Formation Of Trans Isomers Research Articles

Thermal Degradation of Fatty Acids in Biodiesel Production by Supercritical Methanol

In this study, thermal degradation of the fatty acids of sunflower seed oil during biodiesel production by supercritical methanol method was investigated. The term biodiesel means the monoalkyl esters of long chain fatty acids made from biolipids such as vegetable oils, animal fats, tall oil or algae oils. The oils and fats contain polyunsaturated fatty acid chains that their double bonds have highly chemical reactivity. The thermal degradation occurs on the double bonds of unsaturated aliphatic carbons chains in fatty acids. Oxidation of biodiesel is results in the formation of hydroperoxides. The formation of the hydroperoxide follows a well known peroxidation chain mechanism. The olefinic unsaturated fatty acid oxidation is a multi-step reaction process where primary products decompose and chemically interact with each other to form numerous secondary oxidation products. The content of linoleic acid in the sunflower seed oil is 72.4%, while the linoleic acid account for 62.5% of the total fatty acids in the biodiesel. The proportion of the linoleic acid is lower in the biodiesel obtained by supercritical methanol transesterfication method. The viscosity of biodiesel increases with increasing of thermal degradation degree due to the trans isomer formation on double bonds. The decomposition of biodiesel and its corresponding fatty acids linearly increases from 293 K to 625 K. The densities of biodiesel fuels decreased linearly with temperature from 293 K to 575 K. The combustion heat of biodiesel partially decreases with increasing of thermal degradation degree.

Conformational Behavior of N-Acylamino Acid Oil and N-Acylamino Acid Surfactant in Aqueous Solution

The (13)C- and (1)H- NMR spectra of isopropyl N-dodecanoylsarcosinate (SLIP) were measured in CDCl(3), CD(3)OD and in sodium dodecanoylsarcosinate (Sar) aqueous solution. The existence of both cis and trans isomeric forms are observed for SLIP just as for Sar. The trans/cis ratio of SLIP in a dilute CDCl(3) solution is over 3.2, which is indicating that SLIP-trans conformation is more stable in an organic solvent. However, the population of SLIP-trans isomer decreases in aqueous solutions. This may be explained by the interaction of the ester group and N-acyl chain. Addition of SLIP to the water/Sar solution causes the conformational change of both SLIP and Sar. With increasing SLIP concentration, the population of SLIP-trans isomer increases and Sar-cis isomer, which is known to be preferred in the monomer state, also increases. This phenomenon is discussed in the context of the phase transition behavior of SLIP/Sar/water system. At high SLIP and Sar concentration, broadening of (1)H signal relative to 2-CH(2) of Sar occurs both for trans and cis forms, however, broadening of that of Sar N-CH(2) and N-CH(3) is observed only for trans. Analysis of conformation change by NMR was proved to be useful method for phase behavior analysis of an acylamino acid surfactant.

Comparison of two palladium catalysts on different supports during hydrogenation

AbstractSoybean oil was hydrogenated using two different palladium‐based catalysts, 5% palladium on carbon (Pd/C) and 10% palladium on alumina (Pd/A), at various ratios in a 4‐L reactor under constant conditions (165°C, 2 bar H2, and 500 rpm stirring rate). Reaction rate, trans isomer formation, selectivity ratios, and melting behaviors of the samples were monitored. Activity of Pd/C was about 10 times higher than that of Pd/A, and the reaction rate showed a strong dependency on the support material. Increases in the concentrations of both Pd catalysts did not have considerable effect on trans formation, which is slightly dependent on support material. Oleate selectivity (S21) for all runs varied between 2.48 and 30.34, and type of support material did not have an effect on selectivity. Melting behaviors of the samples were mainly dependent on reaction rates.

