Showing papers on "Ether published in 1992"

Metabolism of dibenzo-p-dioxin by Sphingomonas sp. strain RW1.

Abstract: In the course of our screening for dibenzo-p-dioxin-utilizing bacteria, a Sphingomonas sp. strain was isolated from enrichment cultures inoculated with water samples from the river Elbe. The isolate grew with both the biaryl ethers dibenzo-p-dioxin and dibenzofuran (DF) as the sole sources of carbon and energy, showing doubling times of about 8 and 5 h, respectively. Biodegradation of the two aromatic compounds initially proceeded after an oxygenolytic attack at the angular position adjacent to the ether bridge, producing 2,2',3-trihydroxydiphenyl ether or 2,2',3-trihydroxybiphenyl from the initially formed dihydrodiols, which represent extremely unstable hemiacetals. Results obtained from determinations of enzyme activities and oxygen consumption suggest meta cleavage of the trihydroxy compounds. During dibenzofuran degradation, hydrolysis of 2-hydroxy-6-oxo-6-(2-hydroxyphenyl)-hexa-2,4-dienoate yielded salicylate, which was branched into the catechol meta cleavage pathway and the gentisate pathway. Catechol obtained from the product of meta ring fission of 2,2',3-trihydroxydiphenyl ether was both ortho and meta cleaved by Sphingomonas sp. strain RW1 when this organism was grown with dibenzo-p-dioxin.

Lignin–feruloyl ester cross-links in grasses. Part 1. Incorporation of feruloyl esters into coniferyl alcohol dehydrogenation polymers

Abstract: Methyl 5-O-(E)-[γ-13C]feruloyl-α-L-arabinofuranoside (FA-Ara) has been synthesized and incorporated into a synthetic lignin dehydrogenation polymer (DHP) of coniferyl alcohol. Inverse-detected long-range C–H correlation NMR experiments on the DHP lignin gave correlation peaks indicative of the copolymerization of the FA-Ara and coniferyl alcohol into the DHP polymer. The bonding sites and modes, as determined by analysis of the carbonyl region of the long-range C–H correlated 2D NMR experiment, are predictable from free-radical coupling mechanisms. In addition to the abundant 4-O-α′ and 4-O-β′ ether couplings, structures involving the β-position of the feruloyl moiety of FA-Ara in β-ether, phenylcoumaran and pinoresinolide structures were present. The incorporation of feruloyl esters into a lignin DHP results in some structures which would not release ferulic acid by solvolytic schemes currently used for quantitation of ferulic acid in plant materials. Thus the degree to which hydroxycinnamic acids are involved in the lignification of forages may be significantly underestimated.

Biodegradation of diphenyl ether and its monohalogenated derivatives by Sphingomonas sp. strain SS3.

Abstract: The bacterium Sphingomonas sp. strain SS3, which utilizes diphenyl ether and its 4-fluoro, 4-chloro, and (to a considerably lesser extent) 4-bromo derivatives as sole sources of carbon and energy, was enriched from soil samples of an industrial waste deposit. The bacterium showed cometabolic activities toward all other isomeric monohalogenated diphenyl ethers. During diphenyl ether degradation in batch culture experiments, phenol and catechol were produced as intermediates which were then channeled into the 3-oxoadipate pathway. The initial step in the degradation follows the recently discovered mechanism of 1,2-dioxygenation, which yields unstable phenolic hemiacetals from diphenyl ether structures. Oxidation of the structure-related dibenzo-p-dioxin yielded 2-(2-hydroxyphenoxy)-muconate upon ortho cleavage of the intermediate 2,2',3-trihydroxydiphenyl ether. Formation of phenol, catechol, halophenol, and halocatechol from the conversion of monohalogenated diphenyl ethers gives evidence for a nonspecific attack of the dioxygenating enzyme system.

