Function Of Alcohol Concentration Research Articles

Conformational states of NADH in water–alcohol solutions studied by molecular dynamics simulations

Redox reactions in living cells involving a coenzyme nicotinamide-adenine-dinucleotide (NAD) are stereospecific and depend on NAD conformation states and on the structure of enzyme binding sites. Therefore, information on NAD conformation states in various environments is important for understanding of the mechanisms of redox reactions. In this paper the structural dynamics of reduced nicotinamide-adenine-dinucleotide (NADH) in water–methanol and water–ethanol solutions was investigated by means of molecular dynamics simulations. The trajectory analysis revealed three stable conformation groups characterized by the distance RNA−AD between adenine and nicotinamide centers of mass: folded (RNA−AD< 5.5 Å), intermediate (5.5 Å <RNA−AD< 12 Å) and unfolded (RNA−AD> 12 Å). It was shown that conformation equilibrium shifted from the folded conformation group at low alcohol concentrations towards the intermediate conformation group at high alcohol concentrations, while the fractional concentration of unfolded conformation group remained almost constant. The nicotinamide and adenine rings were found to be almost parallel in folded conformations and perpendicular in intermediate conformations, while no preferable positions of the rings were found in unfolded conformations. The results obtained were used for the analysis of experimentally determined rotational diffusion times τrexp in NADH in water–methanol and water–ethanol mixtures. Comparison between the calculated and experimental τr values using the generalized Stokes–Einstein–Debye equation allowed for determination of the wettability coefficient C and effective molecular volume Vm as a function of alcohol concentration. The coefficient C was found to be always less than unity and have a minimum at 40% of alcohol which was more pronounced for ethanol than for methanol mixtures. This dependence was attributed to the influence of solution viscosity that has a maximum at 40% of alcohol. The effective molecular volume Vm was found to be practically constant at alcohol concentrations below 60% and rise dramatically at higher alcohol concentrations. This dependence was attributed to the solvation of NADH at high alcohol concentrations.

An insight into the filling of the nanoheterogeneous structures of1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide by primary alcohols

Mixtures of ionic liquids (ILs) with molecular cosolvents are attracting increased attention for the development of their technological applications. As a result, understanding the interaction between the heterogeneous structure of ILs and molecular cosolvents at a microscopic level with the aim of fine-tuning the properties of ILs is of utmost importance. In this study, the local structure of the IL 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([bmim][TFSA]) in a series of mixtures of primary alcohol (from methanol to 1-dodecanol) is investigated as a function of alcohol concentration by Raman spectroscopy, providing a unique picture of the evolution of the local structure of alcohol clusters formed in [bmim][TFSA]. The Raman spectra reveal the presence of various types of OH species in the [bmim][TFSA]–alcohol mixtures, with the major fractions corresponding to monomers at lower alcohol concentrations. Presented in this study is a plausible mechanism for the filling of the nanoheterogeneous structures of the [bmim][TFSA] matrix by alcohol molecules, revealing the occurrence of conformational changes in the bmim+ cation and TFSA− anion, which involves an increase of the population of the gauche and transoid conformers with alcohol concentration. Interestingly, the results show that the local structures of bmim+ and TFSA− cooperatively change along with the conformational change in the alcohol molecules toward a smaller total volume.

Raman investigation on the local structure of alcohols in 1-butyl-3-methylimidazolium tetrafluoroborate

In this study, we investigated the evolution of the local structure of a series of primary alcohols from methanol to octanol in 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) as a function of alcohol concentration using Raman spectroscopy, with the aim of gaining more insight into the fundamentals of the compelling ionic liquid–molecular solvent interactions at molecular level. The Raman spectra revealed the presence of various types of OH species in the mixtures, with the major fractions at low alcohol concentration corresponding to monomers, which indicates that most of the alcohol molecules are isolated from each other. A plausible picture for the changes in the local structures of alcohol molecules loosely confined in the [bmim][BF4] matrix is presented, which suggests the occurrence of conformational changes in the bmim+ cation and the alcohol molecules. This observation may indicate a unique evolution of the local structure of alcohol clusters formed in the ionic liquid.