Synthesis, Cytotoxic Effect, and Structure−Activity Relationship of Pd(II) Complexes with Coumarin Derivatives

We report the influence of the substituent at the N atom of the ligands on the synthesis, biological activity, and stability of Pd(II) complexes of the general formula PdL(2). The compounds adopt a cis or trans configuration with respect to the substituent at the nitrogen atom. Sterically hindered substituents promote the formation of trans isomers, whereas when the nitrogen atom is unsubstituted, cis isomers are formed. The compounds were characterized by elemental analysis, infrared and 1H NMR spectroscopies, and electrospray mass spectrometry. The complexes were also studied using X-ray diffraction and computational DFT methods. Both complexes cis-3a and trans-3c exhibit square-planar geometries around the Pd(II) atom. The cytotoxic effects of these complexes were examined on two human leukemia cell lines, HL-60 and NALM-6. Pd complex cis-3a showed significant cytotoxic activity. The effects exhibited by this complex were comparable to those reported for carboplatin. Loigand 2a was not cytotoxic. Computational analysis carried out at the PB/B3LYP/LACVP**//mPW1PW91/LanL2DZ level showed excellent correlation between the energy difference of the cis and trans isomers and the cytotoxic activity, rendering computations a useful predictive tool for the design of new drugs.

Monitoring of hydrogenation with various catalyst ratios

AbstractSoybean oil was hydrogenated using two different nickel‐based commercial catalysts (Nysosel 222 and SP‐10) at various ratios in 4‐L reactors under constant conditions (165°C, 2 bar hydrogen pressure, and 500 rpm stirring rate). Trans isomer formation, reaction rates, selectivity (S) ratios, and melting behaviors of the samples were monitored during the reactions. When Nysosel 222 was used at 0.02, 0.03, and 0.04%, iodine values (IV) were reduced from 130.1 to 70.6, 50.9, and 44.7 and total trans isomers increased from 0 to 34.2, 43.3, and 40.5%, respectively, after 100 min of hydrogenation. However, SP‐10 reduced IV from 130.1 to 77.2, 75.7, and 71.3 after 100 min when used at 0.1, 0.15, and 0.2%, respectively, whereas total trans isomers were 58.6, 70.4, and 70.7%. Reaction rates increased with catalyst ratio and time but were higher for Nysosel 222 than for SP‐10 although 5–10 times less Nyosel 22 was used than SP‐10. Linoleate selectivity (S32) was almost constant for Nysosel 222, whereas it was higher but fell with time for SP‐10. Increasing the catalyst ratio decreased the time needed to reach the highest oleate selectivity (S21) ratios, and the IV values where the highest S21 were attained were different for the catalysts. Increases in m.p. of SP‐10 samples were slower after IV values of 80 were attained, where S21 ratios reached to higher values. Solid fat contents (SFC) of these samples fell markedly above 21.1°C, and steeped SFC curves were obtained.

Protective effect of —A marine micro alga, against carbon tetrachloride-induced hepatotoxicity in rats

This is the first report on the hepatoprotective potentials of marine micro algae Dunaliella species. Dunaliella salina, halotolarent green alga was cultivated in modified autotrophic medium. The alga was subjected to light and nutrient stress in order to accumulate (beta-carotene along with other carotenoids. Such beta-carotene enriched yellow cells were fed to rats by mixing with regular feed at the dose of 2.5 and of 5.0gkg(-1) b.w. for 2 weeks. The degree of hepatoprotection was measured up on challenging animals with toxin (2.0gkg(-1) of carbon tetrachloride) by estimation of biochemical parameters like, serum transaminases (serum aspartate transaminase (S)AST and serum alanine transaminase (S)ALT), serum alkaline phosphatase and total protein. The results were compared to animals on normal diet and with group fed with 100mugkg(-1) b.w. of standard all trans beta-carotene. Among the three test groups the group fed with algae of 5.0gkg(-1) body weight, showed maximum protection. The levels of (S)AST and (S)ALT was found to be 61.3+/-6.4 and 80.7+/-5.6%, against 90.8+/-10.5 and 144.7+/-13.9% in case of standard beta-carotene. The protein contents were increased in case of control to 6.1+/-0.7 and the same was found to be significantly less in case of 5.0gkg(-1)Dunaliella fed group, which shown 5.6+/-0.8% total protein. However, the activity of 2.5gkg(-1) was also significant comparatively (P<0.05). The results indicate that Dunaliella, which contains isomeric forms of beta-carotene can act as good antihepatotoxic when compared to synthetic all trans beta-carotene. Dunaliella has shown the presence of both cis and trans isomeric forms of beta-carotene, where as synthetic compounds contain only trans isomer. Hepatoprotectivity may be due to presence of various isomeric forms of carotene and other oxygenated carotenoids (xanthophylls) in algae.

