Chain Carboxylic Acids Research Articles

Synthesis and characterization of carbohydrate-based phospholipids.

Novel carbohydrate-based phospholipids containing two saturated C(12) (dilauroyl ribo-phosphocholine) (DLRPC), C(14) (dimyristoyl ribo-phosphocholine) (DMRPC), and C(20) (diarachadonyl ribo-phosphocholine) (DARPC) carboxylic acid chains were synthesized. The physical properties of the supramolecular structures formed by these compounds were compared to those formed by their direct glycerol analogues dilauroyl phosphocholine (DLPC), dimyristoyl phosphocholine (DMPC), and diarachadonyl phosphocholine (DAPC). Modulated differential scanning calorimetry (MDSC) and X-ray diffraction data indicated that with chain lengths < or =14 carbons, the carbohydrate backbone increased the thermal stability of the bilayer below the phase-transition temperature (T(m)) as compared to the glycerol-based lipids. With longer chains (C(20)), the bilayer structure was destabilized as compared to glycerol-based lipids. NMR studies of a DMRPC vesicle dispersion reveal split choline headgroup signals and distinct magnetization transfer effects arising from the "inner" and "outer" surfaces of the bilayer vesicle. Modulated differential scanning calorimetry also demonstrated that glycerol- and carbohydrate-based lipids mix, as evidenced by a single intermediate T(m). In addition, carbohydrate-based lipid/cholesterol mixtures exhibited a decrease in enthalpy with an increase in cholesterol concentration. Unlike glycerol phospholipids, carbohydrate lipids were resistant to enzymatic degradation by phospholipase A(2) (PLA(2)).

Occurrence of high molecular weight lipids (C 80+) in the trilaminar outer cell walls of some freshwater microalgae. A reappraisal of algaenan structure

The purified cell walls of mother cells (CWM) were isolated from three strains of trilaminar sheath (TLS)- and algaenan-containing freshwater microalgae Chlorella emersonii, Tetraedron minimum and Scenedesmus communis. The chemical structures of CWM and algaenans were investigated by means of tetramethylammonium hydroxide (TMAH) hydrolysis and tetramethylammonium hydroxide thermochemolysis. The compounds released were characterised by 1H and 13C-NMR, gel permeation chromatography and desorption chemical ionisation mass spectrometry. The results show that the outer cell walls of the microalgae are constituted, at least in part, of linear (poly)esters containing extremely long chain alcohol and acid moieties (up to C 80) and that algaenans are mainly composed of extremely long chain (di)carboxylic acids up to C 120. The present results which are in direct contrast to the previous three-dimensional architecture proposed for algaenans, led us to re-interpret the algaenan structure.

Surface characterization and platelet adhesion studies of aliphatic polyurethanes grafted by fluorocarbon oligomers: effect of fluorocarbon chain length and carboxylic acid group.

The surfaces of aliphatic polyurethane films, which were synthesized by 1,6 hexamethylene diisocyanate, poly(tetramethylene glycol) and 1,4 butanediol, were modified by grafting different chain length of fluorocarbon oligomers. The fluorocarbon oligomers on polyurethane surfaces were terminated with trifluorocarbon or carboxylic acid functionality. The alkyl groups were also grafted onto polyurethane surfaces for comparison. The surface characterization and platelet-contacting property were studied using electron spectroscopy for chemical analysis (ESCA), static contact angle analysis and in vitro platelet adhesion experiments. The effects of fluorocarbon oligomers and their terminal functionalities are discussed. The ESCA results demonstrate the fluorocarbon enrichment at the outmost layer in fluorocarbon oligomer grafted polyurethanes. The fluorocarbon content at the surface increases with increasing the chain length of fluorocarbon oligomers. The fluorocarbon oligomer grafted polyurethanes exhibit highly hydrophobic surfaces, while alkyl groups grafted polyurethanes show relatively hydrophobic surfaces compared with the untreated polyurethane. The in vitro platelet adhesion experiments indicated that the fluorocarbon oligomer and carboxylic acid functionality significantly reduced the number and the degree of activation of the adherent platelets.