Subtle Effects of Aliphatic Alcohol Structure on Water Extraction and Solute Aggregation in Biphasic Water/n-Dodecane.

Organic phase aggregation behavior of 1-octanol and its structural isomer, 2-ethylhexanol, in a biphasic n-dodecane-water system is studied with a combination of physical measurement, small-angle X-ray scattering (SAXS), and atomistic molecular dynamic simulations. Physical properties of the organic phases are probed following their mixing and equilibration with immiscible water phases. Studies reveal that the interfacial tension decreases as a function of increasing alcohol concentration over the solubility range of the alcohol with no evidence for a critical aggregate concentration (cac). An uptake of water into the organic phases is quantified, as a function of alcohol content, by Karl Fischer titrations. The extraction of water into dodecane was further assessed as a function of alcohol concentration via the slope-analysis method sometimes employed in chemical separations. This method provides a qualitative understanding of solute (water/alcohol) aggregation in the organic phase. The physical results are supported by analyses of SAXS data that reveals an emergence of aggregates in n-dodecane at elevated alcohol concentrations. The observed aggregate structure is dependent on the alcohol tail group geometry, consistent with surfactant packing parameter. The formation of these aggregates is discussed at a molecular level, where alcohol-alcohol and alcohol-water H-bonding interactions likely dominate the occurrence and morphology of the aggregates.

Nonmonotonic Hydration Behavior of Bovine Serum Albumin in Alcohol/Water Binary Mixtures: A Terahertz Spectroscopic Investigation.

We report the experimental observation of nonmonotonic changes in the collective hydration of bovine serum albumin (BSA) in the presence of alcohols of varying carbon-chain lengths, that is, ethanol, 2-propanol, and tert-butyl alcohol (TBA), by using terahertz (THz) time domain spectroscopy. We measured the THz absorption coefficient (α) of the protein solutions, and it was observed that α fluctuated periodically as a function of alcohol concentration at a fixed protein concentration. For a fixed alcohol concentration, an increase in the protein concentration resulted in nonmonotonic changes in α; thus, it first decreased rapidly and then increased, which was followed by a shallow decrease. An alcohol-induced α helix to random coil transition of the protein secondary structure was revealed by circular dichroism spectroscopy measurements, and the effect was most prominent in TBA. The anomalous change in the hydration was found to be a delicate balance between the various interactions present in the three-component system.

Micellar Growth in Cetylpyridinium Chloride/Alcohol System: Role of Long Chain Alcohol, Electrolyte and Surfactant Head Group

AbstractThe microstructural transition of aqueous 0.1 M cetylpyridinium chloride (CPC) in the combined presence of salt KBr and long chain alcohol (C9OH‐C12OH) has been studied as a function of alcohol concentration, electrolyte concentration and temperature. The viscosity of the CPC/KBr micellar system showed a peaked behavior with alcohol concentration (C0), due to alcohol induced structural transition, which was confirmed by dynamic light scattering (DLS) and rheological analysis. Besides C0, the chain length of alcohol (n) was found to show a remarkable effect on the micellization behavior of CPC/KBr system. It was observed that the ability of alcohol to induce micelle growth diminishes with n, which was well supported by viscosity, rheology and DLS measurements. To examine the effect of the electrolyte on the micellar growth, the salt concentration was varied from 0.05 to 0.15 M and it was observed that with increase in [KBr], the peak position shifts towards lower C0. The effect of temperature on the micellar system showed interesting phase behavior for CPC/KBr/Decanol. The system exhibited a closed solubility loop with an upper critical solution temperature (UCST) &gt; the lower critical solution temperature (LCST), reminiscence of nicotine‐water system. The role of surfactant head group on the structural evolution was revealed by comparing the present results with our previous report for similar micellar system, CTAB/KBr/long chain alcohol.

