Thermodynamic study of the effect of ethanol on two amphiphilic penicillins

The effect of ethanol on the thermodynamic properties on two anionic amphiphilic penicillins, cloxacillin and dicloxacillin, has been investigated. Cloxacillin and dicloxacillin are two molecules that are similar structurally, differing only by an additional chlorine atom on the phenyl ring of dicloxacillin. The penicillins can be considered as hydrotropes if we considered that the term comprises hydrophilic and hydrophobic moieties that form aggregates by a stacking mechanism as is the case of both penicillins. By means of ultrasound velocities and densities, we have calculated the apparent molar volumes and adiabatic compressibilities. The critical concentrations, cc, and partition coefficients, K, have been determined, the latter using an indirect method based on the pseudophase model with the help of apparent molar data. This method has the advantage of allowing one to calculate the distribution coefficients at concentrations of the solubilizate below the saturation. The standard molar energy of Gibbs change, DeltaG0, on transfer from the aqueous to the micelar phase was calculated from the partition coefficient. The effect of the alcohol involves a slight decrease of the critical concentration because of a headgroup repulsion decrease. The enthalpies of dilution of dicloxacillin in a mixture of water and 15% w/v of ethanol were calculated. The aggregation process is more exothermic in ethanol that in pure water.     

最大泡压法测表面张力等温线的数据处理方法比较*

对乙酸、丙酸、正丁酸、2-甲基丁酸、3-甲基丁酸、正戊酸、正己酸、乙醇、丙醇、异丙醇、正丁醇、异丁醇、1,2-丙二醇等13种常用试剂在25 ℃下的表面张力数据拟合方法进行了比较,分析了图解法处理数据及多项式、一阶指数函数、幂函数、Shishkovsky经验公式拟合数据的优缺点。指出Shishkovsky经验公式拟合结果准确,受数据样本量影响小,是理想的表面张力数据拟合方法。     

Effect of Electrolyte on the Surface and Thermodynamic Properties of Amphiphilic Penicillins

Critical micelle concentrations and surface properties of the penicillins cloxacillin, dicloxacillin, and nafcillin in aqueous solution at 303 K and at electrolyte concentrations over the range 0.0–0.4 mol dm⁻³ were determined by surface tension measurements. A mass action model, modified for application to associating systems of low aggregation number, was used to calculate the standard Gibbs energy of micellization of these drugs at each electrolyte concentration.     

Surface tension of four binary systems containing (1-ethyl-3-methyl imidazolium alkyl sulphate ionic liquid + water or + ethanol)

In this work, we present surface tension experimental measurements for eight binary systems containing water or ethanol and an ionic liquid (IL) of the 1-ethyl-3-methyl imidazolium alkyl sulphate family, being the alkyl chain of the anion: ethyl, butyl, hexyl and octyl. Measurements were performed at the temperature of 25.0 °C and atmospheric pressure. All four ILs are completely miscible with water and ethanol, but for a concentration range of the octyl sulphate IL aqueous system the mixture jellifies, and so it is not possible to measure its surface tension. These measurements allow us to study the influence of the anion size on the surface tension for the pure IL compounds, and the role of the two different solvents in the surface tension behaviour. Thus, we observe that it is completely different when mixed with water or with ethanol, as also happens in other mixtures with different ionic liquids. From the experimental data, we extract surface tension deviations using the most popular definition. The calculated deviations for the ethanol based system are fitted using the Redlich–Kister equation and a novel one previously reported by us. Furthermore, we have also calculated the reduced surface pressure for the aqueous mixtures, which is fitted with good agreement using a theoretical equation obtained from the Bahe–Varela pseudo-lattice model.     

Spectroscopic and thermodynamic study of charge transfer complexes of cloxacillin sodium in aqueous ethanol medium

Cloxacillin sodium has been shown to form charge transfer (CT) complexes of 1:1 stoichiometry with a number of electron acceptors in 50% (v/v) aqueous ethanol medium. From the trends in the CT absorption bands, the vertical ionization potential of the drug molecule (cloxacillin sodium) has been estimated to be 7.89 eV. The enthalpies and entropies of formation of two such complexes have been determined by estimating the formation constants spectrophotometrically at five different temperatures. The oscillator strengths and transition dipole moments of these complexes have been determined. It has further been noted that the reduction of o-chloranil by aqueous ethanol is completely inhibited by cloxacillin sodium, a phenomenon that makes the present study of formation equilibrium possible.     

