Phosphatidylglycerol molecular species of photosynthetic membranes analyzed by high-performance liquid chromatography: Theoretical considerations

A reversed-phase high-performance liquid chromatography technique was developed to separate, identify, and quantify individual phsphatidylglycerol (PG) molecular species in thylakoid membranes isolated from higher plant leaves. PG was first separated by thin-layer chromatography; then the dinitrobenzoyl derivatives of diacylglycerols produced after phospholipase C hydrolysis of PG were separated by a C₁₈ reversed-phase column and detected at 254 nm. A linear response of the detector was observed in the range of 0.025 to 12 nmol of PG molecular species. It was established that there was an excellent correlation (r=0.996) between the carbon and double-bond number in the aliphatic residues and the relative retention time of dinitrobenzoyl derivatives. A new equivalent carbon number value (ECN^*) which takes into consideration the number ofcis-(n _c ) andtrans-(n _t ) double bonds per molecular species was defined as ECN^*=CN-2n _c -n _t′ where CN is the number of carbon atoms in the aliphatic residues. The logarithm of the retention time increased linearily as a function of ECN^* value. However, in this type of correlation, it may happen that two molecular species of PG having distinct relative retention times has the same ECN^* value. In this case, the two molecular species can be identified by the linear correlation (r=1) existing between the reciprocal of the relative retention time and the number of double bonds (0≤n≤3) in the separate 18:n/Δ3-trans-hexadecenoic acid [16:1(3t) and 18:n/16:0 molecular species series. The advantages of this method are good separation, short elution time, quantitative precision, and predictable retention times of PG molecular species from chloroplast membranes. The method has been used routinely to identify the ten PG molecular species of thylakoid membranes in squash, potato, lettuce, and spinach leaf: 18:3/16:1(3t), 18:3/16:0, 18:2/16:1(3t), 18:2/16:0, 18:1/16:1(3t), 18:1/16:0, 18:0/16:1(3t), 18:0/16:0, 16:0/16:1(3t), and 16:0/16:0.     

Study on the Thermooxidative Degradation Kinetics of Tetrafluoroethylene-Ethylene Copolymer Filled with Rice Husks Ash

The thermooxidative degradation kinetics of tetrafluoroethylene-ethylene copolymer (TFE-E) and its composites filled with 10 mass% black rice husks ash (BRHA), white rice husks ash (WRHA) or Aerosil A200 Degussa (AR) in air was studied using the Coats-Redfern calculation procedure. The thermooxidative degradation of these composites occurs in two stages and their most probable kinetic mechanisms were established, as well as the values of the activation energy E, frequency factor A in the Arrhenius equation and the changes of Gibbs free energy Δ G ^≠, enthalpy Δ H ^≠ and entropy Δ S ^≠ for the formation of the activated complex from the reagents, respectively. The thermooxidative degradation of the samples studied was accompanied by kinetic compensation effect. The lifetime values were calculated at different temperatures to conclude that the use of BRHA as filler reduced lifetime to the highest extent.     

p-Chloroacetophenone: A study of enolization kinetics

The reaction rate of enolization of p-chloroacetophenone has been studied in the presence of amino acids, namely, β-alanine, DL-alanine, L-alanine, and glycine. Maximum reaction rate was observed in the case of β-alanine at 22M concentration. The effects of parameters such as effect of ketone concentration, effect of dielectric constant, effect of catalysts, etc., have been found to exert a significant effect on the reaction rate. The effect of temperature was studied in the range of 313–328?K, and several thermodynamic parameters such as entropy (ΔS^≠), enthalpy (ΔH^≠), energy of activation (ΔE_a), and Gibbs free energy (ΔF^≠) were found to be ?10.32?e.u., 17.87?cal?mol^?1, 19.24?kcal?mol^?1, and 21.20?cal?mol^?1, respectively. The reaction rate increased from 1.9 to 5.8?min^?1 on increasing the percentage of dimethylformamide from 10 to 50% (v/v).     

Liquid-phase p-t-butyltoluene autoxidation enhanced by electrochemistry: Activation of the catalytic effect of cobalt acetate

The autoxidation of p-t-butyltoluene (TBT) at 80 °C in the liquid phase is carried out with an initial mixture of cobalt(III) and cobalt(II) acetate in an acetic acid solution. The autoxidation kinetics of TBT is appreciably accelerated by electrolysis with a anodic current density of 62.5 A m^–2. The electrolysis increases the concentration of cobalt(III) acetate, the actual catalyst of the autoxidation reaction. The end product of oxidation is p-t-butylbenzoic acid (TBBA). p-t-Butylbenzaldehyde (TBBZ) is an intermediary whose concentration passes through a maximum. The oxidation experiments with TBT were performed with total cobalt acetate concentrations ranging from 0.0188 to 0.169 mol dm^–3. An increase in total cobalt acetate concentration favours the electrochemical regeneration of Co^III and slightly improves the TBBZ selectivity. The duration of TBT oxidation into TBBA is reduced by a factor of 5 compared with a reaction without electrolysis.     

