Evidence for acyl transfer reactions between neutral glycerolipids in dogfish (Squalus acanthias) serum

Radioactively labeled triacylglycerols, 1,3-dioleoyl-2-[1-¹⁴C]-palmitoylglycerol and 1,3-[9,10-³H]-dioleoyl-2-palmitoylglycerol, were incubated with dogfish (Squalus acanthias) serum for periods of up to 10.0 hr. Changes in the positional distributions of carbon-14 and tritium within the triacylglycerols in 5.0 hr and 10.0 hr indicate that intermolecular and intramolecular shifts occur among the fatty acids. In addition, a maximum of 8.3% of the carbon-14 and 5.9% of the tritium was incorporated into 1-alkyl-2,3-diacylglycerols; essentially all of this incorporated radioactivity was associated with the acyl chains in the 1.5 and 5.0 hr incubations. In the 10.0 hr incubations, however, 25% of the tritium incorporated into the 1-alkyl-2,3-diacylglycerols was associated with the 0-alkyl chains. Radioactivity was not incorporated significantly into free fatty acids in the 1.5 and 5.0 hr incubations. These results indicate that acyl transfer reactions take place among molecular species of triacylglycerols, as well as between triacylglycerols and 1-alkyl-2,3-diacylglycerols. In the latter case, the conversions appear to be operative in the virtual absence of net biosynthesis.     

Permeation resistance of poly(ether ether ketone) to hydrogen,nitrogen, and oxygen gases

We studied the gas permeation properties of poly(ether ether ketone) (PEEK) and compared it with two other polymers commonly used in the construction of semiconductor microenvironments, polycarbonate (PC), and poly(ether imide) (PEI). The PEEK specimens consisted of extruded films as well as compression‐ and injection‐molded specimens. The compression‐molded specimens were prepared to achieve the highest crystallinity. Injection‐molded disks, representing products, were milled to a prescribed thickness. Permeation, diffusion, and solubility coefficients were measured on these various PEEK specimens for hydrogen, nitrogen, and oxygen gases. It was found that PEEK generally has better permeation resistance than PC or PEI; showing up to five times lower permeation rates than PC or PEI, depending on grade, crystallinity, and gas. The superior permeation resistance of injection‐molded or extruded PEEK, when compared with similarly processed PC or PEI, comes from its crystallinity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dynamic processes leading to covalent bond formation for S(N)1 reactions

The SN1 reaction mechanism is one of the most fundamental processes in organic chemistry. As such, it has been the subject of study for over 70 years with the purpose of seeking to understand the fundamental parameters that control reactivity. With recent advances in both electronic structure theory and condense-phase reaction dynamics theory as well as in experimental probes of these reactions on the femtosecond and picosecond time scale, we are beginning to gain new insights into the nature of these reactions.     

Increasing the resistance of poly(ether imide) to solvents by blending with poly(trimethylene terephthalate)

We studied the sorption behavior of poly(ether imide) (PEI) upon the addition of minor amounts (10 and 30%) of miscibilized poly(trimethylene terephthalate) (PTT) under acetone and other common solvent environments. Significant solvent sorption (maximum solvent sorption = 8–12 wt %) and changes in mechanical properties were observed only in the case of acetone. The sorption of acetone was Fickian and partially irreversible. Both sorption and solubility decreased markedly upon PTT addition to PEI, most likely as a result of a blending‐induced decrease in the free volume. The decreases in the modulus were attributed to plasticization, and the mixed effects on the elongation at break were attributed to the combined effects of fast plasticization and slower swelling. The joint effects of applied stress and the presence of acetone were studied with creep tests. In these tests, a combination of a free volume increase, plasticization, and superficial cracking of PEI was proposed to occur. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Multiblock poly(arylene ether nitrile) disulfonated poly(arylene ether sulfone) copolymers for proton exchange membranes: Part 1 synthesis and characterization

A series of multiblock copolymers based upon alternating segments of a hydrophilic disulfonated poly(arylene ether sulfone) and a hydrophobic fluorine-terminated poly(arylene ether benzonitrile) (6FPAEB) were synthesized and characterized for use as proton exchange membranes (PEM). The ion-exchange capacity of the block copolymers were varied by utilizing 4,4′-biphenol or hydroquinone in combination with 3,3′-disulfonated-4,4′-dichlorodiphenyl sulfone (SDCDPS) to form the hydrophilic segments. The alternating block copolymer morphology was achieved by using mild temperatures to link the oligomers together and minimize ether–ether interchange reactions. Both the 4,4′-biphenol and hydroquinone based membranes showed high proton conductivity with moderate water uptake and good mechanical properties. The block copolymers displayed nanophase separated morphologies, confirmed by transmission electron microscopy (TEM) and small angle x-ray scattering (SAXS). The strong membrane performance was attributed to the multi-phase morphology.     

