Stereochemistry of the hydroperoxides formed during autoxidation of CLA methyl ester in the presence of α-tocopherol

The initial steps in the autoxidation of CLA methyl ester are poorly understood. The aim of this study was to determine the stereochemistry of the hydroperoxides formed during autoxidation of CLA methyl ester in the presence of a good hydrogen atom donor. For this purpose, 9-cis, 11-trans CLA methyl ester was autoxidized in the presence of α-tocopherol under atmospheric oxygen at 40°C in the dark. The CLA methyl ester hydroperoxides were isolated, reduced to the corresponding hydroxy derivatives, and separated by HPLC. The stereochemistry of seven hydroxy-CLA methyl esters was investigated. The position of the hydroxy group was determined by GC-MS. The geometry as well as the position of the double bonds in the alkyl chain was determined by NMR. In addition, the ¹³C NMR spectra of six hydroxy-CLA methyl esters were assigned using COSY, gradient heteronuclear multiple bond correlation, gradient heteronuclear single quantum correlation, and total correlation spectroscopy experiments. The autoxidation of 9-cis, 11-trans CLA methyl ester in the presence of a good hydrogen atom donor is stereoselective in favor of one geometric isomer, namely the 13-(R,S)-hydroperoxy-9-cis, 11-trans-octadecadienoic acid methyl ester. Three types of conjugated diene hydroperoxides are formed as primary hydroperoxides: trans,trans hydroperoxides (12-OOH-8t,10t and 9-OOH-10t,12t), a cis,trans hydroperoxide with the trans double bond adjacent to the hydroperoxide-bearing carbon atom (13-OOH-9c,11t), and a new type of cis,trans lipid hydroperoxide with the cis double bond adjacent to the hydroperoxide-bearing carbon atom (8-OOH-9c,11t). In addition, three nonkinetic hydroperoxides (13-OOH-9t,11t, 8-OOH-9t,11t, and 9-OOH-10t,12c) are formed. This study supports the theory that CLA methyl ester autoxidizes at least partly through an autocatalytic free radical reaction. The complexity of the hydroperoxide mixture is due to formation of two different pentadienyl radicals. Moreover, the stereoslectivity in favor of one geometric isomer can be explained by the selectivity of the two previous steps: the preferential formation of a W-conformer of the pentadienyl radical over the Z-conformer, and regioselectivity of the oxygen addition to the pentadienyl radical.     

Effects of α-tocopherol and ascorbyl palmitate on the isomerization and decomposition of methyl linoleate hydroperoxides

In order to study antioxidant action on lipid hydroperoxide decomposition, the effects of α-tocopherol (TOH) and ascorbyl palmitate on the decomposition rate and reaction sequences of 9- and 13-cis,trans methyl linoleate hydroperoxide (cis,trans ML-OOH) decomposition in hexadecane were studied at 40°C. Decomposition of cis,trans ML-OOH as well as the formation and isomeric configuration of methyl linoleate hydroxy and ketodiene compounds were followed by high-performance liquid chromatographic analysis. TOH effectively inhibited the decomposition of ML-OOH. The decomposition rate was two times slower at 0.2 mM and more than 10 times slower at 2 and 20 mM of TOH. Ascorbyl palmitale (0.2, 2, and 20 mM) slightly accelerated the decomposition of ML-OOH. Both compounds had an effect on the reaction sequences of ML-OOH decomposition. At high levels TOH inhibited the isomerization of cis,trans ML-OOH to trans,trans ML-OOH through peroxyl radicals and increased the formation of hydroxy compounds. Further, the majority of the hydroxy and ketodiene compounds formed had a cis,trans configuration, indicating that cis,trans ML-OOH decomposed through alkoxyl radicals without isomerization. These results suggest that when inhibiting the decomposition of hydroperoxides, TOH can act as a hydrogen atom donor to both peroxyl and alkoxyl radicals. In the presence of ascorbyl palmitate, cis,trans ML-OOH decomposed rapidly but without isomerization. In contrast to TOH, the majority of hydroxy compounds were cis,trans, but the ketodiene compounds were trans,trans isomers. This indicates that ascorbyl palmitate reduced cis,trans ML-OOH to the corresponding hydroxy compounds. However, the simultaneous formation of trans,trans ketodiene compounds suggests that ML-OOH decomposition, similar to the control sample, also occurred in these samples. Thus, under these experimental conditions, the reduction of ML-OOH to more stable hydroxy compounds did not occur to an extent significant enough to inhibit the radical chain reactions of ML-OOH decomposition.     

