Showing papers in "Journal of Solution Chemistry in 2009"

Aqueous Long-Term Solubility of Titania Nanoparticles and Titanium(IV) Hydrolysis in a Sodium Chloride System Studied by Adsorptive Stripping Voltammetry

Abstract: The solubility of industrially produced titanium dioxide nanoparticles has been studied in aqueous sodium chloride media in the pH range 1 to 13 at 25 °C by using adsorptive stripping voltammetry (AdSV). Kinetic dissolution curves have been obtained as well as long-term solubilities that provide an approximation of the equilibrium solubilities. The titania nanoparticles used in the dissolution experiments have been characterized by nitrogen sorption measurements, XRD and colloid titration. The equilibrium solubilities and titanium(IV) speciation and their dependences on pH have been modelled by assuming the formation of the mononuclear titanium hydroxo complexes [Ti(OH)n](4−n)+ (n=2 to 5) to be the only titanium species present. The solubility product of titanium dioxide and equilibrium constants for titanium(IV) hydrolysis, calculated from the AdSV solubility data, are presented.

Dramatic Change in Viscosities of Pure Ionic Liquids upon Addition of Molecular Solvents

Abstract: Viscosities of binary mixtures of pyridinium based ionic liquids (1-butyl pyridinium tetrafluoroborate, [BP][BF4], 1-butyl 3-methyl pyridinium tetrafluoroborate [3-MBP][BF4], 1-butyl 4-methyl pyridinium tetrafluoroborate, [4-MBP][BF4]), and phosphonium based ionic liquids, (tetrabutyl phosphonium alaninate, [TBP][Ala]; tetrabutyl phosphonium valinate, [TBP][Val]) with the molecular solvents, water, methanol and dichloromethane, have been measured at 298.15 K. A Brookfield ultra-rheometer was employed to measure the reported viscosities. The drop in viscosity in the close vicinity of pure ionic liquid is more prominent in polar solvents like water compared to less polar solvents. The temperature dependence of this observation was also studied for binary mixtures of [4-MBP][BF4] with water in range of 298.15–323.15 K. The Vogel-Fulcher-Tamman (VFT) equation was employed to investigate the temperature dependence of the viscosities of pure pyridinium-based ionic liquids in the temperature range from 298.15–323.15 K.

Stability Constants of Some Univalent Cation Complexes of 2,3-Naphtho-15-crown-5 in Nitrobenzene Saturated with Water

Abstract: The extraction of micro amounts of cesium by nitrobenzene solutions of sodium, potassium and rubidium dicarbollylcobaltates (M+B−;M+=Na+,K+,Rb+) has been investigated in the presence of 2,3-naphtho-15-crown-5 (N15C5, L). The equilibrium data were explained by assuming that ML+ and ML 2 + complexes (M+=Na+,K+,Rb+, Cs+; L=N15C5) were present in the organic phase. The stability constants of the complex species ML+ and ML 2 + have been determined in nitrobenzene saturated with water. It was found that the stability of the complex cation ML+ (where M+=Na+,K+,Rb+, Cs+; L=N15C5) in water-saturated nitrobenzene solutions increases along the series Cs+

Extraction of Metal Ions from Aqueous Solutions Using Imidazolium Based Ionic Liquids

Abstract: This article represents a step towards how to choose an ionic liquid as the solvent to improve metal ion (Ag+ and Pb2+) extraction. The liquid-liquid solvent extraction is proposed with the following imidazolium ionic liquids (ILs): 1-ethyl-3-ethylimidazolium, or 1-butyl-3-ethylimidazolium, or 1-hexyl-3-ethylimidazolium bis{(trifluoromethyl)sylfonyl}imide [EEIM][NTf2], or [BEIM][NTf2], or [HEIM][NTf2], or 1-butyl-3-ethylimidazolium hexafluorophosphate [BEIM][PF6], or 1-hexyl-3-ethylimidazolium hexafluorophosphate [HEIM][PF6] and the popular 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6] for comparison. The effect of anion type (NTf 2 − versus PF 6 − ) and the effect of structural components of an ionic liquid including alkyl chain length at the cation and the ethyl substituent instead methyl at the cation, on the extraction and re-extraction processes by using dithizone as a metal chelator, were studied at 296 K. Dithizone was employed to form neutral metal-dithizone complexes with heavy metal ions to extract them from aqueous solution into the ILs.

Effect of Temperature and Composition on the Density and Viscosity of Binary Mixtures of Ionic Liquid with Alcohols

Abstract: Density and viscosity were determined for the binary mixtures containing the ionic liquid 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]) and 1-alcohols (1-butanol, 1-pentanol and 1-hexanol) at six temperatures (298.15, 308.15, 318.15, 328.15, 338.15 and 348.15) K and ambient pressure. The density and viscosity correlation for these systems was tested by an empirical second-order polynomial and by the Vogel-Fucher-Tammann equation in wide ranges of temperatures. Excess molar volumes were described by the Redlich-Kister polynomial expansions. The density and viscosity variations with composition were described by polynomials. A qualitative analysis of the trend of the properties with solvent and temperature was performed. The obtained results indicate that ionic liquid interactions with 1-alcohols are strongly dependent on the special trend of packing of this ionic liquid into hydroxylic solvents. As previously observed, an increase of the 1-alcohol carbon-chain length leads to lower interactions on mixing.

