Effects Of Short-chain Alcohols Research Articles

Effects of short-chain alcohols and urea on the association of tetradecyltrimethylammonium bromide surfactant and cefixime trihydrate antibiotic: Conductometric and physicochemical analysis

This study explores the interaction of tetradecyltrimethylammonium bromide (TTAB), with an antibiotic drug, cefixime trihydrate (CMT), with a particular focus on conductivity changes as a reliable indicator of micelle formation. Influence of various alcohols (methanol (MeOH), ethanol (EtOH), 1-propanol (1-PrOH), 2-propanol (2-PrOH)), and urea on the physicochemical properties for micellization of TTAB in aq. alcohols/urea solutions of CMT was investigated. As the concentration of alcohol and urea increases, the critical micelle concentration (CMC) undergoes a notable rise, while the degree of counterion binding (β) shows a decreasing trend as a function of [alcohols]/[urea]. Elevated temperatures impede the creation of micelles, directing to an increase in the CMC, thus necessitating a higher surfactant concentration for micelle development. The alterations in free energy (∆Gmo), enthalpy (∆Hmo), entropy (∆Smo), and molar heat capacity (∆Cm0) were analyzed to evaluate the feasibility and driving forces behind the process of micelle development. The negative values of ∆Gmo indicate that the formation of micelles in the system being studied occurs spontaneously. The ∆Hmo and ∆Smo values suggest the existence of electrostatic forces (ion-dipole and H-bonding) between the components (TTAB, CMT, and alcohol) in aq. MeOH media. In contrast, hydrogen bonding, electrostatic forces, and hydrophobic interactions are involved in the solutions of the other three alcohols and urea medium. The thermodynamic parameters of transfer (∆Gm,tr0, ∆Hm,tr0, and ∆Sm,tr0) and enthalpy-entropy compensation variables were computed and discussed for TTAB micelles in the presence of CMT drug in employed solvents. The discoveries hold significant implications for drug formulation and industrial processes concerning surfactants and additives, providing valuable insights for optimizing their performance and properties.

Effect of short-chain alcohols on the physicochemical properties of d-phenothrin emulsions and their insecticidal activity against Aedes aegypti

Oil-in-water (o/w) emulsion is utilized as an insecticide delivery system for mosquito control. However, evaporation inhibition adjuvant is needed to prevent fog drift, inhibit release of insecticidal actives and prolong suspension time. In the current study, we evaluated the effect of different short-chain alcohols, namely, propylene glycol, 1,3-propanediol, glycerol and crude glycerol, as adjuvants on the physicochemical properties of d-phenothrin o/w emulsion system. The bioactivity of optimized formulations containing 20 wt% glycerol (D1), 20 wt% propylene glycol (D2) and without added alcohol (negative control) were tested against larvae, pupae and adult Aedes aegypti (Ae. aegypti). It was found that propylene glycol produced smaller droplets at lower concentrations but poor long-term stability at higher concentrations, whereas glycerol had an appreciable effect on initial droplet size and stability with increasing concentration. According to the dose-response bioassays and room size chamber testing, the highest larvicidal, pupicidal and adulticidal activities were observed with D2, followed by D1 and negative control. Overall, the above study demonstrated improved emulsion stabilities and potency against Ae. aegypti larvae, pupae and adults using glycerol as adjuvant for effective mosquito control.

Short-Chained Alcohols Make Membrane Surfaces Conducive for Melittin Action: Implication for the Physiological Role of Alcohols in Cells.

