Increasing Chain Length Of Alcohol Research Articles

Impact of short-chain alcohols on the formation and stability of nano-emulsions prepared by the spontaneous emulsification method

The principles of formation and stability of nano-emulsions have been extensively investigated in previous research. In this study, we focus on the impact of short-chain alcohols (C<5) on the formation and stability of oil-in-water nano-emulsions prepared by the spontaneous emulsification method. Due to its smaller droplet size and excellent optical transparency, the nano-emulsion stabilized by Cremophor EL was selected for further study. Addition of alcohol facilitated the nano-emulsion formation, moreover, the droplet size decreased with increasing alcohol chain length (C>2) and hydroxyl groups. Nevertheless, the droplet size then increased further with the addition of alcohols, which we ascribed to the effect of alcohols on droplet flocculation. An optimum Cremophor EL-to-1-butanol ratio of 2:1 was employed to construct the ternary phase diagram. It was found that the fine droplets (r<100nm, PDI<0.2) were obtained only when converting the initial oil drops completely into the lamellar liquid crystalline phase and/or bicontinuous phase and then this phase became supersaturated in oil, so that the nucleation of oil drops occurred spontaneously. According to the dynamic light scattering results, coalescence and Ostwald ripening were the main destabilization mechanisms in our systems. Notably, nano-emulsion stability was greatly improved with ethanol in comparison to 1-propanol and 1-butanol.

NMR study of the influence of n‐alkanol co‐surfactants on reverse micelles in quaternary microemulsions of cetyltrimethylammonium bromide (CTAB)

The effects of different n-alkanol co-surfactants on the size, shape, composition and dynamics of reverse micelles (RMs) in cetyltrimethylammonium bromide (CTAB)/n-alkanol/n-hexane/water and CTAB/n-alkanol/n-pentane/water microemulsions were investigated using T2 relaxation and pulsed gradient stimulated echo nuclear magnetic resonance (NMR) measurements and molecular modelling. NMR T2 relaxation times and diffusion coefficients were determined for the surfactant and co-surfactant in these CTAB quaternary reverse microemulsions, for a range of medium chain length alcohol co-surfactants, from 1-butanol to 1-heptanol. These data revealed a slight RM size dependency on co-surfactant chain length, with RM sizes tending to decrease with increasing alcohol chain length. Molecular modelling of CTAB/n-alkanol/n-hexane/water RMs suggested a variation in RM shape with co-surfactant chain length, where those formed with pentanol were found to be least spherical and those formed with heptanol the most spherical. The NMR data also revealed differences in the behaviour of the micellar structures in the CTAB/n-pentanol/n-hexane/water reverse microemulsion, compared with the other reverse microemulsions in this study, where CTAB was found to be distributed between two environments, which then combined to form larger micelles. The origins of these differences remain unclear. Copyright © 2016 John Wiley & Sons, Ltd.

Investigation on the Structure of Water/AOT/IPM/Alcohols Reverse Micelles by Conductivity, Dynamic Light Scattering, and Small Angle X-ray Scattering

We have systematically investigated the effect of alcohols (ethanol, propanol, butanol, and pentanol) on the structure of the water/AOT/IPM system using conductivity, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) techniques. The results show that no percolation phenomenon is observed in the water/AOT/IPM system, whereas the addition of ethanol (propanol and butanol) induces apparently percolation. The threshold water content (W(p)) depends closely on the alcohol type and concentration. The effect of alcohols on the conductance behavior is discussed from the physical properties of alcohols, the interfacial flexibility, and the attractive interactions between droplets. The hydrodynamic diameter of droplets (d(H)) obtained from DLS increases markedly with the increase in water content (W(0)); however, it decreases gradually with increasing alcohol chain length and concentration. SAXS measurements display distinctly the shoulder, the low hump peaks, and the heavy tail phenomenon in the pair distance distribution function p(r) profile, which rely strongly on the alcohol species and its concentration. The gyration radius (R(g)) increases with increasing W(0), and decreases with the increase of alcohol chain length and concentration. Schematic diagram of the conductance mechanism of water/AOT/IPM/alcohol systems is primarily depicted. Three different phases of the discrete droplets, the oligomers, and the isolated ellipsoidal droplets existed in the different W(0) ranges correspond to three different stages in the conductivity-W(0) curve. Coupling the structure characteristics of reverse micelles obtained from DLS and SAXS techniques with conductivity could be greatly helpful to deeply understand the percolation mechanism of water/AOT/IPM/alcohols systems.

