Synthesis of a catechol-based poly(ether ether ketone) ("o-PEEK") by classical step-growth polymerization and by entropically driven ring-opening polymerization of macrocyclic oligomers

An amorphous, catechol-based analogue of PEEK ("o-PEEK") has been prepared by a classical step-growth polymerization reaction between catechol and 4,4'-difluorobenzophenone and shown to be readily soluble in a range of organic solvents. Copolymers with p-PEEK have been investigated, including an amorphous 50: 50 composition and a semicrystalline though still organic-soluble material comprising 70% p-PEEK. o-PEEK has also been obtained by entropy-driven ring-opening polymerization of the macrocyclic oligomers (MCO's) formed by cyclo-condensation of catechol with 4,4'-difluorobenzophenone under pseudo-high-dilution conditions. The principal products of this latter reaction were the cyclic dimer 3a (20 wt %), cyclic trimer 3b (16%) cyclic tetramer 3c (14%), cyclic pentamer 3d (13%) and cyclic hexamer 3e (12%). Macrocycles 3a-c were isolated as pure compounds by gradient column chromatography, and the structures of the cyclic dimer 3a and cyclic tetramer 3c were analyzed by single-crystal X-ray diffraction. A mixture of MCO's, 3, of similar composition, was obtained by cyclodepolymerization of high molar mass o-PEEK in dilute soluion.

Alternative syntheses of linear polyurethanes using masked isocyanate monomers

A range of linear polyurethanes featuring aliphatic, aromatic and ether residues have been prepared by co-polymerisation of novel 'masked' isocyanate A(2)-type monomers and diols. The reactive isocyanate monomers were generated in situ via the triphenylphosphine mediated decomposition of the heterocyclic disulfide, 1,2,4-dithiazolidine-3,5-dione. Two different synthetic approaches were examined and assessed for the construction of the novel A(2)-type monomers, which involved either coupling two 1,2,4-dithiazolidine-3,5-diones together through a spacer group or construction of 1,2,4-dithiazolidine-3,5-diones directly from diamines. The resulting polyurethanes were purified via solvent extraction and analysed using GPC, NMR and IR spectroscopic analyses. Molecular weight data were obtained and compared from both GPC and H-1 NMR (via end-group analysis) spectroscopic analysis. The thermal properties of the polyurethanes were determined using DSC and their solubility in common aprotic organic solvents was also assessed and related to their structural composition. (c) 2006 Elsevier B.V. All rights reserved.

Reversible, nondegradative conversion of crystalline aromatic poly(ether ketone)s into organo-soluble poly(ether dithioketal)s

Crystalline aromatic poly(ether ketone)s Such as PEEK and PEK may be cleanly and reversibly derivatized by dithioketalization of the carbonyl groups With 1,2-ethanedithiol or 1,3-propanedithiol under strong acid conditions. The resulting 1,3-dithiolane and 1,3-dithiane polymers are hydrolytically stable, amorphous, and readily soluble in organic solvents such as chloroform and THF and are thus (unlike their parent polymers) easily characterized by gel permeation chromatography (GPC). GPC analysis of a range of derivatized PEEK samples using light-scattering detection revealed, in some instances, a bimodal molecular weight distribution with a small but potentially significant (and previously undetected) very high-molecular-weight fraction.

Dithioacetalisation of PEEK: a general technique for the solubilisation and characterisation of semi-crystalline aromatic polyketones

The family of semi-crystalline, aromatic, high-temperature thermoplastics known as poly(ether-ketone)s are insoluble in conventional organic solvents, but undergo completely general and quantitatively reversible reactions with alkanedithiols in strong acid media, to give soluble poly(dithioacetal)s, which are readily characterisable by GPC and light scattering techniques.

Poly(ethylene glycol)-supported nitroxyls: branched catalysts for the selective oxidation of alcohols

