Increasing Hydrocarbon Chain Length Research Articles

Removal of n-alcohols from aqueous streams using micellar-enhanced ultrafiltration

Micellar-enhanced ultrafiltration (MEUF) is a membrane separation process which may be used to remove dissolved organic solutes from water. In MEUF, surfactant is added to the aqueous stream and forms aggregates called micelles into which the solute solubilizes. The stream is then forced through an ultrafiltration filter with pore sizes small enough to reject the micelles containing the solute. In this work, the removal of n-hexanol, n-heptanol, and n-octanol from water using MEUF was studied. Alcohol rejections varied from 71% to 98.8% for the conditions studied, demonstrating the feasibility of the method. Rejection increased with increasing hydrocarbon chain length of the alcohol and decreasing alcohol/surfactant ratio. The alcohol in the permeate appears to be in equilibrium with the alcohol in the retentate, the total concentration difference being caused by the presence of micelles on the retentate side. Surfactant rejections were greater than 98% for all cases studied. Excellent fluxes were also observed.

Thin-layer chromatography of ecdysone acyl esters and their 2,3-acetonide derivatives

Thin-layer chromatography (TLC) has been investigated as a means of separating ecdysone 22-acyl esters from each other and from other classes of ecdysteroid. Various types of high-performance TLC (HPTLC) plate have been evaluated with a range of solvent systems of differing polarity. Adsorption HPTLC on silica gives minimal separation of the various ecdysone 22-long-chain fatty acyl esters, either after a single development or after multiple development. Silica HPTLC does, however, clearly resolve the ecdysone 22-long-chain fatty acyl esters from their 2,3-acetonide derivatives and from ecdysone 2-stearate, ecdysone 2,22-distearate, ecdysone 2,3,22-tristearate or from the various ecdysone acetates. Reversed-phase HPTLC of the ecdysone 22-acyl esters and of their 2,3-acetonide derivatives has been extensively investigated on C 8-plates and the results compared with those obtained on C 2−, C 18− and CN-bonded phases. All types of reversed-phase HPTLC plate give good separation of the saturated long-chain fatty acyl esters of ecdysone or their 2,3-acetonide derivatives when a mobile phase of appropriate polarity is used, mobility decreasing with increasing fatty acid carbon chain length and increasing hydrocarbon chain length of the bonded phase. However, the different hydrocarbon chain lengths of the three bonded phases show different selectivities for the unsaturated long-chain fatty acyl esters, relative to the saturated acyl esters. In all systems increased unsaturation results in greater mobility but the magnitude of the increase in mobility is dependent on the hydrocarbon chain length of the bonded phase, being greatest with C 18-plates and least with CN-plates. HPTLC plates with a CN-bonded phase also provide suitable separations in the normal-phase mode, giving slightly better resolution of the various ecdysone 22-long-chain fatty acyl esters than is achieved on silica. The applicability of HPTLC coupled with radioscanning as a means of rapidly detecting the presence of and partially identifying apolar ecdysteroid conjugates in biological studies involving the metabolism of [ 3H]ecdysone is demonstrated and discussed.

Wettability and floatability of galena—xanthate system as a function of solution surface tension

The wettability of galena pre-treated with n-alkyl xanthates of increasing hydrocarbon chain (from methyl to decyl) has been studied as a function of solution surface tension, γ 1v. As the hydrocarbon chain length increases the critical surface tension of wetting, γ c, established in methanol solutions decreases from 30 to 26 mN m −1 and the slope of the wettability lines, β, decreases to zero, then becomes increasingly negative approaching the β value of paraffin wax. The wettability of galena in decyl xanthate solutions was also studied and compared with pre-xanthated galena in methanol solutions. The floatability of pre-xanthated galena as well as the bulk lead xanthate of increasing hydrocarbon chain length was evaluated in relation to γ 1v. A correlation between the minimum flotation recoveries and γ c values is observed. Above these γ c values, increasingly higher γ 1v, values are required for the flotation of particles as the hydrocarbon chain length of xanthate decreases.

Hydrostatic pressure induces hydrocarbon chain interdigitation in single-component phospholipid bilayers.