Liquid–Liquid Phase Equilibria of 1-Propanol + Water + n-Alcohol Ternary Systems at 298.15 K and Atmospheric Pressure

Liquid–liquid equilibrium (LLE) data for the ternary systems 1-propanol + water + n-alcohols (1-pentanol, 1-hexanol, 1-octanol, 1-nonanol, 1-decanol, or 1-dodecanol) were determined at 298.15 K and atmospheric pressure. The n-alcohols from 1-pentanol up to 1-dodecanol can be used as extraction solvents for the separation of 1-propanol from aqueous solutions. The miscibility curves, the conode lines, and the plait points were obtained. The phase diagrams for all of these systems are of type I in according to Trayball classification. The Othmer–Tobias and Hand equations, used to verify the quality of the experimental data, give similar and generally good results for all of the systems. The experimental ternary LLE data were correlated with the universal quasichemical activity coefficient (UNIQUAC) model which represents satisfactorily the obtained experimental data. Distribution coefficients (Di) and separation factors (S) were calculated from tie-line data to evaluate the extracting capability of the solvents, which increases with increasing alcohol chain length.

The determination of volumetric standard states and solute–solute interactions in competitive quaternary aqueous solutions using a self-consistent multivariate approach

A general methodology involving semi-batch experimental design is proposed in order to determine the volumetric standard states as well as homotactic and heterotactic volumetric solute–solute interaction coefficients from the associated quaternary solutions alone. The densities of quaternary aqueous solutions consisting of three alcohol solutes, e.g. methanol, ethanol, and 1-propanol, in the range of concentrations 0.0000 < x solute - i < 0.0093 at 298.15 K and 0.1013 MPa were measured in order to demonstrate the utility of this methodology. The volumetric standard states as well as the interaction coefficients were determined from combined use of a multivariate response surface model together with the McMillan–Mayer formalism and a 3rd-order virial expansion, without relying on either pure component properties or binary/ternary solution information. Since no external measurements are admitted, additional sources of experimentally induced error are eliminated, and the associated numerical sensitivity of the excess volumetric equations is more appropriately treated. The volumes of interaction reveal that hydrophobic–hydrophobic interactions predominate. All homotactic and heterotactic interaction coefficients are negative and their magnitudes increase with increasing alcohol chain length. The coefficients obtained from quaternary-solution multivariate analysis are in good agreement with separate binary and ternary measurements reported in the literature. Such a general approach should provide new opportunities for the understanding of molecular recognition processes in complex solutions.

Substrate Specificity of Carboxylesterase Isozymes and Their Contribution to Hydrolase Activity in Human Liver and Small Intestine

Hydrolase activity from human liver and small intestine microsomes was compared with that of recombinant human carboxylesterases, hCE-1 and hCE-2. Although both hCE-1 and hCE-2 are present in human liver, the dominant component was found to be hCE-1, whereas the hydrolase activity of the human small intestine was found to be predominantly hCE-2. hCE-2 has a limited ability to hydrolyze large acyl compound substrates. Interestingly, propranolol derivatives, good substrates for hCE-2, were easily hydrolyzed by substitution of the methyl group on the 2-position of the acyl moiety, but were barely hydrolyzed when the methyl group was substituted on the 3-position. These findings suggest that hCE-2 does not easily form acylated intermediates because of conformational interference in its active site. In contrast, hCE-1 could hydrolyze a variety of substrates. The hydrolytic activity of hCE-2 increased with increasing alcohol chain length in benzoic acid derivative substrates, whereas hCE-1 preferentially catalyzed the hydrolysis of substrates with short alcohol chains. Kinetic data showed that the determining factor for the rate of hydrolysis of p-aminobenzoic acid esters was V(max) for hCE-1 and K(m) for hCE-2. Furthermore, the addition of hydrophobic alcohols to the reaction mixture with p-aminobenzoic acid propyl ester induced high and low levels of transesterification by hCE-1 and hCE-2, respectively. When considering the substrate specificities of hCE-1, it is necessary to consider the transesterification ability of hCE-1, in addition to the binding structure of the substrate in the active site of the enzyme.