Activation parameters and excitation yields of 1,2-dioxetanes of photogenotoxic interest

The chemiluminescent decomposition of functionalized 1,2-dioxetanes was examined in toluene solution. Activation energies were measured by isothermal and nonisothermal kinetic methods. Quantum efficiencies were determined by Stern-Volmer kinetics, using the fluorescers 9,10-dibromo- and 9,10-diphenylanthracene for the triplet and singlet excitation yields. The derivatives of 3-hydroxymethyl-3,4,4-trimethyl-1,2-dioxetane ( 1a ) have free energies of activation (ΔG^≠) of ca. 25 kcal/mol, but the ΔG^≠ values of the annelated benzofuran-type dioxetanes ( 5 ) are ca. 1 kcal/mol lower. There exists a reasonable correlation between the free energies of activation (ΔG^≠) for the thermal decomposition of the dioxetanes and their triplet excitation flux (E_p^T).     

β-Oxidation of conjugated linoleic acid isomers and linoleic acid in rats

To assess the oxidative metabolism of conjugated linoleic acid (CLA) isomers, rats were force-fed 1.5–2.6 MBq of [1-¹⁴C]-linoleic acid (9c,12c-18∶2),-rumenic acid (9c,11t-18∶2), or-10trans, 12cis-18∶2 (10t, 12c-18∶2), and ¹⁴CO₂ production was monitored for 24 h. The animals were then necropsied and the radioactivity determined in different tissues. Both CLA isomers were oxidized significantly more than linoleic acid. Moreover, less radioactivity was recovered in most tissues after CLA intake than after linoleic acid intake. The substantial oxidation of CLA isomers must be considered when assessing the putative health benefits of CLA supplements.     

Adsorptive performance of calcined <Emphasis Type="Italic">Cardita bicolor</Emphasis> for attenuating Hg(II) and As(III) from synthetic and real wastewaters

The first application of calcined Cardita bicolor oyster shell (CCBS) for Hg(II) and As(III) adsorption from synthetic and real wastewaters was tested. The main elements in CCBS structure were carbon, oxygen, magnesium, phosphor, and calcium. Effects of different parameters like initial pH, contact time, temperature, and CCBS dosage were assessed. The results showed that the maximum recovery of Hg(II) and As(III) adsorption was determined as C₀=10 mg/L, t=80 min, T=25 °C, CCBS dosage=5 g/L, and pH=6 (for mercury ion) and 7 (for arsenic ion). In these conditions, 95.72% Hg(II) and 96.88% As(III) were removed from aqueous solution. The correlation coefficient (R²) values for both adsorbates were obtained >0.98 and >0.96 for Langmuir and Freundlich isotherm models, respectively. Pseudo-second-order kinetic model was more capable to describe kinetic behavior of adsorption process of both metal ions in comparison with pseudo-first-order model. The half life (t_1/2) value for Hg(II) and As(III) with initial concentration of 10 mg/L was 4.032 and 4.957 min, respectively. Moreover, thermodynamic parameters of enthalpy (ΔH ^o ), entropy (ΔS ^o ), and Gibbs free energy (ΔG ^o ) were investigated. Two real wastewaters obtained from a leather factory and a landfill leachate were successfully treated using CCBS. The results confirmed that adsorption process of metals ions was exothermic and spontaneous.     

Selective uptake of fatty acids by the yeast Yarrowia lipolytica

Yarrowia lipolytica, when cultivated on mixtures of free fatty acid substrates was found to remove C12:0, C14:0, ^Δ9C18:1, ^{Δ9, 12}C18:2 and ^{Δ9, 12, 15}C18:3 at significantly higher rates than C16:0 and C18:0, regardless of fatty acid composition of the initial substrate. C12:0, C14:0 and ^{Δ9, 12, 15}C18:3 were specifically and completely removed from the substrate, while ^Δ9C18:1 and ^{Δ9, 12}C18:2 concentrations decreased by 55‐80 wt‐% in comparison with initial concentrations. In contrast, concentration of C18:0 increased 2.1—3.5 fold in the substrate. Although C18:0 was removed slowly from the substrate, this fatty acid was selectively accumulated in the storage lipid. Inversely, only low quantities of ^Δ9C18:1 and ^{Δ9, 12}C18:2 and traces of C12:0, C14:0 and ^{Δ9, 12, 15}C18:3 were accumulated in the storage lipid. During storage lipid breakdown, cellular C16:0 and ^Δ9C18:1 were taken up more rapidly than C18:0. We concluded that the capability of Yarrowia lipolytica to selectively remove several fatty acids from the substrate and accumulate others could be used in modification of the composition of selected mixtures of fatty acids and probably of common fats, to produce “new” fats with a predetermined composition.     