Nitroxyl radicals such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) are highly selective oxidation catalysts for the conversion of primary alcohols into the corresponding aldehydes. In this study, direct tethering of TEMPO units onto linear poly(ethylene glycol) (PEG) has afforded macromolecular catalysts that exhibit solubility in both aqueous and organic solvents. Recovery of the dissolved polymer-supported catalyst has been carried out by precipitation with a suitable solvent such as diethyl ether. The high catalyst activities and selectivities associated traditionally with nitroxyl-mediated oxidations of alcohols are retained by the series of "linker-less" linear PEG-TEMPO catalysts in which the TEMPO moiety is coupled directly to the PEG support. Although the selectivity remains unaltered, upon recycling of the linker-less polymer-supported catalysts, extended reaction times are required to maintain high yields of the desired carbonyl compounds. Alternatively, attachment of two nitroxyl radicals onto each functionalized PEG chain terminus via a 5-hydroxyisophthalic acid linker affords branched polymer-supported catalysts. In stark contrast to the linker-less catalysts, these branched nitroxyls exhibit catalytic activities up to five times greater than 4-methoxy-TEMPO alone under similar conditions. In addition, minimal decrease in catalytic activity is observed upon recycling of these branched macromolecular catalysts via solvent-induced precipitation. The high catalytic activities and preservation of activity upon recycling of these branched systems is attributed to enhanced regeneration of the nitroxyl species as a result of intramolecular syn-proportionation.

A synthetic tripeptide as a novel organo-gelator: a structural investigation

A self-associating synthetic tripeptide [Boc-Ala(1)-Aib(2)-beta-Ala(3)-OMe (Aib: alpha-amino-isobutyric acid, beta-Ala: beta-alanine)] forms thermoreversible transparent gels in various organic solvents and this offers the first example of a peptide gelator whose molecular self-assembly afforded for gelation has been characterised by single-crystal X-ray diffraction and FT-IR and NMR spectroscopic studies. The crystal structure of an analogous synthetic non-gelator tripeptide [Boc-Ala(1)-Gly(2)-beta-Ala(3)-OMe] is also discussed in light of the self-assembly of the gelator tripeptide. (C) 2003 Elsevier Science Ltd. All rights reserved.

Pressure-dependent product distribution of citral hydrogenation over micelle-hosted Pd and Ru nanoparticles in supercritical carbon dioxide

In situ synthesis and testing of Ru and Pd nanoparticles as catalysts in the presence of ammonium perfluorohydrocarbo-carboxylate surfactant in supercritical carbon dioxide were carried out in a stainless steel batch reactor at 40 degrees C over a pressure range of 80-150 bar CO2/H-2. Direct Visualization of the formation of a supercritical phase at above 80 bar, followed by the formation of homogeneous microemulsions containing dispersed Ru nanoparticles and Pd nanoparticles in scCO(2) at above 95-100 bar, were conducted through a sapphire window reactor using a W-0 (molar water to surfactant ratio) of 30. The synthesised RU and Pd nanoparticles showed interesting product distributions in the selective hydrogenation of organic molecules, depending critically oil the density and polarity of the fluid (which ill turn depends on the pressure applied). Thus, selective hydrogenation of the citral molecule, which contains three reducible groups (aldehydes and double bonds at the 23 and 6,7 positions), is feasible Lis a chemical probe. (c) 2005 Elsevier Inc. All rights reserved.

Superacid-catalyzed polycondensation of acenaphthenequinone with aromatic hydrocarbons

A novel series of linear, high molecular weight polymers were synthesized by one-pot, superacid-catalyzed reaction of acenaphthenequinone (1) with aromatic hydrocarbons. The reactions were performed at room temperature in the Bronsted superacid CF3SO3H (trifluoromethanesulfonic acid, TFSA) and in a mixture of TFSA with methanesulfonic acid (MSA) and trifluoroacetic acid (TFA), which was used as both solvent and a medium for generation of electrophilic species from acenaphthenequinone. The polymer-forming reaction was found to be dependent greatly on the acidity of the reaction medium, as judged from the viscosity of the polymers obtained. Polycondensations of acenaphthenequinone with 4,4'-diphenoxybenzophenone (f), 1,3-bis(4-phenoxybenzoyl)benzene (g), 1,4-bis(4-phenoxybenzoyl)benzene (h), 1,10-bis(4-phenoxyphenyl)decane-1,10-dione (i), 2,6-diphenoxybenzonitrile), 2,6-diphenoxybenzoic acid (k), and 2-(4-biphenylyl)-6-phenylbenzoxazole (1) proceeded in a reaction medium of wide range of acidity, including pure TFSA (Hammett acidity function H-0 of pure TFSA is -14.1), whereas condensation of 1 with biphenyl, terphenyl, diphenyl ether, and 1,4-diphenoxybenzene needed a reaction medium of acidity H-0 less than -11.5. A possible reaction mechanism is suggested. The polymers obtained were found to be soluble in the common organic solvents, and flexible transparent films could be cast from the solutions. H-1 and C-13 NMR analyses of the polymers synthesized revealed their linear, highly regular structure. The polymers also possess high thermostability. Char yields for polymers 3a, 3c, 3d, and 3l in nitrogen were close to 80% at 1000 degrees C.