Application of an extended DLVO theory for the calculation of the interactions between emulsified oil droplets in alcohol solutions

The stability of diluted emulsions (0.1% v/v) of n-dodecane in 1 M methanol, ethanol or propanol was studied. The effective diameter and zeta potential were determined by dynamic light scattering. The parameters were measured 5, 30, 60, 120 min and after 1 day after preparation of the emulsions by mechanical mixing at 10 000 r.p.m. for 3 min. Calculations of the free energy interactions between dodecane droplets were conducted applying van Oss et al.’s extended DLVO theory, in which acid–base interactions involving electron donor and electron acceptor parameters are also accounted for. For this purpose the interfacial tensions of oil–alcohol solutions were taken from the literature. The acid–base interactions were evaluated considering two variants. In the first we assumed a close-packed monolayer of alcohol molecules on the droplet surface, interacting by hydrogen bonds with water as well with alcohol molecules. In the second variant, it was considered that in these electrolyte-free systems (pH close to neutral) the measured zeta potentials were due to the oriented alcohol dipoles on the droplet surface. This would mean that the slipping plane is very close to the droplet surface. Both variants lead to the same conclusion that in these system the dominant role is played by attractive acid–base interactions, which is much bigger than the equally attractive apolar Lifshitz–van der Waals interaction. Repulsive electrostatic interactions play only a minor role.     

Continuous wine making by delignified cellulosic materials supported biocatalyst

The continuous making of wine by a delignified cellulosic (DC) material-supported biocatalyst is reported. It was prepared by immobilizing the alcohol resistant strain AXAZ-1 on DC material. The product was found suitable for the continuous process in industrial applications. The operational stability was maintained for 2 mo with monitoring the ethanol concentration, wine, and alcohol productivities as well as the stability of °Be density at the outlet. Wine productivity was three to sixfold higher than obtained by natural fermentation, alcohol concentrations of the wine was in the range of 9.3-211.2% v/v and low volatile acidities of 0.15-20.36 g acetic acid/L were obtained. The effect of total acidity and flow rate of must were also examined. To demonstrate that the operational stability of the bioreactor is due to DC material that promotes the fermentation, and it takes place at even higher ethanol levels, an analogous system of kissiris supported biocatalyst was studied. Likewise, the tolerance in the alcohol concentration, as compared with free cells, were studied by their stability of the activity in the repeated batch fermentation of must.     

Effect of anionic surfactant and short-chain alcohol mixtures on adsorption at quartz/water and water/air interfaces and the wettability of quartz

Measurements of the advancing contact angles for aqueous solutions of sodium dodecyl sulfate (SDDS) or sodium hexadecyl sulfonate (SHS) in mixtures with methanol, ethanol, or propanol on a quartz surface were carried out. On the basis of the obtained results and Young and Gibbs equations the critical surface tension of quartz wetting, the composition of the surface layer at the quartz-water interface, and the activity coefficients of the anionic surfactants and alcohols in this layer as well as the work of adhesion of aqueous solutions of anionic surfactant and alcohol mixtures to the quartz surface were determined. The analysis of the contact angle data showed that the wettability of quartz changed visibly only in the range of alcohol and anionic surfactant concentration at which these surface-active agents were present in the solution in the monomeric form. The analysis also showed that there was a linear dependence between the adhesion and the surface tension of aqueous solutions of anionic surfactant and alcohol mixtures. This dependence can be described by linear equations for which the constants depend on the anionic surfactant and alcohol concentrations. The slope of all linear dependence between adhesion and surface tension was positive. The critical surface tension of quartz wetting determined from this dependence by extrapolating the adhesion tension to the value equal to the surface tension (for contact angle equal zero) depends on the assumption whether the concentration of anionic surfactant or alcohol was constant. Its average value is equal to 29.95mN/m and it is considerably lower than the quartz surface tension. The positive slope of the adhesion-surface tension curves was explained by the possibility of the presence of liquid vapor film beyond the solution drop which settled on the quartz surface and the adsorption of surface-active agents at the quartz/monolayer water film-water interface. This conclusion was confirmed by the work of adhesion of aqueous solutions of anionic surfactants and short-chain alcohol mixtures to the quartz surface determined on the basis of the contact angle data and molar fraction of anionic surfactants and alcohols and their activity coefficient in the surface layer.     

