Trans Double Bond Research Articles

Engineering polypeptide folding through trans double bonds: transformation of miniature β-meanders to hybrid helices.

Utilization of conjugated double bonds to engineer the novel folded miniature β-meander type structures, single step transformation of miniature β-meanders into ααγ(4)-hybrid peptide 10/12-helices using catalytic hydrogenation, their solution and single crystal conformations are reported.

Chiral phase-HPLC separation of hydroperoxyoctadecenoic acids and their biosynthesis by fatty acid dioxygenases.

Fatty acid oxygenases are often characterized by steric analysis of their hydroxy or hydroperoxy metabolites. Chiral phase-HPLC (CP-HPLC) can be used to separate enantiomeric hydroperoxyoctadecenoic acids. This method is based on analysis of seven octadecenoic fatty acids with double bonds at positions 6Z to 13Z, which were oxidized to hydroperoxides by photooxidation. A stationary phase, Reprosil Chiral NR, was found to resolve these hydroperoxy fatty acids with 1-hydroperoxy-2-propene and with 3-hydroperoxy-1-propene elements so that the S hydroperoxy fatty acids consistently eluted before the R stereoisomers. The chiral selector has not been disclosed, but it is described as an aromatic chiral phase with π-donor and π-acceptor groups of Pirkle type. The MS(3) spectra of the hydroperoxides showed characteristic fragments, which were influenced by the distance between the hydroperoxy and the carboxyl groups and the relative position of the double bond. Octadecenoic fatty acids can be oxidized by fungal and bacterial dioxygenases to hydroperoxides with cis or trans double bond configuration. Steric analysis of the hydroperoxy metabolites can be performed by this method, and it can also be used for preparative purposes.

Metathesis Cyclopolymerization of Imidazolium-Functionalized 1,6-Heptadiyne toward Polyacetylene Ionomer

Metathesis cyclopolymerization (MCP) of ionic 1,6-heptadiyne is successfully applied to synthesize polyacetylene (PA) ionomer in different solvents especially in imidazolium-based ionic liquid (IL), and MCP of ionic monomer in the mixture of THF/IL proceeded in a controlled manner by the action of Grubbs second and third generation catalysts (Ru–II, Ru–III). The influence of catalysts and solvents on polymerization behavior and chain microstructure was investigated, and the results revealed that the isolated polymer yield could reach to 97% and 82% by Ru–III and Ru–II, respectively, in 1:2 THF/IL after optimization, and PAs incorporating imidazolium pendent contained ≥95% five-membered-ring structure and almost all trans-double bonds along the backbone. PAs formed in different solvents reflected significant variance in optical absorption properties, and a bathochromic shift effect was observed with the mixture of THF/IL.

Synthesis, characterization, and photovoltaic properties of a solution-processable two-dimensional-conjugated organic small molecule containing a triphenylamine core

A novel solution-processable two-dimensional-conjugated organic small molecule based on triphenylamine (TPA) core, (E)-2-(3-(4-(bis(4-(3-hexyl-5-(7-(4-hexylthiophen-2-yl)benzo[c] [1,2,5] thiadiazol-4-yl)thiophen-2-yl)phenyl)amino)styryl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (TPA-TBT), has been designed and synthesized by Knoevenagel reaction. Different from the linear or star-shaped TPA derivatives, in TPA-TBT, two arms of the TPA core are symmetrically connected with the acceptor segment 4,7-di(2-thienyl)-2,1,3-benzothiadiazole (DTBT), but the third arm is connected with a strong acceptor group, 2-(5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (DCM), connected through a trans double bond with the TPA core. TPA-TBT has a relatively low optical band gap (1.91 eV) and a deep highest occupied molecular orbital (HOMO) energy level (−5.53 eV). Bulk heterojunction photovoltaic devices were fabricated using TPA-TBT as the donor and (6,6)-phenyl C61-butyric acid methyl ester (PCBM) as the acceptor with the weight blend ratio of 2:1, 1:1, and 1:2. All the devices have a high open-circuit voltage (Voc) of about 0.9 eV. Device with 1:1 blend ratio and LiF modification to the cathode exhibited a better performance with a short circuit current (Jsc) of 4.86 mA cm−2 and a power conversion efficiency (PCE) of 1.13 %.