Soft X-ray Spectroscopy and Spectromicroscopy Studies of Organic Molecules in the Environment

Organic molecules are found everywhere and play an important role in almost all biogeochemical processes occurring on the surface of the Earth (Aiken et al. 1985; Thurman 1985; Schwartzenbach et al. 1993; Senesi and Miano 1994). They are found in soluble and insoluble phases, coatings on mineral and colloidal particles, and in gas phase molecules in soils, sediments and aquatic systems. The activities of macro- and micro-fauna and flora release organic molecules of various sizes and composition. Photochemical reactions in the atmosphere also add certain small chain molecules to the organic carbon content in the environment. Significant compositional variations occur in natural organic molecules, which include small chain carboxylic acids, alcohols and amino acids; and polymeric, polyfunctional and polydisperse macromolecules such as humic and fulvic acids. The behavior of small chain molecules and their influence on different geochemical reactions is well understood. However, understanding of the chemistry of biopolymers and their role in different biogeochemical processes in the environment is poor, which may be attributed to the unavailability of instrumentation to examine the chemistry of natural organic molecules in their pristine state. Two important properties that dictate the behavior of natural organic molecules and biopolymers in the environment are: functional group chemistry and (macro)molecular structure (Schnitzer 1991). Evaluation of these two properties is complicated by the compositional and structural heterogeneity of the naturally occurring organic molecules, and their ability to form intramolecular and intermolecular H-bonds, which further modify their structure and chemical reactivity. These two properties are interrelated and one influences the other. The chemical composition of natural waters (pH, ionic composition and concentration, redox conditions) and soil and sediment particle surface chemistry (composition, coordination environment, number of reactive groups) also modify their behavior. It is not well understood how each of these environmental variables influences the …

Use of Treated Bark for the Removal of Lipids from Water

Raw, biologically treated bark and bark impregnated with transition metal ions were used to retain the lipids from synthetic emulsions. Several experimental parameters affecting the lipid removal efficiency (RE) were studied (initial concentration of lipids, temperature, time, pH, carboxylic acid chain length, etc.). Saturated bark was characterized using Fourier transform infrared (FTIR) spec-troscopy and light microscopy, and the treated bark wetting index was determined. Results show that lipid removal can exceed 95% of the initial concentration at a pH lower than 7. The uptake of lipids by these sorbents varied from 0.2 to 2.5 g/g of dry bark. Trials for regenerating the sorbent saturated by lipids allowed the recovery of ~95% of lipids. The calorific value of the saturated bark was ~79% that of domestic fuel and can be considered as an energy source, thus avoiding its waste disposal. These results may upgrade the treatment of wastewater generated by several industrial sectors, such as the food industry, surface treatment, and so on.

Structure–hepatoprotective activity relationship of 3,4‐dihydroxycinnamic acid (caffeic acid) derivatives

3,4-Dihydroxycinnamic acid (caffeic acid, CAF) is a natural product containing a catechol group with an alpha,beta-unsaturated carboxylic acid chain that has shown hepatoprotective properties. The aim of this work was to determine the importance of the 4-hydroxy, 3-hydroxy, 3,4-dihydroxy substituents and the double bond moiety on the hepatic pharmacological effects of the molecule. We compared the ability of the caffeic, 4-hydroxycinnamic, 3-hydroxycinnamic, cinnamic and 3,4-dihydroxyhydrocinnamic (a caffeic acid analogue without the double bond) acids at a dose of 50 mg kg(-1), p.o., to reduce the liver damage produced by CCl(4) (4 g kg(-1), p.o.) intoxication in the rat. Cinnamic acid, the non-hydroxylated analogue, only modestly protected the experimental animals challenged with CCl(4), suggesting that hydroxyl groups participate in the pharmacological properties of CAF. The 3,4-dihydroxyhydrocinnamic derivative did not show any significant differences when compared with the CAF effect in this model, suggesting that the double bond does not account for the liver pharmacological properties of CAF. In contrast, the 4-hydroxy substituent seems to be very important for hepatoprotective activity because the 4-hydroxy analogue improved almost every hepatic injury marker altered by CCl(4), and in a better way than CAF did.

