Critical Ethanol Concentration Research Articles

Sigmoidal temporal increase in shear viscosity of titania–toluene–ethanol colloidal suspensions

The shear viscosity of toluene-based TiO2 nanoparticle/poly(vinyl acetate) suspensions initially increased gradually, then increased steeply, and finally levelled off under shearing in the presence of ethanol as a polar additive. This non-linear response followed a sigmoidal function with a characteristic rate constant for a given composition. The rate constant reached a maximum at a critical ethanol concentration, resulting in maxima of the final viscosity and storage modulus that have not been previously reported for non-aqueous macroscopically miscible systems. This viscosity anomaly was attributed to the preferential adsorption of the polar solvent and the resulting alcohol-clustering-induced particle networking in the non-polar medium. The temporal variations in viscosity were reproduced using a proposed kinetic model that newly considered inter-particle bonding assisted by ethanol adsorption. These results elucidate the transient rheological responses of suspensions containing polar/non-polar solvents for coating applications.

Rheological properties of cellulosic thickeners in hydro-alcoholic media: The science behind the formulation of hand sanitizer gels

Cellulosic-based thickeners are commonly used in the preparation of hydro-alcoholic hand sanitisers. Yet, little is known about the behaviour of these polymeric dispersions in hydro-alcoholic mixtures. Here, we studied the dispersion ability and rheology of hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose and sodium carboxymethyl cellulose in water–ethanol mixtures. Hydroxypropyl cellulose formed transparent dispersions across the entire range of ethanol concentrations, while a critical ethanol concentration (CEC), above which dispersions became turbid, was found for all the other polymers. At and below the CEC, all the rheological parameters followed a bell-like shape profile as a function of ethanol concentration. Moreover, the molecular weight and degree of substitution of the polymers influenced the rheological properties. The CEC and rheological behaviour of the dispersions were both dependent on the ethanol/polymer and water/polymer interactions. As hand disinfectants should contain 60–95% ethanol, polymers of higher CEC, such as hydroxypropyl cellulose and hydroxypropyl methylcellulose, are recommended.

Destabilization of Insulin Hexamer in Water-Ethanol Binary Mixture.

We report combined experimental and simulation studies which reveal that the structural integrity of insulin hexamer, the storehouse of the important hormone in our body, is compromised by the interactions with ethanol. X-ray crystal structures suggest that ethanol replaces water molecules inside the insulin hexamer cavity. At the maximum physiologically tolerable concentration of ethanol (∼0.6% v/v), molecular dynamics simulations show that ethanol molecules get exchanged between the bulk and the cavity with a free energy cost of ∼5 kcal mol-1. However, biological time scales are orders of magnitude longer than that achievable by molecular dynamics simulations. Hence, to accelerate the process we investigate insulin hexamer in ∼30% v/v ethanol concentration. We find that the entrance and exit of ethanol from the hexamer cavity lead to the modification of atomic contacts in the protein. This causes large-scale fluctuations that force the protein out of its native state free energy minimum. Structural perturbations are also observed at lower ethanol concentration. The computational findings are consistent with dynamic light scattering experiments that suggest an abrupt reduction in the population of insulin hexamers at a critical ethanol concentration. The structural changes triggered by interaction of ethanol with the insulin hexamer are likely to represent a general dynamic event of amphiphilic cosolvent induced changes in macromolecular assemblies with the consequent effects on cellular homeostasis.

Bubbles with tunable mobility of surfaces in ethanol-NaCl aqueous solutions

The mobility of bubble surfaces in aqueous solutions can be hindered by even a trace amount of contaminants at the air-liquid interface. Adding ethanol into an aqueous solution is expected to modify the activity of the contaminants and hence their level at the air-liquid interface, which can possibly tune the mobility of the bubble surface. The mobility of the bubble surface was characterized by measuring dynamic interactions between a millimeter-size air bubble and a flat mica surface in ethanol-NaCl aqueous solutions using the newly developed dynamic force apparatus and quantified by the Stokes-Reynolds-Young-Laplace model. For a given bubble approach velocity, the hydrodynamic boundary condition at the air-liquid interface deviated from a tangentially immobile boundary at a critical ethanol concentration and converged gradually to fully mobile boundary with further increasing the ethanol concentration. Increasing the bubble approach velocity was found to reduce the critical ethanol concentration that was needed to change the mobility of the bubble surface. By adding surfactants to the system of high ethanol concentration and fully mobile air-liquid interface, the boundary condition became immobile when the amount of surfactant reached a critical concentration. This study introduced a method to control the hydrodynamic boundary condition at the air-liquid interface in mixed liquids.