Biohydrogenation of C20 polyunsaturated fatty acids by anaerobic bacteria

The PUFAs include many bioactive lipids. The microbial metabolism of C18 PUFAs is known to produce their bioactive isomers, such as conjugated FAs and hydroxy FAs, but there is little information on that of C20 PUFAs. In this study, we aimed to obtain anaerobic bacteria with the ability to produce novel PUFAs from C20 PUFAs. Through the screening of ∼100 strains of anaerobic bacteria, Clostridium bifermentans JCM 1386 was selected as a strain with the ability to saturate PUFAs during anaerobic cultivation. This strain converted arachidonic acid (cis-5,cis-8,cis-11,cis-14-eicosatetraenoic acid) and EPA (cis-5,cis-8,cis-11,cis-14,cis-17-EPA) into cis-5,cis-8,trans-13-eicosatrienoic acid and cis-5,cis-8,trans-13,cis-17-eicosatetraenoic acid, giving yields of 57% and 67% against the added PUFAs, respectively. This is the first report of the isolation of a bacterium transforming C20 PUFAs into corresponding non-methylene-interrupted FAs. We further investigated the substrate specificity of the biohydrogenation by this strain and revealed that it can convert two cis double bonds at the ω6 and ω9 positions in various C18 and C20 PUFAs into a trans double bond at the ω7 position. This study should serve to open up the development of novel potentially bioactive PUFAs.

Synthesis of aromatic sphingosine analogues by diastereoselective amination of enantioenriched trans-γ,δ-unsaturated β-hydroxyesters.

An effective route to N-Boc-protected aromatic sphingosine analogues is accomplished. The strategy is based on the diastereoselective amination of enantioenriched trans-γ,δ-unsaturated β-hydroxyesters to establish anti,N-Boc-α-hydrazino-β-hydroxyesters. Nonreductive E1cB elimination is essential for the successful N-N bond cleavage of hydrazine while preserving the trans double bond. Either the (3R,2S) and (3S,2R) enantiomer of N-Boc-protected sphingosine analogues has been synthesized in five steps with excellent optical purity with ∼99% ee and >99% de.

Monomer sequencing and microstructural analysis on polymers of dimethyl norbornene dicarboxylate and 7‐oxanorbornene dicarboxylic derivatives employing ruthenium catalysts by ring‐opening metathesis polymerization

ABSTRACTThe physiochemical properties, comonomer sequencing, and regiospecificity of the linkages between monomeric units within homo/copolymers based on 5,6‐di‐substituted norbornene and 7‐oxanorbornene type monomers by ring‐opening metathesis polymerization are reported and correlated to their primary and secondary structural elements. In general, first‐generation Grubbs‐I1 ruthenium catalyst generates polymers with high trans content that exhibits an extended secondary structure with exo,exo substituents, whereas second‐generation Grubbs‐I2 catalyst produces polymers with high cis content that forms tight turns, resulting in a compact structure. Furthermore, I2‐produced polymers exhibit a high level of alternating cis–trans double bonds along their polymeric backbone. In stark contrast, both first‐ and second‐generation Grubbs catalysts display complete reversal in cis/trans selectivity when an oxygen atom is in position‐7 of the norbornene‐ring along with mono‐endo‐substitution in position‐5 or 6, and hence highlighting the importance of stereoelectronic complexation by the catalyst with the next incoming monomer for cis/trans selectivity. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2477–2501

Dietary Trans Fatty Acids and Cardiovascular Disease Risk: Past and Present

Dietary trans double bond containing fatty acids have been associated with increased risk of cardiovascular disease. There are two main sources of dietary trans fatty acids: meat and dairy fats, and partially hydrogenated fats. Because of a number of factors, including changes in federal labeling requirements for packaged foods, and local bans and grassroots pressure on the use of partially hydrogenated fat, trans fat intake has declined in recent years. Similar to saturated fatty acids, trans fatty acids increase plasma low density lipoprotein (LDL)-cholesterol concentrations. In contrast to saturated fatty acids, trans fatty acids do not increase high density lipoprotein (HDL)-cholesterol concentrations. These differences have been attributed to lipoprotein catabolic rate rather than production rate. When reported, effects of partially hydrogenated fat on glucose homeostasis, C-reactive protein, blood pressure, and LDL oxidation are modest. Although at this time some issues remain unresolved regarding trans fatty acids and CVD risk factors other than plasma lipoprotein concentrations, they should not affect the final dietary recommendation to limit intake.

