Long-chain Compounds Research Articles

IR spectra, conformational lability, and intermolecular interactions in long-chain aliphatic compounds

Investigations of the conformational lability and intermolecular interactions in long-chain aliphatic compounds (LACs), namely, in carboxylic acid derivatives (alkyl- and alkoxybenzoic acids; alkylcyclohexanecarboxylic acids and their completely or partially fluoroalkyl-substituted derivatives), 4-cyano-4′-p-alkoxybiphenyls, 4-cyano-4′-p-alkylbiphenyls, and cholesterol p-n-butyloxybenzoate are reviewed. Major attention is paid to experimental and theoretical IR spectroscopy data. Differential thermal analysis, polarization microscopy, and X-ray diffraction data are also taken into account. A more detailed treatment is presented on IR spectrum simulation based on data about the conformational lability of molecules and their specific (H-bonding) intermolecular interactions. The first mechanism is responsible for the conformational type of polymorphism in LACs and for the structure of the latter in solid crystal (SC) and liquid crystal (LC) states and in isotropic liquids (ILs). The second mechanism complements the structure-forming aspect of polymorphism in carboxylates, which is due to a rearrangement of hydrogen bond systems in H-complexes during polymorphic transitions to the LC and IL states. Both mechanisms are reflected in IR absorption spectra. A more adequate interpretation is possible in order to explain the many spectral features associated with the structure of LAC polymorphs and their H-complexes if these mechanisms are taken into account.

Long-Chain Acetylenic Ketones from the Micronesian Sponge Haliclona sp. Importance of the 1-yn-3-ol Group for Antitumor Activity

Two new long-chain C33 polyacetylenic compounds, halicynones A and B were isolated from the marine sponge Haliclona sp. along with known analogs. The known compound pellynol A possessing a 1-yn-3-ol terminus, exhibited strong antitumor activity against the human colon tumor cell line HCT-116 (IC50 0.026 μg/mL), however, the corresponding 1-yn-3-one, halicynone A, was inactive, which suggests an important role for the terminal 1-yn-3-ol functional group in mediating cytotoxic activity.

Chemosensory proteins of Locusta migratoria.

Two different classes of chemosensory proteins (CSPs) in Locusta migratoria have been identified on the basis of the molecular cloning of a series of different cDNAs from the antennae of this insect. Several CSP isoforms have been purified and biochemically characterized from antennal and wing extracts, some of them corresponding to expression products predicted for the identified cDNAs. In wings, the nature of the main endogenous ligand binding to these proteins was determined as oleoamide by a gas chromatography-mass spectrometric approach. One of these isoforms has been expressed in a bacterial system with high yield and used in a fluorescent binding assay. Competitive binding experiments have indicated the presence of long-chain compounds among the best ligands.

Tracking the Putative Biosynthetic Precursors of Oxygenated Mycolates of Mycobacterium tuberculosis: STRUCTURAL ANALYSIS OF FATTY ACIDS OF A MUTANT STRAIN DEVOID OF METHOXY- AND KETOMYCOLATES

Disruption of the mma4 gene (renamed hma) of Mycobacterium tuberculosis has yielded a mutant strain defective in the synthesis of both keto- and methoxymycolates, with an altered cell-wall permeability to small molecules and a decreased virulence in the mouse model of infection (Dubnau, E., Chan, J., Raynaud, C., Mohan, V. P., Lanéelle, M. A., Yu, K., Quémard, A., Smith, I., and Daffé, M. (2000) Mol. Microbiol. 36, 630-637). Assuming that the mutant would accumulate the putative precursors of the oxygenated mycolates of M. tuberculosis, a detailed structural analysis of mycolates from the hma-inactivated strain was performed using a combination of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, proton NMR spectroscopy, and chemical degradation techniques. These consisted most exclusively of alpha-mycolates, composed of equal amounts of C(76)-C(82) dicyclopropanated (alpha(1)) and of C(77)-C(79) monoethylenic monocyclopropanated (alpha(2)) mycolates, the double bond being located at the "distal" position. In addition, small amounts of cis-epoxymycolates, structurally related to alpha(2)-mycolates, was produced by the mutant strain. Complementation of the hma-inactivated mutant with the wild-type gene resulted in the disappearance of the newly identified mycolates and the production of keto- and methoxymycolates of M. tuberculosis. Introduction of the hma gene in Mycobacterium smegmatis led to the lowering of diethylenic alpha mycolates of the recipient strain and the production of keto- and hydroxymycolates. These data indicate that long-chain ethylenic compounds may be the precursors of the oxygenated mycolates of M. tuberculosis. Because the lack of production of several methyltransferases involved in the biosynthesis of mycolates is known to decrease the virulence of the tubercle bacillus, the identification of the substrates of these enzymes should help in the design of inhibitors of the growth of M. tuberculosis.