Alcohols are a part of cellular metabolism, but their physiological roles are not well understood. We investigated the effects of short-chain alcohols on Daphnia pulex and model membranes mimicking the lipid composition of eukaryotic inner mitochondrial membranes. We also studied the synergistic effects of alcohols with the bee venom membrane-active peptide, melittin, which is structurally similar to endogenous membrane-active peptides. The alcohols, from ethanol to octanol, gradually decreased the heart rate and the mitochondrial ATP synthesis of daphnia; in contrast, in combination with melittin, which exerted no sizeable effect, they gradually increased both the heart rate and the ATP synthesis. Lipid packing and the order parameter of oriented films, monitored by EPR spectroscopy of the spin-labeled probe 5-doxylstrearic acid, revealed gradual alcohol-assisted bilayer to non-bilayer transitions in the presence of melittin; further, while the alcohols decreased, in combination with melittin they increased the order parameter of the film, which is attributed to the alcohol-facilitated association of melittin with the membrane. A 1H-NMR spectroscopy of the liposomes confirmed the enhanced induction of a non-bilayer lipid phase that formed around the melittin, without the permeabilization of the liposomal membrane. Our data suggest that short-chain alcohols, in combination with endogenous peptides, regulate protein functions via modulating the lipid polymorphism of membranes.

Influence of Short Carbon-Chain Alcohol (Ethanol and 1-Propanol)/Diesel Fuel Blends over Diesel Engine Emissions

Oxygenated fuels, in this case short carbon-chain alcohols, have been investigated as alternative fuels to power compression ignition engines. A major advantage of short-chain alcohols is that they can be produced from renewable resources, i.e., cultivated commodities or biomass-based biorefineries. However, before entering the market, the effects of short-chain alcohols on engine performance, exhaust emissions, noise and sound quality need to be understood. This work sheds light on the relationship between the physicochemical properties of the alcohol/diesel fuel blends (ethanol and 1-propanol) on engine performance, exhaust emissions and, for the first time, on noise and sound quality. It has been demonstrated that when the content of alcohol in blends increased, soot and soluble organic material emissions drastically decreased, mainly due to the increase of oxygen content in the fuel. Reduction in soot emissions combined with higher thermodynamic efficiency of alcohol fuels, with respect to diesel fuel, enable their utilization on compression ignition engines. There is also an improvement in the soot-NOx trade off, leading to large reductions on soot with a small effect on NOx emissions. The oxygen content within the fuel reduces CO and THC emissions at extra-urban driving operation conditions. However, hydrocarbons and CO emissions increased at urban driving conditions, due to the high heat of vaporization of the alcohol fuels which reduces cylinder temperature worsening fuel atomization, vaporization and mixing with air being more significant at lower cylinder temperature conditions (low engine loads and speeds). Similarly, the higher the presence of alcohol in the blend, the higher the noise emitted by the engine due to their low tendency to auto-ignition. The optimization of alcohol quantity and the calibration of engine control parameters (e.g., injection settings) which is out of the scope of this work, will be required to overcome noise emission penalty. Furthermore, under similar alcohol content in the blend (10% v/v), the use of propanol is preferred over ethanol, as it exhibits lower exhaust emissions and better sound quality than ethanol.

Effect of Simple Anesthetics on SNARE Fusion Proteins and on Fusing Membranes

For over 170 years, simple molecules like ether have been used to induce anesthesia in humans. Nevertheless, the mechanisms of action for many general anesthetics are not known. Here we explore the effect of short chain alcohols and diethyl ether on the folding of SNARE proteins, known to drive exocytosis in neurons, and also on membrane-membrane fusion, the final step in neurotransmitter release. The SNARE proteins SNAP-25, syntaxin, and VAMP provide the four helical regions (SNARE domains) that form a coiled-coil complex required for neurotransmitter release. This complex is continually formed and unwound as exocytotic vesicles fuse and are recycled. Circular Dichroism was used to measure secondary structure of SNAP-25 and its two SNARE domains following addition of alcohols and ether. We observed an increase in α-helical structure when methanol is added or the temperature is lowered. This increase in helicity occurred for each domain and for the entire protein. This is similar to the helical shift observed when SNAP-25 forms a complex with syntaxin and VAMP. We utilized the nystatin/ergosterol fusion assay to measure fusion of liposomes to a membrane in the absence of SNARE proteins. Changes in fusion rates were observed in response to increasing doses of ether or short-chain alcohols on one or both sides of the membrane. Alcohols applied to the trans side of the membrane (side opposite the vesicles) inhibited fusion at physiologically-relevant doses (Paxman et al. 2017. Biophys J. 112:121-132.). Therapeutic doses of ether also decreased fusion rates when added trans. These data show that some anesthetics may induce their effects by altering the SNARE fusion machine and/or raising the activation energy of membrane-membrane fusion, decreasing neurotransmitter release.