Oxidation of 1-O-(alk-1-enyl)-2,3-di-O-acylglycerols: Models for plasmalogen oxidation

Alk-1-enyl diacyl glycerides, model compounds for plasmalogen lipids, were synthesized for use as substrates in oxidation studies. The neutral plasmalogen glycerides prepared included 1-O-(hexadec-1-enyl)-2,3-di-O-stearoylglycerol (4a) and 1-O-(hexadec-1-enyl)-2-O-linoleoyl-3-O-stearoylglycerol (4b). Oxidative disappearance of these glycerides was followed directly by high performance liquid chromatography (HPLC). The extent of oxidation of the side chains of these glycerides, i.e. the alkenyl ether and fatty acyl functions, was monitored by conversion of the side chains to dimethylacetal and methyl ester by methanolysis, followed by subsequent gas chromatography (GC) of the methanolysis products. Both analytical approaches show that the alkenyl ether function of neat4a oxidizes more slowly than neat ethyl linoleate. However, the rate of alkenyl ether loss from4a is accelerated in the presence of added ethyl linoleate. Moreover, when the linoleoyl group is incorporated into the 2-position of the alkenyl glyceride, as in4b, the rate of loss of the alkenyl group was shown to be similar to the rate of loss of the linoleoyl group. These results suggest that oxidation of plasmalogen glycerides should not be ignored as a factor that contributes to the oxidative instability of animal tissue. Presented in part at the American Oil Chemists' Society 77th Annual Meeting, Honolulu, HI, May 1986.     

Intermolecular charge-transfer and the cleavage of the dioxygen bond at metal surfaces: Oxygen at Zn(0001)

Evidence is provided for the participation of surface pyridine-dioxygen charge transfer complexes in the pyridine accelerated cleavage of the dioxygen bond at Zn(0001) surfaces.We acknowledge gratefully support from both SERC and V.G. Scientific.     

Enhancing resistance of poly(ether ketone ketone) to high-temperature steam through crosslinking and crystallization control

Poly(aryl ether ketone)s (PAEKs) are promising materials for harsh environments, such as in high-temperature steam applications. Here, the effect of high-temperature steam on the crystallinity and mechanical properties of existing poly(ether ether ketone) (PEEK) and PEKK(T/I) polymers is investigated. Differential scanning calorimetry (DSC), wide-angle X-ray scattering or diffraction (WAXD), and dynamic mechanical analysis experiments show these materials undergo significant crystallization and reorganization after prolonged exposure to steam and suffer from embrittlement. In addition, we show that xanthydrol-based crosslinks can provide the dimensional stability and stabilize the PEKK crystal structure. Mechanical tests demonstrate that the ductility is preserved for longer exposures to steam compared to neat PEKK, whereas DSC and WAXD data indicate xanthydrol crosslinks effectively stabilize the crystal structure against steam-assisted crystallization. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47727.     

Solvent effect on reductive bond cleavage of 1-chloro-10-methyltribenzotriquinacene: Change from the concerted to the stepwise mechanism

Electrochemical reduction of 1-chloro-10-methyltribenzotriquinacene in benzonitrile, acetonitrile and N,N-dimethylformamide (DMF) is compared. A two-electron DISP1 mechanism was found in C₆H₅CN at glassy carbon and mercury electrodes with C-Cl bond cleavage as the rate determining step. In CH₃CN and DMF the hydrogen atom abstraction from solvent molecules by a radical formed in bond cleavage results in the one-electron process. In the above-mentioned solvents an analysis of a potential dependence of the transfer coefficient, obtained from convoluted voltammetric curves at mercury electrode, showed the concerted mechanism. A change from the stepwise process in C₆H₅CN to the concerted one in CH₃CN and DMF is explained by acceleration of bond cleavage in the radical anion due to stronger solvation of product chloride anions by CH₃CN and DMF.     