Ceramides and skin function.

Ceramides are the major lipid constituent of lamellar sheets present in the intercellular spaces of the stratum corneum. These lamellar sheets are thought to provide the barrier property of the epidermis. It is generally accepted that the intercellular lipid domain is composed of approximately equimolar concentrations of free fatty acids, cholesterol, and ceramides. Ceramides are a structurally heterogeneous and complex group of sphingolipids containing derivatives of sphingosine bases in amide linkage with a variety of fatty acids. Differences in chain length, type and extent of hydroxylation, saturation etc. are responsible for the heterogeneity of the epidermal sphingolipids. It is well known that ceramides play an essential role in structuring and maintaining the water permeability barrier function of the skin. In conjunction with the other stratum corneum lipids, they form ordered structures. An essential factor is the physical state of the lipid chains in the nonpolar regions of the bilayers. The stratum corneum intercellular lipid lamellae, the aliphatic chains in the ceramides and the fatty acids are mostly straight long-chain saturated compounds with a high melting point and a small polar head group. This means that at physiological temperatures, the lipid chains are mostly in a solid crystalline or gel state, which exhibits low lateral diffusional properties and is less permeable than the state of liquid crystalline membranes, which are present at higher temperatures. The link between skin disorders and changes in barrier lipid composition, especially in ceramides, is difficult to prove because of the many variables involved. However, most skin disorders that have a diminished barrier function present a decrease in total ceramide content with some differences in the ceramide pattern. Formulations containing lipids identical to those in skin and, in particular, some ceramide supplementation could improve disturbed skin conditions. Incomplete lipid mixtures yield abnormal lamellar body contents, and disorder intercellular lamellae, whereas complete lipid mixtures result in normal lamellar bodies and intercellular bilayers. The utilization of physiological lipids according to these parameters have potential as new forms of topical therapy for dermatoses. An alternative strategy to improving barrier function by topical application of the various mature lipid species is to enhance the natural lipid-synthetic capability of the epidermis through the topical delivery of lipid precursors.

Bioactive macrolides and polyketides from marine dinoflagellates

Abstract Absolute stereochemistry of amphidinolides G and H, potent cytotoxic 27- and 26-membered macrolides, respectively, isolated from a marine dinoflagellate Amphidinium sp., was determined by X-ray diffraction analysis, synthesis of a degradation product, and chemical interconversion. Six new macrolides, amphidinolides H2~H5, G2, G3, and W, have been isolated from a marine dinoflagellate Amphidinium sp. (strain Y-42), and the structures were elucidated by 2D NMR data and chemical means. The structure-activity relationship of amphidinolide H-type macrolides for cytotoxicity was examined. The biosynthetic origins of amphidinolides B, C, H, J, T1, and W were investigated on the basis of 13C NMR data of 13C-enriched samples obtained by feeding experiments with [1-13C], [2-13C], and [1,2-13C2] sodium acetates in cultures of the dinoflagellates. Five novel long-chain polyhydroxyl compounds, colopsinols A~E, were obtained from the Amphidinium sp. (strain Y-5).

Modified Silica Sol Coatings for Water-Repellent Textiles

The preparation of water repellent textiles by coating with different modified silica sols has been investigated. For this, pure and with 3-glycidoxypropyl triethoxysilane co-condensed silica sols were modified by three types of additives: alkyltrialkoxysilanes, polysiloxane derivatives and a fluorine containing silane. Hydrophobic properties of the coated fabrics of polyamide and of polyester mixed with cotton were determined using contact angle measurements. The hydrophobicity increases with increasing concentration of the alkylsilane additive in the silica sol and the length of the alkyl chain but with high additive concentrations plateau values in hydrophobicity were reached. Analogously textile coatings with high hydrophobicity were gained using hydrophobic polysiloxane or fluorine containing silicon compounds. The comparison of the different variants reveals that high wash-out stabilities were reached only by silica sols containing fluorine compoundsand hexadecylsilane additives. Therefore long-chain alkyltrialkoxysilane compounds could be used as substitutes for fluorine compounds for the surface modification of textiles in some practical applications.