Mechanism of sonochemical reduction of permanganate to manganese dioxide in aqueous alcohol solutions: Reactivities of reducing species formed by alcohol sonolysis

The sonochemical reduction of MnO4− to MnO2 in aqueous solutions was investigated as a function of alcohol concentration under Ar. The rate of MnO4− reduction initially decreased with increasing alcohol concentration, and then increased when the alcohol concentration was increased further. The concentrations at which the reduction rates were minimum depended on the hydrophobic properties of the added alcohols under ultrasonic irradiation. At low concentrations, the alcohols acted as OH radical scavengers; at high concentrations, they acted as reductant precursors: Rab, formed by abstraction reactions of the alcohols with sonochemically formed OH radicals or H atoms, and Rpy, formed by alcohol pyrolysis under ultrasonic irradiation. The results suggest that the reactivity order of the sonochemically formed reducing species with MnO4− at pH 7–9 is the sum of H2O2 and H>Rpy>Rab. The peak wavelengths of MnO2 colloidal solutions formed at high 1-butanol concentrations shifted to shorter wavelengths, suggesting the formation of small particles at high 1-butanol concentrations. The rates of sonochemical reduction of MnO2 to Mn2+ in the presence of 1-butanol were slower than that in the absence of 1-butanol, because the sonochemical formation of H2O2 and H, which act as reductants, was suppressed by 1-butanol in aqueous solutions.

A study of alcohol and temperature effects on aggregation of β-lactoglobulin by viscosity and small-angle X-ray scattering measurements

Small-angle X-ray scattering (SAXS) of aqueous solutions of methanol and 2,2,2-trifluoroethanol (TFE) of β-lactoglobulin (β-Lg) in concentrations of 30 and 63mg/mL was measured as a function of alcohol concentration in a temperature range of 298–363K to investigate the effects of alcohol and temperature on aggregation of the protein. The viscosity of aqueous solutions of methanol, ethanol and TFE of β-Lg in a concentration of 2mg/mL was also measured as a function of alcohol concentration at an ambient temperature. The relative viscosity, η/η0, where η and η0 are the viscosities of the protein solutions and the solvents, respectively, showed a maximum at around 50%, 40% and 20% of the methanol, ethanol and TFE solutions, respectively. This finding suggests that the aggregation of β-Lg of a low concentration occurs at the specific alcohol concentrations. The SAXS data showed that the aggregation of β-Lg in terms of the aggregation number and the radius of gyration initiates at an alcohol concentration of ~40% for the methanol solutions and ~10% for the TFE solutions and increases with alcohol concentration at ambient temperature. Furthermore, the temperature of thermal denaturation of β-Lg decreased by ~30K for the TFE solution and by ~20K for the methanol solution, compared with the case for water (348K). Thus, the addition of TFE promoted the thermal denaturation of the protein more effectively than methanol. The aggregation structure of the thermally denatured protein was independent of type and concentration of alcohol in the concentrated protein solutions. Furthermore, the fractal dimension of the aggregates was ~2.6, indicating a three dimensional network structure. However, in the diluted protein solutions, the aggregate structure after the thermal denaturation was likely to be a low cross-linked network gel in the methanol solution, which was similar to that in water. On the other hand, more complex aggregates tended to form in the TFE solution.

Hydration Shell Parameters of Aqueous Alcohols: THz Excess Absorption and Packing Density

