Spectroscopic and thermodynamic study of charge transfer complex formation between cloxacillin sodium and riboflavin in aqueous ethanol media of varying composition

Cloxacillin sodium has been shown to form a charge transfer complex of 2:1 stoichiometry with riboflavin (Vitamin B(2)) in aqueous ethanol medium. The enthalpy and entropy of formation of this complex have been determined by estimating the formation constant spectrophotometrically at five different temperatures in pure water medium. Pronounced effect of dielectric constant of the medium on the magnitude of K has been observed by determining K in aqueous ethanol mixtures of varying composition. This has been rationalized in terms of ionic dissociation of the cloxacillin sodium (D(-)Na(+)), hydrolysis of the anion D(-) and complexation of the free acid, DH with riboflavin.     

Absorption spectrometric study of charge transfer complex formation between 4-acetamidophenol (paracetamol) and a series of quinones including vitamin K3

The formation of charge transfer (CT) complexes of 4-acetamidophenol (commonly called 'paracetamol') and a series of quinones (including Vitamin K3) has been studied spectrophotometrically in ethanol medium. The vertical ionisation potential of paracetamol and the degrees of charge transfer of the complexes in their ground state has been estimated from the trends in the charge transfer bands. The oscillator and transition dipole strengths of the complexes have been determined from the CT absorption spectra at 298 K. The complexes have been found by Job's method of continuous variation to have the uncommon 2:1 (paracetamol:quinone) stoichiometry in each case. The enthalpies and entropies of formation of the complexes have been obtained by determining their formation constants at five different temperatures.     

Surface charge properties of Fe2O3 in aqueous and alcoholic mixed solvents

Iron oxide (Fe2O3) was identified and characterized by surface area, X-ray diffractometry, and FTIR analyses. Surface charge densities, point of zero charge (PZC), and surface ionization constants were determined from the potentiometric titration data in various aqueous and aqueous organic mixed solvents in the temperature range 293-313 K. The surface charge densities were observed to decrease with the increase in temperature and concentration of metal ions in both the aqueous and aqueous organic mixed solvents. The absolute values of the surface charge density were found to change in the order aqueous > aqueous/methanol > aqueous/ethanol. Further, the PZC of the iron oxide was observed to shift to the higher pH values in the order ethanol > methanol > aqueous solution, which indicated a decrease in the acidity of the surface -OH groups. The pKa1 and pKa2 values of iron oxide were also determined and then used for determination of the surface potential (psi0) of the solid in aqueous and aqueous organic mixed solvents. The surface potential-surface charge curves generally supplemented the results derived from psi0-pH curves.     

Synthesis, characterization, spectroscopic and thermodynamic studies of charge transfer interaction of a new water-soluble cobalt(II) Schiff base complex with imidazole derivatives

The water-soluble cobalt(II) tetradentate Schiff base complex [Co(II)L](ClO4)(2), L: (N,N'-bis(5-[(triphenylphosphonium)-methyl]salicylidine)-o-phenylenediamineperchlorate has been synthesized and characterized. This complex forms charge transfer (CT) complexes with imidazole and 1-methylimidazole. The formation constant, molar absorptivity (epsilon'), and thermodynamic parameters for charge transfer complexes formation of cobalt(II) Schiff base complexes with imidazole derivatives were determined by using UV-vis spectrophotometric method in aqueous solutions at constant ionic strength (I=0.2mol dm(-3) KNO3) at pH 6.0 and various temperatures between 292 and 315K.     

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.     

Stability constants of nickel(II)-nicotinamide complexes in aqueous-ethanol solutions

The change in stability of 1: 1 and 1: 2 nicotinamide nickel(II) complexes in an aqueous ethanol with ethanol contents of 0 to 0.85 molar fractions is studied via potentiometry at 298.2 ± 0.1 K and a ionic strength of 0.25 (NaClO₄). The constant of complex formation for the first step increases at concentrations of organic solvent lower than 0.5 molar fractions and decreases at a higher content of ethanol. The weakening of the solvation of the donor center in nicotinamide corresponds to the observed change in the stability of the complex. A linear interrelation between the change in the coordination equilibrium constant and the difference between the effect of solvent composition on the solvation of the complex ions and complexing agent is revealed.     