Understanding the formation mechanism of lipid nanoparticles in microfluidic devices with chaotic micromixers.

Lipid nanoparticles (LNPs) or liposomes are the most widely used drug carriers for nanomedicines. The size of LNPs is one of the essential factors affecting drug delivery efficiency and therapeutic efficiency. Here, we demonstrated the effect of lipid concentration and mixing performance on the LNP size using microfluidic devices with the aim of understanding the LNP formation mechanism and controlling the LNP size precisely. We fabricated microfluidic devices with different depths, 11 μm and 31 μm, of their chaotic micromixer structures. According to the LNP formation behavior results, by using a low concentration of the lipid solution and the microfluidic device equipped with the 31 μm chaotic mixer structures, we were able to produce the smallest-sized LNPs yet with a narrow particle size distribution. We also evaluated the mixing rate of the microfluidic devices using a laser scanning confocal microscopy and we estimated the critical ethanol concentration for controlling the LNP size. The critical ethanol concentration range was estimated to be 60–80% ethanol. Ten nanometer-sized tuning of LNPs was achieved for the optimum residence time at the critical concentration using the microfluidic devices with chaotic mixer structures. The residence times at the critical concentration necessary to control the LNP size were 10, 15–25, and 50 ms time-scales for 30, 40, and 50 nm-sized LNPs, respectively. Finally, we proposed the LNP formation mechanism based on the determined LNP formation behavior and the critical ethanol concentration. The precise size-controlled LNPs produced by the microfluidic devices are expected to become carriers for next generation nanomedicines and they will lead to new and effective approaches for cancer treatment.

Robust industrial Saccharomyces cerevisiae strains for very high gravity bio-ethanol fermentations

The application and physiological background of two industrial Saccharomyces cerevisiae strains, isolated from harsh industrial environments, were studied in Very High Gravity (VHG) bio-ethanol fermentations. VHG laboratory fermentations, mimicking industrially relevant conditions, were performed with PE-2 and CA1185 industrial strains and the CEN.PK113-7D laboratory strain. The industrial isolates produced remarkable high ethanol titres (>19%, v/v) and accumulated an increased content of sterols (2 to 5-fold), glycogen (2 to 4-fold) and trehalose (1.1-fold), relatively to laboratory strain. For laboratory and industrial strains, a sharp decrease in the viability and trehalose concentration was observed above 90 g l⁻¹ and 140 g l⁻¹ ethanol, respectively. PE-2 and CA1185 industrial strains presented important physiological differences relatively to CEN.PK113-7D strain and showed to be more prepared to cope with VHG stresses. The identification of a critical ethanol concentration above which viability and trehalose concentration decrease significantly is of great importance to guide VHG process engineering strategies. This study contributes to the improvement of VHG processes by identifying yeast isolates and gathering yeast physiological information during the intensified fermentation process, which, besides elucidating important differences between these industrial and laboratory strains, can drive further process optimization.

Structural Basis of the 1H-Nuclear Magnetic Resonance Spectra of Ethanol–Water Solutions Based on Multivariate Curve Resolution Analysis of Mid-Infrared Spectra

The (1)H-nuclear magnetic resonance (NMR) chemical shifts of ethanol and water hydroxyl groups show a pattern change at a critical ethanol concentration. Below the critical value (20 mol% at 400 Hz), only one hydroxyl peak appears due to fast proton exchange, whereas above the critical concentration, the ethanol hydroxyl peak splits from the water peak emerging as an individual chemical shift. The structural basis of the NMR pattern change was interpreted by a multivariate curve resolution-alternating least squares (MCR-ALS) analysis of the mid-infrared (mid-IR) spectra obtained for ethanol-water solutions. Results suggest that the NMR pattern change is due to the formation of ethanol-ethanol clusters. Below the critical concentration, no ethanol-ethanol clusters exist. Therefore, the NMR does not detect the ethanol environment. Above the critical ethanol concentration, ethanol-ethanol clusters first appear such that a distinct ethanol hydroxyl peak emerges. The basis for the dependence of the critical concentration on working frequency is also interpreted. High frequency NMR measurements are more sensitive to ethanol content, resulting in a lower critical ethanol concentration.