Preparation of poly(methyl methacrylate) macromonomer by radical polymerization in the presence of methyl α-(bromomethyl)acrylate and copolymerization of the resultant macromonomer

Radical polymerization of methyl methacrylate (MMA) in the presence of methyl -(bromomethyl) acrylate yielded poly-(MMA) bearing the 2-methoxycarbonylallyl end group through chain reaction involving bimol ecular termination. The molecular weight of the resultant polymer was effectively controlled with a small amount of the bromomethylacrylate added; the chain transfer constant was estimated to be 0.9. The poly (MMA) with the unsaturated end group (

Isomerization of α-pinene oxide in the presence of methyltrioxorhenium(VII)

The catalytic performance of methyltrioxorhenium(VII) (MTO) has been investigated for the first time in the isomerization of α-pinene oxide (PinOx) into campholenic aldehyde (CPA). The high isomerization activity of MTO is coupled with high selectivity to CPA: CPA yield of up to 87% (100% conversion) was obtained by using α,α,α-trifluorotoluene as solvent at 15 °C. Catalyst recycling is possible in a relatively simple fashion by using MTO coupled to an appropriate ionic liquid. The catalytic application of MTO in the isomerization of PinOx versus the integrated epoxidation–isomerization process of the conversion of α-pinene into CPA is discussed.     

Hydrolysis of methyl α- and β-D-glucopyranosides in the presence of a dealuminated H-Y faujasite

Hydrolysis of methyl α- and β-D-glucopyranosides was performed in the presence of protonic-form zeolites such as a dealuminated Y-faujasite with a Si/Al ratio of 15, at temperatures ranging between 100 and 150°C, and in water as the solvent. The β/α ratio for the hydrolysis reaction rates was found to be equal to 5–6, whereas a ratio of 2–3 was reported in the literature for the homogeneous reaction. The observed higher β/α ratio is proposed to result from the reinforcement of stereoelectronic effects which were shown to apply in reactions taking place on the surface of a solid. Those effects operate in a classical manner on a molecular standpoint, but they are reinforced due to the favorable interaction of oxygen electron lone pairs with the electron-deficient species present on the surface of the solid, protonic species in the case of zeolites. This revised version was published online in August 2006 with corrections to the Cover Date.     

A rigorous kinetic model for β-carotene oxidation in the presence of an antioxidant, α-tocopherol

Oxidation of β-carotene in an inert solvent, n-decane, in the presence of various concentrations of the antioxidant α-tocopherol was studied. The progress of carotene oxidation was suppressed as long as the tocopherol remained in the system. A rigorous kinetic model for carotene oxidation in the presence of an antioxidant was proposed based on a reaction mechanism in which not only the antioxidation but also the co-oxidation and radical-exchange reaction of tocopherol with carotene were incorporated. The model quantitatively described the oxidation behavior of carotene over a wide range of temperatures, oxygen compositions, and initial antioxidant concentrations.     

Fourier transform infrared spectroscopy evaluation of low density lipoprotein oxidation in the presence of quercetin,catechin, and α-tocopherol

We investigated the changes in human LDL primary and secondary lipid oxidation products and modification of the apolipoprotein B-100 (apoB-100) secondary structures during Cu²⁺-mediated oxidation by FTIR spectroscopy in the presence of catechin, quercetin, and α-tocopherol at physiological concentrations. Catechin- and quercetin-containing samples had slower rates and longer lag phases for conjugated diene hydroperoxide (CD) formation than α-tocopherol-containing samples; however, all antioxidant-treated LDL samples generated similar CD levels (P<0.05). A lower maximum (98.4 nmol/mg LDL protein) of carbonyl compounds was produced in the quercetin- and catechin-treated samples than in α-tocopherol samples. Modification of the apoB-100 secondary structures corresponded closely to the formation of carbonyls and was hampered by the presence of antioxidants. Physiological concentrations of catechin and quercetin offered similar levels of protection against modification by carbonyls of the apoB-100 at advanced stages (carbonyls ∼96.0 nmol/mg LDL protein) but not at the intermediate stages (carbonyls ∼58.0 nmol/mg LDL protein) of LDL oxidation probably owing to differences in the protein-binding mechanisms of catechin and quercetin. Relationships between peroxide formation, carbonyl products, and LDL protein denaturation were shown by the FTIR approach. The FTIR technique provided a simple new tool for a comprehensive evaluation of antioxidant performance in protecting LDL during in vitro oxidation.     

A spectroscopic analysis of conformational distortion in the α′ phase of poly(lactic acid)

Simulations in conjunction with Raman scattering were performed to determine the conformational distortion of the α′ form of poly(lactic acid) (PLA). Based on packing constraints of an overall helical structure, the chain conformation can only be approximated by slight deviations from a tg’t chain conformation. Models were generated with different types of random departures from the expected dihedral angles. Raman active vibrations in the 700 cm⁻¹ region that are sensitive to changes in chain conformation were analyzed. The model that showed the best fit to the experimental data contains a majority (80%) of tg’t-10₃ sequences with randomly distributed tg’t-3₁ units. Departure of the O-C_α dihedral angle was also proved. The mechanism of order formation was established. As PLA chains crystallize at low temperatures, only the α′ phase with a disordered helix can be formed which at elevated temperatures can transform to the more ordered α phase. The conformation distortion is then due to the inability for some chains to complete the transition to 10₃ helicity, thus resulting in the formation of the distorted α′ structure.     