Solvation in water requires minimizing the perturbations in its hydrogen bonded network. Hence solutes distort water molecular motions in a surrounding domain, forming a molecule-specific hydration shell. The properties of those hydration shells impact the structure and function of the solubilized molecules, both at the single molecule and at higher order levels. The size of the hydration shell and the picoseconds time-scale water dynamics retardation are revealed by terahertz (THz) absorption coefficient measurements. Room-temperature absorption coefficient at f = 0.28 [THz] is measured as a function of alcohol concentration in aqueous methanol, ethanol, 1,2-propanol, and 1-butanol solutions. Highly diluted alcohol measurements and enhanced overall measurement accuracy are achieved with a THz absorption measurement technique of nL-volume liquids in a capillary tube. In the absorption analysis, bulk and interfacial molecular domains of water and alcohol are considered. THz ideal and excess absorption coefficients are defined in accordance with thermodynamics mixing formulations. The parameter extraction method is developed based on a THz excess absorption model and hydrated solute molecule packing density representation. First, the hydration shell size is deduced from the hydrated solute packing densities at two specific THz excess absorption nonlinearity points: at infinite alcohol dilution (IAD) and at the THz excess absorption extremum (EAE). Consequently, interfacial water and alcohol molecular domain absorptions are deduced from the THz excess absorption model. The hydration shell sizes obtained at the THz excess absorption extremum are in excellent agreement with other reports. The hydration shells of methanol, ethanol, 1- and 2-propanol consist of 13.97, 22.94, 22.99, and 31.10 water molecules, respectively. The hydration shell water absorption is on average 0.774 ± 0.028 times the bulk water absorption. The hydration shell parameters might shed light on hydration dynamics of biomolecules.

Alcohol induced structural and dynamic changes in β-lactoglobulin in aqueous solution: A neutron scattering study

Structural and dynamic properties of β-lactoglobulin (β-LG) were revealed as a function of alcohol concentration in ethanol- and trifluoroethanol(TFE)-water mixtures with circular dichroism (CD), small-angle neutron scattering (SANS) and quasi-elastic neutron scattering (QENS). The CD spectra showed that an increase in TFE concentration promotes the formation of the β-sheet structure of β-LG. The SANS-intensities were fitted using form factors for two attached spheres for the native and native-like states of the protein. At higher alcohol concentrations, where aggregation takes place, a form factor modelling diffusion limited colloidal aggregation (DLCA) was employed. The QENS-data were analyzed in terms of internal motions for all alcohol concentrations. While low concentrations of TFE (10% (v/v)) lead to an increase of the mean square amplitudes of vibrations <u2> and a retention of a native-like structure — but not to an increase of the characteristic radius of proton diffusion processes a. Addition of 20% (v/v) of TFE induces aggregation, going along with a further increase of <u2>. Further increase of TFE concentration to 30% (v/v) changes the nanoscale structure of the oligomeric nucleate, but induces no further significant changes in <u2>. The present study underlines the necessity of methods sensitive to the dynamics of a system to obtain a complete picture of a molecular process.

The adsorption properties of short chain alcohols and Triton X-100 mixtures at the water–air interface

The adsorption behaviour at the water–air interface of aqueous solutions of Triton X-100 and methanol (ethanol) mixtures at constant Triton X-100 (TX-100) concentration equal to 10 −7, 10 −6, 10 −5, 10 −4, 6 × 10 −4 and 10 −3 M, respectively, in a wide range of alcohol concentration was investigated by surface tension measurements of solutions. The obtained values of the surface tension of aqueous solutions of “pure” methanol and ethanol and their mixtures with TX-100, as well as the values of propanol solutions and their mixtures with TX-100 as a function of alcohol concentration taken from the literature were compared with those calculated from the Szyszkowski, Connors and Fainerman and Miller equations. On the basis of this comparison it was stated that these equations can be useful for description of the solution surface tension in the wide range of alcohol concentration, but only at the concentrations of Triton X-100 corresponding to its unsaturated layer in the absence of alcohol. It was also stated that the Connors equation is more adequate for concentrated aqueous organic solutions. The measured values of the surface tension were used in the Gibbs equation to determine the surface excess concentration of Triton X-100 and alcohol. Next, on the basis of Gibbs adsorption isotherms those of Guggenheim and Adam and real adsorption isotherms were established. From the obtained adsorption isotherms it results that alcohol influences the shape of TX-100 isotherms in the whole range of alcohol and TX-100 concentration, but TX-100 influences the alcohol isotherms only at TX-100 concentration at which the saturated monolayer at the solution-air interface is formed in the absence of alcohol. This conclusion was confirmed by analysis of the composition of the surface layer in comparison to the composition of the bulk phase in the equilibrium state.