AFM Study of Morphology of Ethanol Induced Gelatin Coacervation

ABSTRACT AFM studies have been carried out on coacervating 1% (w/v) aqueous alkali processed gelatin (Type-B) solutions titrated with ethanol close to its iso-electric pH = 5.01 (pI = 4.9). Turbidity measurements performed at 450 nm clearly established the transition points in terms of the percentage of volume of alcohol added relative to that of the total volume corresponding to the first occurrence of turbidity (Vt = 47±2%v/v) and a point of turbidity maximum (). Addition of more alcohol drove the system towards precipitation. The values of Vt and Vp characterized the initiation of intramolecular collapse and intermolecular aggregate formation of the charge neutralized gelatin molecules, and the subsequent micro coacervate droplet formation. The gelatin molecules in the solution were observed to undergo a series of micro-structural transformations as seen by AFM until the coacervates phase was reached. At a critical ethanol concentration of fractal clusters of aggregated polypeptide molecules having fractal dimension were observed.

Yeast growth: lag phase modelling in alcoholic media

A simple non-structured model is proposed here to evaluate the lag phase before yeast growth as a function of the ethanol concentration in the medium. Indeed, ethanol is the main yeast growth inhibitor acting in wine. So different cultures of Brettanomyces were run varying the initial ethanol content (0–90 g/l). Its influence on yeast growth was shown. A term representing the critical ethanol concentration was introduced in the model as an indicator of the ethanol tolerance. This model fairly represented the behaviour of Brettanomyces intermedius yeast, a wine spoilage micro-organism. The convenience of the model was also observed with literature data obtained for Saccharomyces sp. yeasts. Such a model can be applied in predictive microbiology, to determine a risk-free time lag towards the development of a given yeast.

Aggregated DNA in ethanol solution

A recently developed mechanochemical method has provided a new, efficient tool for studies on the thermal stability and structure of aggregated DNA in ethanol-water solutions. At low ethanol concentrations DNA is fully soluble and is in the B form. However, with increasing ethanol concentration the melting temperature of DNA, T m, decreases. At a critical ethanol concentration dependent on the nature and concentration of the counterion, aggregation of the DNA molecules sets in. This is reflected in a marked increase in T m indicating that the aggregated DNA molecules are thermally more stable than the dissolved ones. However, they are still in the B form. In general, T m of aggregated DNA also decreases with further increasing ethanol concentration and is dependent on the nature of the counterion, but T m is not affected by the concentration of the counterion (excess salt) in the ethanol-water solution. When the ethanol concentration reaches the range of 70–80% (v/v), the B-to-A conformational transition occurs in the case of Na-, K- and CsDNA. Above this transition point the A form is more stable than the B form due to the reduced water activity and to increased interhelical interactions. At very high ethanol concentrations, above 85% and dependent on the nature of the counterion, a drastic change in the thermal behaviour is observed. Apparently such a strong interhelical interaction is induced in the aggregated DNA that the DNA is stabilized and cannot adopt a random coil state even at very high temperatures. This stability of DNA in the P form is fully reversed if the ethanol concentration is lowered and the activity of water, thereby, is restored.

Phase transition in swollen gels. 21. Effect of acrylamide quaternary salts with various alkyl lengths on the collapse, mechanical, and SAXS behavior of poly(acrylamide) networks