Selective deposition oftrans-8- andcis-9-octadecenoates in egg and tissue lipids of the laying hen

The deposition oftrans-8-octadecenoate-8(9)-³H (8t-18∶1-³H) was compared tocis-9-octadecenoate-10-¹⁴C (9c-18∶1-¹⁴C) in the major egg yolk neutral lipids and phospholipids and in organ lipids from the laying hen.trans-8-Octadecenoate was preferentially incorporated into only the phosphatidylethanolamines (PE), whereas discrimination against 8t-18∶1-³H occurred in the phosphatidylcholines (PC), triglycerides (TG) and cholesteryl esters (CE). The 1-acyl position of both PE and PC contained three times more 8t-18∶1-³H than 9c-18∶1-¹⁴C. Almost total exclusion of the 8t-18∶1-³H from the 2-acyl position of these phospholipids was found. Preferential incorporation of 9c-18∶1-¹⁴C occurred at the combined 1- and 3-acyl positions and at the 2-acyl position of yolk TG. Tissue lipid analyses indicated that there was preferential deposition of 9c-18∶1-¹⁴C into all organs. Individual liver lipid classes displayed the same relative order of discrimination against 8t-18∶1-³H as did egg yolk lipids (CE>TG>PC>PE).     

Preparation and fractionation of conjugated trienes from α-linolenic acid and their growth-inhibitory effects on human tumor cells and fibroblasts

Conjugated α-linolenic acid (ClnA) was prepared from α-linolenic acid (9,12,15–18∶3n−3, LnA) by alkaline treatment; we fractionated CLnA into three peaks by reversed-phase column-HPLC as evidenced by monitoring absorbance at 205, 235, and 268 nm. Peak I was a conjugated dienoic FA derived from LnA, whereas Peaks II and III were conjugated trienoic LnA. Proton NMR analysis showed that Peak III consisted of the all-trans isomer. The methylated Peak III was further divided into five peaks (Peaks IV–VIII) by silver ion column-HPLC. Peak V, a major constituent in the Peak III fraction, was identified as conjugated 10t,12t,14t-LnA by GC-EIMS and ¹H NMR analysis. Peaks III and V, which consisted of conjugated all-trans trienoic LnA, had stronger growth-inhibitory effects on human tumor cell lines than the other collected peaks and strongly induced lipid peroxidation as compared with Peaks I, II, and LnA. We propose that conjugated all-trans trienoic FA have the strongest growth-inhibitory effect among the conjugated trienoic acids and conjugated dienoic acids produced by alkaline treatment of α-LnA, and that this effect is mediated by lipid peroxidation.     

Peptide Synthesis at High Pressure: Activation volume of a peptide coupling,synthesis of a glutathione derivative

From the pressure-induced rate enhancement the activation volume of the peptide coupling 1 with the sodium salt of glycine 2 leading to the corresponding dipeptide derivative 3 was determined to be strongly negative (ΔV^≠ = −(19.3 ± 0.5) cm³mol⁻¹ at 51.7 °C, CH₃OH). This finding indicates that and association with the developing of charge proceeds in the rate-determining transition state. The pressure-induced peptide coupling was exploited to synthesize a derivative ( 12a, b ) of glutathione (γ-Glu-Cys-Gly), a biologically important tripeptide, starting from either glycine or glutamic acid.     

3D-Supramolecular Coordination Polymers as Effective Oxidizing Agents Towards 2,4-Dichlorophenol and 2,6-Di-<Emphasis Type="Italic">t</Emphasis>-butylphenol

3D-supramolecular coordination polymers (SCP) of the type [(R₃Sn)₃Fe^III(CN)₆]; R = CH₃ (I), n-Butyl (II) and phenyl (III) contain wide expandable channels capable of encapsulating and in situ oxidizing 2,4-dichlorophenol (DClP) and 2,6-di-t-butylphenol (DBP) to 2-chloro-1,4-benzoquinone (2-ClBQ) and 3,5,3,5-tertra-t-butyl-4,4-diphenoquinone (BDPQ), respectively, to form new host–guest supramolecular coordination polymers (HGSCP) (1–6). The oxidation products are investigated by spectrophotometry and HPLC methods. A kinetic study indicated a first-order reaction with respect to the hosts SCP I–III. The mechanism and rate of oxidation are discussed in relation to the structure of the SCP.     