Synthesis of cyclic poly(methyl methacrylate) by the intramolecular cyclization of α-amino, ω-carboxyl heterodifunctional poly(methyl methacrylate)

Summary α-Amino, ω-carboxyl heterodifunctional poly(methyl methacrylate) was prepared by a living anionic polymerization of methyl methacrylate using N,N'-diphenylethylenediamine monolithium amide and succinic anhydride as an initiator and terminator, respectively. Its intramolecular cyclization was carried out to obtain a well-defined cyclic poly(methyl methacrylate). Received: 27 June 2001/Accepted: 16 July 2001     

Regulation of the α-tocopherol transfer protein in mice: Lack of response to dietary vitamin E or oxidative stress

The α-tocopherol transfer protein (TTP) plays an important role in the regulation of plasma α-tocopherol concentrations. We hypothesized that hepatic TTP levels would be modulated by dietary vitamin E supplementation and/or by oxidative stress. Mice were fed either a High E (1150 mg RRR-α-tocopheryl acetate/kg diet) or a Low E (11.5 mg/kg diet) diet for 2 wk. High E increased plasma and liver α-tocopherol concentrations approximately 8- and 40-fold, respectively, compared with Low E-fed mice, whereas hepatic TTP increased approximately 20%. Hepatic TTP concentrations were unaffected by fasting (24 h) in mice fed either diet. To induce oxidative stress, chow-fed mice were exposed for 3 d to environmental tobacco smoke (ETS) for 6 h/d (total suspended particulate, 57.4±1.8 mg/m3). ETS exposure, while resulting in pulmonary and systemic oxidative stress, had no effect on hepatic α-tocopherol concentrations or hepatic TTP. Overall, changes in hepatic TTP concentrations were minimal in response to dietary vitamin E levels or ETS-related oxidative stress. Thus, hepatic TTP concentrations may be at sufficient levels such that they are unaffected by either modulations of dietary vitamin E or by the conditions of environmentally related oxidative stress used in the present studies. The first and second investigators contributed equally to this work.     

Impedance spectroscopic investigation of the interactions between phosphatidylethanolamine and α-tocopherol in bilayer membranes

Electric capacity and electric conductance of lipid membranes composed of phosphatidylethanolamine and α-tocopherol were determined by electrochemical impedance spectroscopy. These components were chosen for the study because they are present in biological membranes and they fulfill essential functions in lively organisms. A domain structures appear as a result of phosphatidylethanolamine-α-tocopherol membrane formation. Formation of the domains can explain the deviation from the additivity rule. This equilibrium was described by mathematical equations and was further verified experimentally. Based on the derived equations, the surface area of domain was calculated; it amounts to 320 Å². This value is consistent, taking into consideration ordering and condensation effects of α-tocopherol on the phosphatidylethanolamine, with a stoichiometry of such a domain equal to 4:1.     

Effects of liquid–liquid phase separation on crystallization of poly(ethylene glycol) in blends with isotactic poly(methyl methacrylate)

To analyze the interplay between crystallization and liquid–liquid phase separation (LLPS), isothermal crystallization behavior of poly(ethylene glycol) (PEG) in blends with isotactic poly(methyl methacrylate) (i-PMMA) was investigated by differential scanning calorimetry (DSC). The blend system had an upper critical solution temperature (UCST) type phase diagram. When the crystallization occurred simultaneously with LLPS, the overall crystallization rate was enhanced at high crystallization temperatures T_c, relatively compared with that of neat PEG. This behavior was interpreted by the combination of the effects of spinodal quench depth ?T_s and usual supercooling degree ?T_c, according to the theory of Mitra and Muthukumar, namely, the crystallization rate is enhanced by the concentration fluctuation-assisted nucleation at high T_c. In the crystallization after LLPS proceeded, on the other hand, the overall crystallization rate was slow and less dependent on the blend composition. In addition, it was revealed by small-angle X-ray scattering measurements that amorphous i-PMMA was excluded from the interlamellar region of PEG crystals in SQ as well as WQ.     

