Nitsa K. Kiriakidou Kazemifar
Abstract Thermal treatment of [Os3(CO)12] with diphenyl(2-thienyl)phosphane, Ph2P(C4H3S), results in the formation of [Os3(CO)12,x{Ph2P(C4H3S)}x] (x = 1,3, 1,3), but no C,H bond activation was observed. Reaction of [H2Os3(CO)10] with diphenyl(2-thienyl)phosphane at ambient temperature affords [HOs3(,-H)(CO)10{Ph2P(C4H3S)}] (4), but when the samereaction is repeated at elevated temperatures, the cyclometallated species [(,-H)Os3(CO)9{,3 -Ph2P(C4H2S)}] (5) and[(,-H)Os3(CO)8{,3 -Ph2P(C4H2S)}{Ph2P(C4H3S)}] (6) are formed. In addition, two more products, tentatively assigned as [(,-H)Os3(CO)6{,3 -Ph2P(C4H2S)}{,-Ph2P(C4H3S)}{Ph2P(C4H3S)}] (7) and [(,-H)Os3(CO)7{,-Ph2P(C4H2S)}{,-Ph2P(C4H3S)}{Ph2P(C4H3S)}] (8) are obtained. The dynamic behaviours of 2, 5 and 6 have been studied by variable-temperature (VT) 1H and 31P{1H} NMR spectroscopy. The VT 31P{1H} NMR spectra of [Os3(CO)10{Ph2P(C4H3S)}2] (2) demonstrate that a mixture of two isomers, which are in rapid exchange at room temperature, is present and that the less common cis - trans isomer, whose structure has been determined by X-ray crystallography, is favoured for this cluster. The VT 1H NMR spectra of 5 indicate the presence of two isomers which are proposed to arise from an oscillation of the ,,,2 -vinyl group of the thienyl moiety between two metal atoms. A similar fluxional process is proposed to occur in 6 and the assignment of the room-temperature structure(s) of this cluster was confirmed by 1H- 187Os 2D HMQC spectroscopy. In addition to 2, the solid-state structures of 3, 5 and 6 have been determined by X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Synthesis, Characterization, and Electrochemical Properties of Dinuclear Complexes Assembled from Asymmetric CoIII Bis(dioximates) and Boronic Acids

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2005
Renata Dreos
Abstract Bis(methylphenylglyoximate)cobalt(III) complexes exist both as cis and trans isomers due to the asymmetry of the equatorial ligand, and, when the axial ligands are different, the trans isomer is chiral. The reaction of racemic trans -[CH3Co(mpgH)2py] (1) with either 3- or 4-pyridylboronic acid affords dimeric units arranged on a crystallographic symmetry center such that the pyridyl nitrogen of one moiety coordinates to the Co atom of the symmetry-related unit. In principle, three structurally different dimeric species (two homodimers and one heterodimer) can be obtained. Time-resolved 1H NMR spectra of a 1:1 mixture of racemic 1 and either 3- or 4-pyridylboronic acid in CDCl3/CD3OD show that the reaction does not converge toward a unique species in solution. Nevertheless, X-ray structures show that the heterochiral dimers are the only products that crystallize from the reaction mixture. The nature of the dioximate side groups does not affect the geometry of the dimeric arrangements assembled by 4-pyridylboronic acid ("molecular box"). On the contrary, the geometry of the species assembled by 3-pyridylboronic acid varies from the "molecular parallelogram" obtained from the bis(dimethylglyoximates) to the highly squeezed "molecular box" obtained from bis(methylphenylglyoximates). Cyclic voltammetry studies show that the metal centers in the dimeric species do not interact with each other and undergo a simultaneous redox process. However, depending on the geometry of the systems, the redox process involves a single four-electron reduction for 3 and 5 or two consecutive two-electron reduction steps for 4 and 6. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Structures and Thermodynamics of the Sulfuranes SF3CN and SF2(CN)2 as well as of the Persulfurane SF4(CN)2 , An ab initio MO Study by the G3(MP2) Method

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2003
Yana Steudel
Abstract At the G3(MP2) level of theory the trans isomer 1a of the hypothetical molecule SF4(CN)2 is more stable than the cis isomer 1b by 8 kJ·mol,1. The isomerization of 1a to 1b requires an activation enthalpy of 319 kJ·mol,1 at 298 K. The decomposition of trans -SF4(CN)2 to SF2(CN)2 and F2 is endothermic (,Ho298 = 395 kJ·mol,1) but the elimination of FCN from trans -SF4(CN)2 is exothermic by ,7 kJ·mol,1. The elimination of (CN)2 from cis -SF4(CN)2 is exothermic by ,137 kJ·mol,1. The activation enthalpies for the latter two reactions were calculated as 251 and 311 kJ·mol,1, respectively. Thus, SF4(CN)2 should be a thermally stable compound. In the sulfuranes SF3CN and SF2(CN)2 the CN ligands prefer the equatorial positions; mutual exchange of an axial F atom by an equatorial CN group requires a reaction enthalpy of 51 kJ·mol,1 [SF3CN] or 58 kJ·mol,1 [SF2(CN)2]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Asymmetric Synthesis of ,-Fluorinated ,-Amino Acid Derivatives