Base-dependent formation of cis and trans olefins and their application in the synthesis of 5-oxo-ETE receptor antagonists

5-Oxo-ETE is the most potent eosinophil chemoattractant among lipid mediators. We have developed two 5-oxo-ETE receptor antagonists. In the course of the work, we have developed a procedure to selectively introduce a cis and trans double bond in an alkyl side chain. Reacting indolecarboxaldehydes with alkyl ylides using the Li base affords the trans olefins, whereas using the K base yields the cis olefins.

Branching degree and rheological response correlation in peroxide-modified linear low-density polyethylene

Correlations between rheological behavior and degree of long chain branching (LCB) of linear low-density polyethylene (LLDPE) upon a peroxide (dicumyl peroxide [DCP]) modification process under various conditions are discussed in this paper. The gel content analysis revealed negligible insoluble crosslinked fraction implying that incorporation of DCP to LLDPE predominately leads to branching rather than crosslinking. The slight changes in average molecular weight and molecular weight distribution induced by peroxide modification under various conditions revealed that formation of low-molecular-weight fractions due to chain scission is also negligible. The changes in terminal, trans, and pendant double bonds concentration of the modified samples with different amounts of peroxide were well depicted by Fourier transform infrared spectroscopy. Considering insignificant changes in molecular weight and molecular weight distribution during peroxide modification, the deviation observed in zero-shear-rate viscosity (η0) values of the modified LLDPE with that of power-law equation related to the linear PEs could be reliably attributed to the presence of LCB in the peroxide modified samples. Increasing the DCP content at roughly constant molar mass led to increasing of η0 values as a result of increased degree of LCB. The increase in η0 values was ascribed to prolonged relaxation times of the polymer molecules due to the retarded reptation motion-driven relaxation mechanism. Copyright © 2014 John Wiley & Sons, Ltd.

The role of the trans double bond in skin barrier sphingolipids: permeability and infrared spectroscopic study of model ceramide and dihydroceramide membranes.

Dihydroceramides (dCer) are members of the sphingolipid family that lack the C4 trans double bond in their sphingoid backbone. In addition to being precursors of ceramides (Cer) and phytoceramides, dCer have also been found in the extracellular lipid membranes of the epidermal barrier, the stratum corneum. However, their role in barrier homeostasis is not known. We studied how the lack of the trans double bond in dCer compared to Cer influences the permeability, lipid chain order, and packing of multilamellar membranes composed of the major skin barrier lipids: (d)Cer, fatty acids, cholesterol, and cholesteryl sulfate. The permeability of the membranes with long-chain dCer was measured using various markers and was either comparable to or only slightly greater than (by up to 35%, not significant) that of the Cer membranes. The dCer were less sensitive to acyl chain shortening than Cer (the short dCer membranes were up to 6-fold less permeable that the corresponding short Cer membranes). Infrared spectroscopy showed that long dCer mixed less with fatty acids but formed more thermally stable ordered domains than Cer. The key parameter explaining the differences in permeability in the short dCer and Cer was the proportion of the orthorhombic phase. Our results suggest that the presence of the trans double bond in Cer is not crucial for the permeability of skin lipid membranes and that dCer may be underappreciated members of the stratum corneum lipid barrier that increase its heterogeneity.