Effect of short-chain alcohols on the bulk-phase reaction between glyoxal and ammonium sulfate

The chemical and physical properties of secondary organic aerosol (SOA) may be influenced by the aqueous environment within which SOA-forming reactions occur. Bulk-phase reactions between glyoxal and ammonium sulfate produce light-absorbing compounds such as imidazole-2-carboxaldehyde (IC) and biimidazole (BI) and model aerosol-phase chemistry. The effect of solvent composition on IC and BI production kinetics were examined for solutions containing a series of short-chain alcohols (methanol, ethanol, 1-propanol, 2-propanol, 2-butanol, tert-butanol, and 3-methyl-2-butanol), as functions of the species and concentration added. The addition of an alcohol likely altered the solvent by inducing the formation of micro-heterogeneities of hydrated alcohol molecules. An increased alcohol concentration in solution resulted in a general increase in the production of IC and BI, with ethanol and the secondary alcohols causing the largest changes. The rate constants for IC and BI production in solutions that do not contain alcohol are found to be (4.03 ± 2.02) x 10−6 s−1 and (3.48 ± 1.75) x 10−6 s−1, respectively. In solutions that do contain an alcohol, rate constant values range from 3.23 × 10−6 s−1 to 6.61 × 10−6 s−1 for IC and 0.985 × 10−6 s−1 to 6.87 × 10−6 s−1 for BI, depending on the alcohol and the concentration. While these prevailing trends of more alcohol in solution leading to amplified production of imidazoles were observed for all seven alcohols, the diversity of responses implies the mode of action depends strongly on the species of alcohol added. Properties that describe a solution in bulk, such as dielectric constant, are not found to be reliable predictors of subsequent system behavior. Solvent composition influences SOA chemistry, and interactions between relevant functional groups within solution drive this influence, which suggests the importance of understanding individual relationships between aerosol-phase chemicals and SOA properties and production.

Effect of Short Chain Alcohols on Yield of Biodiesel Produced from Pongamia Oil

The crude oil prices in world market is increasing day by day and focus is being shifted to find out substitutes of petroleum diesel and biodiesel has emerged out to be potential alternative fuel. In earlier times, biodiesel was mainly being produced from edible oils but that has led negative impact due to scarcity of food crops in developing nations. So non-edible oils are found to be suitable for biodiesel production and Pongamia oil is selected as it is 2nd in availability among non-edible oils. Main hindrance towards production of biodiesel is the technologies adopted. Up till now, only methanol and to a lesser extent ethanol has been preferred for transesterification. There is scope of using higher alcohols for production of biodiesel and as n-butanol can be obtained from renewable sources, it also holds good prospect. As per the literature, optimised reaction parameters have been studied and followed for transesterification reactions to reduce the cost of production which includes, 1% Catalyst Concentration of NaOH by weight of oil, 6:1 alcohol to oil molar ratio, 60 °C reaction temperature and 60 minutes reaction time. Yield of biodiesel prepared from different short chain alcohols (methanol, ethanol, 2-propanol and n-butanol) and fuel properties were compared for optimising the selection of alcohol.