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2005
Deepak M. Shendage
Abstract Asymmetric alkylation of (S)-Boc-BMI (1a, BMI = 2- tert -butyl-3-methylimidazolidin-4-one) and its ,-methyl derivative 1b with 2-fluoroallyl tosylate, subsequent mild acidic deprotection of the products 2a and 2b, and basic hydrolysis of the thus formed N -methylamides 4a and 4b gave (S)-2-amino-4-fluoropent-4-enoic acid (5a) and (S)-2-amino-4-fluoro-2-methylpent-4-enoic acid (5b). Basic hydrolysis of compound 4a was accompanied by partial racemization, which was overcome by applying a new stereoconservative deamidation procedure. The alkylated cis -configured product 2a formed under kinetic control epimerized on refluxing with 2 n NaOH to give the thermodynamically more stable trans isomer 9. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Solvent-Dependent Conformational Behaviour of Model Tetrapeptides Containing a Bicyclic Proline Mimetic

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2004
Andrea Trabocchi
Abstract Two model tetrapeptides containing bicyclic analogues of either D - or L -proline were synthesised and their conformational properties were studied by NMR in different solvent systems and by molecular modelling techniques. Compound 1, with the bicyclic D -proline mimetic in the i+1 position, generated a unique trans isomer, and the peptide showed a well organised structure, in accordance with the tendency of D -proline to act as a good turn inducer with respect to its enantiomer. Peptide 2 displayed structures equilibrating from type I,II to type VI ,-turns, thus confirming the hypothesised relationship between the chirality of BGS/Bgs and proline enantiomers on nucleating compact turns. Moreover, such behaviour suggested a tool for peptidomimetic design of reverse turn peptides containing BGS/Bgs bicyclic proline mimetics, as the choice of chirality might influence the generation either of compact ,- and ,-turns or of flexible equilibrating reverse turn structures. The effect of solvent on conformational behaviour was also studied. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

An Efficient synthesis of orthogonally protected trans - and cis -4-aminopipecolic acid

JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2006
István Szatmári
A straightforward synthesis of orthogonally N,/N, -protected trans - and cis -4-aminopipecolic acid is reported, starting from methyl cis -4-hydroxypiperidine-2-carboxylate. The two diastereomers were synthesized with the aid of C-4 inversion (the trans isomer) or double C-4 inversion (the cis isomer). [source]

Palladium-Catalyzed Cyclopropanation of Alkenyl Silanes by Diazoalkanes: Evidence for a Pd0 Mechanism

CHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2009
Guillaume Berthon-Gelloz Dr.
Abstract Pd0does the trick! Alkenyl silanes are efficiently cyclopropanated by diazoalkanes at low Pd loadings (see scheme). Clear evidence for the involvement of a Pd0 resting state for this reaction is given. Alkenyl silanes are efficiently converted to the corresponding silyl cyclopropanes in the presence of a slight excess of diazomethane (2,4,equiv) and a low loading of Pd(OAc)2 (<0.5,mol,%). Diazoethane and diazobutane can also be employed and yield silyl cyclopropanes with diastereoselectivities of up to 10:1 for the trans isomer. When conducted on a 4,g scale, the reaction only required a catalyst loading of 5×10,3,mol,%, which corresponds to a turnover frequency of 40,000,h,1. Competition experiments revealed that vinyl silanes can be selectively cyclopropanated in the presence of an aliphatic terminal alkene and styrene. The complex [Pd02(DVTMS)3] (38, DVTMS=divinyltetramethyldisiloxane) proved to be an exceptionally active catalyst for the cyclopropanation reaction, giving complete conversion at ,35,°C in 1,min. Intermolecular and intramolecular competition experiments with DVTMS (36), both with Pd(OAc)2 and 38, provided strong evidence for a Pd0(alkenyl silane)3 resting state. Detailed density functional calculations on the reaction pathways for the cyclopropanation of trimethylvinylsilane and DVTMS by diazomethane with Pd0 corroborated the experimental observations. [source]

G,G Base-Pairing in Nucleobase Adducts of the Anticancer Drug cis -[PtCl2(NH3)(2-picoline)] and Its trans Isomer

CHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2005
Geraldine McGowan
Abstract cis -[PtCl2(NH3)(2-picoline)] (AMD473) is a sterically-hindered anticancer complex with a profile of chemical and biological activity that differs significantly from that of cisplatin. Adducts of AMD473 with neutral 9-ethylguanine (9-EtGH) and anionic (N1-deprotonated) 9-ethylguanine (9-EtG) as perchlorate and nitrate salts, and also a nitrate salt of the trans isomer (AMD443), were prepared and their structures determined by X-ray crystallography: cis -[Pt(NH3)(2-pic)(9-EtGH)2](ClO4)2 (1),2,H2O,Me2CO, cis -[Pt(NH3)(2-pic)(9-EtGH)2](NO3)2 (2),2,H2O, cis -[Pt(NH3)(2-pic)(9-EtGH)(9-EtG)]NO3 (3),3.5,H2O, trans -[Pt(NH3)(2-pic)(9-EtGH)(9-EtG)]NO3 (4),8,H2O. In all cases, platinum coordination is through N7 of neutral (1, 2) and anionic (3, 4) guanine. In each complex, the guanine bases are arranged in the head-to-tail conformation. In complex 1, there is an infinite array of six-molecule cycles, based on both hydrogen bonding and ,,, stacking of the 2-picoline and guanine rings. Platinum(II) coordinated at N7 acidifies the N1 proton of neutral 9-ethylguanine (pKa=9.57) to give pKa1=8.40 and pKa2=8.75 for complex 2, and pKa1=7.77 and pKa2=9.00 for complex 4. In complexes 3 and 4, three intermolecular hydrogen bonds are formed between neutral and deprotonated guanine ligands involving O6, N1 and N2 sites. Unusually, both of the platinated guanine bases of complexes 3 and 4 participate in this triple GG hydrogen bonding. This is the first report of X-ray crystal structures of nucleobase adducts of the promising anticancer drug AMD473. [source]

Bulky Monodentate Phosphoramidites in Palladium-Catalyzed Allylic Alkylation Reactions: Aspects of Regioselectivity and Enantioselectivity

CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2004
Maarten D. K. Boele Dr.
Abstract A series of bulky monodentate phosphoramidite ligands, based on biphenol, BINOL and TADDOL backbones, have been employed in the Pd-catalysed allylic alkylation reaction. Reaction of disodium diethyl 2-methyl malonate with monosubstituted allylic substrates in the presence of palladium complexes of the phosphoramidite ligands proceeds smoothly at room temperature. The regioselectivities observed depend strongly on the leaving group and the geometry of the allylic starting compounds. Mono-coordination occurs when these ligands are ligated in [Pd(allyl)(X)] complexes (allyl=C3H5, 1-CH3C3H4, 1-C6H5C3H4, 1,3-(C6H5)2C3H3; X=Cl, OAc). The solid-state structure determined by X-ray diffraction of [Pd(C3H5)(1)(Cl)] reveals a non-symmetric coordination of the allyl moiety, caused by the stronger trans influence of the phosphoramidite ligand relative to X,. In all of these complexes, the syn,trans isomer is the major species present in solution. Because of fast isomerisation and high reactivity of the syn,cis complex, the major product formed upon alkylation is the linear product, especially for monosubstituted phenylallyl substrates in the presence of halide counterions. In the case of biphenol- and BINOL-based phosphoramidites, however, a strong memory effect is observed when 1-phenyl-2-propenyl acetate is employed as the substrate. In this case, nucleophilic attack competes effectively with the isomerisation of the transient cinnamylpalladium complexes. The asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate afforded the chiral product in up to 93,% ee. Substrates with smaller substituents gave lower enantioselectivities. The observed stereoselectivity is explained in terms of a preferential rotation mechanism, in which the product is formed by attack on one of the isomers of the intermediate [Pd{1,3-(C6H5)2C3H3}(L)(OAc)] complex. [source]

Geometric H/D Isotope Effects and Cooperativity of the Hydrogen Bonds in Porphycene

CHEMPHYSCHEM, Issue 2 2007
Mohamed F. Shibl Dr.
Abstract We investigate the primary, secondary, and vicinal hydrogen/deuterium (H/D) isotope effects on the geometry of the two intramolecular hydrogen bonds in porphycene. Multidimensional potential energy surfaces describing the anharmonic motion in the vicinity of the trans isomer are calculated for the different symmetric (HH/DD) and asymmetric (HD) isotopomers. From the solution of the nuclear Schrödinger equation the ground-state wavefunction is obtained, which is further used to determine the quantum corrections to the classical equilibrium geometries of the hydrogen bonds and thus the geometric isotope effects. In particular, it is found that the hydrogen bonds are cooperative, that is, both expand simultaneously even in the case of an asymmetric isotopic substitution. The theoretical predictions compare favorably with NMR chemical-shift data. [source]