Efficient liquid phase acylation of alcohols over basic ETS-10 molecular sieves

Acylation of alcohols with acetic acid can be carried out efficiently in the liquid phase over microporous titanosilicate ETS-10-type catalysts. The reaction was studied over ETS-10 exchanged with, Li, Na, K, Rb, Cs, Ba and H ions. Activity for acylation of primary alcohols depends on the exchanged alkali ion and increases in the order Li<Na<K<Ba∼H∼Rb∼Cs–ETS-10. These molecular sieves are also suitable for the acylation of secondary alcohols and esterification with long chain carboxylic acids.

Chiral recognition in gas-phase cyclodextrin: amino acid complexes—is the three point interaction still valid in the gas phase?

The validity of the “three-point interaction” model is examined in the guest exchange reaction involving complexes of cyclodextrins and amino acids. The amino acid guest is exchanged in the gas phase in the presence of a gaseous alkyl amine. The net reaction is proton transfer between the protonated amino acid and the alkyl amine. The amino acid is lost as a neutral species. This reaction is sensitive to the chirality of the amino acid. Several amino acids are examined as well as the respective methyl esters to determine the role of the three interacting groups (ammonium, carboxylic acid, and side chain) in enantioselectivity. We find that the three-point interaction model is indeed valid in the gas phase. Enantioselectivity is optimal when two points of attraction and one repulsion is present in the gas-phase complex. The results are supported by molecular modeling calculations. A mechanism for the exchange is proposed.

Crystallization kinetics of poly(butylene terephthalate) (PBT): Influence of additives and free carboxylic acid chain ends

AbstractDegradation of poly(butylene terephthalate) (PBT) induced by blending time at 260°C leads to an increase of both carboxylic end groups and melt viscosity index and a decrease of the molecular weights. Crystallization kinetics of pure PBT and PBT blended with and epoxide, which was used to reduce the free carboxylic acid concentration, were compared. Lower carboxylic acid concentrations were obtained, but the molecular weights still decreased. The crystallization kinetics of PBT blended with pigments and/or mineral fillers were also studied. Dyes, some of which are known for their nucleation activity, were used for differentiating extruded PBT tubes in optical fiber loose cables. Post‐shrinkage appeared to depend on the type of pigment used. Pigments Concentration, particle size and chimical nature have been correlated to the PBT crystallization kinetics. An increase of the nonisothermal crystallization temperature was observed, more or less important according to the pigment used. Talc and mica were also tested in PBT blends, with and without pigments. Their mucleation activity parameters were measured and compared with those for the pigments. An average value of the crystallization temperature, nearly constant and independent of the Pigment, was obtain controlled shrinkage on industrial products with strict dimension requirements.

Chemical composition of precloacal secretions of Liolaemus lizards.

Interspecific chemical variation of precloacal pore secretions of Liolaemus lizards was characterized in 20 species, and intraspecific chemical variation was characterized using nine individuals of L. bellii. The latitude (Chile, 18 degrees to 33 degrees South latitude) and altitude (100 to 4350 m.a.s.l.) of the capture sites were recorded, as well as the number of precloacal pores of each lizard. Secretions were analyzed by GC-MS. A total of 49 compounds were found distributed among the 20 species of Liolaemus. Different chemical patterns occurred at intra- and interspecific levels. Compounds belonged to three main families: n-alkanes, long chain carboxylic acids, and steroids. Cholesterol and five carboxylic acids (tetradecanoic, hexadecanoic, hexadecenoic, octadecanoic, and Z-9-octadecenoic) appeared in all species. The number of precloacal pores correlated positively with altitude and negatively with latitude, suggesting that lizards produce more secretions under harsh environments.