Film-forming polymers containing in the main-chain dibenzo crown ethers with aliphatic (C-10-C-16), aliphatic-aromatic, or oxyindole spacers

Novel, linear, soluble, high-molecular-weight, film-forming polymers and copolymers in which main-chain crown ether units alternate with aliphatic (C-10-C-16) units have been obtained for the first time from aromatic electrophilic substitution reactions of crown ethers by aliphatic dicarboxylic acids followed by reduction of the carbonyl groups. The crown ether unit is dibenzo-18-crown-6, dibenzo-21-crown-7, dibenzo-24-crown-8, or dibenzo-30-crown-10; the aliphatic spacer is derived from a dicarboxylic acid (sebacic, 1,12-dodecanedicarboxylic, hexadecanedioic or 1,4-phenylenediacetic acids). The reactions were performed at 35 degrees C in a mixture of methanesulfonic acid (MSA) with phosphorus pentoxide, 12:1 (w/w), (Eaton's reagent). The carbonyl groups in the polyketones obtained were completely reduced to methylene linkages by treatment at room temperature with triethylsilane in a mixture of trifluoroacetic acid and dichloromethane. Polymers containing in the main chain crown ethers alternating with oxyindole fragments were prepared by one-pot condensation of crown ethers with isatin in a medium of Eaton's reagent. A possible reaction mechanism is suggested. According to IR and NMR analyses, the polyacylation reactions lead to the formation of isomeric (syn/anti-substituted) crown ether units in the main chain. The polymers obtained were soluble in the common organic solvents, and flexible transparent films could be cast from the solutions. DSC and X-ray studies of the polymers with "symmetrical" crown ethers reveal the presence of the endotherms corresponding to the supramolecular assemblies.

Enhancing the oxidative stability of rice crackers by addition of the ethanolic extract of phytochemicals from Cratoxylum formosum Dyer

Craloxylum formosum Dyer is consumed throughout the year as food and medicine in Thailand. It contains large amounts of chlorogenic acid and quinic acid derivatives. The antioxidative activity of the extract was studied in refined soybean oil coating on rice crackers without any seasoning. They were stored in accelerated oxidation conditions at 40 degrees C, 80% relative humidity (RH) in the dark for 18 days. The oxidative state of each sample was monitored by analyzing of the peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) as well as by odor analysis by quantitative descriptive analysis (QDA). The C formosum extract was more effective than alpha-tocopherol due to metal ions present in the crackers, which resulted in alpha-tocopherol being less effective as an antioxidant. Sensory odor attributes of rice crackers were related more closely to TBARS than to PV values by linear regression analysis. The present study indicated that C. formosum extract was a promising source of a natural food antioxidant and was effective in inhibiting lipid oxidation in rice crackers.

Strongly nucleophilic RhI centre in square-planar complexes with terdentate (κ3) 2,2′:6′,2′′-terpyridine ligands: crystallographic, electrochemical and density functional theoretical studies

Rh-I-terpyridine complexes have been unambiguously formed for the first time. The 2,21:6',2"-terpyridine (tpy), 4'-chloro-2,2':6',2"-terpyridine (4'-Cl-tpy) and 4'-(tert-butyldimethylsilyl-ortho-carboranyl)-2,2':6',2"-terpyridine (carboranyl-tpy) ligands were used for successful syntheses and characterisation of the corresponding Rh-I complexes with halide coligands, [Rh(X)(4'-Y-terpyridine)] (X = Cl, Y = H, Cl, carboranyl; X = Br, Y = H). All four neutral Rh-tpy complexes are square planar, with Rh-X bonds in the plane of the 4'-Y-terpyridine ligands. Full characterisation of these dark blue, highly air-sensitive compounds was hampered by their poor solubility in various organic solvents. This is mainly due to the formation of pi-stacked aggregates, as evidenced by the crystal structure of [Rh(Cl)(tpy)]; in addition, [Rh(Cl)(carboranyl-tpy)] merely forms discrete dimers. The (bonding) properties of the novel Rh-I-terpyridine complexes have been studied with single-crystal X-ray diffraction, (time-dependent) density functional theoretical (DFT) calculations, far-infrared spectroscopy, electronic absorption spectroscopy and cyclic voltammetry. From DFT calculations, the HOMO of the studied Rh-I-terpyridine complexes involves predominantly the metal centre, while the LUMO resides on the terpyridine ligand. Absorption bands of the studied complexes in the visible region (400-900 nm) can be assigned to MLCT and MLCT/XLCT transitions. The relatively low oxidation potentials of [Rh(X)(tpy)] (X = Cl, Br) point to a high electron density on the metal centre. This makes the Rh-I-terpyridine complexes strongly nucleophilic and (potentially) highly reactive towards various (small) substrate molecules containing carbon-halide bonds.