Dietary Lycopene: Its Properties and Anticarcinogenic Effects

COMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETY, Issue 3 2008
Preeti Singh
ABSTRACT:, Lycopene is the principal pigment of the carotenoids naturally found in tomatoes and is important not only because of the color it imparts but also because of the recognized health benefits associated with its presence. Red tomatoes typically contain about 95% of their lycopene as the all -trans isomer, the most stable form. In tangerine tomatoes, on the other hand, the lycopene is present as tetra-cis -lycopene, a geometric isomer of all -trans lycopene. Lycopene is a major component found in blood serum. This carotenoid has been extensively studied for its antioxidant and cancer-preventing properties. Prevention of heart disease has been shown to be another antioxidant role played by lycopene because it reduces the accumulation of platelets that eventually lead to blood clots, heart attacks, and strokes. In contrast to many other food phytonutrients whose effects have only been studied in animals, lycopene from tomatoes has been repeatedly studied in humans and found to be protective against several cancers, which now include colorectal, prostate, breast, lung, and pancreatic cancers. This review outlines the background information dealing with lycopene and presents the most comprehensive and current understanding of its potential functional role in human health. [source]

Synthesis of 1,3-Diphospha-2,3-dihydro-1H -phenalenes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2010
Arkadii Tarasevych
Abstract The reaction of 1,8-dilithionaphthalene (1) with methylenebis[(dialkylamino)chlorophosphanes] [R2N(Cl)PCH2P(Cl)NR2; R = Me (2a), Et (2b)] leads to the formation of new heterocyclic compounds, 1,3-diphospha-2,3-dihydro-1H -phenalenes 3a,b as a mixture of cis and trans isomers. DFT calculations indicate that the cis isomers are thermodynamically more stable by about 1,3 kcal/mol than the trans isomers. Compounds 3a,b can be converted into dithio the derivatives 5a,b and the borane complexes 6a,b, which were characterized by NMR spectroscopy and investigated by X-ray diffraction analysis. The dialkylamino groups in 3 can be substituted by chlorine to give the chlorophosphane 7. [source]

Reactions of Aminobis(phenolate)-Supported Dioxidotungsten(VI) and Dioxidomolybdenum(VI) Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2006
Ari Lehtonen
Abstract The dioxidotungsten(VI) and -molybdenum(VI) complexes [WO2(O2NOMe)] (1), [MoO2(O2NOMe)] (2) and [{MoO2(O2NMe)}2] (3) [O2NOMe methoxyethylamino- N,N -bis(2-methylene-4,6-dimethylphenolate) dianion, O2NMe = methylamino- N,N -bis(2-methylene-4,6-dimethylphenolate) dianion] can react with chloride sources (Me3SiCl, SOCl2) to form resultant monooxido dichloro compounds [WOCl2(O2NOMe)] (4), [MoOCl2(O2NOMe)] (5) and [MoOCl2(O2NMe)] (6), respectively. The reaction of tungsten complex yields of the mixture of cis - 4 and trans - 4, which can be separated and characterized. The reactions of analogous molybdenum complexes with Me3SiCl yield trans isomers of 5 and 6 as individual products. Reaction of dioxidotungsten complex 1 with isopropyl isocyanate was found to produce a tungsten(VI) complex [W(O2NOMe)(N- iPr)(L)] (7) (L = N,N,-diisopropylureate) with a terminal imido group and a bidentate ureate ligand. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Oxovanadium(IV) Complexes with Pyrazinecarboxylic Acids:The Coordinating Properties of Ligands with the (Naromatic, COO,) Donor Set

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2006
Eugenio Garribba
Abstract Complex formation between the VIVO ion and four pyrazine derivatives, 2-pyrazinecarboxylic acid (pzc), 5-methyl-2-pyrazinecarboxylic acid (5-Mepzc), 2,3-pyrazinedicarboxylic acid (3-COOHpzc) and 5-hydroxy-2-pyrazinecarboxylic acid (5-OHpzc), was studied in aqueous solution and in the solid state through the combined application of potentiometric and spectroscopic (EPR and FT-IR) techniques. The results indicate that in acidic and neutral aqueous solution all theligands form mono(chelated), bis(chelated) and dinuclear species of composition VOL, VOL2 and (VO)2L2H,2. Hexacoordinated VOL2 complexes are characterised by a cis/trans isomerism, where cis and trans are the species with a water molecule bound in the cis or trans position with respect to the V=O group. The trans arrangement is favoured over the cis arrangement. Three solid derivatives, [VO(5-Mepzc)2] (1), cis -[VO(pzc)2(H2O)] (2) and cis -[VO(3-COOHpzc)2(H2O)] (3), were isolated and characterised. Based on the experimental results and on the data in the literature, the stability of cis and trans isomers in aqueous solution and in the solid state has been discussed, showing that with ligands of comparable basicity and size of the chelate ring the hydrophilicity favours the cis species and determines the relative amount of the two isomers. The analysis of the magnetic properties of the hydroxo-bridged VIVO dimers suggests that for the (VO)2L2H,2 species the anti -coplanar arrangement is realised. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Synthesis, Characterization, and Electrochemical Properties of Dinuclear Complexes Assembled from Asymmetric CoIII Bis(dioximates) and Boronic Acids