Synthesis and characterization of palladium (II) complex of Schiff base ligand: CS bond cleavage and catalytic activity

Reaction of ligand, L-CH₂Ph with Pd(CH₃CN)₂Cl₂ in acetonitrile in presence of PPh₃ and subsequent addition of NaClO₄ yielded Pd(II) complex, [Pd(L)(PPh₃)](ClO₄) 1 due to the SC (CH₂Ph) bond cleavage during complexation. Complex 1 was characterized by spectral analysis and the structure was authenticated by single crystal X-ray diffraction. The diffraction analysis revealed that the monoanionic ligand binds with palladium (II) in (N, N, S) fashion in a distorted square planar geometry where the fourth position is occupied by one tri phenyl phosphine group. One ClO₄⁻ ion satisfies the charge of the former aggregate, [Pd(L)(PPh₃)]⁺. The complex [Pd(L)(PPh₃)](ClO₄), 1 exhibits a very good catalytic activity towards CC bond formation.     

Study on blooming of tetrabromobisphenol a bis(2,3‐dibromopropyl ether) in blends with polypropylene

Blends of polypropylene/tetrabromobisphenol A bis(2,3‐dibromopropyl ether) (PP/TBAB) were prepared by twin‐screw extruder, and then were molded into PP/TBAB plaques. Blooming of TBAB on the surface of PP/TBAB plaques were studied through heat aging test and theoretical calculation. The heat aging test at 70°C for 45 days was performed. Mass of the blooming TBAB on the surface of the plaque was measured every day in the period. Based on Fick's second law of diffusion, a mathematical method was developed to achieve concentration profile of TBAB dependent on time in the PP/TBAB plaques. Diffusion coefficients of TBAB were calculated by using the set concentration equation of TBAB with the experimental data. It was obtained that the diffusion coefficient of TBAB in PP/18 wt % TBAB is larger than that in PP/45 wt % TBAB. For the sample of PP/18 wt % TBAB, diffusion of TBAB reached an equilibrium after the heat aging for 40 days at 70°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 20–24, 2006     

Poly(arylene ether sulphones) by polyetherification: 1. Synthesis of halogenophenols

Several 4-halogenophenylsulphonylphenols, useful as intermediates for the synthesis of poly(arylene ether sulphones), have been prepared by partial hydrolysis of the corresponding dihalides and/or by the reaction of 4-halogenoarylsulphonyl chlorides with diaryl carbonates under Friedel—Crafts conditions followed by hydrolysis of the sulphonylated carbonates. The novel reagent, diphenyl carbonate-4,4′-disulphonyl chloride, has been prepared by chlorosulphonylation of diphenyl carbonate and used to introduce the 4-hydroxyphenylsulphonyl group into aryl halides, thus providing a third general route to the halogeno phenols. 4-Fluoro-3′-hydroxydiphenyl sulphone and the 4-fluoro-2′-hydroxy derivative have been synthesised by classical procedures.     

Synthesis of tertiary amyl methyl ether (TAME): Influence of internal and external mass transfer resistance

An experimental set-up is presented for the measurement of reaction rates in the liquid phase synthesis of tertiary amyl methyl ether (TAME) from methanol and a mixture of 2-methyl-1-butene and 2-methyl-2-butene using an acidic ion exchange resin (Lewatit SPC 118) as catalyst. The reaction was performed in a continuous-flow recycle reactor at a temperature of 333.15 K and a pressure of 1.6 MPa. Determination of the age distribution (Fcurve) of the reactor showed that mixed flow is approached at a recycle ratio of R = 10. Experiments were performed to reveal the limits of operating conditions where the various resistances do not affect the rate. In agreement with estimation of Reynolds numbers, hindrance by external mass transfer can be excluded at a volumetric flow rate of 10 ml/min and a recycle ratio of R = 10. The maximum temperature increase of the whole particle resulting from limitation of external heat transfer was estimated to be about 3 K. Variation of the size of resin particles revealed the existence of a critical methanol concentration, above which reaction rates can be determined without influence of internal mass transport phenomena. The maximum temperature increase in the particle was estimated to be 0.3 K.     

Evidence for trail-pheromone precursor in termiteReticulitermes speratus (Kolbe) (Rhinotermitidae: Isoptera)

Whole body extracts of the termite,Reticulitermes speratus, were subjected to various chemical operations and bioassays to examine the presence of trail-pheromone precursor. Fractions that mainly contained fatty acid esters were obtained from hexane extracts by means of silica gel column chromatography. Trail-following activity of the fractions was activated by alkaline hydrolysis, while the original fractions did not show any conspicuous activity. Bioassay showed that the activity of hydrolyzed product was approximately 20 times as high as the original hexane extract. This suggests that the precursor candidate could be stored in termite bodies as an esterified form. Chemical analyses revealed that the complete structure of the hydrolyzed product was coincident with that of the native pheromone ((Z,Z,E)-3,6,8-dodecatrien-1-ol).     