STRUCTURAL CHARACTERIZATION OF POLY(ϵ-CAPROLACTONE) AND POLY(ϵ-CAPROLACTONE-b-ISOBUTYLENE-b-ϵ-CAPROLACTONE) BLOCK COPOLYMERS BY MALDI-TOF MASS SPECTROMETRY

Poly(ϵ-caprolactone)(PC1) and PC1-polyisobutylene-PC1 (PC1-PIB-PC1) block copolymers were synthesized in anhydrous toluene by in situ conversion of 2-methyl-1-propanol (2M1P) and α,ω-dihydroxy PIB, respectively, to the corresponding aluminum alkoxide by reaction with a stoichiometric amount of triethylaluminum (TEA) followed by the addition of e-caprolactone. Structural characterization of 2M1P-initiated PCl by gel permeation chromatography (GPC) and matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry (MS) demonstrated the presence of cyclic oligomers, which are produced by intramolecular transesterification reactions that become significant at high monomer conversions. A minor fraction of chains bearing carboxylic acid termini was also observed in the MALDI-TOF mass spectrum; however, carboxylic acid chain ends could not be detected by 13C NMR analysis. Thus, the likely origin of the carboxylic acid termini is fragmentation of the initiator residue from the chain end during MALDI-TOF analysis. For PCl-PIB-PCl block copolymers, two different α,ω-telechelic PIB diols were used as macroinitiators, one derived from allyl and one from isopropenyl terminated PIB. Terminal olefins were converted to primary alcohols via regioselective hydroboration followed by alkaline hydrogen peroxide oxidation. After reaction with ϵ-caprolactone, formation of a block copolymer was evidenced by a shift of the polymer peak to lower elution volume in GPC analysis. Block copolymers possessed molecular weight distributions ≤1.4, and molecular weights of the PCl blocks calculated from GPC were in excellent agreement with those found using MALDI-TOF MS. Structural analysis indicated that the PCl end blocks were severed from the crude block copolymer during MS analysis, for both allyl- and isopropenyl-derived materials. For allyl-derived materials the PCl blocks were found to predominantly carry a C2 residue at the point of detachment of the PIB block; however, the isopropenyl-derived block copolymers showed a complex mixture of different residues suggesting a complex fragmentation mechanism during loss of the PIB block.

Transient Behavior of the Velocity Profile in Channel Flow of a Langmuir Monolayer

We have observed the surface pressure-driven flow of Langmuir monolayers through a narrow channel by means of Brewster angle microscopy (BAM). The monolayers, composed of long chain carboxylic acids, were studied in a “hexatic” liquid crystalline mesophase (L2 phase). The velocity profile across the channel demonstrated transient behavior; i.e., it evolved from the expected parabolic shape to triangular as a function of flow rate, location along the channel, and time elapsed after start-up of flow. These transient effects appear to be related to the total strain in the system and suggest the importance of elasticity in the monolayer flow response. For situations in which the velocity profile was triangular, the distribution of domain widths across the channel indicated that the degree of domain stretching was systematically less than expected from the amount of strain the monolayer had experienced. This implied that elasticity of domain boundaries and/or slippage between domains resists domain stretching and may contribute to the observed non-Newtonian behavior of the monolayer.

Fatty-acid biosynthesis in a branched-chain α-keto acid dehydrogenase mutant ofStreptomyces avermitilis