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2005
Renata Dreos
Abstract Bis(methylphenylglyoximate)cobalt(III) complexes exist both as cis and trans isomers due to the asymmetry of the equatorial ligand, and, when the axial ligands are different, the trans isomer is chiral. The reaction of racemic trans -[CH3Co(mpgH)2py] (1) with either 3- or 4-pyridylboronic acid affords dimeric units arranged on a crystallographic symmetry center such that the pyridyl nitrogen of one moiety coordinates to the Co atom of the symmetry-related unit. In principle, three structurally different dimeric species (two homodimers and one heterodimer) can be obtained. Time-resolved 1H NMR spectra of a 1:1 mixture of racemic 1 and either 3- or 4-pyridylboronic acid in CDCl3/CD3OD show that the reaction does not converge toward a unique species in solution. Nevertheless, X-ray structures show that the heterochiral dimers are the only products that crystallize from the reaction mixture. The nature of the dioximate side groups does not affect the geometry of the dimeric arrangements assembled by 4-pyridylboronic acid ("molecular box"). On the contrary, the geometry of the species assembled by 3-pyridylboronic acid varies from the "molecular parallelogram" obtained from the bis(dimethylglyoximates) to the highly squeezed "molecular box" obtained from bis(methylphenylglyoximates). Cyclic voltammetry studies show that the metal centers in the dimeric species do not interact with each other and undergo a simultaneous redox process. However, depending on the geometry of the systems, the redox process involves a single four-electron reduction for 3 and 5 or two consecutive two-electron reduction steps for 4 and 6. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Retention behavior of trans isomers of eicosapentaenoic and docosahexaenoic acid methyl esters on a polyethylene glycol stationary phase

EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 6 2008
Svein A. Mjøs
Abstract A polyethylene glycol (PEG) stationary phase was evaluated for the separation of mono- trans isomers of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) methyl esters. The resolution patterns were compared to patterns achieved with previously applied conditions on a cyanopropyl phase. There were no overlaps between all- cis EPA/DHA and their mono- trans isomers on the PEG phase. Because of overlap between 22:0 and 22:1 isomers, the PEG column is not a good choice for analyses of EPA trans isomers in crude fish oils. However, if the saturated and monounsaturated fatty acids are not present in significant amounts, PEG can be a better choice than cyanopropyl columns. [source]

A DFT study on the hydrolysis mechanism of NH-tautomeric antitumors of [HL][trans -RuCl4L(dmso- S)]

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2010
Jin Can Chen
Abstract The hydrolysis process of Ru (III) complex [Htrz][trans -RuCl4(1- H -1,2,4-triazole)(dmso- S)] 1, a potential antitumor complex similar to the well-known anticancer agent [ImH][trans -RuCl4(Im)(dmso- S)] (NAMI-A), has been investigated by using density functional theory (DFT) method, and the solvent effect was also considered and calculated by conductor-like polarizable calculation model (CPCM). Meanwhile, the hydrolysis process of the NH-tautomeric isomer, [Htrz][trans -RuCl4(4- H -1,2,4-triazole)(dmso- S)] 2, was also modeled and predicted by the same methods. The structural characteristics and the detailed energy profiles for the hydrolysis processes of two isomers have been obtained. The analysis of thermodynamic and kinetic characteristics of hydrolysis reaction suggests the following: for the first hydrolysis step, the Complex 1 has lower hydrolysis rate than the reported anticancer drug NAMI-A, and the result is in accordance with experimental one. However, Complex 1 has obviously higher hydrolysis rate than its isomer Complex 2, and the result was reasonably explained in theory. For the second hydrolysis step, the formation of cis -diaqua species is thermodynamic preferred to that of trans isomers. In addition, the trend in nucleophilic attack abilities (A) of hydrolysis products by pertinent biomolecules was revealed and predicted. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

Production of conjugated linoleic acid by probiotic Lactobacillus acidophilus La-5

JOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2009
M. Macouzet
Abstract Aims:, To study the ability of the probiotic culture Lactobacillus acidophilus La-5 to produce conjugated linoleic acid (CLA), which is a potent anti-carcinogenic agent. Methods and Results:, The conversion of linoleic acid to CLA was studied both by fermentation in a synthetic medium and by incubation of washed cells. Accumulation of CLA was monitored by gas chromatography analysis of the biomass and supernatants. While the fermentation conditions applied may not be optimal to observe CLA production in growing La-5 cells, the total CLA surpassed 50% of the original content in the washed cells after 48 h under both aerobic and micro-aerobic conditions. The restriction of oxygen did not increase the yield, but favoured the formation of trans, trans isomers. Conclusions:, The capability of L. acidophilus La-5 to produce CLA is not dependant on the presence of milk fat or anaerobic conditions. Regulation of CLA production in this strain needs to be further investigated to exploit the CLA potential in fermented foods. Significance and Impact of the study:, Knowledge gained through the conditions on the accumulation of CLA would provide further insight into the fermentation of probiotic dairy products. The capacity of the nongrowing cells to produce CLA is also of great relevance for the emerging nonfermented probiotic foods. [source]

Predictive and interpolative biplots applied to canonical variate analysis in the discrimination of vegetable oils by their fatty acid composition

JOURNAL OF CHEMOMETRICS, Issue 9 2004
M. Rui Alves
Abstract The fatty acid profiles of 120 commercial unblended peanut, corn, soybean and sunflower vegetable oils and 17 commercial brands of blended edible oils were determined by HRGC/FID/capillary column, including several cis and trans isomers of mono-, di- and tri-unsaturated fatty acids as well as fatty acids with an odd number of carbon atoms. Although many statistical techniques may show some usefulness in the description and analysis of the data obtained, predictive biplots applied to canonical variate analysis prove to be a very useful way of carrying out interpretations and an important aid in building up models, while interpolative biplots display great advantages in the utilization of models for classification purposes on a day-to-day basis. Furthermore, these biplots require only a modest understanding of statistical tools, since all judgements are made regarding original fatty acids and original measuring units. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Interpolative biplots applied to principal component analysis and canonical correlation analysis

JOURNAL OF CHEMOMETRICS, Issue 11 2003
M. Rui Alves
Abstract The multivariate statistical analysis of cis and trans isomers of fatty acid profiles of eight margarine brands obtained by HRGC/FID/capillary column was carried out based on biplots applied to principal component analysis (PCA) and canonical correlation analysis (CCA). It is shown that while predictive biplots are the best choice for interpretation purposes, interpolative biplots are very useful for classification of new observations that were not used for the construction of the principal component or canonical dimension axes. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Assessment of the Oxidative and Hydrolytic Degradation of Oils Used as Liquid Medium of In-oil Preserved Vegetables

JOURNAL OF FOOD SCIENCE, Issue 1 2003
F. Caponio
ABSTRACT: An experimental investigation was carried out on several in-oil preserved vegetables to evaluate the quality and genuineness of different oils used as liquid medium. The results obtained showed that the lipids released by vegetables to the oils are negligible, and that the routine analyses are not fully effective to assess the quality of the oils. More reliable results may be achieved from the percent determination of trans isomers, and from the classes of oxidation, polymerization, and hydrolysis substances contained in the polar compounds. In sunflower seed oils, much higher contents of trans isomers (p < 0.001), triglyceride oligopolymers, and oxidized triglycerides (p < 0.01) have been observed as compared to olive and extra virgin olive oils. [source]

Conformational analysis, Part 41.