Micellisation thermodynamics of sodium lauroylsarcosinate in water–alcohol binary mixtures

Aggregation of sodium lauroylsarcosinate (SLS) in aqueous solutions of methanol, ethanol, propanol and ethylene glycol at 288–313 K has been determined from conductivity measurement in the range 0–20% v/v of additives. The precise values of the critical micelle concentration (CMC) and the degree of counter-ion dissociation of micelles were obtained at each temperature by fitting the specific conductivity-surfactant concentration curve to the integrated form of the Boltzmann-sigmoid equation. The CMC was found to increase with increase in additive concentrations in the case of methanol and ethylene glycol, while it decreases with increase in ethanol and propanol concentration. The equilibrium model of micelle formation was applied to obtain the thermodynamic parameters of micellisation. The Gibbs free energies were observed to vary only slightly with temperature and additive concentrations. Enthalpy–entropy compensation was observed for all the systems with a constant compensation temperature of ≈300 K and negative compensation enthalpy.     

Hydrogenolysis of benzofuran using aqueous ethanol solution over graphite-supported platinum catalyst

Graphite-supported platinum catalysts (Pt/G) were highly active for the hydrogenolysis of benzofuran to o-ethylphenol in aqueous ethanol solution at 523 K without using any external hydrogen gas. The hydrogenolysis activities and selectivity to o-ethylphenol in ethanol solution over Pt/G were higher than those with a conventional method using externally supplied hydrogen gas. Both water and ethanol were indispensable for the hydrogenolysis in aqueous ethanol solution at 523 K.     

Kinetic study of paracetamol on prolidase activity in erythrocytes by capillary electrophoresis with Ru(bpy)(3) (2+) electrochemiluminescence detection

We explored the CE with (bpy) (2+) (3) electrochemiluminescence detection for the kinetic study of drug-enzyme interaction. Effects of four nonsteroidal anti-inflammatory drugs including aspirin, paracetamol, sodium salicylate and phenacetin on prolidase (PLD) activity in erythrocytes were investigated. Aspirin enhanced PLD activity whereas the other three had inhibiting effects. This may reveal their different effects on the collagen biosynthesis and catabolism that influence tumor invasiveness. Kinetic study of paracetamol on PLD showed that the value of Michaelis constant K(m) for PLD was 1.23 mM. The mechanism of PLD inhibition by paracetamol is noncompetitive inhibition, and the inhibitor constant K(i) value obtained in our research was 9.73 x 10(3) microg/L.     

Adsorption of iodide ions on the Cd(0001) single crystal plane in methanol

The adsorption of I⁻ ions on the Cd(0001) single crystal plane from solutions in methanol has been investigated by impedance measurement method. The ionic charge due to the specific adsorption has been obtained using the mixed-electrolyte method for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of adsorption of ions has been calculated using the different modifications of the virial adsorption isotherm. It was found that under comparable conditions, the results obtained at constant electrode potential and at constant electrode charge are coincident and the adsorption of I⁻ anion increases in the sequence of solvents: water < methanol, ethanol, and metals: Cd < Bi. The electrosorption valency has been calculated. It was found that on the Cd(0001) plane the electrosorption valency of I⁻ anions has a constant value that is similar for methanol and ethanol and also for these solvents on Bi single crystal planes.     

Electrical double layer and adsorption of iodide ions at the Bi | acetonitrile interface

The adsorption of I^? ions on the Bi(111) single crystal plane from solutions in acetonitrile has been investigated by impedance measurement method. The ionic charge due to the specific adsorption has been obtained using the mixed electrolyte method applied for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of ions adsorption has been calculated using the virial adsorption isotherm. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident and the Gibbs energy of I^? anion adsorption increases in the sequence of solvents: methanol < ethanol < propylene carbonate < acetonitrile. The electrosorption valency has been calculated and it was found that this parameter increases in the sequence propylene carbonate < ethanol < methanol < acetonitrile.     