Fatty-acid biosynthesis by a branched-chain alpha-keto acid dehydrogenase (bkd) mutant of Streptomyces avermitilis was analyzed. This mutant is unable to produce the appropriate precursors of branched-chain fatty acid (BCFA) biosynthesis, but unlike the comparable Bacillus subtilis mutant, was shown not to have an obligate growth requirement for these precursors. The bkd mutant produced only straight-chain fatty acids (SCFAs) with membrane fluidity provided entirely by unsaturated fatty acids (UFAs), the levels of which increased dramatically compared to the wild-type strain. The levels of UFAs increased in both the wild-type and bkd mutant strains as the growth temperature was lowered from 37°C to 24°C, suggesting that a regulatory mechanism exists to alter the proportion of UFAs in response either to a loss of BCFA biosynthesis, or a decreased growth temperature. No evidence of a regulatory mechanism for BCFAs was observed, as the types of these fatty acids, which contribute significantly to membrane fluidity, did not alter when the wild-type S. avermitilis was grown at different temperatures. The principal UFA produced by S. avermitilis was shown to be delta9-hexadecenoate, the same fatty acid produced by Escherichia coli. This observation, and the inability of S. avermitilis to convert exogenous labeled palmitate to the corresponding UFA, was shown to be consistent with an anaerobic pathway for UFA biosynthesis. Incorporation studies with theS. avermitilis bkd mutant demonstrated that the fatty acid synthase has a remarkably broad substrate specificity and is able to process a wide range of exogenous branched chain carboxylic acids into unusual BCFAs.Key words: Streptomyces avermitilis, fatty acid biosynthesis, avermectin.

Mechanisms of oiliness additives

Ultrathin film interferometry has been used to measure the boundary film-forming behaviour of long chain, carboxylic acid oiliness additives. It has been shown that in dry conditions, these acids form very thin films of around 2–3 nm thickness. However when water is present, some acids form significantly thicker films, around 10 nm in thickness. The behaviour of these films is very similar to that previously seen with metal carboxylate additive films, including thick film collapse at high rolling speeds followed by film reformation at slow speeds. It is suggested thick films formed by long chain carboxylic acid additives result from reaction of the acids at the rolling solid surfaces in the presence of water to form deposits of insoluble iron carboxylate.

Influence of synthetic sheep urine on the microbial biomass, activity and community structure in two pastures in the Scottish uplands.

The impact of urine on the microbial biomass, activity and community structure was compared in the soil beneath two pastures in the Scottish uplands; Fasset, a natural Agrostis capillaris–Festuca ovina–Galium saxatile grassland and Strathfinella, a semi-natural grassland, improved with fertiliser addition. Community level physiological profiles (CLPP) were used to characterise the microbial communities. The utilisation of sugars, oligosaccharides, alcohols, carboxylic acids, long chain aliphatic acids, acidic, basic and neutral amino acids, amide N, phenolic acids and long chain aliphatic acids was used to compare the soils and the impact of synthetic urine addition. In the untreated soils, the utilisation of all the substrates decreased from the first week in May through to October. Averaged over all times and urine treatment, the potential utilisation of all substrates except for phenolic acids, long chain aliphatic acids and carboxylic acids was greater in the improved and more intensively grazed Strathfinella site. When averaged over all sample times, urine increased the utilisation of sugars, oligosaccharides, basic amino acids and amide N and the increases were greater in the unimproved, less intensively grazed, Fasset soil than that at Strathfinella. The effect of urine tended to be greatest during the period between 2 and 5 weeks after urine addition when utilisation of alcohols, acidic and neutral amino acids was also increased. Microbial biomass C in the control soils was 155.9 and 112.7 g C m−2 at Fasset and Strathfinella, respectively. Values did not change significantly with time and were unchanged by the addition of urine. However, urine addition significantly increased basal respiration rates at Fasset and decreased them at Strathfinella. Urine also increased bacterial numbers in both soils, but had no consistent effect on fungi or yeasts. The significance of these findings for studies of soil microbial community structure and activity in grazed upland grasslands is discussed.