Soap-free emulsion polymerization of n-butyl acrylate in aqueous solution in the presence of α- and methylated β-cyclodextrin

Butyl acrylate, a relative hydrophobic monomer, was found to become completely water soluble simply by mixing with either α-cyclodextrin or methyl-β-cyclodextrin. The both cyclodextrins were found to form 1:1 host–guest complexes with butyl acrylate. The complexes formed exhibited similar supramolecular structures, i.e., butyl group of butyl acrylate included in the cavity of cyclodextrins, but the double bond of the monomer locating outside of the cavity. Association constant values for α-cyclodextrin and methyl-β-cyclodextrin were determined to be 407.3 and 45.8?L/mol, respectively, indicating the better fitting of butyl acrylate with α-cyclodextrin than with methyl-β-cyclodextrin. It was found that the addition of either α-cyclodextrin or methyl-β-cyclodextrin, even at very low concentration, could markedly improve the reaction rate, reduce the amount of coagulum, and narrow the molecular weight distribution and particle-size distribution, in which α-cyclodextrin exhibited a better effect on polymerizations because of its stronger interaction with the monomer.     

Ring-opening polymerization of ?-caprolactone by poly(propyleneglycol) in the presence of a monomer activator

The ring-opening polymerization of ?-caprolactone (CL) was induced by using polypropylene glycol (PPG) as an initiator in the presence of the monomer activator HCl·Et₂O to synthesize triblock copolymers composed of PPG and poly(?-caprolactone) (PCL). The degree of CL conversion and the molecular weight of PCL increased linearly with the polymerization time or with the feed ratio of CL to PPG in the presence of HCl·Et₂O in CH₂Cl₂ at 25 °C. The PCLs obtained had molecular weights close to the theoretical values calculated from the CL:PPG molar ratios and exhibited monomodal GPC curves with narrow polydispersity indexes. The apparent rate constant (k_app) for the polymerization of CL activated by HCl·Et₂O was greatly affected by the ratio of HCl·Et₂O/PPG. The activation energy for the polymerization of CL in this system was estimated to be 49.8 kJ/mol K. We successfully prepared PPG and PCL triblock copolymers using this activated monomer mechanism.     

Electrical characteristic fluctuation of 16-nm-gate high-κ/metal gate bulk FinFET devices in the presence of random interface traps

In this work, we study the impact of random interface traps (RITs) at the interface of SiO _x /Si on the electrical characteristic of 16-nm-gate high-κ/metal gate (HKMG) bulk fin-type field effect transistor (FinFET) devices. Under the same threshold voltage, the effects of RIT position and number on the degradation of electrical characteristics are clarified with respect to different levels of RIT density of state (D_it). The variability of the off-state current (I_off) and drain-induced barrier lowering (DIBL) will be severely affected by RITs with high D_it varying from 5 × 10¹² to 5 × 10¹³ eV⁻¹ cm⁻² owing to significant threshold voltage (V_th) fluctuation. The results of this study indicate that if the level of D_it is lower than 1 × 10¹² eV⁻¹ cm⁻², the normalized variability of the on-state current, I_off, V_th, DIBL, and subthreshold swing is within 5%.     

One-step synthesis of ?-caprolactam via the liquid phase catalytic nitrosation of cyclohexane in the presence of concentrated sulfuric acid

A simple and efficient approach for the synthesis of ?-caprolactam via the liquid phase nitrosation of cyclohexane and nitrosyl sulfuric acid in the presence of concentrated sulfuric acid has been developed. A series of novel AlVPO composites were prepared by an impregnation method and the composites were then employed to catalyze the nitrosation reaction of cyclohexane and nitrosyl sulfuric acid. Compared to the reaction using fuming sulfuric acid, the selectivity for the desired product was significantly improved using this one-step catalytic process. This method affords a shortcut to prepare ?-caprolactam and its analogs from cyclohexane.     

Study of the Effect of Fluorine Atom(s) on Fluoromethylated Imines in the Tandem Mannich–Michael-type Reaction

Differences in chemical behavior between non-fluorinated and fluorinated methylimines in the tandem Mannich–Michael-type reaction are described based on NMR and computational studies.     

Application of nickel(II) complexes to the efficient synthesis of α- or β-amino acids

Nonproteinogenic α- or β-amino acids have attracted tremendous attention, as they are widely utilized for biological, biochemical, pharmaceutical, and asymmetric chemical investigations. Recently, we developed a series of new strategies for preparing achiral and chiral nickel(ii) complexes for the synthesis of amino acids. We applied these new methods utilizing chiral nickel(ii) complexes for the asymmetric Mannich reaction to synthesize enantiopure α,β-diamino acids, the enantioselective tandem conjugate addition-elimination reaction to prepare glutamic acid derivatives, the Suzuki coupling reaction to yield β(2)-amino acid derivatives, the asymmetric Mannich reaction to synthesize 3-aminoaspartate, the asymmetric Michael addition reaction to give β-substituted-α,γ-diaminobutyric acid derivatives, the asymmetric alkylation reaction to prepare linear ω-trifluoromethyl containing amino acids, and the asymmetric Michael addition reaction to synthesize syn-β-substituted tryptophans.