High Sensitive Gas Sensor Application Based on a Small Defect in Silicon Waveguide

A small defect in silicon nanowire waveguides is applied for gas sensors. Small defects with some special shapes and indexes can produce strong resonances with the incident light and induce large loss. Since the silicon waveguide has air cladding, the position of resonant peaks will be sensitive for the variation of the ambient air composition. The sensor based on the principle has a high sensitivity. As an example, we monitored the change of the position of the resonance peak as a function of alcohol concentrations in air. Results showed that a ~5-mg/L ethanol vapor in the air can result in a ~20-nm wavelength shift of the resonance.

Structure of hexafluoroisopropanol–water mixture studied by FTIR-ATR spectra and selected chemometric methods

The FTIR spectra of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)–water binary solutions have been obtained by means of attenuated total internal reflection (ATR) spectroscopy. The spectral properties of the system have been analyzed as a function of alcohol concentration by following methods: multivariate curve resolution based on alternating least-square procedure (MCR-ALS) preceded by evolving factor analysis (EFA), kernel analysis, and two-dimensional (2D) correlation spectroscopy. From all the information obtained by these methods the four-component model describing the aggregation of HFIP and water molecules in HFIP–water mixtures was proposed. In characterization of properties of the components not only changes in the aggregation process were taken into account but also variations in relative population of different HFIP conformations were considered. The case reported is a very good example to show how the MCR-ALS and 2D analysis could complement each other, leading to enhancement of the multicomponent data interpretation.

Hydration of alcohol clusters in 1-propanol-water mixture studied by quasielastic neutron scattering and an interpretation of anomalous excess partial molar volume

Quasielastic neutron scattering measurements have been made for 1-propanol-water mixtures in a range of alcohol concentration from 0.0 to 0.167 in mole fraction at 25 degrees C. Fraction alpha of water molecules hydrated to fractal surface of alcohol clusters in 1-propanol-water mixture was obtained as a function of alcohol concentration. Average hydration number N(ws) of 1-propanol molecule is derived from the value of alpha as a function of alcohol concentration. By extrapolating N(ws) to infinite dilution, we obtain values of 12-13 as hydration number of isolated 1-propanol molecule. A simple interpretation of structural origin of anomalous excess partial molar volume of water is proposed and as a result a simple equation for the excess partial molar volume is deduced in terms of alpha. Calculated values of the excess partial molar volumes of water and 1-propanol and the excess molar volume of the mixture are in good agreement with experimental values.

Lifting a Wet Glass from a Table: A Microscopic Picture

Why is it so hard to lift a wet glass from a table? Is it easier when there is whiskey between the glass and the table? Macroscopically, the picture is quite simple: two surfaces have to be disrupted that are connected indirectly through hydrogen bonds and/or van der Waals forces. In the beginning, a surface has to be created leading to surface tension, and after that a liquid bridge has to be broken. Here we study the phenomenon at the microscopic level using molecular dynamics simulations. The effective force between two quartz plates is measured at different distances and with different alcohol/water mixtures between them. This allows us to compute the total work necessary to "lift the glass from the table". Different aspects of the process, such as clustering and liquid ordering are discussed. We compare the structure of the liquid/glass interface to that of a liquid/vapor interface, for which we present simulation results, like surface tension, as well. On the basis of the simulations, we are able to provide a detailed description of the energetics during the separation process as a function of alcohol concentration. It is shown that there is a net entropy loss upon separating two plates with water or a 10% MeOH solution between them, whereas for higher alcohol concentrations, there is net entropy gain. These findings increase our understanding of the properties of colloid suspensions which is important for process technology.