Fatty-acid biosynthesis in a branched-chain α-keto acid dehydrogenase mutant of &lt;i&gt;Streptomyces avermitilis&lt;/i&gt;

Fatty-acid biosynthesis by a branched-chain alpha-keto acid dehydrogenase (bkd) mutant of Streptomyces avermitilis was analyzed. This mutant is unable to produce the appropriate precursors of branched-chain fatty acid (BCFA) biosynthesis, but unlike the comparable Bacillus subtilis mutant, was shown not to have an obligate growth requirement for these precursors. The bkd mutant produced only straight-chain fatty acids (SCFAs) with membrane fluidity provided entirely by unsaturated fatty acids (UFAs), the levels of which increased dramatically compared to the wild-type strain. The levels of UFAs increased in both the wild-type and bkd mutant strains as the growth temperature was lowered from 37 degrees C to 24 degrees C, suggesting that a regulatory mechanism exists to alter the proportion of UFAs in response either to a loss of BCFA biosynthesis, or a decreased growth temperature. No evidence of a regulatory mechanism for BCFAs was observed, as the types of these fatty acids, which contribute significantly to membrane fluidity, did not alter when the wild-type S. avermitilis was grown at different temperatures. The principal UFA produced by S. avermitilis was shown to be delta 9-hexadecenoate, the same fatty acid produced by Escherichia coli. This observation, and the inability of S. avermitilis to convert exogenous labeled palmitate to the corresponding UFA, was shown to be consistent with an anaerobic pathway for UFA biosynthesis. Incorporation studies with the S. avermitilis bkd mutant demonstrated that the fatty acid synthase has a remarkably broad substrate specificity and is able to process a wide range of exogenous branched chain carboxylic acids into unusual BCFAs.

Manipulation of polyketide biosynthesis for new drug discovery.

Modular polyketide synthases (PKS) are large multifunctional proteins which direct the condensation of activated short chain carboxylic acids into products of defined length and functionality using a dedicated set of active sites, or module, for each step in the polymerization. The structure of the product is directly related to the number, content and sequence of modules in a PKS. Technology is described which allows the rational manipulation of the biosynthesis of these compounds and enables the generation of specific novel polyketide structures. Examples of polyketide drugs whose structures may be manipulated using this technology are given.

Formation of ethyl esters of long chain carboxylic acids

Ethanol was extracted from the aqueous phase of fermentation into octane in a hollow fibre membrane module and converted using long-chain carboxylic acids into the corresponding esters by immobilized lipase in a reactor integrated into the octane recycle loop. The esters separated from the acids by extraction were recovered and acids and the residue esters re-extracted into octane and recycled.

Standard molar enthalpies of formation of three branched alkyl carboxylic acids

The standard (po= 0.1 MPa) molar enthalpies of combustion in oxygen at T= 298.15 K of three branched alkyl chain carboxylic acids, 2-methylpropanoic, 2,2-dimethylpropanoic, and 3-methylbutanoic, were measured by static bomb combustion calorimetry, from which their standard molar enthalpies of formation were derived.The standard molar enthalpies of formation at T= 298.15 K of the gaseous carboxylic acids were derived using literature values of their standard molar enthalpies of sublimation or vaporization.

Combinatorial approach to flavor analysis. 1. Preparation and characterization of a S-methyl thioester library.

A new method for the "one-pot" synthesis of S-methyl thioesters has been developed by reacting methyl chlorothiolformate with carboxylic acids. The resulting "flavor library" contained all the intended thioesters and a single major impurity, identified by GC-MS as S, S-dimethyldithiocarbonate. Quantification of individual compounds present in the library was performed by GC analysis using two independent methods of detection, SCD and FID. It was shown that apart from S-methyl thioacetate (0.8 mol %), molar concentrations of other thioesters varied in a relatively narrow range from 4.2 mol % for S-methyl thiopropionate to 14.1 mol % for S-methyl thiohexanoate. In general, medium chain S-methyl thioesters were present in slightly higher molar concentrations than those prepared from short or long chain carboxylic acids. This variation was attributed to partial loss of the most volatile components during extraction and the lower reactivity of higher homologues. The library was used for the characterization of some physicochemical parameters of thioesters. In particular, lipophilicity coefficients (log k(w)) and thioester retention in 10, 20, and 33% triolein (used as a model lipid phase) were determined directly by reverse-phase HPLC and extrapolated from the respective data. This analysis illustrates that substantial information can be generated using a library containing a relatively large number of compounds in effectively the same way as is necessary for the analysis of a single sample.