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2006
-unsaturated carbonyl compounds, A modelling, LIS/NMR investigation of the conformations of
Abstract A novel Lanthanide Induced Shift Analysis (LISA) is presented. In this analysis both the paramagnetic and the diamagnetic lanthanide induced chemical shifts are normalised separately in contrast to previous techniques in which only the paramagnetic shifts were normalised. This procedure is used together with molecular mechanics (MMFF94) and ab initio (RHF/6-31G, RHF/6-311G** and B3LYP/6-311G**) calculations to investigate s - cis/s - trans isomerism in some ,,, -unsaturated aldehydes, ketones and esters. In tiglic aldehyde 1 and trans -cinnamaldehyde 4 the s - trans conformer predominates with energy differences ,E (s - cis,s - trans) of 1.64 and 1.76,kcal/mol. In methyl vinyl ketone 2 and trans -cinnamyl methyl ketone 5 the populations of the s - cis and s - trans isomers are almost equal (,E 0.24 and 0.0,kcal/mol) and in methyl crotonate 3 and methyl trans -cinnamate 6 the s - cis conformer is more stable (,E ,0.72 and ,0.41,kcal/mol). These results are in agreement with both the MMFF94 and ab initio calculated energies for the compounds except tiglic aldehyde 1 in which all the calculated values are too large and cinnamyl ketone 5. In this compound the ab initio calculations predict the s - cis form to be more stable than the s - trans in contrast to both the MM calculations and the observed result which give both forms of equal energy. Also in both the MM and ab initio calculations phenyl substitution in the ketone (2 vs. 5) considerably stabilises the s - cis form. This is not observed in practise. In phenyl acetate 7 the B3LYP calculations give two equally stable structures, one planar one non-planar. The MMFF94 and MP2 calculations and the LIS analysis support the existence of only the non -planar conformer in solution, which is also the conformation of phenyl acetate in the crystal. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Spectroscopy and Photoreactivity of Trichochromes: Molecular Components of Pheomelanins,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2006
John D. Simon
ABSTRACT The trichochromes are a class of small molecules present in pheomelanin (the red melanin) and absent in eumelanin (the black melanin). Herein trichochrome F (TF) and decarboxy-trichochrome C (dTC) are examined. Both trichochromes are characterized by a visible absorption band, which is shown to be the result of overlapping transitions of the cis and trans isomers. The temperature dependence of the absorption spectrum of dTC suggests the additional presence of equilibrium between the enol and keto forms of the molecule. These conclusions are supported by ground-state energies of these isomers obtained using a continuum solvation model. Near-infrared emission measurements were not able to detect photoproduction of 1O2, and spin-trapping experiments revealed formation of O2*- . DNA nicking assays also revealed a low level of light-induced aerobic activity of dTC, suggesting a quantum efficiency of at most 5 × 10 -6 for the photo-generation of O2*- . These results are consistent with pump-probe optical experiments, which reveal efficient and nearly complete ground-state recovery within a few picoseconds of excitation. Both trichochromes are efficient quenchers of 1O2, exhibiting a bimolecular rate constant comparable with vitamin C. These results suggest that trichochromes could serve a protective role in pheomelanin pigments. [source]

Solid-state compounds of stereoisomers: cis and trans isomers of 1,2-cyclohexanediol and 2,3-tetralindiol

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2007
Michael A. Lloyd
The phases of 1,2,3,4-tetrahydro-2,3-naphthalenediol (or 2,3-tetralindiol) and of 1,2-cyclohexanediol have been investigated. The structure of a very stable 1:1 compound (or co-crystal) of the cis and trans isomers of 2,3-tetralindiol, the existence of which has been known for nearly a century, has finally been determined. No evidence of any analogous compound between the cis and trans isomers of 1,2-cyclohexanediol has been found. The formation of solid-state compounds of stereoisomers is rare; it probably occurs only if the crystal packing of at least one of the isomers is unfavorable, e.g. if at least one of the melting points is lower than expected. Compound formation is usually unlikely because of the difficulty of simultaneously optimizing the translational spacings for both isomers, but that packing problem is avoided in the cis/trans compound of 2,3-tetralindiol because the two isomers are in very similar environments. In the structures of the individual 2,3-tetralindiol isomers there are clear conflicts between the competing packing requirements of the 1,2-diol moiety and the aromatic ring system; these conflicts are resolved better in the co-crystal than in the structures of the individual isomers. [source]

(1R,3R,4S)-1-Benzyl-3-(tert -butyldimethylsilyloxy)-4-(hydroxymethyl)pyrrolidine,borane: novel B,H...H,O hydrogen bonding

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2010
Graeme J. Gainsford
The absolute configuration of the title cis -(1R,3R,4S)-pyrrolidine,borane complex, C18H34BNO2Si, was confirmed. Together with the related trans isomers (3S,4S) and (3R,4R), it was obtained unexpectedly from the BH3·SMe2 reduction of the corresponding chiral (3R,4R)-lactam precursor. The phenyl ring is disordered over two conformations in the ratio 0.65:0.35. The crystallographic packing is dominated by the rarely found donor,acceptor hydroxy,borane O,H...H,B hydrogen bonds. [source]

cis,cis -Ceratospong­amide N,N -di­methyl­acet­amide hemisolvate in the presence of twinning