Ultrasonic Studies of Alcohol-Induced Transconformation in β-Lactoglobulin: The Intermediate State

In mixed alcohol-water solvents, bovine β-lactoglobulin undergoes a cooperative transition from β-sheet to a high α-helix content conformer. We report here the characterization of β-lactoglobulin by compressibility and spectroscopy measurements during this transconformation. Both the volume and compressibility increase as a function of alcohol concentration, up to maximal values which depend on the chemical nature of the three alcohols used: hexafluoroisopropanol, trifluoroethanol, and isopropanol. The order of effectiveness of alcohols in inducing the compressibility transition is identical to that previously reported for circular dichroism and thus independent of the observation technique. The highly cooperative sigmoidal curves found by compressibility determination match closely those obtained by circular dichroism at 222 nm, indicating a correlation between the two phenomena measured by the two different techniques. The presence of an equilibrium intermediate form was shown by the interaction of β-lactoglobulin with 8-anilino-1-naphthalene sulfonic acid, a probe widely used to detect molten-globule states of proteins. It was correlated with the plateau region of the volume curves and with the inflexion points of the sigmoidal compressibility curves. Ultrasound characterization of proteins can be carried out in optically transparent or nontransparent media.

Determination of sensoric parameters of porous silicon in sensing of organic vapors

Photoluminescence (PL) properties of as-prepared and surface derivatized porous silicon (PS) in the presence of organic compounds in gas phase were studied. Surface derivatization, aimed at increasing stability of porous silicon properties, was performed by Lewis acid mediated hydrosilylation with methyl 10-undecenoate. We have systematically measured changes in photoluminescence intensity for a set of alcohols from C 1 to C 6. From the variation of the photoluminescence quenching response as a function of alcohol concentration, we determine the sensitivities and detection limits of our porous silicon sensors and these correlate with physical and chemical properties of studied species. For methyl 10-undecenoate derivatized PS samples, we have observed a remarkable enhancement of the selectivity for C 4–C 6 alcohols as compared with C 1–C 3 alcohols.

Examination by dynamic light scattering of lysozyme in water/alcohol mixtures

The technique of intensity photon correlation spectroscopy has been utilized to investigate the native conformation of lysozyme in water/ethanol and in water/tert-butanol mixtures as a function of alcohol concentration in the water-rich region of composition (cosolvent mole fraction x2<0.08). A non-trivial behavior of the hydrodynamic radius is obtained, characterized by a minimum at x2=0.02 and a maximum at x2=0.06 in water/ethanol mixtures and by a minimum at x2=0.005 and a maximum at x2=0.02 in water/tert-butanol mixtures. These values of x2 are close to those at which structural changes in the mixtures occur as inferred from compressibility and infrared absorption measurements. The results are discussed in connection to the effect of alcohol in modulating solvent-mediated interactions.

Supersolubilization in Chlorinated Hydrocarbon Microemulsions: Solubilization Enhancement by Lipophilic and Hydrophilic Linkers

In this paper, the effect of linker molecules on the solubilization capacity of an anionic surfactant system (sodium dihexyl sulfosuccinate) is studied. N-Alkyl alcohols are used as lipophilic linkers in middle-phase microemulsions of trichloroethylene, tetrachloroethylene, and hexane. The lipophilic linker effect increases the solubilization capacity of the anionic surfactant system. The solubilization parameter for both hydrocarbons and chlorinated hydrocarbon oil increases as a function of alcohol concentration. As the alkyl chain length of the alcohol linker molecule increases, the solubilization capacity increases. Moreover, the longer chain alcohol is more effective at linking oil molecules for hexane than for chlorinated hydrocarbon oils, indicating that the linker effect is more effective for higher equivilant alkane carbon number (EACN) oils. Sodium mono- and dimethylnaphthalenesulfonate is proposed as a hydrophilic linker to enhance the solubilization of lower EACN oils. The combination of lipophilic and hydrophilic linkers synergistically enhances the solubilization capacity of chlorinated hydrocarbon microemulsions.

Role of hydrophobic interactions on the stabilisation of native state of globular proteins

The technique of intensity photon correlation spectroscopy has been utilised to investigate the native conformation of lysozyme in water/ethanol mixture as a function of alcohol concentration in the water-rich region of composition (cosolvent mole fraction x 2<0.08). A non-trivial behaviour of the hydrodynamic radius is obtained, characterised by a minimum at x 2=0.02 and a maximum at x 2=0.06. This behaviour is similar to that of partial molar volume of ethanol in water and reflects changes in the alcohol/water structure. The results are discussed in connection to the effect of alcohol in modulating solvent-mediated interactions.