Investigating the effect of an arterial hypertension drug on the structural properties of plasma protein

Propanolol is a betablocker drug used in the treatment of arterial hypertension related diseases. In order to achieve an optimal performance of this drug it is important to consider the possible interactions of propanolol with plasma proteins. In this work, we have used several experimental techniques to characterise the effect of addition of the betablocker propanolol on the properties of bovine plasma fibrinogen (FB). Differential scanning calorimeter (DSC), circular dichroism (CD), dynamic light scattering (DLS), surface tension techniques and atomic force microscopy (AFM) measurements have been combined to carry out a detailed physicochemical and surface characterization of the mixed system. As a result, DSC measurements show that propranolol can play two opposite roles, either acting as a structure stabilizer at low molar concentrations or as a structure destabilizer at higher concentrations, in different domains of fibrinogen. CD measurements have revealed that the effect of propanolol on the secondary structure of fibrinogen depends on the temperature and the drug concentration and the DLS analysis showed evidence for protein aggregation. Interestingly, surface tension measurements provided further evidence of the conformational change induced by propanolol on the secondary structure of FB by importantly increasing the surface tension of the system. Finally, AFM imaging of the fibrinogen system provided direct visualization of the protein structure in the presence of propanolol. Combination of these techniques has produced complementary information on the behavior of the mixed system, providing new insights into the structural properties of proteins with potential medical interest.     

Surface Tension of Binary Mixtures of 1-Alkyl-3-Methyl-Imidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids with Alcohols

New experimental surface tension data have been provided at 283.15, 298.15, 313.15 K and atmospheric pressure for binary mixtures of 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide and 1-octyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquids with the alcohols: methanol, ethanol, 1-propanol, 2-propanol, l-butanol and 1-pentanol. The experimental results show that the surface tensions of these mixtures depend systematically on the alkyl chain length of the ionic liquid and alcohol, composition and temperature. Surface tension changes on mixing have been calculated and adequately fitted by the Redlich–Kister polynomial equation. The adjustable parameters and the standard deviations between experimental and calculated values are reported.     

High-performance liquid chromatographic analysis of ampicillin and cloxacillin and its application to an intramammary veterinary preparation

Summary Reverse phase high-performance liquid chromatography with ultra-violet detection has been used for the simultaneous identification and determination of ampicillin, cloxacillin and some of their degradation products following their extraction from an intramammary preparation used in veterinary medicine. Extraction of the intramammary base into petroleum ether (40–60°C) and partition of the penicillins into the mobile phase gave a mean recovery of 100.8% for ampicillin with coefficient of variation of 1.0 and 103.4% for cloxacillin with coefficient of variation of 1.2 (n=6). Using optimised HPLC conditions ampicillin eluted in approximately 2 min and cloxacillin in approximately 8 min. The overall method was found to be stability indicating, since cloxacillin and ampicillin eluted independently of their degradation products.     

Thermodynamics of Association of Structurally Related Amphiphilic Penicillins

Critical micelle concentrations (CMCs) of the penicillins cloxacillin and dicloxacillin in water were determined by conductivity measurements over the temperature range 288.15 to 313.15 K. Both penicillins showed minimum CMCs at temperatures close to 298.15 K. Thermodynamic parameters of aggregate formation were derived from the variation of the CMC with temperature using a modified form of the mass action model applicable to systems of low aggregation number. Values for the enthalpy of aggregate formation, DeltaH(0)(m), calculated by this method showed that the aggregation of both cloxacillin and dicloxacillin became increasingly exothermic with increase in temperature. The predicted DeltaH(0)(m) at 298.15 K was in good agreement with the value determined experimentally by calorimetry for each drug. Copyright 2000 Academic Press.     

Self-Assembling Behavior of Polyglyceryl-Modified Silicone Surfactant in Aqueous Solution

We report interesting self-assembly behavior of a polyglyceryl-modified silicone surfactant in the aqueous solution; the sample has been characterized through measurements of surface tension, transmission electron microscopy (TEM), dynamic light scattering (DLS), and small-angle x-ray scattering (SAXS). Aqueous solutions of this surfactant had a low critical aggregation concentration (CAC) and surface tension (21.5 mN · m^?1), substantially lower than those reported for polyether-modified silicone surfactants with a similar molecular architecture. DLS and TEM revealed self-assembled spherical micelles with a narrow size distribution. At higher concentrations (10 wt%), linear packing of micelles was observed, while the micelle size distribution remained similar (50–90 nm). SAXS data could be fitted through the use of a core–shell model and implied that the core radius remained roughly 4.3–6.0 nm for all solutions of the surfactant analyzed. The origin of its curious aggregates behavior is attributed to hydrogen bonding, steric effects, and the directionality of bond angle from the polyglyceryl block of this novel class of silicone surfactant. This type of surfactant coupling lipophilic segments assembles the cores of the micelles in water which may find positive factors for potential applications such as microreaction compartmentalization.     