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2003
Akiko Asano
Ceratospong­amide (CS) is a potent inhibitor of secreted phospho­lipase A2, and cis,cis and trans,trans isomers, related with respect to the two proline amide bonds, are known. Crystals of cis,cis -CS were grown from N,N -di­methyl­acet­amide solution, giving the title compound, the cyclic ester of isoleucyl­oxazolinyl­phenyl­alanyl­prolyl­thia­zolyl­phenyl­alanyl­pro­line [cyclo(-Ile,Oxz,Phe,Pro,Thz,Phe,Pro-)] N,N -di­methyl­acet­amide hemisolvate, C41H49N7O6S·0.5C4H9NO. The structure is the third example of cis,cis -CS to be investigated and comprises twinned crystals, in which the a and b axes are interchanged. The ratio of co-existing twin crystals is approximately 50%. The peptide has a `saddle-like' structure and is very similar to previously reported structures of cis,cis -CS, which implies that the structure of cis,cis -CS is very stable in spite of differences in crystallization conditions. [source]

The Reaction of Hydrogen Atoms with Methionine Residues: A Model of Reductive Radical Stress Causing Tandem Protein,Lipid Damage

CHEMBIOCHEM, Issue 11 2006
Carla Ferreri Dr.
Abstract The occurrence of tandem damage, due to reductive radical stress involving proteins and lipids, is shown by using a biomimetic model. It is made of unsaturated lipid vesicle suspensions in phosphate buffer in the presence of methionine, either as a single amino acid or as part of a protein such as RNase A, which contains four methionine residues. The radical process starts with the formation of H. atoms by reaction of solvated electrons with dihydrogen phosphate anions, which selectively attack the thioether function of methionine. The modification of methionine to ,-aminobutyric acid is accompanied by the formation of thiyl radicals, which in turn cause the isomerization of the cis fatty acid residues to the trans isomers. The relationship between methionine modification and lipid damage and some details of the reductive radical stress obtained by proteomic analysis of irradiated RNase A are presented. [source]

Electronic Properties of 3,3,-Dimethyl-5,5,-bis(1,2,4-triazine): Towards Design of Supramolecular Arrangements of N-Heterocyclic CuI Complexes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2007
Blandine Courcot Dr.
Abstract A new efficient and safe synthesis of 3,3,-dimethyl-5,5,-bis-(1,2,4-triazine) is presented. The electron-density distribution and electrostatic properties (charge, electrostatic potential) of this molecule were analyzed. These properties were derived from a high-resolution single-crystal X-ray diffraction experiment at 100,K and compared to the results obtained from ab initio DFT quantum-mechanical calculations. Comparisons of its electrostatic potential features and integrated atomic charges (quantum theory of atoms in molecules, QTAIM) have been made with those of related molecules such as bipyrimidine ligands. Two methods were used to derive integrated charges: one is based on the conventional analytical procedure and the second uses a steepest-ascent numerical algorithm. Excellent agreement was obtained between these two methods. Charges and electrostatic potential were used as predictive indices of metal chelation and discussed in the light of complexation abilities of the title compound and related molecules. The crystal structure of a CuI complex of 3,3,-dimethyl-5,5,-bis(1,2,4-triazine) is reported here. In the solid state, this complex forms a three-dimensional multibranch network with open channels in which counterions and solvent molecules are located. This architecture involves both cis and trans isomers of the title compound. [source]

Chemoenzymatic Route to Both Enantiomers of a 1-Isopropyl-3a-methyloctahydroinden-4-one Derivative: A Synthetic Intermediate for Sesqui- and Diterpenoids

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2005
Shigeo Fujieda
Abstract On the way to a chemoenzymatic synthesis of a key intermediate for sesquiterpenoids and diterpenoids, 2-methyl-2-(4-methyl-3-oxopentyl)-1,3-cyclohexanedione was reduced with the whole cells of yeast biocatalysts. Torulaspora delbrueckii NBRC10921 reduced a cyclic ketone of three carbonyl groups in an enantiofacially selective manner (re -face attack), but there was poor enantiotopic group selectivity between two carbonyl groups on the cyclohexane ring to yield a mixture of diastereomeric products. Candida floricola IAM13115 reduced mainly the pro -(R) carbonyl group. In contrast, the reduction proceeded in an enantiofacially poorly selective manner to give another set of diastereomeric products. In both cases, another carbonyl group on the side chain worked as a ,trapping arm' of the resulting secondary alcohol. The diastereomeric products were effectively separated as the ,syn' or ,cis' isomer exclusively exist in the intramolecular hemiacetal structure, while ,anti' or ,trans' isomer being an equilibrated mixture of cyclic hemiacetal and open-chain hydroxyketone (ca. 0.7,:,1). Starting separately from the enantiomerically enriched products as above, both enantiomers of the target compound, a key intermediate for terpenoids, were efficiently prepared via stereoselective ring closure under pinacol coupling reaction conditions. Furthermore, a daucane sesquiterpene intermediate, a hydroazulene derivative, was provided after one-carbon homologation of the six-membered ring. [source]