Direct iminization of PEEK

Semi-crystalline poly(ether ketone)s are important high-temperature engineering thermoplastics, but are difficult to characterize at the molecular level because of their insolubility in conventional organic solvents. Here we report that polymers of this type, including PEEK, react cleanly at high temperatures with low-volatility aralkyl amines to afford stable, noncrystalline poly(ether-imine)s, which are readily soluble in solvents such as chloroform, THF and DMF and so characterizable by conventional size-exclusion chromatography.

Effect of TAG composition on performance of low saturate shortenings in puff pastry

Four blends formulated with low saturated fatty acid content, with the saturated component rich in stearic acid, were prepared from shea stearin, interesterified shea stearin, fully hardened soybean oil and high oleic sunflower oil in order to study their performance as shortenings in puff pastry products. The blends had a low saturated fatty acid content (30.1 ± 1.1%) compared to butter (65.9%). Saturates in the four blends examined came mainly from SSS, SOS, SSO and SOO. Puff pastry prepared from the blend that contained SOS as the main source of saturates had better properties than the other blends. It was similar to butter in compressibility of the baked product. The β-polymorphic form was present in all blends, although blends containing the highest levels of SSS also showed some β′ crystals.

The multiple antibiotic resistance (mar) locus and its significance

Chromosomally encoded systems involved in low level resistance of bacteria to different classes of antibiotics (mainly beta-lactams, chloramphenicol, quinolones and tetracycline), disinfectants and in resistance to organic solvents have been the focus of considerable interest in recent years. The multiple antibiotic resistance (mar) locus of Escherichia coli and Salmonella is perhaps the best described system involved in this type of resistance which is induced by MarA, the activator protein encoded by the marRAB locus. The mar-locus is reported to mediate resistance primarily by up-regulating efflux of some antibiotics, disinfectants and organic solvents via the AcrAB-TolC efflux pump and down regulating influx through Outer Membrane Protein F (OmpF). Whilst the level of antibiotic resistance conferred by marRAB is only low level, there are increasing data to suggest that marRAB and related systems are important in clinical antibiotic resistance, possibly as a 'stepping stone' to higher levels of resistance. Other related systems include up-regulation of RobA, SoxS and AcrAB which give rise to a similar resistance phenotype to that conferred by up-regulation of MarA. The aim of this paper is to review the function and significance of the mar-locus and related systems with a particular focus on its implications in veterinary medicine. (C) 2002 Published by Elsevier Science Ltd.

Prevalence of multiple antibiotic resistance in 443 Campylobacter spp. isolated from humans and animals

Aims: In view of recent findings that a multidrug efflux pump CmeABC exists in Campylobacter jejuni, 391 C. jejuni and 52 Campylobacter coli of human and animal origin were examined for a multidrug resistance phenotype. Materials and methods: The MICs of ampicillin, chloramphenicol, ciprofloxacin, erythromycin, kanamycin, tetracycline, cetrimide, triclosan, acridine orange, paraquat and ethidium bromide were determined. Resistance to organic solvents and the effect of salicylate (known inducer of the marRAB operon in Escherichia coli and Salmonella) were also examined. Results: Two C. coli and 13 C. jejuni isolates, mainly from pigs or poultry, were resistant to three or more antibiotics and 12 of these strains had reduced susceptibility to acridine orange and/or ethidium bromide. Strains (n=20) that were less susceptible to acridine orange, ethidium bromide and triclosan were significantly more resistant (P<0.05) to ampicillin, chloramphenicol, ciprofloxacin, erythromycin, nalidixic acid and tetracycline, with two- to four-fold increases in MIC values compared with strains (n=20) most susceptible to acridine orange, ethidium bromide and triclosan. Growth of strains with 1 mM salicylate caused a small (up to two-fold) but statistically significant (Pless than or equal to0.005) increase in the MICs of chloramphenicol, ciprofloxacin, erythromycin and tetracycline. Conclusions: These data indicate that multiple antibiotic resistant (MAR)-like Campylobacter strains occur and it may be postulated that these may overexpress cmeABC or another efflux system.