Toward the Rationalization of Facilitated Hydrotropy: Investigation with the Ternary Dimethyl Isosorbide / Benzyl Alcohol / Water System

Solubility enhancement has been achieved by facilitated hydrotropy for the dimethyl isosorbide (DMI) / benzyl alcohol / water system. Facilitated hydrotropy has been studied via three different approaches: the solubilization in water of a hydrophobic dye, the evolution of the surface tension and dynamic light scattering, all as a function of the benzyl alcohol concentration. The facilitated hydrotropy has been rationalized from the solubilization properties of the system according to the ratio between the insoluble hydrotrope (here benzyl alcohol, a preservative used in parenteral injections) and the bio-sourced co-solvant (here the dimethyl isosorbide ether, DMI, a solvent used in pharmaceutical formulation). The presence of self-associated nanostructures has been detected by dynamic light scattering (DLS). It appears that the cosolvent, DMI, has an antagonistic action: DMI increases the facilitated hydrotrope (benzyl alcohol) solubility in the aqueous solution (favoring solute solubilization) but simultaneously decreases the hydrotropic efficiency of benzyl alcohol.     

Light scattering studies of amphiphilic drugs promethazine hydrochloride and imipramine hydrochloride in aqueous electrolyte solutions

Two amphiphilic drugs, promethazine hydrochloride (PMT) and imipramine hydrochloride (IMP), have been studied using both static and dynamic light scattering techniques. Due to having rigid tricyclic hydrophobic moieties in their molecules, these drugs show interesting association behavior. The static light scattering (SLS) measurements show that the self-association commenced above a well-defined critical micellar concentration ( cmc), which decreases with increasing NaBr concentration. The Gibbs energy of micellization, DeltaG(0)M, in all cases, is negative. The colloidal stability of the system in terms of the interparticle interaction at different NaBr concentrations was studied using the dynamic light scattering (DLS) technique. The experimentally evaluated interparticle interaction parameter ( k D ) was compared with the Derjaguin-Landau-Verwey-Overbeek (DLVO) model. Interestingly, these two drugs with similar molecular structure show difference in their interparticle interactions, e.g., PMT showed complete agreement with the DLVO model whereas IMP showed clear deviation from this model at lower concentrations and agreement at higher concentrations of NaBr.     

Study of colloidal particle Brownian aggregation by low-coherence fiber optic dynamic light scattering

The aggregation kinetics of particles in dense polystyrene latex suspensions is studied by low-coherence fiber optic dynamic light scattering. Low-coherence fiber optic dynamic light scattering is used to measure the hydrodynamic radius of the aggregates. The aggregation kinetics data obtained can be fitted into a single exponential function, which is the characteristic of slow aggregation. It is found that the aggregation rate of particles increased with higher electrolyte levels and with larger particle concentrations. The experimental results can be explained by use of the Derjaruin-Landau-Verwey-Overbeer (DLVO) theory.     

表面力仪的改进及溶液中DLVO理论的验证

改进了现有表面力仪,使之具有更低的造价和更高的实验精度.利用改进后的表面力仪测量了0.1mol/L的NaCl溶液中两云母表面间的作用力-距离曲线;通过与计算得到的曲线对比验证了DLVO理论.结果表明:在0.1mol/L的NaCl溶液中,两云母表面间在距离较大时的作用力测量值与DLVO理论值相符合,但在距离较小时测量值出现附加的短程斥力,且此斥力呈现指数衰减规律.     

Formation of micelles of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide in N-methyl acetamide—alcohol and N,N-dimethyl acetamide—alcohol mixtures

The critical micelle concentrations of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide in solutions of in N-methylacetami de and in N,N-dimethyl acetamide with added methanol, ethanol, n-propanol, n-butanol and n-pentanol were determined using electrical conductivity and surface tension measurements at various temperatures. Both methods show that micelles are formed in N-methyl acetamide and N, N-dimethyl acetamide solutions in a presence of n-alcohols. Critical micelle concentrations were also determined as functions of concentration of added alcohol. The data suggest that alcohol adding leads to an enhancement of penetration of alcohol into the micelle external shell that depends on the alcohol chain length. Thermodynamic parameters for micellar systems in a presence of n-alcohols were also calculated.     

Effects of cationic head groups of ionic liquid on micellization in aqueous solution of PEO-PPO-PEO triblock copolymer

The interaction of ionic liquids (ILs) with non-ionic triblock copolymer, Pluronic® P123 in aqueous solutions has been investigated using DLS, surface tension, and viscosity measurements. The addition of ILs increased the Critical Micelle Concentration (CMC) of P123, which appears to be logistic. As the added IL enhances the solubility of PPO moiety (and PEO), which makes them to behave like a more hydrophilic block copolymer that would be micellized at high copolymer concentration. The DLS data is in good agreement to the results observed from surface tension measurements. Viscosity results show the propensity in micellar size reduction upon addition of ILs, and hence, intrinsic viscosity decreases as compared to pure P123 aqueous solution. The results are studied and discussed as a function of cationic head groups of N-octyl-pyridinium/imidazolium chloride based ILs.