Otimização da reação de interesterificação química do óleo de palma

The Brazilian market has been showing a growing concern with nutritional values of oil components of foods. Chemical interesterification is a promising alternative to the current processes of modifying the consistency of oils. Chemical interesterification of deodorized palm oil was studied on a laboratory scale. The best results were obtained with 0.4% MeONa and heating for 20 min at 100 °C. These conditions are based on the largest variation in triacylglycerols as compared to a control. The trisaturated values varied from 6.2 to 9.9%, showing that the consistency of the oil improved for it to be used in margarines, without the formation of trans isomers.

The Study of cis-trans Equilibrium and Complexation with DNA of meso-Substituted Carbocyanine Dyes

The effect of DNA was studied on cis-trans equilibrium and spectral and fluorescent properties of a number of meso-substituted carbocyanine dyes: 3,3′-diethyl-9-thiomethylthiacarbocyanine iodide (K1), 3,3′-diethyl-9-methoxythiacarbocyanine iodide (K2), 3,3′-9-triethylthiacarbocyanine iodide (K3), 3,3′-dimethyl-9-ethyloxacarbocyanine iodide (K4), 3,3′-9-triethyl-5,5′-dimethyloxacarbocyanine iodide (K5), and 3,3′,9-triethyl-6,6′-dimethoxyoxacarbocyanine iodide (K6). Equilibrium between the cis and trans isomeric forms was detected for the thiacarbocyanine dyes in a number of organic solvents, with a shift of the equilibrium toward the cis-isomer caused by an increase in the solvent polarity. The oxacarbocyanines are present only in the form of trans-isomers in both polar and nonpolar solvents. Interaction of the dyes with DNA leads to the formation of stable noncovalent complexes. The complexation of the thiacarbocyanine dyes results in a shift of the isomeric equilibrium and occurs predominantly via the cis-form of the dye. The oxacarbocyanine dyes produce complexes with DNA in the initial trans-form.

Trans lipid formation induced by thiols in human monocytic leukemia cells

Trans lipids in humans originate exogenously from the ingestion of isomerized fats. An endogenous path comprising a thiyl radical-catalyzed cis– trans isomerization of cis-unsaturated phospholipids was proposed. However, whether an isomerization process might be feasible in eukaryotic cells remained to be established. Here we report the presence of trans lipids in human monocytic leukemia cell membranes (THP-1) before and after treatment with a 10 mM series of thiols. Oleic, linoleic, and arachidonic acid residues of membrane phospholipids were analyzed and, unexpectedly, an initial trans lipid content was found in control cells. Then, incubation for 24 h with thiols under physiological conditions slightly increased trans lipid content. Formation of trans isomers was also evaluated in the presence of thiol and under free radical stress induced by γ-irradiation or by thermal decomposition of azo-compounds. The similarity of isomer trends formed under incubation and stress conditions, together with the reactivity order of fatty acid residues (arachidonic > linoleic ≈ oleic), indicated a common radical path and some mechanistic considerations are advanced. These results offer the first evidence that trans lipids are formed in eukaryotic cells and confirm that thiyl radicals are harmful to the integrity of cis lipid geometry. This work motivates further studies into the relationship between lipid isomerization outcome and thiyl radicals in cellular systems, as well as the formation of trans lipids and the metabolic response to such a perturbation introduced into biological membranes.