Partially Oxidised Cellulose Nanofibril Gels for Rheology Modification

Partially C6-oxidised cellulose nanofibrils form a transparent, slightly viscous suspension in water. These materials, sourced from soft-wood waste, have shown excellent potential for use as a rheology modifier in aqueous formulations, when mixed with salt and minimal amounts of anionic surfactants [1] or with short chain alcohols. The interaction with anionic surfactants is particularly surprising as the cellulose fibrils themselves carry a net negative charge. The gels formed are transparent, mild on the skin and have excellent suspending properties while also being strongly shear thinning making application eg via spraying possible. The partially oxidised cellulose nanofibrils can also be used to stabilize oil-in-water Pickering emulsions. Both the gels and emulsions are of interest for use in personal care products such as creams, sanitizers and shower gels. We have probed the micelle-fibril interactions in water and in the presence of ethanol using contrast matching SANS on the gels and also on the cellulose-stabilized Pickering emulsion droplets. SAXS has also been used to probe the effect of short chain alcohols on the nanofibril structures in the gels as a function of alcohol chain length, while neutron reflectivity was used to probe surfactant-fibril binding for anionic and nonionic surfactants in thin nanofibril layers. The nanostructures formed in suspensions of partially oxidised cellulose nanofibrils with a range of salts, alcohols and surfactants will be correlated with their rheological behaviour. These factors will be discussed and brought together to give insights into how and why these systems form gels.

Room temperature ordering of dipalmitoyl phosphatidylserine bilayers induced by short chain alcohols

Using differential scanning calorimetry and small and wide angle X-ray diffraction, we show that, following extended incubation at room temperature, methanol, propanol, and three of the isomers of butanol can induce ordering in dipalmitoyl phosphatidylserine (DPPS) gel phase bilayers. The organization of the bilayers in the presence of ethanol, described previously, is now observed to be a general effect of short chain alcohols. Evidence is presented for tilting of the acyl chains with respect to the bilayer normal in the presence of ethanol or propanol. However, the different chain lengths of the alcohols, and isomeric form, influence the thermal stability of the ordered gel to different extents. This behavior is unlike that of the gel state phosphatidylcholine analog which, in the presence of short chain alcohols, undergoes hydrocarbon chain interdigitation. Dipalmitoyl phosphatidylcholine added to DPPS in the presence of 20vol% ethanol, acts to suppress the ordered gel phase.

Effect of acetone accumulation on structure and dynamics of lipid membranes studied by molecular dynamics simulations

The modulation of the properties and function of cell membranes by small volatile substances is important for many biomedical applications. Despite available experimental results, molecular mechanisms of action of inhalants and organic solvents, such as acetone, on lipid membranes remain not well understood. To gain a better understanding of how acetone interacts with membranes, we have performed a series of molecular dynamics (MD) simulations of a POPC bilayer in aqueous solution in the presence of acetone, whose concentration was varied from 2.8 to 11.2mol%. The MD simulations of passive distribution of acetone between a bulk water phase and a lipid bilayer show that acetone favors partitioning into the water-free region of the bilayer, located near the carbonyl groups of the phospholipids and at the beginning of the hydrocarbon core of the lipid membrane. Using MD umbrella sampling, we found that the permeability barrier of ∼0.5kcal/mol exists for acetone partitioning into the membrane. In addition, a Gibbs free energy profile of the acetone penetration across a bilayer demonstrates a favorable potential energy well of −3.6kcal/mol, located at 15–16Å from the bilayer center. The analysis of the structural and dynamics properties of the model membrane revealed that the POPC bilayer can tolerate the presence of acetone in the concentration range of 2.8–5.6mol%. The accumulation of the higher acetone concentration of 11.2mol% results, however, in drastic disordering of phospholipid packing and the increase in the membrane fluidity. The acetone molecules push the lipid heads apart and, hence, act as spacers in the headgroup region. This effect leads to the increase in the average headgroup area per molecule. In addition, the acyl tail region of the membrane also becomes less dense. We suggest, therefore, that the molecular mechanism of acetone action on the phospholipid bilayer has many common features with the effects of short chain alcohols, DMSO, and chloroform.