A series of ionic networks were prepared by copolymerization of acrylamide, methylenebis-(acrylamide), and N-[2-(alkyldimethylammonio)ethyl]acrylamide with Cl, C4, C6, C8, C12, and C16 straight-chain alkyls (mole fraction of the last comonomer x I = 0-0.15). Small-angle X-ray scattering, swelling, and mechanical behavior of the networks were investigated in water-ethanol mixtures. For the gels with C1-C8 alkyls collapse was found ; both the volume jump and the critical ethanol concentration at which the transition takes place, e c , increase with increasing content of the ionic component, x I . Increasing the alkyl length stabilizes the expanded state of the gel and increases the e c values, probably due to preferential sorption of ethanol by hydrophobic regions. Different swelling behavior was found for gels with C12 and C16 alkyls, where mostly a decrease in swelling in water at low ethanol concentrations was observed with increasing x I . This is caused by a distinct amphiphilic character of salts with the two longest alkyls ; in networks with the C16 alkyl formation of micelles was proved by SAXS. Mechanical behavior of the networks is predominantly determined by the degree of swelling ; a jumpwise change in the gel volume is accompanied by a similar change in the equilibrium modulus.

Effects of alcohol-induced lipid interdigitation on proton permeability in L-alpha-dipalmitoylphosphatidylcholine vesicles

6-Carboxyfluorescein was employed to examine the effect of alcohol-induced lipid interdigitation on proton permeability in L-alpha-dipalmitoylphosphatidylcholine (DPPC) large unilamellar vesicles. Proton permeability was measured by monitoring the decrease of 6-carboxyfluorescein fluorescence after a pH gradient from 3.5 (outside the vesicle) to 8.0 (inside the vesicle) was established. At 20 degrees C and below 1.2 M ethanol, the fluorescence decrease is best described by a single exponential function. Above 1.2 M ethanol, the intensity decrease is better described by a two-exponential decay law. Using the fitted rate constants and the vesicle radii determined from light-scattering measurements, the proton permeability coefficient, P, in DPPC vesicles was calculated as a function of ethanol concentration. At 20 degrees C, P increases monotonically with increasing ethanol content up to 1.0 M, followed by an abrupt increase at 1.2 M. The vesicle size also exhibits a sudden increase at around 1.2 M ethanol, which has been shown to result from vesicle aggregation rather than vesicle fusion. The abrupt increases in P and in vesicle size occur at the concentration region close to the critical ethanol concentration for the formation of the fully interdigitated gel state of DPPC. At 14 degrees C, the abrupt change in P shifts to 1.9-2.0 M ethanol, completely in accordance with the ethanol-temperature phase diagram of interdigitated DPPC. Effects of methanol and benzyl alcohol on lipid interdigitation have also been examined. At 20 degrees C, DPPC large unilamellar vesicles exhibit a dramatic change in P at 3 M methanol and at 40 mM benzyl alcohol. These concentrations come close to the critical methanol and benzyl alcohol concentrations for the formation of fully interdigitated DPPC structures determined previously by others. It can be concluded that proton permeability increases dramatically as DPPC is transformed from the noninterdigitated gel to the fully interdigitated gel state by high concentrations of alcohol. This marked increase in proton permeability can be attributed to the combined effect of the changes in membrane thickness and surface charge density, due to the ethanol-induced lipid interdigitation. The possible effects of the increased proton permeability caused by ingested ethanol on gastric mucosal membranes are discussed.

Micelle formation and phase behavior of dodecylammonium heptafluorobutyrate in a water-ethanol mixture

Solubility and critical micelle concentration of dodecylammonium heptafluorobutyrate were determined at various temperatures as a function of ethanol content in a water-ethanol mixture. These were used to draw the phase diagram of the ternary system (H 2O-ethanol-cationic surfactant), with temperature as one of the coordinate axes. The solubility increased with ethanol content of the mixture, and the critical ethanol concentration for micellization was found to correspond to the Krafft temperature for micellization resulting from aqueous solubility increase with temperature. The enthalpy change of dissolution was positive and increased with ethanol content in the mixture from 12.6 in pure water to 46.6 kJ mol −1 in 15.0 wt% ethanol solution.