Semicrystalline morphology of poly(aryl ether ether ketone)/poly(ether imide) blends

Abstract: Although poly(aryl ether ether ketone) (PEEK) and poly(ether imide) (PEI) blends are compatible in the melt, phase separation occurs during crystallization of the PEEK component. At high temperatures (∼320°C) compact PEEK spherulites are observed even for dilute blends containing only 25% PEEK and the accumulation of rejected PEI is primarily interspherulitic. At intermediate temperatures, PEI segregates primarily to pockets between bundles of lamellae within a spherulite. The length scale of segregation is progressively smaller at lower temperatures

An FTIR–ATR investigation of in vivo poly(ether urethane) degradation

Abstract: Surface degradation of implanted poly (ether urethane) s was studied quantitatively with a micro-ATR-FTIR technique. Substantial degradation was observed particularly in the soft segment at the α-carbon adjacent to the ether linkage. The degradation caused changes in the concentration profiles of the soft-segment groups in the depth direction, and the affected depth was up to 10 microns after implantation for 10 weeks. Inhibition of degradation by antioxidants indicated the oxidative nature of degradation. An in vivo poly (ether urethane) degradation mechanism was proposed

Photo-oxidation of organic compound in the presence of titanium dioxide: determination of the efficiency

Abstract: The photo-oxidation of 23 compounds (benzene, haloaromatics, chloroalkenes, haloalkanes, bis-(2-chloroethyl)ether, 1-hydroxyethane-1, 1-diphosphonate and ethylenediamine-N,N,N′,N′-acetic acid) in aqueous solution with titanium dioxide as the photocatalyst was investigated. The plots of photo-oxidation rate vs. irradiation time were analysed on the basis of a simple kinetic model for homogeneous reactions. This model yielded formal rate constants which serve as a general measure for the efficiency of photo-oxidation.

The Reactions of Hydroxyl Radicals with Aromatic Rings in Lignins, Studied with Creosol and 4-Methylveratrol

Abstract: Creosol and its methyl ether (4-methylveratrol), two simple model compounds representing phenolic and non-phenolic nuclei in lignins, were reacted in aqueous solution at ambiant temperature and pressure with hydroxyl radicals generated by γ-radiolysis. The reactions were conducted at different pH levels (2-12) and in the presence and absence of oxygen. After fractionation of the reaction mixtures, more than 40 products from each model compound were identified by HPLC-UV, GC-MS and/or NMR analyses.

Isopropenyl glycosides and congeners as novel classes of glycosyl donors: theme and variations

Abstract: Isopropenyl glycosides have been synthesized in high yiekds by reactings the corresponding anomeric acetates with the Tebbe reagent. These compounds undergo glycosylation with primary or secondary carbohydrate alcohols in the presence of trimethylsilyl triflate or boron trifluoride etherate, probably via a mixed acetal glycoside intermediate. On the basis of this principle, a quite efficient glysosylation of monosaccharide hemiacetal donors with acceptors bearing an isopropenyl ether function at a primary or secondary position has been developed

A new reagent for the removal of the 4-methoxybenzyl ether : application to the synthesis of unusual macrocyclic and bolaform phosphatidylcholines

Abstract: The total synthesis of two novel polymerizable phosphatidylcholines has been accomplished using 3-(4-methoxybenzyl)-sn-glycerol 10 as starting material. Diacylation of 10 with 13-tetradecynoic acid followed by oxidative coupling of the alkynes gives a 32-membered glycerol macrocycle . Sequential acylation of 10 with palmitic acid and 15-hexadecynoic acid followed by oxidative coupling gives bolaform , tethered at the 2-position of the glycerol. A new method for the cle avage of 4-methoxybenzyl ethers using dimethylboron bromide at -78 o C in dichloromethane is described

Novel thiazolidine-2,4-diones as potent euglycemic agents.

Abstract: A new series of thiazolidine-2,4-diones was obtained by replacing the ether function of englitazone with various functional groups, i.e., a ketone, alcohol, or olefin moiety. These compounds lower blood glucose levels in the genetically obese and insulin-resistant ob/ob mouse. Appending an oxazole-based group at the terminus of the chain provided highly potent compounds.