Morphology Related to Phase Separation for the Mixed Monolayer of Fluorinated Comb Polymer and Hydrogenated Long-Chain Compound

Abstract From observations of the atomic and friction force microscopies, it has been found that the mixed monolayers of the comb polymer having the fluorocarbon side-chains and the hydrogenated amphiphile, exhibit a characteristic phase separation behavior at the micro- and mesoscopic resolutions. The regularity for molecular orientation in the mixed film was compared with that in the pure monolayer of the fluorinated comb polymer by using polarized NEXAFS spectroscopy.

Biological markers and their carbon isotopes as an approach to the paleoenvironmental reconstruction of Nansha area, South China Sea, during the last 30 ka

Paleoenvironmental changes over the last 30 ka have been documented for the Nansha area, South China Sea, from the biomarkers and their carbon isotopic composition of 314 sediment samples from core 17962. The concentrations of marine lipids indicate that the paleoceanographic and paleoclimatic conditions were not stable in the Nansha area during the last glacial period. The accumulation rates of C 37 alkenones and C 30 alkyl diols show that marine paleoproductivity was higher during the last glaciation than in the Holocene, and correlate well with those of terrestrial biomarkers. Simultaneous variations in accumulation rates of marine biomarkers and terrigenous long-chain compounds during the last glacial period suggest that this enhancement of marine productivity was caused by an increase in terrestrial nutrient supply from the Sunda Shelf. The stable carbon isotopic composition of terrigenous long-chain compounds, such as n-alkanes ( δ 13C=−28.6∼−34.2‰), n-alkanoic acids ( δ 13C=−27.1∼−31.8‰) and n-alkanols ( δ 13C=−26.6∼−35.3‰), indicates that these compounds were derived from C 3 plants, and the surrounding area of southern South China Sea was not dry during the last glacial.

Detection of Hg2+ using microcantilever sensors.

Trace amounts of Hg2+ are detected by using a microcantilever coated with gold. The microcantilever undergoes bending due to accumulation of Hg2+ on the gold surface. It is found that a concentration of 10(-11) M Hg2+ can be detected using this technology. Other cations, such as K+, Na+, Pb2+, Zn2+, Ni2, Cd2+, Cu2+, and Ca2+ have little or no effect on the deflection of the cantilever. The selectivity of the Hg2+ sensor could be improved by coating the gold surface of microcantilever with a self-assembled monolayer of a long-chain thiol compound.

Asymmetric synthesis of water-soluble analogues of galactosylceramide, an HIV-1 receptor: new tools to study virus-glycolipid interactions.

Galactosylceramide (GalCer) is a glycosphingolipid (GSL) receptor that allows HIV-1 infection of CD4-negative cells from neural and intestinal tissues. A water-soluble analogue of GalCer that features its polar head and the characteristic galactose-ceramide linkage but lacks the carbohydrate chains was prepared as a single enantiomer from (S)-serine. This analogue was not recognized in binding tests with the HIV-1 surface envelope glycoprotein gp120 in solution, which revealed the crucial importance of the ceramide alkyl chains. Two series of water-soluble GalCer analogues that contained either a hexanoic or a decanoic acyl unit and a saturated nine-carbon sphingosine moiety were designed by using molecular modeling results from natural GSLs and analogues with truncated alkyl chains. The longer chain compounds exhibit the characteristic fundamental conformation of GalCer. Seven analogues were prepared from Garner's aldehyde according to a straightforward and efficient asymmetric synthesis. All of these compounds proved to be water soluble but did not bind to gp120 in a solid-phase binding assay. These analogues were thus tested by using surface pressure measurements on a monomolecular film of GalCer, which served as a model of the plasma membrane. The incorporation of analogues very similar to GalCer into a GalCer monolayer prevented the insertion of gp120, whereas a structurally different derivative was not active. Based on these data, the molecular bases for recognition of GSLs by gp120 were elucidated. The essential importance of the GSL conformation in the primary interaction event and the crucial role of the alkyl chains of the ceramide moiety in the secondary interactions and the insertion process were clearly established.

Ferrocene Groups Tethered to Clay Surfaces : Effect of Surfactant Chain Length on Electroactivity

A homologous series of ferrocenyl surfactants, where 6, or 11, have been intercalated into thin clay films in an effort to design novel electroactive nanocomposites. Cyclic voltammetry of clay-modified electrodes has been used to investigate the electrochemical properties of the surfactants. The rate of intercalation into the clay and steady-state currents were found to be highly dependent on chain length. Of the three, the compound containing one carbon in the chain is the only molecule to be effectively modeled by an ion-exchange mechanism, implying that the ferrocene resides close to the surface of the clay. The electrochemistry of the two longer chain compounds is markedly different from the one with a single carbon in the chain. The six- and eleven-carbon chain compounds have been shown to generate a larger capacitive current in the clay and represent possible charge-storage devices. © 2002 The Electrochemical Society. All rights reserved.