The effect of environmental conditions on the steric stabilization of casein micelles

In an attempt to characterize the steric stabilizing sheath around the casein micelles of bovine milk, photon correlation spectroscopy techniques have been used to measure the micellar radius on exposure to ethanolic buffers of varying pH, ionic strength and calcium concentration. It is shown that on exposure to alcohol, the stabilizing protein sheath undergoes dimensional collapse and that immediately prior to aggregation, a minimum or core radius is reached, characteristic of the diluting buffer conditions. Defining barrier thickness as the difference between the micellar radius in alcohol-free buffer and this minimum radius, the same linear relationship is observed between barrier thickness and the critical ethanol concentration required to reach the core radius and induce subsequent aggregation, whether those variations in barrier thickness were achieved by altering the pH, ionic strength or calcium level of the buffer. Considering the initial rate of response to added ethanol as a measure of barrier strength, it is observed that thicker barriers are weaker whereas thinner barriers are more resistant to collapse and hence intrinsically stronger. This paradox is qualitatively resolved by considering the stabilizing sheath to possess some of the characteristics of a weak or soft gel, whose rigidity or extent of cross-linking is influenced by the variations in buffer conditions.

Continuous production of ethanol in a two-stage fermentation process using a protein — Phospholipid complex as a protective agent

A two-stage continuous fermentation process, using a continuous stirred tank fermenter (CSTF) and a tower fermenter (TF) connected in series, has been studied for ethanol production from d-glucose. The addition of a protein-phospholipid complex as a protective agent (PA) in the TF led to a three-fold increase in ethanol productivity and a 23.63% increase in final ethanol concentration in the tower effluent. The results are consistent with our previous findings on a cascade operation of CSTFs, namely, that the addition of PA to the tower increases cell tolerance towards ethanol at ethanol concentrations up to 70 gl −1. Both studies indicate that beyond this experimentally determined critical ethanol concentration, ethanol production is significantly inhibited. Mathematical modelling of the behaviour of a single flocculated yeast floc suggested that, for yeast flocs up to 1 mm diameter, neither internal nor external diffusion of substrate is limiting. Therefore, a simplified mathematical method was developed for the analysis of the TF system. By plotting the calculated values from the derived performance equation and the experimental values of substrate conversion vs. residence time, good agreement was obtained between these two for the addition of PA. However, a small deviation was observed for the PA-free system.

Temperature dependence of the effect of ethanol, as a model substance, on cod

Using an improved apparatus allowing determinations on fish of varying size, the rotatory-flow technique was applied in studies of the effect of ethanol on the fitness of cod ( Gadus morrhua L.). This substance is considered to act exclusively on the central nervous system (CNS). As a measure of fitness the “reaction quotient,” i.e., the quotient between the critical peripheral velocity and the standard length of the individual fish, was used. Ethanol was administered via the medium, and blood concentrations sufficiently high to reduce the reaction quotient significantly were attained after 2.0 hours. Each sample of fish was tested on the first day of the experiment as a control and, on the following day, after exposure to ethanol. The fish were not fed. The critical peripheral velocity was correlated to the length of the fish in all cases, and also in the intoxicated fish, when the length varied sufficiently. By varying the concentration of ethanol in the medium, a critical concentration in the blood was found which just caused the mean reaction quotient to decrease significantly. With increasing temperature (from 5 to 19°C) the mean critical ethanol concentration in the blood decreases significantly above 10°C.

The interaction of serum albumin with ethanol

The reduced viscosity and specific rotation of 1% solutions of bovine serum albumin in aqueous ethanol were obtained at pH's 2, 3, and 4 at low ionic strength, and at high salt concentration at the isoionic point. The data are consistent with increased helical content and the breaking of hydrophobic bonds as a result of adding ethanol at low pH. Similar measurements in low ionic strength phosphate buffer near pH 7 in aqueous ethanol show aggregation occurring at a critical ethanol concentration with the destruction of a sufficient amount of hydrophobic bonding. At the isoionic point and near pH 7, where the protein is in a compact form, the changes in viscosity are much less pronounced than in acid solution where the protein is expandable. The inhibition of aggregation by p-chloromercuribenzoate indicates the importance of sulfhydryl-disulfide interchange in the aggregation process, and the solubility in 10 M urea of a gel obtained at high protein concentration shows that other bonds are also involved in maintaining the aggregate. Spectrophotometric studies of the binding of methyl orange by bovine and human serum albumins in borate buffer, pH 9.2, in aqueous ethanol showed that the binding sites responsible for the specific effect of human albumin on the spectrum of methyl orange may not be separated by ethanol. The results indicate the importance of hydrophobic bonds in maintaining the native structure of albumin, and that ethanol denatures by breaking hydrophobic bonds rather than hydrogen bonds.