Cis and trans conformations in 3-substituted thietane-1-oxide

For a series of 3-substituted-thietane-1-oxide (3-R-TOX) derivatives (R=chloro, methyl, ethyl, acetate, t-buthyl, phenyl and p-chlorophenyl), the cis⇔ trans isomerization reactions have been theoretically studied in the frame of molecular orbital theory. Optimized geometries have been obtained at HF/6-31G** level, whereas the energetics and thermodynamics were calculated with basis sets that include polarization, diffuse functions and electron correlation at the second-order Møller–Plesset perturbation theory. The size and nature of the substituent seems to exert no influence on the structure of the thietane-1-oxide ring. Gas phase thermodynamics predict the cis isomers to be the preferred structure in these compounds as a result of the H10⋯O9 non-bonded interaction. The exception to this trend are the chloro and acetate derivatives where a 14 and 46% of the trans isomer, respectively, is predicted. In CCl 4 solution, the isomerization reaction would take place in large extent. The calculated 1H-NMR chemical shifts correlate well with the experimental data and demonstrate that the β-protons (H10) are magnetically sensible enough to allow the cis and trans isomeric forms to be distinguished. The β-protons chemical shifts calculated in CCl 4 do not differ appreciably from the gas phase values. The 17O-NMR signals have also been derived and the potentiality of this nucleus to be used to assign the preferred geometry as well as to follow the isomerization reaction, in this kind of compounds is pointed out. The present work also indicates that the S O stretching mode can be used to assign either a cis or trans conformation in these species, though this vibrational mode is strongly coupled with some ring and H–C–H angle deformation modes.

Neural network modeling of trans isomer formation and unsaturated fatty acid changes during vegetable oil hydrogenation

A multi-layer neural network model with back-propagation training algorithms was designed to predict total trans isomer content, as well as oleic acid, linoleic acid and linolenic acid during vegetable oil hydrogenation. Eight variables including reaction temperature, H 2 pressure, catalyst concentration, mixing rate, iodine value, and initial unsaturated fatty acid contents including oleic, linoleic, and linolenic acid have strong effects on forming trans isomer which is produced during vegetable oil hydrogenation. So the eight variables were considered as independent variables and used as inputs to the Artificial Neural Network (ANN) model. The neural network was trained, tested, and evaluated by use of a large number of experimental data obtained from a pilot-plant hydrogenation reactor and using experimental data of a published paper the network generalization was evaluated. Experimental data were statistically compared with predicted results such that the network predictability was assessed. Statistical assessments showed a very good agreement of predicted and observed results.

Altered lipid cell membrane profile in children affected by atopic dermatitis

Rationale An abnormal essential fatty acid (EFAs) metabolism and a higher unsaturated trans FA (TFA) levels have been associated with allergy suggesting a link between fatty acid (FA) structures and atopic diseases. The aim of the present study was to correlate the atopic status with FA profile and TFA presence in cell membrane. Methods We studied the erythrocyte and T lymphocyte membranes obtained from 10 children affected by atopic dermatitis (AD). Total phospholipid fractions were analyzed by an innovative protocol made of two parallel gas chromatography (GC) analysis which include the cis/trans isomer identification of FA. Results In all patients the saturated/monounsaturated FA (SFA/MUFA) ratio was higher than normal range (1.7-2). The percentage of arachidonate 20:4 FA was normal but, in 3 patients, it was replaced by 20:3. The GC profile of C20 FA, compared with the profile of arachidonate isomerization, showed the presence of trans isomers at high levels . Moreover, trans isomer of oleic acid residues was also found in 50% of the patients and 20:5 (EPA) and 22:6 (DHA) FA were very low or absent in all the patients. Conclusions In erythrocyte and T cell membranes of our AD children a serious impairment of lipid metabolism was observed, consistent with a reduced rate of activity of delta 6 desaturase. The altered SFA/MUFA ratio together with the higher percentage of the trans isomeric forms might affect membrane structure or fluidity and consequently lead to an alteration of the immune receptor complexes within the lipid microdomains (rafts).