Homogeneous nucleation of n-propanol, n-butanol, and n-pentanol in a supersonic nozzle

We have measured the nucleation conditions of n-propanol, n-butanol, and n-pentanol in a supersonic Laval nozzle, and estimated that the maximum nucleation rate J is 5 x 10(16) cm(-3) s(-1) with an uncertainty factor of 2. Plotting the vapor pressures p(J(max) ) and temperatures T(J(max) ) corresponding to the maximum nucleation rate as ln(p) versus 1T, produces a series of well separated straight lines. When these values are scaled by their respective critical parameters, p(c) and T(c), the data lie close to a single straight line. Comparing the experimental data to the predictions of classical nucleation theory reveals much higher experimental rates, and the deviation increases with increasing alcohol chain length and decreasing temperature. A scaling analysis in terms of Hale's scaled nucleation model [Phys. Rev. A 33, 4156 (1986); Metall. Trans. A 23, 1863 (1992)], clearly shows that our data are consistent with experimental nucleation rates measured using other devices that have characteristic rates many orders of magnitude lower.

Binding of small alcohols to a lipid bilayer membrane: does the partitioning coefficient express the net affinity?

The total vapor pressures at 26°C of binary (water–alcohol) and ternary (water–alcohol–vesicle) systems were measured for six short chain alcohols. The vesicles were unilamellar dipalmitoyl phosphatidylcholine (DMPC). The data was used to evaluate the effect of vesicles on the chemical potential of alcohols expressed as the preferential binding parameter of the alcohol–lipid interaction, Γ 23. This quantity is a thermodynamic (model-free) measure of the net strength of membrane–alcohol interactions. For the smaller investigated alcohols (methanol, ethanol and 1-propanol) Γ 23 was negative. This is indicative of so-called preferential hydration, a condition where the affinity of the membrane for water is higher than the affinity for the alcohol. For the longer alcohols (1-butanol, 1-pentanol, 1-hexanol) Γ 23 was positive and increasing with increasing chain length. This demonstrates preferential binding, i.e. enrichment of alcohol in the membrane and a concomitant depletion of the solute in the aqueous bulk. The measured values of Γ 23 were compared to the number of alcohol–membrane contacts specified by partitioning coefficients from the literature. It was found that for the small alcohols the number of alcohol–membrane contacts is much larger than the number of preferentially bound solutes. This discrepancy, which is theoretically expected in cases of very weak binding, becomes less pronounced with increasing alcohol chain length, and when the partitioning coefficient exceeds approximately 3 on the molal scale (10 2 in mole fraction units) it vanishes. Based on this, relationships between structural and thermodynamic interpretations of membrane partitioning are discussed.

Measurement of the molecular content of binary nuclei. IV. Use of the nucleation rate surfaces for the n-nonane-n-alcohol series

In a previous paper the molecular content of binary water-n-alcohol nuclei has been determined from nucleation rate measurements. A strong mutual enhancement of water and alcohol in forming the nuclei was observed, although macroscopically the higher alcohols are only partially miscible with water. In this paper we replace water by n-nonane, that is, we examine n-nonane-CiH2i+1OH systems with i=2–6. Using the nucleation pulse technique nucleation rates in the range 105&amp;lt;J/cm−3 s−1&amp;lt;109 are measured. Ranging from pure n-nonane to pure n-alcohol the n-nonane and n-alcohol activities, a1 and a2, respectively, are varied for each system with about eight intermediate compositions at a constant temperature of T=230 K. A rather reluctant conucleation of the n-alcohols with n-nonane is found, the most stubborn being ethanol. However, one observes that with increasing alcohol chain length the nucleation process tends to become more ideal. We present the full experimental nucleation rate surface J(a1,a2) for n-nonane-n-propanol as an example. From the nucleation rate surface for each system the onset activities corresponding to a reference nucleation rate of J0=107 cm−3 s−1 are determined. From the slopes of the nucleation rate surfaces one obtains the individual numbers of molecules in the critical cluster ni*≈∂ ln J/∂ ln ai. As noted previously, determining the molecular content this way does not involve any particular theoretical model, nor does it depend on the structure of the critical cluster. Accordingly, the average composition of the critical clusters is obtained. An alcohol depletion of the nuclei at low alcohol activity fraction is found for all alcohols examined, the degree diminishing with increasing alcohol chain length. Macroscopically all alcohols are miscible with nonane. Similarly, a depletion of n-nonane in the nuclei is observed at low n-nonane activity fractions. The approach towards a macroscopic miscibility gap for the shorter alcohols is reflected in quantitative but no qualitative changes of the composition of the microscopic nuclei.