Studies of solvation in homogeneous and heterogeneous media by electronic spectroscopic method

Solvation characteristics in homogenous (pure and mixed binary solvents) and heterogeneous media (aqueous micelles, beta- and gamma-cyclodextrine solutions) have been studied by monitoring the emission characteristics of a newly synthesised dye. The longest wavelength absorption and emission band of the dye arise due to transition between S(0) and S(1) state. The maximum energy of electronic transition involving intramolecular charge transfer is found to be dependent on both the hydrogen-bond donating ability and the polarity-polarisability in pure solvent. The dipole moment in the S(1) state, as determined by solvatochromic procedure, agrees well with the value obtained by theoretical calculation at the AM1 level. Preferential solvation of the dye by alcohols has been found to occur in ethanol+water, propan-1-ol+water, propan-2-ol+water binary mixtures. In aqueous micellar media the dye molecule is located at the water-micelle interface. The binding constant for the dye-micelle interaction has also been determined. The results have been compared with those for a structurally related symmetrical ketocyanine dye.     

Volumetric,Viscosity and Self-Diffusion Coefficient Studies of [18-Crown-6:M]A Complexed Species in Water at 298.15 K

Density and viscosity measurements were made for aqueous solutions of electrolytes containing 18-crown-6 (18C6) at 298.15 K. A method is proposed to extract the volumetric and viscosity data of the [18C6:M]A complexed species in aqueous solutions from ternary mixtures using the thermodynamic equilibrium constant values at 298.15 K. The apparent molar volume of the [18C6:M]A complexed species have been estimated for these binary solutions. Further, the viscosity data thus obtained were subjected to analysis using the Jones-Dole equation to get viscosity A- and B-coefficients of complexed ions in water. The hydration number and molecular radius of the hydrated complexes in water have been estimated. It was observed that hydration of the complexed ion is strongly influenced by the charge density of the metal ions in the complexed state. The self-diffusion coefficient and correlation time values for the complexes in water were calculated using viscosity data, which indicated that diffusion of complexed species was faster than that of the host ligand 18C6 (D_3d structural entity) in water at 298.15 K. It was suggested that the ionic radii estimated in this work for large hydrophobic cations can be of use in studying electrostatic and hydrophobic interactions especially in aqueous solutions.     

Equilibrium constant of the gamma-sultone and extraction constant of sodium and potassium ions from water into benzene in presence of 18-crown-6 and bromocresol green

An extraction procedure for the spectrophotometric determination of sodium or potassium involving a 1:1:1 metal ion: crown ether: sulfonephthalein dye monoanion ion associate has been described in the literature. In a recent paper from this laboratory the total dye content of the organic phase resulting from partitioning bromocresol green (HBCG) alone between water and benzene was determined from back extraction into an aqueous phosphate buffer. In benzene, bromocresol green is present to a large extent as a colorless lactone form, or gamma-sultone. The sultone equilibrium constant, K(dist) (sultone)=[sultone](o)/[BCG(-)](w)gamma(BCG(-))(w)a(H(+)) was found to be 373+/-42 mol(-1) dm(3). In the present study, sodium was extracted from water into benzene with 18-crown-6 and BCG(-), yielding K(dist) (sultone)=232 mol(-1) dm(3) and the conventional extraction constant, K(ex), of (5.49+/-0.49)x10(3) mol(-2) dm(6). Corresponding values from potassium extraction data are 256 mol(-1) dm(3) and (4.80+/-0.51)x10(6) mol(-2) dm(6), respectively. In the absence of ethanol, the calibration plot of sodium closely followed Beer's law, but that of potassium curved downward, approaching linearity in 15% ethanol. High 18-crown-6, low bromocresol green concentrations are analytically favorable for the extraction of potassium from the 15% aqueous ethanol mixture. All plots from the back-extractions (a measure of the total dye content in the benzene phase) were linear. Ethanol markedly reduced the reagent blank, when C(MCl)=0, as a result of the sultone being partitioned less favorably into benzene.     