Catalytic performances of copper and lead (2-guanidino-benzimidazoliume) complexes in polybutadiene (PB) and hydroxyl-terminated PB epoxidation

Polybutadiene (PB) and hydroxyl-terminated PB were epoxidized using in situ-generated dimethyl dioxirane as an oxidant in the attendance of different concentrations of copper and lead (2-guanidinobenzimidazoliume) (GBH) complexes as the catalyst at 25°C. The potential of cis, trans, and vinyl double bonds toward epoxidation was considered in detail at various reaction times. The products were characterized using proton nuclear magnetic resonance and Fourier transform infrared spectroscopy techniques and data revealed that the formation of desired products were obtained without any side reaction. The results indicated the performance of calculated 0.252 mmol of GBH complexes in obtaining maximum epoxidation yield as well as selectivity in the epoxidation of cis double bonds in comparison with trans and vinyl ones.

A comparative calorimetric study of the effects of cholesterol and the plant sterols campesterol and brassicasterol on the thermotropic phase behavior of dipalmitoylphosphatidylcholine bilayer membranes

We present a comparative differential scanning calorimetric study of the effects of the animal sterol cholesterol (Chol) and the plant sterols campesterol (Camp) and brassicasterol (Bras) on the thermotropic phase behavior of dipalmitoylphosphatidylcholine (DPPC) bilayers. Camp and Bras differ from Chol in having a C24 methyl group and, additionally for Bras, a C22 trans-double bond. Camp and especially Bras decrease the temperature, cooperativity and enthalpy of the DPPC pretransition more than Chol, although these effects are attenuated at higher sterol levels. This indicates that they destabilize gel-state DPPC bilayers to a greater extent, but are less soluble, than Chol. Not surprisingly, all three sterols have similar effects on the sterol-poor sharp component of the DPPC main phase transition. However, Camp and especially Bras less effectively increase the temperature and decrease the cooperativity and enthalpy of the broad component of the main transition than Chol. This indicates that at higher sterol concentrations, Camp and Bras are less miscible and less effective than Chol at ordering the hydrocarbon chains of the sterol-enriched fluid DPPC bilayers. Overall, these alkyl side chain modifications generally reduce the ability of Chol to produce its characteristic effects on DPPC bilayer physical properties. These differences are likely due to the less extended and more bent conformations of the alkyl side chains of Camp and Bras, producing sterols with a greater effective cross-sectional area and reduced length than Chol. Hence, the structure of Chol is likely optimized for maximum solubility in, as opposed to maximum ordering of, phospholipid bilayers.

English

Sunflower oil is extensively used in frying in Algeria as an alternative to olive oil due to its low cost. However, the high level of unsaturated fatty acids (FA) contained in sunflower oil enhances its susceptibility to oxidation. In our study, the sunflower oil was heated at 99±2°C with incorporation of 9 L of oxygen/second for 52 h continuously in the absence of foodstuff. Heating polyunsaturated fatty acids (PUFAs) in the presence of air causes a greater degree of lipid peroxidation. The oil oxidation degree was monitored through several physicochemical analyses. The products of thermal oxidation were monitored using UV- spectrophotometric method and Fourier transform infrared spectroscopy (FT-IR). Compared to fresh oil, the free-fatty acid contents, peroxide value, density and moisture of the thermally oxidized sunflower oil increased. In addition, the iodine and saponification values decreased during thermal treatment. The treatment applied had a negative effect on FA composition; the most significant effects were on C18:2, C18:1 and C16:0 contents. Analysis of chromatographic profile of thermoxidized sunflower oil showed a reduction in linoleic acid (LA) and an increase in oleic and palmitic acids; decrease of linoleic acid content is used as an indicator of lipid oxidation. Moreover, during the early stages, conjugated dienes (CDs), absorbing at 233 nm, were formed upon decomposition of hydroperoxides. In our study, the early stages of lipid oxidation were measured by UV-spectrophotometric method. Hydroperoxides broke down into secondary products and were revealed by FT-IR; these scission products are generally odoriferous by nature. The C=O stretching band at 1739-1724 cm-1 of the aldehydes was much more intense. Formation of conjugated double bond systems and the isomerisation of cis to trans double bonds was observed in the C=C stretching region at 980 to 965 cm-1. The results obtained reveal that even fresh oil contains products of peroxidation and isomerization of C18:2, n-6; indeed, CDs can be produced during the refining process of oil. The treatment applied increased the rate of these products and conferred a marked rancid taste and a thick texture to the thermoxidized sunflower oil.   Key words: Sunflower oil, Linoleic acid, thermally oxidative treatment, alteration level. 