Deactivation Behavior of Bifunctional Pt/H-Zeolite Catalysts during Cyclopentane Hydroconversion

Cyclopentane hydroconversion was used as a probe reaction to study the coking behavior of selected large-pore zeolites loaded with 0.5% Pt under identical conditions. The zeolites studied, namely, Y zeolite, zeolite beta, mordenite, LTL, and ZSM-12, were also tested at several different Si/Al ratios. The zeolite pore structure was the most important factor determining the deactivation behavior. Zeolites like Y and L that possess large cavities connected to smaller pore openings allow polyaromatic molecules to form and also trap these coke molecules to a great extent, resulting in rapid deactivation. This was confirmed by the analysis of soluble coke, which revealed the presence of large amounts of benzoperylene and coronene. Zeolite beta, which possesses an intersecting three-dimensional pore system, but no large cages, was the most stable. Apart from its pore structure, the excellent stability of the zeolite beta catalysts could also be partly attributed to the electronic state of platinum in the catalyst. The absence of aromatic compounds in the product stream and the aliphatic nature of coke indicated that the platinum in zeolite beta selectively opened the cyclopentane ring and did not dehydrogenate it, preventing the formation of cyclopentadiene that condenses via a Diels–Alder mechanism into polyaromatic coke. Mordenite and ZSM-12 showed reasonably good stability. Interestingly, the soluble coke in mordenite consisted of both polyaromatic and long-chain aliphatic compounds, indicating that the selectivity of the metal function changes with time. The amount of “hard coke” deposited in the zeolites was strongly related to the initial activity of the acid function, with the more active catalysts having a larger amount of coke. However, this trend was not followed in ZSM-12 which showed a shape-selective behavior that restricted the deposition of hard coke to a great extent. Apart from pore structure, variation of the acid site density (Si/Al ratio) affected metal dispersion and metal/acid balance and caused significant differences in the catalytic performance within a particular type of zeolite. However, the nature of the acid sites (Brønsted or Lewis) did not have a significant effect. Catalysts that had Si/Al ratios in the range 15 to 40 showed a minimum in the C1/C3 ratio indicating a good balance between the metallic and acidic functions and showed good time stability.

Orientational Mechanism for Long-Chain Organic Molecules During Physical Vapor Deposition

Molecular orientations during physical vapor deposition of various linear long-chain compounds are interpreted on the basis of a simple model for the initial stage of anisotropic crystal growth. In this model, the initial stage involves adsorption from vapor, surface migration, re-evaporation from the substrate, capture into a cluster, re-evaporation from a cluster, and re-orientation, where the anisotropy of the molecules are considered. In addition, two fundamental orientations of initial small nuclei are assumed to be under thermal equilibrium. The set of differential equations for the individual elementary processes can be solved numerically. The calculated results agree well with actual orientational phenomena of long-chain molecules at various substrate temperatures, i.e., a higher substrate temperature results in a higher degree of normal orientation.

Anti-inflammatory prodrugs as plasticizers for biodegradable implant materials based on poly(3-hydroxybutyrate).

Salicylic and acetylsalicylic acid esters were tested as plasticizers for biodegradable poly(3-hydroxybutyrate) (PHB). The aim is the combination of plasticizing and anti-inflammatory properties in the fabrication of implant materials. Solution-cast films made of mixtures of PHB and 30% ester showed plasticization accompanied by a decrease of elastic modulus and an increase in elongation at break in comparison with pure PHB films. However, the number of usable plasticizers from the group of the salicylic acid and acetylsalicylic acid esters is limited. Short-chain derivatives are volatile while long-chain compounds tend to crystallize. In both cases PHB films embrittle within short time. Moreover, some derivatives show a fast release in an aqueous environment. As alternative nonsteroidal anti-inflammatory prodrugs arylpropionic acid esters were tested as plasticizers. The addition of ketoprofen ethyl ester led to PHB films with decreased brittleness. In summary, various esters of anti-inflammatory drugs show plasticizing effects on solution-cast PHB films comparable with those of commonly used citric acid esters.