Microemulsions of triglyceride and non-ionic surfactant — effect of temperature and aqueous phase composition

The phase behavior of soybean oil, polyoxyethylene (40) sorbitol hexaoleate and water—ethanol was investigated. Regions of water-in-oil (W/O) microemulsions were determined and were found to be strongly dependent on temperature and water:alcohol ratios. At a water:ethanol ratio of 80/20 (wt.%), an oil:surfactant ratio of 2/3 and a temperature of 25°C, the microemulsion region extended continuously from the oil—surfactant axis to the phase diagram center. However, at the hydrophilic—lipophilic balance (HLB) temperature (20–22°C) and a water:ethanol ratio of 80/20 or 75/25 (wt.%), a single-phase area separated from the original microemulsion region. Conductivity measurements and dynamic light scattering intensifies at 25°C indicated that association structures were formed with increasing aqueous phase concentrations above 15 wt.%. At 20°C, the single-phase scattering intensifies increased sharply with increasing aqueous phase concentrations (38–46 wt.%) and a plateau in the conductivity was detected.

Transmission electron microscopy results supported the finding that more particles are formed with increasing aqueous phase and form connected particles, resulting in constant conductance.     

Electrosorption of tert-butanol at the Hg/aqueous NaF solution interface

Electrosorption of tert-butanol (TBUOH) on Hg from aqueous NaF solution has been investigated by means of electrocapillary measurements. The results are analyzed in terms of isotherms at constant potential and constant electrode charge density. The Frumkin isotherm with an attractive interaction parameter is satisfactorily fitted at every potential and electrode charge investigated. The relevant adsorption parameters are also discussed.     

Pt／YSZ固体电解质界面氧的电荷传递过程研究

用极化法研究了不同温度和氧分压下Ｐｔ／ＹＳＺ界面氧的电荷传递过程．研究发现氧电荷传递过程的阴、阳极电荷传递系数为１，不随温度和氧分压而变．从实验和反应机理推导得到，Ｐｔ／ＹＳＺ界面的交换电流密度和氧分压之间存在，ｉ０＝２ＦＫｒ（ＫＯ２ＰＯ２）１／４（１＋ＫＯ２ＰＯ２）１／２的关系．通过数学分析还获电化学反应速度常数，氧在Ｐｔ表面上吸附平衡常数等重要参数     

Ion-exchange equilibrium distribution studies of some metal ions in nitrite media

Ion-exchange equilibrium distribution of some metal ions has been studied in nitrite media, with cation- as well as anion-exchangers. The distribution coefficients (K(D)) show the utility of a new nitrite medium which is a complexing medium for most transition metal ions giving anionic complexes in aqueous solution. Similar studies have been performed in aqueous ethanol. Increase in the concentration of ethanol led to increased complex formation and changed K(D) values.     

The effect of ultrasound on the solvolysis of 2-chloro-2-methylpropane in aqueous ethanol

Ultrasonic irradiation has been found to accelerate the solvolysis of 2-chloro-2-methylpropane in aqueous ethanol mixtures from 20 to 60% w/w in ethanol at temperatures between 10° and 25°. The effects are more marked at lower temperatures and higher alcohol compositions with a 20 fold rate acceleration occurring at 10° and 60% w/w. The results also lend independent support to two previous observations that (a) the position of maximum in solvent structuredness is 50% w/w and (b) a logarithmic relationship exists between solvent vapour pressure and ultrasonically enhanced rate constant. At solvent compositions of 50 and 60% w/w ethanol the absolute rate of reaction under irradiation increases with decreasing reaction temperature below 20°.     

Spectroscopic and thermodynamic study of charge transfer interaction between vitamin B6 and p-chloranil in aqueous ethanol mixtures of varying composition

Charge transfer complexes of 1:1 stoichiometry have been found to form between vitamin B(6) (pyridoxine hydrochloride) and a series of electron acceptors including p-chloranil. Since vitamin B(6) is soluble in water while the electron acceptors are insoluble in water but soluble in ethanol, the medium chosen for study is water-ethanol mixture. From the trends in the CT absorption bands the vertical ionization potential of vitamin B(6) has been determined to be 8.12 eV. The enthalpy and entropy of formation of the complex between p-chloranil and vitamin B(6) have been determined by estimating the formation constant (K) spectroscopically at four different temperatures in 75% ethanol-water mixture. Again, the magnitude of K has been found to decrease noticeably with decrease in dielectric constant of the medium (as the percentage of ethanol in the aqueous-ethanol mixture is increased). A plausible explanation for this has been given in terms of hydrolysis of pyridoxine hydrochloride.