By use of neutron diffraction for structural analysis, the temperature-pressure phase diagrams of several fully hydrated single-component phospholipid bilayers have been explored up to hydrostatic pressures of 2 kbars. The gel to liquid-crystalline phase transition temperature Tm increases linearly with pressure over a 10(-3)-2 kbar range in accordance with the Clausius-Clapeyron relationship giving dTm/dP values of 23.0 degrees C/kbar for 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 28.0 degrees C/kbar for 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC). The so-called pretransition was not observed in the isothermal pressure experiments, suggesting that no appreciable volume change occurs at this transition. These results are in good agreement with those reported using other techniques. In addition, at pressures higher than the isothermal liquid-crystalline to gel transition pressure, a new pressure-induced phase transition was observed for DPPC and DSPC in which the hydrocarbon chains from apposing monolayers become interdigitated with the chains occupying a cross-sectional area approximately equal to 5% less than in the gel phase. The temperature-pressure phase diagrams show the gel-interdigitated phase boundaries to be highly curved and the minimum pressure at which interdigitation occurs to decrease with increasing hydrocarbon chain length.

A semi-empirical conformational analysis of the interaction of n-alkanols with dipalmitoylphosphatidylcholine

The interaction of a homologous series of saturated aliphatic n-alkanols (containing 1–13 carbon atoms) with dipalmitoylphosphatidylcholine was studied by a semi-empirical conformational analysis. The minimal conformational energy of the isolated molecule at the hydrocarbon-water interface was calculated as the sum of the contributions resulting from the Van der Waals, torsional, electrostatic and transfer energies. From the conformers of minimal energies were calculated the hydrophilic-hydrophobic balance, the distance between hydrophilic and hydrophobic centres and the energies of interaction between homologous alkanols and between alkanols and lipids. Using these parameters, different modes of conformation, orientation and interaction of n-alkanols and dipalmitoylphosphatidylcholine were described. For methanol, ethanol and n-propanol, the gauche conformers were the most probable interacting only with the lipid polar heads. Only all- trans conformers were obtained for alkanols with longer acyl chains. n-Butanol to n-octanol form clusters in the lipid matrix. Longer n-alkanols are randomly distributed in the lipid layer. However, due to the increase in hydrocarbon chain-length, n-nonanol and higher alkanols have an interaction energy identical or superior to that found in a pure lipid monolayer, leading to a more ordered alkanol-lipid organization.

The Selectivity Characteristics of Surfactant Ion-sensitive Nitrobenzene-membrane Electrode

Abstract The selectivity coefficients of nitrobenzene-membrane electrode containing dodecyltrimethylammonium dodecyl sulfate as an ion exchanger were determined. For a homologous series of surfactant ions, the logarithm of the selectivity coefficient was found to increase linearly with increasing hydrocarbon chain length. The selectivity sequence for anionic surfactant ions with the same alkyl chain length became alkyl-benzenesulfonate ion>alkyl sulfate ion>>alkanesulfonate ion, while that for cationic ones became alkyltrimethyl-ammonium ion≈1-alkylpyridinium ion>>alkylammonium ion. These results can reasonably be interpreted in terms of the partition coefficient of surfactant ion between aqueous and membrane phases. A tentative estimation based on the theory of liquid-membrane electrode led to −2900 J mol−1 for the standard free energy of transfer of a methylene group from water to nitrobenzene.

Protein—Non‐ionic Detergent Interaction

The binding isotherms of bovine serum albumin with octylglucoside and decyl glucoside were determined at 7 degrees C and 25 degrees C at pH 7.4 and ionic strength 0.1 M. The average number of detergent molecules bound was found to increase with increasing hydrocarbon chain length. Competitive binding indicates that alkylglycosides combine with the same sites as alkyl sulphates. Native bovine serum albumin has about 12 and 10 sites for non-ionic ligands at 7 degrees C and about 15 and 13 sites at 25 degrees C for octyl and decyl glucosides respectively. The values for standard free energy changes--delta G0, were calculated from the intrinsic association constants. Fourier-transformed infrared spectroscopy was used to study the effects of alkyl glucosides on the conformation of albumin. The results obtained indicate that there are no significant changes in protein structure.