Short-Chain Alcohols Strip X-Type Ligands and Quench the Luminescence of PbSe and CdSe Quantum Dots, Acetonitrile Does Not

The effect of short-chain alcohols and acetonitrile on the ligand shell composition and the photoluminescence quantum yield of purified PbSe and CdSe quantum dots is analyzed by solution NMR and photoluminescence spectroscopy. We find that short-chain alcohols induce the release of X-type carboxylate ligands with a concurrent reduction of the photoluminescence quantum yield, while acetonitrile does not. We interpret this difference in terms of the protic or aprotic character of both nonsolvents, where only the protic alcohols can provide the protons needed to desorb carboxylate ligands. We find similar differences between short-chain alcohols and acetonitrile when used as nonsolvents during the purification of crude synthesis products, a result stressing the importance of using aprotic nonsolvents for nanocrystal purification or processing.

Effect of short-chain alcohols on surfactant-mediated reversed-phase liquid chromatographic systems

The behaviour of β-blockers in a reversed-phase liquid chromatographic (RPLC) column with mobile phases containing a short-chain alcohol (methanol, ethanol or 1-propanol), with and without the surfactant sodium dodecyl sulphate (SDS), was explored. Two surfactant-mediated RPLC modes were studied, where the mobile phases contained either micelles or only surfactant monomers at high concentration. Acetonitrile was also considered for comparison purposes. A correlation was found between the effects of the organic solvent on micelle formation (monitored by the drop weight procedure) and on the nature of the chromatographic system (as revealed by the retention, elution strength and peak shape of β-blockers). When SDS is added to the mobile phase, the free surfactant monomers bind the C18 bonded chains on the stationary phase, forming an anionic layer, which attracts strongly the cationic β-blockers. The retention is modified as a consequence of the solving power of the organic solvent, micelles and surfactant monomers. The molecules of organic solvent bind the micelles, modify their shape, and may avoid their formation. They also bind the monomers of surfactant, desorbing them from the stationary phase, which affects the retention. The remaining surfactant covers the free silanols on the siliceous support, avoiding the interaction with the cationic solutes. The retention of β-blockers results from a combination of electrostatic and hydrophobic interactions, the latter being weaker compared to the hydro-organic system. The peak efficiencies and asymmetries are excellent tools to probe the surfactant layer on the stationary phase in an SDS/organic solvent system. The peaks will be nearly symmetrical wherever enough surfactant coats the stationary phase (up to 60% methanol, 40% ethanol, 35% 1-propanol, and 50% acetonitrile).

Thermodynamic Modeling of the Duality of Linear 1-Alcohols as Cosurfactants and Cosolvents in Self-Assembly of Surfactant Molecules

The effect of adding an alcohol to surfactant systems depends much on the alcohol chain length. Investigations on the effect of alcohols in micellar systems point out that medium-chain alcohols are appreciably incorporated in the micellar phase whereas short-chain alcohols are localized mainly in the aqueous phase. Nonetheless, penetration of the hydrocarbon chain of alcohols in the micellar shell has been experimentally observed for the entire homologous series of linear 1-alcohols. We present a thermodynamic model in which the alcohol molecules play two roles: cosurfactant and cosolvent. The cosurfactant effect of the alcohols is included by assuming that the alcohol molecules are nonionic surfactants. The cosolvent effect is modeled by accounting for the changes in the free energy to relocate the surfactant tail from the solvent to the aggregate core. The effects of short-chain alcohols in the macroscopic interfacial tension and dielectric constant of the solvent medium are also taken into account. For short-chain alcohols the partition coefficient of the alcohols between water and liquid hydrocarbons provides knowledge of the fraction of the molecules that participate in each function. Our proposed thermodynamic model improves the modeling of the effect of short- and medium-chain alcohols in self-assembly of molecules that are of increasing importance in modern scientific research and technological processes.