Carbon-hydrogen activation in aqueous medium. The diverse roles of platinum(II) and metallic platinum in the catalytic and stoichiometric oxidative functionalization of organic substrates including alkanes

Abstract: The oxidation of ethers, alcohols, esters, and light alkanes (ethane, propanes) byu K 2 Pt/l 4 and Pt/O 2 in aqueous medium has been studied. Results appear to indicate that unactivated C-H bonds were attacked and oxidized by Pt(II) whereas C-H bonds α to an oxygen were activated and catalytically oxidated by metallic Pt in the presence of O 2 . For example, Pt(II) was found to oxidize ethane selectively to the alcohols, ethanol, and ethylene glycol. In the presence of metallic Pt and O 2 , further oxidation of the alcohol functionality occurred to generate the corresponding carboxylic acids

Dietary ether lipid incorporation into tissue plasmalogens of humans and rodents

Abstract: Chronic feeding of 1-O-octadecyl-sn-glycerol (batyl alcohol) to patients suffering from congenital deficiency in tissue ether glycerolipids showed an increase in the plasmalogens content of their erythrocytes However, nothing is known about the ether lipid content of other tissues in these patients Feeding 1-O-heptadecyl-sn-glycerol to young rats showed that this uncommon ether lipid was incorporated to a high extent into the plasmalogens of all tissues except brain Comparative studies with other precursors, such as 3-O-heptadecyl-sn-glycerol, heptadecanol and heptadecanoic acid, indicated a stereospecific incorporation of the dietary 1-O-alkyl-sn-glycerols into tissue plasmalogens without cleavage of the ether bond Dietary ether lipids were also shown to be transferred from mothers to suckling rats, but not from pregnant rats to fetuses The implication of these results to possible dietary ether lipid therapy for patients suffering from peroxisomal disorders is discussed

Infrared study of lignin: reexamination of aryl-alkyl ether C-O stretching peak assignments

Abstract: Infrared (IR) C-O ether stretching peak assignments of beta- O-4 interunit bonds and methoxyl groups have been assigned by isotope labeling The C aryl -O peak for both types of ethers was typically found at 1262-1224 cm -1 , but syringyl and 3,5-dimethoxyl derivatives gave C aryl -O peaks of 1328-1295 cm -1 and 1254-1204 cm -1 The C alkyl -O peak for all ethers was found at 1047-1004 cm -1 These assignments are similar to values reported in general IR tables for aryl-alkyl ethers, except for the unusually high C aryl -O stretch for syringyl and 3,5- dimethoxyl compounds IR shift tables also often list a peak at 1176 cm -1 associated with the C alkyl -O bond of aryl-alkyl ethers It is doubtful the peaks observed in this region are due to the C alkyl -O bond

Stabilized, aqueous, film-forming antimicrobial compositions of hydrogen peroxide

Abstract: What is provided herein is a stabilized, aqueous, film-forming, antimicrobial composition of hydrogen peroxide. The active, oxygen-generating hydrogen peroxide component in the composition is stabilized in an aqueous-polyol solvent system of predetermined polarity containing PVP. In contrast, similar formulations without PVP experienced a loss of peroxide activity upon standing. Suitably, the composition herein includes about 1-20% by weight hydrogen peroxide, about 0.1-50% by weight PVP, and about 0.1-80% by weight of a polyol, the rest being water. Preferably, about 5-20% by weight of water is present in the composition. Additional solvents may be included therein, such as alcohols, ether oxides, esters, triglycerides of fatty acids, hydrocarbons, N-vinyl lactams, silicone oils, and polyether oligomers.

Poly(aryl ether oxadiazoles)

Abstract: A general method for the preparation of poly(aryl ether oxadiazoles) has been developed where the generation of an aryl ether linkage was the polymer-forming reaction Two synthetic approaches were investigated based on either an oxadiazole-activated halo displacement with phenoxides or a hydrazide-activated halo-displacement with phenoxides The hydrazide may be subsequently thermally cyclodehydrated to the oxadiazole heterocyclic In each case, the negative charge developed in the transition state could be stabilized through a Meisenheimer Complex, analogous to conventional activating groups (eg, sulfone and ketone), and the electron affinity, as judged by 1H NMR, was comparable to that of other activating groups An appropriately substituted diarylfluoro oxadiazole was prepared and polymerized with various bisphenols in an NMP/CHP solvent mixture in the presence of K2CO3 High molecular weight poly(aryl ether oxadiazoles) were synthesized with viscosities ranging from 044 to 076 dL/g and Tg's in the 200°C range Conversely, the hydrazide activated halo-displacement as a means of preparing poly(aryl ether hydrazides) was not as successful, since it appears that the hydrazide was of sufficient acidity to form a salt with K2CO3 preventing solubility and polymerization