C. M. C., counterion binding and thermodynamics of ethoxylated anionic and cationic surfactants

The properties of a series of ionic ethoxylated surfactants of the typeR m (OC2H4) χ SO4Na andR m (OC2H4) χ TAB (m = 10, 12, 14 or 16 andx = 0, 1, 2 or 3) were studied. Surface areas obtained from surface tension measurements increased as the ethoxy group number increased whereas increasing the hydrocarbon chain length had little effect. The c.m.c.'s obtained from conductivity decreased with increase in hydrocarbon chain length and to a smaller extent as the ethoxy group number increased. Values ofΔG° showed the methylene group to be four fold as effective as the ethoxy group in promoting micellisation. As the temperature was varied between 5 and 60 °C all the surfactants exhibited a minimum c.m.c. value close to 25 °C which decreased as the surfactant became more hydrophobic and increased as the surfactant became more hydrophilic. Counterion binding from specific ion electrode measurements increased with increase in hydrocarbon chain length but decreased with increase in ethoxy group number. Counterion binding decreased with increase in temperature.

Micellar molecular weights and hydration of ethoxylated anionic and cationic surfactants

Further work on the micellar properties of ethoxylated anionic and cationic surfactants is reported. Micellar molecular weights in water obtained from light scattering and corrected for charge effects, increased with increase in hydrocarbon chain length but decreased with increase in ethoxy group number. Micellar size of the ethoxylated surfactants was smaller than usual for paraffin chain salts. Micellar weights decreased 18% as the temperature increased from 25 to 45 °C. Addition of 0.1M. electrolyte increased micellar weight four fold. Analysis of the hydrodynamic data showed the ethoxylated micelles were hydrated with two molecules of water per ethoxy group. The hydrocarbon chain had little effect on hydration.

Dielectric Relaxation of Water in Aqueous Solutions of n‐Alkylamine Hydrochlorides Part 1: Solute Concentrations Smaller than the Critical Micelle Concentrations

AbstractThe solutes are the homologous salts CH3(CH2)nNH3Cl with n = 3, 5, 6, and 7. The complex permittivity of the solutions has been measured in dependence of frequency between 5 and 37 GHz at 25°C.From the analysis of the frequency dependence of the complex permittivity, statements are made on the orientational polarizability, the reorientation time and the number of the hydration water molecules of the n‐alkylammonium ions. The orientational polarizability of the hydration water does not markedly differ from that of pure water. The reorientation time and the numbers of the disturbed water molecules around the cations strongly increase with increasing hydrocarbon chain length of the cations.The reorientation times and the numbers of the hydration water molecules of the n‐alkylammonium ions are compared with those of the tetra‐alkylammonium ions. From this comparison is clearly established that the hydrophobic interaction around the former ions is more pronounced than around the latter.

Kinetics of the reaction of the hydrophobic ester 4-nitrophenyl decanoate with long-chain N-alkylimidazoles above and below their critical micelle concentration

The kinetics of the reaction of 4-nitrophenyl decanoate with a series of straight-chain N-alkylimidazoles have been studied at 25� in water and aqueous ethanol. In water, below the critical micelle concentration of the N-alkylimidazole, hydrophobic interaction between the hydrocarbon chains of the reactants caused substantial increases in the reaction rate (up to about 200-fold) compared with the rate of reaction of 4-nitrophenyl acetate with N-methylimidazole. The rate constants, though, differed from those previously reported which were measured with a higher initial concentration of ester. No increase in rate with increasing hydrocarbon chain length could be detected in the presence of a large concentration of ethanol (mole fraction of 0.31) but a rate increase did occur in the presence of a more moderate concentration of ethanol (mole fraction of 0.10), confirming that hydrophobic interactions persist in this mixed solvent. The long-chain ester reacts rapidly with N-alkylimidazole micelles. Association constants (K) for binding the ester to the micelles and rate constants for the reaction of the bound ester (km) were estimated by following the conventional treatment of the kinetics of micelle-catalysed reactions. The value of K was found to increase sharply with increasing hydrocarbon chain length of the micelle but km showed the opposite trend.

N-acylsuccinimides as acylating agents for proteins: the selective acylation of lysine residues.