Solvent dependence of homogeneous and inhomogeneous broadenings in β-carotene solutions

Solvent dependencies of homogeneous and inhomogeneous broadenings are investigated by measurements of absorption and fluorescence spectra of β-carotene at 175 K. Methanol, ethanol. 1-propanol, 3-methyl-1-butanol and 3-methylpentane are used as solvents. Obtained value of inhomogeneous width decreases from 430 to 350 cm −1 with increasing alcohol chain length, while the homogeneous width is independently 290 cm −1. The homogeneous width is sensitive to the existence of -OH comparing the result of 3-methyl-1-butanol and 3-methylpentane solutions.

Measurement of the molecular content of binary nuclei. III. Use of the nucleation rate surfaces for the water-n-alcohol series

In two preceding papers the molecular content of binary ethanol-hexanol and water-ethanol nuclei, respectively, was determined from nucleation rate measurements. While nucleation of ethanol-hexanol mixtures behaved nearly ideal, a strong mutual nucleation enhancement for water-ethanol was observed. Here we extend the investigations to include the longer chain alcohols, that is water −CiH2i+1OH systems with i=2 to 6. Using the nucleation pulse technique developed in the past few years nucleation rates in the range 105&amp;lt;J/cm−3 s−1&amp;lt;109 are measured. Ranging from pure water to pure alcohol the water and alcohol activities, a1 and a2, respectively, are varied for each system with about ten intermediate compositions at constant temperature T=260 K. Aside from a remarkably similar behavior of the various alcohols, one observes that with increasing alcohol chain length the mutual nucleation enhancement decreases. Since all water-alcohol systems behave qualitatively similar, we confine ourselves to present the full experimental nucleation rate surface J(a1,a2) for one system, water-n-pentanol, as an example. From the nucleation rate surface for each system the onset activities corresponding to a reference nucleation rate of J0=107 cm−3 s−1 are determined. From the slopes of the nucleation rate surfaces one obtains the individual numbers of molecules in the critical cluster ni* because ∂ ln J/∂ ln ai≊ni*. As noted previously, determining the molecular content this way does not involve any particular theoretical model, nor does it depend on the structure of the critical cluster. Accordingly, the average composition of the critical clusters can be obtained. An alcohol enrichment of the nuclei at low alcohol activity fraction is found for all alcohols examined, the degree diminishing with increasing alcohol chain length. The appearance of a macroscopic miscibility gap for the higher alcohols is not reflected in any qualitative change of the composition of the microscopic nuclei.

Enhanced permeation of polar compounds through human epidermis. I. Permeability and membrane structural changes in the presence of short chain alcohols

The influence of alcohol chain length on polar compound permeation in human skin was investigated to further understand alcohol-enhanced permeation mechanisms. Both thermodynamic and kinetic variables associated with the enhanced permeation of mannitol were ascertained in the presence of high concentrations of short chain alcohols. Permeation of mannitol through human epidermis in the presence of 75% (v/v) alcohol-saline mixtures was determined in symmetric, side-by-side diffusion cells at 32°C. Permeability coefficients increased with increasing alcohol chain length ( iso-propanol > ethanol > methanol ). Uptake of mannitol into the epidermal tissue increased in the presence of the short chain alcohols, but was independent of alcohol chain length. In addition, mannitol solubility decreased in the presence of the short chain alcohols, but again was independent of alcohol chain length. Therefore, increased mannitol permeability with increasing alcohol chain length could not be attributed to thermodynamic variables. Changes in the amount and conformation of stratum corneum lipids and proteins were determined by Fourier transform infrared (FTIR) spectroscopy. Stratum corneum lipid conformation and mobility was not significantly altered in the presence of the short chain alcohols. However, decreased absorbance of the alkyl chain suggested lipid extraction, which increased with increasing alcohol chain length. Stratum corneum protein conformation was altered in the presence of the short chain alcohols. Decreased infrared absorbance of the Amide I band maximum suggested extraction of stratum corneum proteins, which increased with increased alcohol chain length. These results suggest a correlation between enhanced permeation and extraction of lipids as well as proteins from human skin in the presence of 75% (v/v) aqueous alcohol solutions.