A novel and practical preparation of .alpha.,.alpha.-difluoro functionalized phosphonates from iododifluoromethylphosphonate

Abstract: The addition reaction of iododifluoromethylphosphonate 1 with alkenes is catalyzed by tetrakis(triphenylphosphine) palladium or copper metal under mild conditions. A variety of functional groups, including alkyl, trimethylsilyl, hydrory, epoxy, acetory, ketone, and ester, in the alkenescould be tolerated under the reaction conditions. Reaction of 2 equiv of 1 with dienes gives the corresponding biphosphonates. Although the palladium complex fails to induce addition of 1 to cycloherene, the addition reaction proceeds readily with copper at 85 o C. With diallyl ether, a tetrahydrofuran derivative is obtained

Polymers and ceramics based on icosahedral carboranes. Model studies of the formation and hydrolytic stability of aryl ether, ketone, amide and borane linkages between carborane units

Abstract: The synthesis and hydrolysis to free carborane (R–CB10H10C–H) and a carboxylate under alkaline but not neutral conditions, of five 1,2- and 1,7-carboranyl ketones (R–CB10H10C–CO-R′) is described in a study of the optimum sequence of ether, ketone, carborane and phenylene groups for poly(ether ketone)(PEK) polymers. 1, 2-Dicarba-closo-dodecaborane (12) behaves as a better leaving group than the 1, 7 isomer from a proposed intermediary anionic adduct of hydroxide to carbonyl carbon. 1-(4-Fluorophenyl)-1, 2-dicarba-closo-dodecaborane (12)(F-C6H4-CB10H10C-H) suffers cage degradation and not nucleophilic substitution with sodium phenoxide, precluding polymerisation by this method, but 1,2-carboranebenzoic acids (R–CB10H10C–C6H4–CO2H) condense cleanly with aryl ethers in trifluoromethanesulfonic acid (TFSA), as do phenoxyphenyl-1, 2-carboranes (R–CB10H10C–C6H4–O–C6H5) with benzoic acid. 1, 2- and 1, 7-carboranyl N-monosubstituted amides (R–CB10H10C–CO–NHR') hydrolyse relatively slowly to free carboranes (R–CB10H10C–H) and amines in alkali, suggesting initial deprotonation at NH rather than nucleophilic addition. Synthesis of four model boranes is described; those with 1, 2-carborane bonded to boron are readily hydrolysed by water, bis[1, 7-dicarba-closo-dodecaborane(12)yl]phenylborane [(H–CB10H10C–)2B–C6H5] reacts slowly, but 1, 7-bis(diphenylboryl) 1,7-dicarba-closo-dodecaborane(12)[(C6H5)2B – CB10H10C – B(C6H5)2] required alkaline conditions. Formation of free carboranes and B-hydroxy compounds is consistent with a mechanism analogous to hydrolysis of the corresponding ketones. The relative reactivities of the boranes correspond to the leaving-group abilities of the isomeric carboranes and the build-up of steric compression in a proposed tetrahedral borate intermediate. The most promising polymer structures are inferred from the hydrolytic experiments.

Investigation of a model for 1,2-asymmetric induction in reactions of .alpha.-carbalkoxy radicals: a stereochemical comparison of reactions of .alpha.-carbalkoxy radicals and ester enolates

Abstract: The stereochemical course of reductions and allylations of α-carbalkoxy radicals with chiral centers at the β-position are reported. Radicals without polar substituents, with alkoxyl oracetoxyl groups, and with hydroxyl groups at the β-position were examined. Reactions showed selectivities ranging from low (50:50) to high (99:1). The results are discussed in terms of transition-state models that emphasize the importance of (1) allylic conformational analysis (minimization of A 1,3 and A 1,2 strain), (2) torisonal strain (minimization of eclipsed interactions), and (3) stereoelectronic effects