Effect of Short Chain Alcohols upon Viscosity of TTAB Solution

The effect of ethanol (C2H5OH), propanol (C3H7OH), and butanol (C4H9OH) upon the viscosity of tetradecyltrimethylammonium bromide (TTAB) solution in the presence or absence of KBr at 30 C was investigated, where the surfactant concentration CS is kept constant. In the absence of KBr, the relative viscosity r of TTAB solution increases linearly with the alcohol concentration CA, indicating that the alcohols do not promote micelle formation of TTAB. In the presence of KBr, r linearly decreases with CA for C2H5OH, but it exhibits a maximum with increasing CA for C3H7OH or C4H9OH. The facts reveal that C2H5OH or C4H9OH promotes the micelle formation of TTAB. A possible explanation is that the hydrophobicity of the micellar interior is enhanced by KBr, so that C2H5OH or C4H9OH can dissolve in micelle and promotes micelle formation. In the presence of KCl, which is less efficient in promoting the micelle formation of cationic surfactant, both C3H7OH and C4H9OH have only a slight effect on the micelle formation. In contrast, due to the hydrophilicity, C2H5OH cannot dissolve in micelles in the presence of KBr or KCl.

Formulation of food-grade microemulsions with glycerol monolaurate: effects of short-chain alcohols, polyols, salts and nonionic surfactants

The formulation of food-grade microemulsions with glycerol monolaurate (GML) for antimicrobial applications has been studied. The compositions included water, GML, short-chain alcohols (such as ethanol), polyols (propylene glycol and glycerol), salts (organic, such as sodium benzoate, sodium lactate and sodium propionate, and inorganic, such as NaCl) and several nonionic surfactants [such as ethoxylated sorbitan esters, sucrose esters (SEs)]. The phase behavior of these systems is discussed with respect to the influence of composition on the degree of oil solubilization in the aqueous phase. The oil solubilization was dramatically improved in the presence of the short-chain alcohols and polyols, organic salts contributed to the improvement of oil solubilization as hydrotropes. Tween 20 being the most hydrophilic surfactant in Tweens solubilized the maximum oil, but in the presence of SEs it is hard to form oil-in-water microemulsions. Viscosity measurements along selected dilution lines indicate that at a certain composition the system inverts from a water-in-oil to an oil-in-water microemulsion.

Effects of short chain alcohols on the styrene emulsion polymerization

AbstractThe effects of a series of short chain alcohols, 1‐butanol (C4OH), 1‐pentanol (C5OH), and 1‐hexanol (C6OH), on the styrene (ST) emulsion polymerization mechanisms and kinetics were investigated. The CMC of the ST emulsions stabilized by sodium dodecyl sulfate (SDS) first decreases rapidly and then levels off when the CiOH (i = 4, 5, or 6) concentration ([CiOH]) increases from 0 to 72 mM. Furthermore, at constant [CiOH], the CMC data in decreasing order is CMC (C4OH) > CMC (C5OH) > CMC (C6OH). The effects of CiOH (i = 4, 5, and 6) on the ST emulsion polymerization stabilized by 6 mM SDS are significant. This is attributed to the reduction in CMC by CiOH, the different oil–water interfacial properties, the different concentrations of monomer within latex particles, and the different effectiveness of SDS/CiOH in stabilizing latex particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4406–4411, 2006

Effect of short-chain alcohols on the oil-in-water microemulsion polymerization of styrene

The influence of short-chain alcohols, 1-butanol (C4OH), 2-pentanol (C5OH) and 1-hexanol (C6OH), on the formation of oil-in-water styrene microemulsions and the subsequent free-radical polymerization was studied. Sodium dodecyl sulfate was used as the surfactant. The overall performance of C4OH as the cosurfactant is quite different from C5OH and C6OH. The range of the microemulsion region in decreasing order is C4OH > C5OH > C6OH. The primary parameters selected for the microemulsion polymerization study were the concentrations of cosurfactant and styrene. Only a small fraction of microemulsion droplets initially present in the reaction system can be successfully transformed into latex particles and the remaining droplets serve as a reservoir to supply the growing particles with monomer. Limited flocculation of latex particles also occurs during polymerization and the degree of flocculation is most significant for the C4OH system.