The suitability of N‐acylsuccinimides as reagents for the selective acylation of reactive side chains in proteins has been examined. A detailed study of the reaction of N‐acetylsuccinimide with ribonuclease and bovine serum albumin showed that acetylation occurred in the pH range 3 to 8. Lysine side chains were acetylated selectively, with little or no modification of tyrosine side chains. There was no evidence for acetylation of serine, threonine or histidine side chains. The analogous N‐propionyl, N‐n‐butyryl, N‐i‐butyryl and N‐n‐valerylsuccinimides also selectively acylate lysine side chains in proteins. This series of reagents, capable of changing the charge of lysine side chains and adding acyl groups of increasing hydrocarbon chain length, should prove a useful tool in studies of protein structure.

Molecular forces governing non-electrolyte permeation through cell membranes

The relations between the chemical structure of non-electrolytes and their ability to permeate cell membranes are analysed at the level of molecular forces, using the measurements of reflexion coefficients in gall-bladder epithelial cells tabulated in the preceding paper. Stronger solute:water forces and weaker solute:membrane forces are associated with lower permeating power. The portions of the membrane controlling non-electrolyte permeation behave as nearly pure hydrocarbons with very few hydrogen-bonding sites. Most substituents (hydroxyl, ether, carbonyl, ester, amino, amide, urea, nitrile) are shown to decrease permeation in proportion to the number and strength of intermolecular hydrogen bonds which they form with water, while intramolecular hydrogen bonding accelerates permeation. Carbon-carbon double bonds and triple bonds and aromatic residues decrease permeability due to hydrogen bonds involving π electrons. Inductive effects, in which a substituent indirectly modifies permeability by withdrawing or releasing electrons at an adjacent hydrogen bonding site, are most noticeable for halogens, the nitro group, double and triple bonds, and branched alkyl groups. Altered forces between membrane hydrocarbons and the solute retard the permeation (weaker forces) of fluorine compounds and branched compounds, and slightly accelerate the permeation (stronger forces) of other halogen derivatives and compounds with long carbon chains. The main factor in the increase of permeability with increasing hydrocarbon chain length is an entropy effect associated with a change in local water structure; and this effect is partly responsible for the decrease in permeability with chain branching, whose origin is particularly complex.

Molecular forces governing non-electrolyte permeation through cell membranes.

The relations between the chemical structure of non-electrolytes and their ability to permeate cell membranes are analysed at the level of molecular forces, using the measurements of reflexion coefficients in gall-bladder epithelial cells tabulated in the preceding paper. Stronger solute: water forces and weaker solute: membrane forces are associated with lower permeating power. The portions of the membrane controlling non-electrolyte permeation behave as nearly pure hydrocarbons with very few hydrogen-bonding sites. Most substituents (hydroxyl, ether, carbonyl, ester, amino, amide, urea,nitrile) are shown to decrease permeation in proportion to the number and strength of intermolecular hydrogen bonds which they form with water, while intramolecular hydrogen bonding accelerates permeation. Carbon-carbon double bonds and triple bonds and aromatic residues decrease permeability due to hydrogen bonds involving nelectrons. Inductive effects, in which a substituent indirectly modifies permeability by withdrawing or releasing electrons at an adjacent hydrogen bonding site, are most noticeable for halogens, the nitro group, double and triple bonds, and branched alkyl groups. Altered forces between membrane hydrocarbons and the solute retard the permeation (weaker forces) of fluorine compounds and branched compounds, and slightly accelerate the permeation (stronger forces) of other halogen derivatives and compounds with long carbon chains. The main factor in the increase of permeability with increasing hydrocarbon chain length is an entropy effect associated with a change in local water structure; and this effect is partly responsible for the decrease in permeability with chain branching, whose origin is particularly complex.

X‐ray diffraction powder data of some thiol esters of long chain fatty acids

SummaryX‐ray diffraction powder data were obtained for 14 thiol esters of long chain fatty acids including benzyl, β‐naphthyl,n‐amyl, andn‐hexyl thiol myristates; thiol palmitates; thiol stearates; and in some cases thiol laurates. All the individual compounds can be readily distinguished and identified by the diffraction data. Long spacings increase regularly with increase in hydrocarbon chain length. The benzyl and β‐naphthyl thiol esters crystallize in tilted bimolecular layers while then‐amyl andn‐hexyl thiol derivatives crystallize in tilted monomolecular layers.