Phosphorus(V) Porphyrin−Azoarene Conjugates: Synthesis, Spectroscopy, cis−trans Isomerization, and Photoswitching Function

A series of photochemically active, “axial-bonding” type phosphorus(V) porphyrin−azoarene (P−A) conjugates, viz., [(TTP)PV(-O-AZM)2]+, [(TTP)PV(-O-AZT)2]+, [(TTP)PV(-O-AZB)2]+, and [(TTP)PV(-O-AZN)2]+ (TTP is 5,10,15,20-tetra(4-methylphenyl)porphyrinato dianion and O-AZM, O-AZT, O-AZB, and O-AZN are the axially coordinated 4-methoxy azophenoxo, 4-methyl azophenoxo, azophenoxo, and 4-nitro azophenoxo ligands, respectively) have been synthesized and fully characterized by mass (FAB), infrared, UV−visible, proton nuclear magnetic resonance (1D and 1H-1H COSY), and electrochemical methods. The spectroscopic data suggest that the two azoarene subunits in these hexa-coordinated systems exist in their trans isomeric forms and that there is minimal ground-state interaction between the axial ligands and the basal porphyrin π plane in each case. Continuous irradiation of CH3CN solutions containing these new P−A conjugates at 345±5 nm results in isomerization of the phosphorus-bound azoarene subunits to produce the ...

Complexation of 3-(2-pyridyl)substituted N-methyl isoxazolidine with Pd(II), Zn(II) and Cu(II): stereochemistry of co-ordination compounds in solution and solid-state

2-Methyl-3-(2-pyridyl)isoxazolidine ( L) and its Pd(II), Zn(II) and Cu(II) complexes have been prepared and characterized by IR, 1H, 13C 1D and HMBC, NOESY 2D NMR spectroscopies. The stereochemistry of the ‘free’ and co-ordinated ligand has been assigned by nuclear Overhauser effect (NOE). The molecular structures of [Zn( cis- L)Cl 2]·0.5CHCl 3 ( 2a), [Zn( cis-/ trans- L)Cl 2] ( 2a– b) and [Cu( cis-/ trans- L)Cl 2] 2 ( 4a– b) have been established by means of X-ray crystallography. The crystal structure of 2a consists of a racemic mixture of cis- L (3 SR,5 RS), while the crystal structure of 2b comprises a racemate of cis- and trans-isomeric forms. For both complexes the zinc atoms adopt nearly tetrahedral co-ordination with two chlorine atoms and N, N-bidentate co-ordinated L. The crystal structure of 4a– b consists of dinuclear [Cu( cis-/ trans- L)Cl 2] 2 moieties with N, N-bidentate co-ordinated ligands. The square pyramidal co-ordination spheres of copper ions are completed by a bridging chloride ligand at the apex (CuCl 2.79, 2.82 Å).

Rational design and synthesis of novel 2,5-disubstituted cis- and trans-piperidine derivatives exhibiting differential activity for the dopamine transporter

Herein, we report the rational design and synthesis of novel 2,5-disubstituted piperidine derivatives in the cis and trans isomeric forms. Out of these two isomers, the cis-isomer, 7a, was found to exhibit the most potent activity and selectivity for the dopamine transporter. These novel derivatives represent conformationally constrained version of piperidine analogue of GBR compounds.

Molecular modeling of the olefin metathesis by tungsten(0) carbene complexes

Density functional and second-order Moller–Plesset theory were used to model W(0) carbene mediated homogeneous metathesis reaction of propylene. The calculations show that the rate determining step of the metathesis is the initiation. After the initiation has been completed the rate determining step becomes dissociation of olefin–metallocarbene complex. The low stereoselectivity of the olefin metathesis reaction is due to the close matching of activation energies for cis and trans isomer formation and the fast cis– trans isomerization caused by the catalysts. The non-productive olefin metathesis reaction always dominates the reaction mixture owing to its very low activation energy. The electronic structure of metal carbene olefin complexes can be described as a combination of donor–acceptor interactions between HOMO of the olefin and LUMO of metal carbene located at carbene carbon on the one hand, and the Dewar, Chatt and Duncanson back donation scheme on the other.