Photochemistry of trichloro(phenylazo)bis(triphenylphosphine)ruthenium(II) induced by Ru to phenyldiazonium MLCT excitation

The complex trichloro(phenylazo)bis(triphenylphosphine)ruthenium(II) shows a longest-wavelength absorption at λ_max = 520 nm which is assigned to a Ru(II) → phenyldiazonium⁺ MLCT transition. MLCT excitation leads to the oxidation of the metal and reduction of the diazonium cation which decays to nitrogen and phenyl radical.     

Placental transport oftrans fatty acids in the rat

Placental transport of 9-trans [1-¹⁴C] octadecenoic (elaidic) and 9-trans,12-trans [1-¹⁴C] octadecadienoic (linoelaidic) acids was demonstrated in rats. On the 18th day of gestation, a¹⁴C-labeled albumin complex of elaidic or linoelaidic acid was injected into the jugular vein of pregnant rats. For comparison, 9-cis [1-¹⁴C] octadecenoic (oleic) or 9-cis,12-cis [1-¹⁴C] octadecadienoic (linoleic) acid also was injected into the maternal circulation of rats. All animals were sacrificed 1 hr following injection. Lipid composition and distribution of label were determined in maternal plasma, placental and fetal tissues. Differences in specific activities of plasma, placental and fetal total lipids indicated a decreasing concentration gradient for bothcis andtrans isomers of octadecenoic and octadecadienoic acids. Distribution of radioactivity in various lipid components was determined by thin layer chromatography. Irrespective of the label, the highest percentage of total radioactivity was carried by triglycerides (TG) in maternal plasma (∼60–80%), and was incorporated mainly in phospholipids (PL) of fetal tissues (∼50–60%). A nearly equal distribution of the label was found between PL and TG of placental lipids (∼40%). Radioactivity of fatty acid methyl esters (FAME) determined by radiogas liquid chromatography indicated that after injection of linoelaidate, radioactivity of maternal plasma, placental and fetal tissue FAME was associated only witht,t-18∶2. Following injection of elaidate, all the radioactivity in placental FAME was associated witht-18∶1; however, in fetal tissues, the label was distributed between 16∶0 andt-18∶1. These findings suggest that, in contrast to linoelaidic acid, rat fetal tissues can metabolize elaidic acid via β oxidation to form acetyl CoA and palmitic acid.     

Non-conjugated cis/trans 18:2 in Beef Fat are Mainly Δ-9 Desaturation Products of trans-18:1 Isomers

Human liver cells (HepG2) were cultured with individual trans (t) 18:1 including t6‐, t12‐, t13‐, t14‐, t15‐ and t16‐18:1, and retention times of their Δ‐9 desaturation products were determined using 100‐m biscyanopropyl‐polysiloxane and SLB‐IL111 columns. Corresponding peaks were found in beef adipose tissues known to have different delta‐9 desaturase activities. Further lines of evidence indicating the presence of Δ‐9 desaturation products of t‐18:1 isomers in beef fat were developed by analysis of fatty acid methyl esters (FAME) fractionated using Ag⁺‐TLC, and by GC/MS. Some of the Δ‐9 desaturation products of t‐18:1 have been previously identified in ruminant fat (c9, t12‐ and c9, t13‐18:2). Some of the Δ‐9 desaturation products of t‐18:1 (c9, t14‐ and c9, t15‐18:2) have been previously tentatively identified as different fatty acids, and for the first time we provide evidence of the presence of c9, t16‐18:2, and where t6, c9‐18:2 may elute during analysis of FAME from beef fat.     

Competitive deposition oftrans-12- andcis-9-octadecenoates into egg yolk lipids

The deposition oftrans-12-octadecenoate-12(13)-³H (12t-18∶1-³H) was compared tocis-9-octadecenoate-10-¹⁴C (9c-18∶1-¹⁴C) in the major egg yolk neutral lipids and phospholipids.trans-12-Octadecenoate was preferentially incorporated into cholesteryl esters (CE), phosphatidylcholines (PC), and phosphatidylethanolamines (PE) but was discriminated against in triglycerides (TG). Isotopic ratios indicate that 5.9 and 5.6 times more 12t-18∶1-³H than 9c-18∶1-¹⁴C was esterified at the 1-acyl position of PE and PC, respectively. The combined 1- and 3-acyl positions of TG and the 2-acyl position of TG, PE and PC were each preferentially esterified with 9c-18∶1-¹⁴C.     