26-Desmethyl-2-methylene-22-ene-19-nor-1α,25-dihydroxyvitamin D3 compounds selectively active on intestine

Six new analogs of 2-methylene-19-nor-1α,25-dihydroxyvitamin D3, 6–7 and 8a,b–9a,b, have been synthesized. All compounds are characterized by a trans double bond located in the side chain between C-22 and C-23. While compounds 6 and 7 possess C-26 and C-27 methyls, compounds 8a,b and 9a,b lack one of these groups. A Lythgoe-based synthesis, employing the Wittig–Horner reaction was used for these preparations. Two different types of Δ22E-25-hydroxy Grundmann’s ketone, having either only one stereogenic center located at position C-20 (20 and 21), or two stereogenic centers located at 20- and 25-positions (24a,b–25a,b) were obtained by a multi-step procedure from commercial vitamin D2. The introduction of a double bond at C-22 appeared to lower biological activity in vitro and in vivo. Further removal of a 26-methyl in these analogs had little effect on receptor binding, HL-60 differentiation and CYP24A expression but markedly diminished or eliminated in vivo activity on bone calcium mobilization while retaining activity on intestinal calcium transport.

Molecular origins of bending rigidity in lipids with isolated and conjugated double bonds: The effect of cholesterol

We examine the effects of cholesterol (Chol) on the mechanical properties of membranes consisting of 16:0/18:1 POPC lipid and of lipids with conjugated linoleic acid (CLA), cis-9/trans-11 CLA (C9T11) and trans-10/cis-12 CLA (T10C12). Atomistic molecular dynamics (MD) simulations of POPC–Chol and CLA-Chol mixtures at various Chol concentrations are employed within a recently developed and validated computational methodology (Khelashvili et al., 2013) that calculates from MD trajectories the bending rigidity (KC) for these systems. We have found that the addition of 30% Chol stiffens POPC lipid membranes much more significantly (2.3-fold) than it does C9T11 (1.5-fold) or T10C12 (1.75-fold) lipid bilayers. Extensive comparative structural analysis of the simulated mixtures supports a molecular mechanism for the differential effects of cholesterol, whereby the sterol molecules tilt more significantly in CLA membranes where they also insert deeper inside the hydrocarbon core. The observed distinct arrangement of Chol molecules in CLA and POPC bilayers, in turn, is dictated by the interplay between the specific location of the trans double bond in the two CLA lipid isomers and the preferential interaction of the rigid Chol ring with the saturated segments of the lipid tails. The simulations and analysis described in this paper provide novel insights into the specific modes of molecular interaction in bilayers composed of mixtures of Chol and unsaturated lipids that drive emergent macroscopic properties, such as the membrane's bending modulus.

Chemical Synthesis of Functional Poly(4-hydroxybutyrate) with Controlled Degradation via Intramolecular Cyclization

We report the synthesis, characterization, and degradation of a new type of functional poly(4-hydroxybutyrate) (P4HB). The polyesters were obtained via the Passerini multicomponent polymerization (MCP) of (E)-4-oxobut-2-enoic acid with two different isocyanides at room temperature and the subsequent hydrogenation. The trans-double bond in the monomer was designed to inhibit the formation of five-membered lactone and promote the polymerization. Two different side groups were incorporated into the side chains of the polyesters by varying the isocyanide component. All the polymers were thoroughly characterized by a variety of methods. Degradation of the polyester under acidic and neutral conditions was investigated by 1H NMR and GPC. In both cases head-to-tail degradation via intramolecular cyclization by the attack of the hydroxyl end group to the ester carbonyl moiety occurred and yielded a nonacidic γ-butyrolactone derivative as the single degradation product. On the basis of control experiments with small model compounds and other types of polyester, we proposed the degradation mechanism. In acidic condition, random scission of the ester group occurred simultaneously at a much slower rate than that of the head-to-tail degradation, while in neutral condition, random scission did not occur and the polymers degraded in a controllable unzipping depolymerization manner.