Effect of short-chain alcohols as co-surfactants on pseudo-ternary phase diagrams containing lecithin

Lecithin is a natural amphiphilic molecule, the microemulsions of which are often employed as a transdermal delivery medium of drugs and cosmetics. However, it constructs a microemulsion and lamellar phase in a phase diagram without co-surfactant only at a narrow range of composition. In this study, the effect of several short-chain alcohols on pseudo-ternary phase diagrams composed of lecithin, water and dodecane containing 1.0 wt% lidocaine (local anesthetic) was investigated in relation to the application of lecithin-based microemulsion for transdermal drug delivery. The phase diagram for an aqueous solution containing 80.0 wt% ethanol showed a lamellar structure (LC) and bicontinuous isotropic regions. When the mixing ratio of lecithin to alcohols (1-propanol, 1-butanol and n-pentanol) was 2: 1, water-in-oil (L2) and oil-in-water (L1) microemulsions and LC were obtained in a certain range of compositions. The maximum solubilization of water into L2 phase was 38 wt% when the total surfactant was 43 wt% with butanol as cosurfactant.

Use of isothermal titration calorimetry to study the interaction of short-chain alcohols with lipid membranes

The molecular mechanisms by which ethanol and other short-chain alcohols exert their effect in biological systems have been suggested to involve specific interactions with proteins and/or non-specific interactions with the lipid bilayer part of the cell membrane. To gain insight into the effect of short-chain alcohols on lipid bilayers, isothermal titration calorimetry (ITC) has been used to determine the energy involved in the association of the alcohols with lipid bilayers. Pure unilamellar DMPC liposomes and DMPC liposomes incorporated with different amounts of cholesterol, sphingomyelin and ganglioside (GM 1) were investigated at temperatures above, and below, the main phase-transition temperature of DMPC. The alcohols used were ethanol, 1-propanol, and 1-butanol. The calorimetric results reveal that the interaction of short-chain alcohols with the lipid bilayer is endothermic and strongly dependent on the lipid bilayer composition. In the presence of high concentrations of cholesterol, the binding enthalpy of ethanol is decreased, whereas the presence of ceramides enhances the enthalpic response of the lipid bilayer to ethanol. Isothermal titration calorimetry offers a new methodology of investigating molecular interactions and for determining partitioning coefficients for alcohols into lipid bilayers. We have estimated the partitioning coefficients for the three alcohols between the aqueous phase and the lipid bilayers of various lipid composition on the basis of calorimetric results.

Effects of Short-Chain Alcohols and Pyridine on the Hydration Forces between Silica Surfaces

Forces between fully hydroxalated silica surfaces were measured using an atomic force microscope. The measurements were conducted in Nanopure water and in solutions containing various organic solutes such as methanol, ethanol, trifluoroethanol (TFE), and pyridine. The results obtained in Nanopure water showed a strong short-range repulsive force at distances below 15 nm. This non-DLVO force can be fitted to a double-exponential force law with its longer decay length (D2) of 2.4 nm. On the other hand, the force curve obtained at 15% methanol by volume can be fitted to the DLVO theory perfectly, showing no signs of hydration force. These results suggest that the hydration force originate from the unique water structure in the vicinity of silica, which apparently is seriously disrupted in the presence of methanol. Methanol may adsorb on silica, displacing water molecules from the silanol groups and, thereby, breaking the H-bond network within the hydration sheath around silica. The displacement of water by methanol is thermodynamically possible because the latter is more basic than the former. In 10–20% ethanol solutions,D2decreases to 1.1–1.2 nm, indicating that ethanol also adsorbs on silica but to a lesser extent than methanol. In TFE and pyridine solutions, the hydration force changes little, suggesting that these solutes cannot readily displace water molecules from silanol groups. The results presented in this communication may have a bearing on the intoxication of humans by alcohols, which may be related to the dehydration of lipid membranes.