ORGANOPHOSPHORUS COMPOUNDS AS POTENTIAL FUNGICIDES. PART VI.1 PREPARATION, CHARACTERIZATION, AND BIOLOGICAL ACTIVITY OF ANALOGUES AND DERIVATIVES OF 1-AMINOPROPANEPHOSPHONIC ACID

α-Aminopropane-phosphonous,-methylphosphinic, and-phenylphosphinic acids do not exhibit comparable antifungal activity to that shown by α-aminopropanephosphonic acid (ampropylfos) against Drechslera teres, when applied as seed dressings. It is concluded that the phosphonic acid function is necessary for this type of activity. Moderate activity against several organisms was nevertheless shown by α-aminopropane-and α-aminoethane-phosphonous acids in foliar spray tests, although longer chain compounds were found to be inactive, α-Ureidopropanephosphonate (ammonium salt) also showed activity in foliar tests at 1000 ppm. A range of new ureylene-and thioureylene-bisphosphonates, prepared as potential profungicides of ampropylfos, proved to be inactive as seed dressings although tetrakis(2,2,2-trifluoroethyl) thioureylenebis(1-propylphosphonate) gave 75–100% control of Puccinia recondita as a foliar spray (1000 ppm). Characterization of the various compounds by nmr spectroscopy and mass spectrometry is discussed.

An Exploration of Long Range Electronic Effects in Substituted Alkanes

An analysis of the results of ab initio quantum mechanical calculations has been performed on a large number of substituted ethanes, pentanes, hexanes, and dodecanes. The bond critical points of the Atoms in Molecules (AIM) method have been ascertained for these molecules and each is expressed as a FCP, which is defined as the fraction of the bond distance at which the critical point is located. In the ethyl derivatives, the FCPs for the methyl C−H bonds correlate with the charge on the hydrogen atoms. In the longer chain compounds, the FCP for the Cm−Cn bond of charged substituents is related to the difference in inverse distances of the carbon atoms from the charged substituent. An investigation of the amount of s character used in bonds showed that two measures of this quantity, a partial Mulliken overlap population analysis, and a method involving orthogonal Natural Bonding Orbital (NBO) theory orbitals, correlate well with the methylene H−C−H bond angle. In the NBO results for most C−C bonds, the amo...

Structure and Dynamics of Selectively Deuterated Self-Assembled Silver n-Octadecanethiolate Layered Materials

The dynamics of the alkyl chains below and above the chain-melting transition temperature of long-chain silver n-alkanethiolate layered compounds were studied using variable-temperature 2H NMR and IR spectroscopies. Two specifically deuterated compounds, silver-d35-octadecanethiolate [AgSCH2(CD2)16CD3] and silver-1,1-d2-octadecanethiolate [AgSCD2(CH2)16CH3], were used to identify the behavior of different regions of the chains. The 2H NMR studies provide details about the alkyl chain motion, whereas IR spectroscopy provides details of the alkyl chain conformation. A key structural component of these materials is a polymeric −Ag−S− backbone from which the alkyl chains extend outward from both sides. The result is a two-dimensional, ribbonlike structure. The alkyl chains are highly ordered and adopt an extended all-trans conformation, which is maintained up to a few degrees below the phase transition temperature. The occurrence of a significant gauche population is observed above the phase transition temper...

Mesomorphic behaviour of praseodymium(III) alkanoates

In this paper, we describe the synthesis, characterization and thermal behaviour of praseodymium(III) alkanoates. The compounds have the stoichiometry [Pr(C x H2x+1COO)3], where x = 5-19, and were characterized by elemental analysis and infrared spectroscopy. The thermal behaviour was investigated by hot-stage polarizing optical microscopy, DSC and high temperature X-ray diffraction. A highly viscous mesophase M and a smectic A phase were observed for the shorter chain compounds (x = 5-8), whereas only a smectic A phase was observed for the longer chain compounds of this type of metallomesogens. The chain length has a pronounced effect on the transition temperatures.

Novel layered superstructures in mixed ultralong n-alkanes.

Two new types of layered structures were found in binary mixtures of n-alkanes ranging from C122H246 to C294H590. At high temperatures a semicrystalline form is the stable phase, having a regular structure of alternating crystalline and amorphous layers. The two long-chain compounds are mixed in the crystalline layers and the amorphous layers consist of the surplus length of the longer chains. At lower temperatures a reversible transition occurs to a triple layer superlattice structure with a periodicity of up to 50 nm. These two new phases allow the existence of binary solid solutions of chains with a length ratio of up to 1.7 and a chain length difference of 100 CH2 groups.