Synthesis and molecular structure of the 1-phenyl-2-(2-pyridyl)ethanol intermediate obtained from the condensation reaction of 2-picoline and benzaldehyde

The 1-phenyl-2-(α-pyridyl)ethanol [or 1-phenyl-2-(2-pyridyl)ethanol] compound was obtained from the Knoevenagel condensation reaction between 2-methylpyridine with benzaldehyde without catalyst or solvent. The compound was characterized by IR, 1H-NMR, and by single crystal X-ray diffraction. The X-ray structure clearly revealed that the compound crystallizes in a monoclinic system with centrosymmetric space group, P21/c, with Z′ = 1. The unit cell dimensions are a = 5.2481(3), b = 8.2862(4), c = 23.8498(14) A, and β = 96.761(5)°. The crystal structure showed the formation of one intermolecular hydrogen bond O–H···N between the oxygen atom of the O–H and the nitrogen atom of the pyridine group of the adjacent molecule. The crystallography data gave evidence that the intermediate compound is a new stable 1-phenyl-2-(2-pyridyl)ethanol intermediate which presents an interesting relationship between stability and hydrogen bonds formation in the structure for obtaining similar compounds that have been proposed in the literature. Also, it is shown that it is just before the dehydration process which yields the trans double bond of the 1-phenyl-2-(2-pyridyl)ethene.

J-TYPE DIPOLE STACKING AND STRONG π-π INTERACTIONS IN THE CRYSTALS OF DISTYRYLBENZENE DERIVATIVES: THE CRYSTAL STRUCTURES, HIGH LUMINESCENCE PROPERTIES AND PREDICTION OF HIGH MOBILITY

The crystal structures of three analogs of trans-DPDSB (2,5-diphenyl-1,4-distyrylbenzene with two trans double bonds) are very similar to that of rubrene, which have face-to-face molecular packing mode with relative displacement along the molecular long axis. The very strong intermolecular π-π interactions enable the crystal to have the potential of high charge-carrier mobility predicted by the theoretical calculations. Most important, the crystals of these materials have very high photoluminescence (PL) efficiency of about 50% due to the J-type dipole stacking, which is different from the crystal of rubrene. The crystal structures give the prediction of combining both high luminescence and high mobility in one crystal by constructing J-type dipole stacking with strong π-π interactions.

Polymeric microstructures and dielectric properties of polynorbornenes with 3,5-bis(trifluoromethyl)biphenyl side groups by ring-opening metathesis polymerization

exo-Polynorbornenes containing bis(trifluoromethyl)biphenyl side groups were synthesized by ring-opening metathesis polymerization using different Grubbs' catalysts, the microstructures of the polymer chains were established using NMR and IR spectroscopy. The influence of monomer and catalyst structures on chain microstructure was revealed and the correlation of properties with microstructure was investigated in detail. The exo-poly(N-3,5-bis(trifluoromethyl)biphenyl-norbornene-pyrrolidine) (exo-PTNP) and exo-poly(N-3,5-bis(trifluoromethyl)biphenyl-norbornene-dicarboximide) (exo-PTNDI) formed using Ru-I show a trans double bond bias of 67% and 83%, respectively, whereas the corresponding polymers formed using Ru-III have lower contents of trans double bond, 30% and 50%, respectively. Compared to the highly trans endo-PTNP formed using Ru-I, which is isotactic and has a dielectric constant of about 20, the endo-PTNP formed using Ru-III, the exo-PTNDIs and the exo-PTNPs formed using Ru-I and Ru-III all have different proportions of trans and cis double bonds, they are atactic and display relatively low dielectric constants, in the range 6 to 9. DSC measurements indicate some dependence of Tg, varying 161 to 221 °C, on tacticity and cis/trans ratios with higher trans contents tending towards higher Tg. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4786–4798