Selective hydrogenation of sunflower seed oil in a three‐phase catalytic membrane reactor

AbstractContinuous hydrogenation of sunflower seed oil has been carried out in a novel three‐phase catalytic membrane hydrogenation reactor. The membrane reactor consisted of a membrane impregnated with Pd as the active catalyst, which provided a catalytic interface between the gas phase (H2) and the oil. Hydrogenations were carried out at different pressures, temperatures, and selectivities, and the formation of trans isomers was monitored during the hydrogenation runs. For the three‐phase catalytic membrane reactor, interfacial transport resistances and intraparticle diffusion limitations did not influence the hydrogenation reaction. Hydrogenation runs under kinetically controlled conditions showed that oleic and elaidic acid were not hydrogenated in the presence of linoleic acid. Initial formation of stearic acid was caused by direct conversion of linoleic acid into stearic acid by a shunt reaction. Furthermore, high selectivities led to high trans levels, which is in accordance with the many published data on hydrogenation of vegetable oils in slurry reactors. Finally, the catalytic membrane showed severe catalyst deactivation. Only partial recovery of the catalyst activity was possible.

Hydrogenation of palm olein catalyzed by polymer stabilized Pt colloids

Polyvinylpyrolidone stabilized Pt colloids with different polymer: Pt ratios with average particle sizes of between 1.4 and 2.9 nm and narrow size distribution were found to be active for the hydrogenation of palm olein at 35°C and atmospheric pressure. The initial hydrogen consumption rate was high, corresponding to the hydrogenation of the linoleate and slowed down thereafter, corresponding to the oleate hydrogenation. The rate constants for the two competing reactions were determined and the selectivity calculated to be between 10 and 100. The particle size of the Pt clusters influences the rate of the diene much more significantly than the monoene. The smaller the average particle size, the higher is the rate for the diene and hence the higher the selectivity. The trans-isomer formation was comparative low and was found to be a consequence of the partial saturation of the diene rather than the isomerization of the monoene.

Theoretical Study of the Low-Lying Electronically Excited States of Diacetylene

The complete-active-space SCF and CASMP2 methods are used to characterize the low-lying excited singlet and triplet states of diacetylene. With the exception of the 1 1Δu state, all excited states considered are found to have geometrical structures distorted away from linear. Three of the triplet states are predicted to have non-planar C2-symmetry structures. The other states are predicted to be planar, existing as both cis (C2v) and trans (C2h) isomeric forms. Vibrational frequencies are calculated for the low-lying electronically excited states, and vertical and adiabatic excitation energies are reported.

Spectroscopy and IVR in the S1 State of Jet-Cooled p-Alkoxyphenols

Vibronic spectroscopy and intramolecular vibrational relaxation studies were carried out on jet-cooled hydroquinone, p-methoxyphenol, and p-ethoxyphenol using laser-induced fluorescence measurements. The cis and trans isomeric forms of all three compounds exist even under jet-cooled conditions. Hole-burning spectroscopy was used to separate the transitions due to each of them. Vibrational assignments were made with the help of dispersed fluorescence spectra after single vibronic excitations. The fluorescence spectra were also used to deduce the onset of mode mixing, a precursor to IVR. The IVR onset in the case of hydroquinone was quite high, i.e., 1650 cm-1, and it decreased substantially in p-methoxyphenol. It did not decrease any further for p-ethoxyphenol. One of the objectives of this study was to compare the IVR behavior in this series to that in p-alkoxyanilines, or more specifically, to compare the effect of the presence of an −OH group vs an −NH2 group in the para position on IVR.