Heat capacities, self-association and complex formation in alcohol–ester systems

The apparent molar heat capacity, Φc, its associative part, Φc(assoc), and the excess heat capacity, CEp, have been obtained at 25 °C through the concentration range for methanol, hexan-1-ol and decan-1-ol in a series of proton acceptor solvents: methyl acetate, ethyl acetate, octyl acetate, methyl octanoate, decyl acetate and methyl tetradecanoate. The results are explained quantitatively by the Treszczanowicz–Kehiaian (TK) association model and the Flory lattice model in terms of alcohol self-association into tetramers, characterized by an OH—OH equilibrium constant and enthalpy, and by alcohol–ester complex formation characterized by an OH—COO equilibrium constant and enthalpy, each independent of alcohol and ester chain length. As predicted, Φc(assoc) at infinite alcohol dilution is independent of the choice of alcohol, but increases with increasing ester chain length. With increasing alcohol concentration Φc(assoc) passes through a maximum which is much reduced compared with the inert solvent case. For each alcohol, CEp increases with increasing ester chain length, while for the same ester, CEp decreases with increasing alcohol chain length. dCEp/dT is positive for mixtures of methanol and methyl acetate, as predicted by the TK model. It is negative for decanol with methyl acetate, contrary to the TK model, but consistent with a non-random distribution of alcohol tetramers in the solution.

Aqueous dissolution of crystalline and amorphous amylose-alcohol complexes

Complexes of amylose, the linear starch polysaccharide, with linear alcohols having chain lengths varying from 4 to 8 carbon atoms, were prepared. Either crystalline or amorphous complexes could be formed depending on preparation conditions. Crystalline complexes gave sharp X-ray diffraction patterns, characteristic of the V H form of amylose, whereas no observable pattern was obtained from the amorphous form. Thermal dissociation of the complexes occurred at increasing temperatures with increasing alcohol chain length. Crystalline complexes dissociated at temperatures approximately 23°C higher than their amorphous counterparts and the enthalpy of dissociation was also greater for the crystalline samples. Enthalpy values were independent of alcohol chain length. Differences in thermal behaviour of the two types of complex may be described in terms of the polymer crystal lattice energy and may explain the variability of reported results for complex dissociation in the literature.

Solubilization and phase equilibria of water-in-oil microemulsions: II. Effects of alcohols, oils, and salinity on single-chain surfactant systems

The solubilization and phase equilibria of water-in-oil (w/o) microemulsions have been studied to elucidate how the molecular structure of various components of microemulsions and salinity influence two interfacial parameters of the system, namely the spontaneous curvature and elasticity of interfacial films. Most solubilization and phase equilibria data presented are explained by the change of these two parameters. It is indicated that oil can influence the property of an interfacial film by a solvation effect. Oil molecules with small molecular volume or high aromaticity produce a strong solvation effect and consequently lead to a greater penetration of oil molecules into the surfactant chain layer, thus increasing the rigidity and curvature of the interface. The addition of alcohol exhibits strong effects on the elasticity and spontaneous curvature of an interface. Decreasing alcohol chain length can increase the fluidity of the interfacial film and hence increase the attractive interdroplet interaction. On the other hand, increasing alcohol chain length often increases the rigidity and curvature of an interface. For alcohols which increase the interfacial fluidity, increasing alcohol partitioning at the interface will increase the fluidity and natural radius of the interface. The addition of electrolytes results in tighter molecular packing at the interface and a decrease in the natural radius and interfacial fluidity. There often exists an optimal salinity for a given w/o microemulsion system at which a maximum brine solubilization occurs. The maximum solubilization is interpreted as a result of counteracting effects of attractive interdroplet interaction of fluid interfaces and the bending stress of rigid interfaces. As a result of this study, phenomenological guidelines for the formulation of microemulsions have been proposed. It is inferred that the addition of a small amount of alcohol at optimal salinity together with the condition of chain length compatibility can result in the largest possible brine solubilization in a given w/o microemulsion.

A microscopic electrophoretic study of the rutile/n-aliphatic alcohol system

The nature and origin of the charge on rutile particles dispersed in primary alcohols (from methanol to decanol) has been investigated by microscopic electrophoresis. With increasing alcohol chain length the sign of the charge changes from negative to positive, with a zero point of electrokinetic potential at about pentanol and apparently independent of surface pre-treatment. The charge is associated with an acid-base equilibrium between surface and alcohol, the resulting charge being determined by the concentration of solvated protons in the liquid phase.