Synthesis,characterization and catalytic activities of ruthenium complexes containing triphenylphosphine/triphenylarsine and tetradentate Schiff bases

Ruthenium(II) complexes of the type [Ru(CO)(B)(L)] (B=AsPh₃, pyridine, piperidine or morpholine; L=dianion of tetradentate Schiff bases) have been synthesized and characterized by physico-chemical methods. These complexes are found to be effective catalysts in the oxidation of primary and secondary alcohols using N-methylmorpholine-N-oxide as oxidant. The catalytic activity of these triphenylarsine complexes have been compared with that of triphenylphosphine complexes and with similar ruthenium(III) complexes. The formation of high valent Ruⁿ⁺²O species as catalytic intermediate is proposed for the catalytic processes.     

Oxidation of carbidic carbon on a rhodium surface

Different mechanisms of atomic carbon and oxygen recombination on a rhodium surface are studied with Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The kinetics of adsorbed carbidic carbon oxidation (carbon coverage _c 0.1–0.3 ML) by gas-phase oxygen that proceeds by a Langmuir-Hinshelwood reaction mechanism, provides the value of the activation energy for recombination (E _rec ^t 170±20 kJ/mol).E _rec ^t depends slightly on the carbon coverage. An Eley-Rideal type of reaction was observed for adsorbed oxygen and atomic gas-phase carbon recombination which occurs in a dynamic regime. The low value found for the activation energy (near zero) is consistent with the mechanism that this exothermic reaction is too fast for energy dissipation into the substrate; the energy is mainly transferred into translational, vibrational and rotational energy of CO.On leave from A.F. Ioffe Institute, St. Petersburg, Russia.     

Investigation of electron-transfer reaction between alkaline hexacyanoferrate(III) and ranitidine hydrochloride – a histamine H2 receptor antagonist,in the presence of homogenous ruthenium(III) catalyst

The ruthenium(III)-catalyzed electron-transfer reaction between hexacyanoferrate(III) and ranitidine hydrochloride is studied in alkaline medium at 25°C and at an ionic strength of 1.10?mol/dm³. The reaction stoichiometry is established and is found to be 1:4, that is, for the oxidation of one mole of ranitidine, four moles of hexacyanoferrate(III) are consumed. The reaction products were characterized by spectral studies such as IR, GC-MS, ¹H-NMR and ¹³C-NMR. The reaction rate shows a less than unit order in substrate and alkali and a first-order dependence in oxidant, [Fe(CN)₆]^3? and the catalyst, ruthenium(III) concentrations. The active species of ruthenium(III), [Ru(H₂O)₅OH]²⁺, forms an intermediate complex with the substrate. The attack of complex by hexacyanoferrate(III) in the rate determining step produces a radical cation, which is further oxidized in the subsequent step to form the oxidation product. The effect of the reaction environment on the rate constant upon adding varying concentrations of KNO₃ and t-butanol was studied. The initially added products did not have any significant effect on the reaction rate. A plausible mechanism is proposed based on the experimental results. The effect of varying temperature on the reaction rate was also studied. The activation parameters for the slow step and the thermodynamic quantities for the equilibrium steps were evaluated.

The mechanism of title reaction has been studied and one mole of ranitidine consumes four moles of [Fe(CN)₆]^3?, as shown in the following equation:     

NMR properties of poly(dimethyl siloxane) colloids as new contrast agents for NMR imaging

By connecting the field‐gradient spin‐echo theory to spin–spin relaxation, we have found that the relationship between the tube‐reptation model and spin–spin relaxation can be represented by G(t) = exp[−(t/T₂) ⁿ] in which n = 1 and 0.5 for regimes IV and III, respectively. In our experiments, the spin–spin relaxation of linear poly(dimethyl siloxane) (PDMS) agrees with G(t) = exp[−(t/T₂)] while that of crosslinked PDMS coincides with G(t) = exp[−(t/T₂)^0.5]. These results reflect that in the time interval 8–800 ms the dynamics of linear PDMS are in regime IV (governed by reptation motions) and those of the crosslinked PDMS are in regime III (dominated by wriggling motions). The line‐shapes of NMR spectra of crosslinked PDMS are consistent with the Lorentzian rather than the Gaussian model. This can be accounted for by supposing that the PDMS chains between crosslinks have liquid‐like motions even though crosslinked PDMS is a solid. The liquid‐like motions of crosslinked PDMS could be regarded as wriggling motions described by the tube‐reptation model. In addition, the experimental results of diameter distribution, viscosity, NMR image and spin–lattice relaxation are presented in this work. © 2000 Society of Chemical Industry