Synthesis of Alkyl (±)-2,3-Di-O-acylglycerates and Attempts Directed to their Conversion into Alkyl (R)-2,3-Di-O-acylglycerates by Enzyme-catalyzed Enantioselective Deacylation Reactions [1]

By screening several lipases and proteases as catalysts for an enantioselective partial deacylation of methyl (±)-2,3-di-O-acylglycerates, it was found that methyl (R)-2,3-di-O-butanoylglycerate can be obtained with an enantiomeric excess of >96% and a yield of 20% related to the racemic starting material. This was prepared from methyl acrylate through dihydroxylation with potassium permanganate at −30°C and a subsequent bisacylation.     

Studies on the oxidative cleavage of the CC triple bond during the Autoxidation of Acetylenic Hydrocarbons 1. Evidence for α-dicarbonyl compounds as intermediates

Examination of oxidation mixtures of 1-phenylprop-1-yne, 1-phenylbut-1-yne and 1-phenyl-3-methylbut-1-yne revealed the presence of hitherto not reported interesting products, especially the α-dicarbonyl compounds 1-phenylpropane-1,2-dione, 1-phenylbutane-1,2-dione and 1-phenyl-3-methylbutane-1,2-dione respectively in minor quantities. Some other typical products like benzil, benzoic anhydride and phenyl benzoate were also characterized. Although the oxidation of diphenylacetylene is very slow, benzil could be found as the main detectable product along with traces of benzoic acid. The α-diketones corresponding to the 1-phenylalk-1-ynes were oxidized at 110°C. In each case benzoic acid and the lower carboxylic acids as in the case of the autoxidation of the corresponding acetylenes were obtained. Benzil, benzoic anhydride and phenyl benzoate were also characterized in all the cases. Therefore, α-diketones are considered as intermediates responsible for the formation of the oxidative cleavage products of the CC triple bond.     

Influence of silica content in sulfonated poly(arylene ether ether ketone ketone) (SPAEEKK) hybrid membranes on properties for fuel cell application

Sulfonated poly(arylene ether ether ketone ketone) (SPAEEKK) copolymer containing pendant sulfonic acid group (sulfonic acid content (SC) = 0.67) was synthesized from commercially available monomers such as sodium 6,7-dihydroxy-2-naphthalenesulfonate (DHNS), 1,3-bis(4-fluorobenzoyl)-benzene (BFBB), and hexafluorobisphenol A (6F-BPA). SPAEEKK/silica hybrid membranes were prepared using the sol-gel process under acidic conditions. The SPAEEKK/silica hybrid membranes were fabricated with different silica contents and the membranes were modified to achieve improved proton conductivity incorporating P-OH groups (H₃PO₄ treatment).The silica particles within the membranes were used for the purpose of blocking excessive methanol cross-over and for forming a pathway for proton transport due to water absorption onto the hydrophilic SiOH surface. The proton conductivities of H₃PO₄-doped membranes were somewhat higher than the un-doped (H₃PO₄-free) membranes due to increasing hydrophilicity of the membranes. The presence of silica particles within the organic polymer matrix, which decreases the ratio of free water to bound water due to the SiOH on the surface of silica derived from sol-gel reaction, results in hybrid membranes with reduced methanol permeability and improved proton conductivity.     

Liquid-phase dehydrocondensation of 1-pentanol to di-n-pentyl ether (DNPE) over medium and large pore acidic zeolites

The present paper deals with the liquid-phase synthesis of di-n-pentyl ether (DNPE) by dehydration of 1-pentanol over H-Beta, H-ZSM-5, H-mordenite and H-Y zeolites. Their SiO₂/Al₂O₃ ratios were about 25 for H-Beta, 28 for H-ZSM-5, 35 for H-mordenite and 6 for H-Y. Experiments were performed in a batch reactor in the temperature range 140–180 °C at 1.6 MPa. Comparison of the catalysts behaviour shows that H-Beta is the most active and selective to DNPE, although it is less active than microporous ion-exchange resins. Kinetics of DNPE synthesis was studied. The best kinetic model for all the catalysts stems from a reaction mechanism whose rate-limiting step is the surface reaction between two 1-pentanol molecules adsorbed on adjacent sites, to yield DNPE and water both adsorbed on single site. Activation energy, on each single catalyst, was estimated to be in the range 94–118 kJ mol^?1.