Spectroscopic Studies on the Interaction of Vitamin C with Bovine Serum Albumin

Abstract: The mechanism of binding of vitamin C (VC) with bovine serum albumin (BSA) was investigated by spectroscopic methods under simulated physiological conditions. VC effectively quenched the intrinsic fluorescence of BSA. The binding constants K A, and the number of binding sites, n, and corresponding thermodynamic parameters ΔG Θ , ΔH Θ and ΔS Θ between VC and BSA were calculated at different temperatures. The primary binding pattern between VC and BSA was interpreted as being a hydrophobic interaction. The interaction between VC and BSA occurs through static quenching and the effect of VC on the conformation of BSA was also analyzed using synchronous fluorescence spectroscopy. The average binding distance, r, between the donor (BSA) and acceptor (VC) was determined based on Forster’s theory and was found to be 3.65 nm. The effects of common ions on the binding constant of VC-BSA were also examined.

Temperature Dependence of Physical Properties of Imidazolium Based Ionic Liquids: Internal Pressure and Molar Refraction

Abstract: Density, speed of sound and refractive index of the imidazolium-based ionic liquids (ILs), 1-methyl-3-octylimidazolium chloride [C8mim][Cl], 1-butyl-3-methylimidazolium methyl sulfate [C4mim][C1OSO3], and 1-butyl-3-methylimidazolium octyl sulfate [C4mim][C8OSO3], have been measured in the temperature range from 283.15 to 343.15 K. Experimental density and speed of sound have been used to calculate the internal pressure p i of the ILs. The p i values were found to be higher than those of water and molecular organic liquids, but lower than those of classical molten salts. We also calculated molar refraction R M from the measured refractive index n D in the temperature range from 288.15 to 343.15 K. Refractive indices of ILs were also higher than those of normal organic liquids, but comparable to long-chain hydrocarbon organic solvents. The structure-property correlation of the ILs has been discussed and the results have been compared to our earlier studies (Kumar in J. Solution Chem. 37:203–214, 2008).

Binding Interaction of Xanthoxylin with Bovine Serum Albumin

Abstract: Three independent techniques have been used to investigate the interaction between bovine serum albumin (BSA) and xanthoxylin (XT). UV-Vis absorption spectroscopy measurements showed that there is a XT-BSA complex formed with an overall binding constant of K=1.01×105 L⋅mol−1. Spectroscopic techniques including synchronous fluorescence and Fourier transform infrared (FT-IR) were used to assess the structural effects of XT binding on BSA. The FT-IR experiments showed that there is a decrease of the amount of α-helix from 50.2 to 48.1% and an increase of the β-sheet from 32.9 to 36.9% in the XT-BSA complex. In addition, XT binds to site I of the protein with a distance of 2.07 nm between tryptophan residues and XT.

The Hydrolysis of AuCl 4 − and the Stability of Aquachlorohydroxocomplexes of Gold(III) in Aqueous Solution

Abstract: The equilibria AuCl 4 − +jOH−+kH2O⇌AuCl4−j−k (OH) j (H2O) −1 +(j+k)Cl−, β jk (0≤j,k≤4) have been studied spectrophotometrically at 20 °C in aqueous solution. For I=2 mol⋅dm−3(HClO4) the conventional constants, β * , of the equilibria, Au*+iCl− ⇌AuCl * , are equal to log 10 β 1 * =(6.98±0.08); log 10 β 2 * =(13.42±0.05); log 10 β 3 * =(19.19±0.09); and log 10 β 4 * =(24.49±0.07), where [AuCl * ]=∑[AuCl i (OH) j (H2O)4−i−j ] at i=const. The hydrolysis and other transformations of AuCl 4 − in aqueous solution are discussed. On the basis of new and known data, a full set of equilibrium constants, β jk , or their estimates has been obtained.

Static Dielectric Constants and Kirkwood Correlation Factor of the Binary Mixtures of N-Methylformamide with Formamide, N,N-Dimethylformamide and N,N-Dimethylacetamide

Abstract: Static dielectric constant values of the binary mixtures of N-methylformamide with formamide, N,N-dimethylformamide and N,N-dimethylacetamide have been measured in the whole composition range at 303 K. The Kirkwood correlation factor values of the amide–amide mixtures were determined from the measured values of the static dielectric constant and high-frequency limit dielectric constant. The evaluated values of the excess dielectric constant and deviation in the Kirkwood correlation factor infer that deviations of their mixture values occur from the mole-fraction mixture law. Results confirm that there are strong hydrogen-bond interactions between unlike molecules of amide–amide mixtures and that 1:1 complexes are formed.

Metastable Phase Equilibrium in the Aqueous Ternary System K2SO4+MgSO4+H2O at (288.15 and 308.15) K

Abstract: The metastable solubilities and densities of the aqueous ternary system K2SO4+MgSO4+H2O at (288.15 and 308.15) K were determined with the isothermal evaporation method. Using the experimental results, the metastable phase diagram and the densities versus composition diagram were plotted. In the metastable phase diagrams of the ternary system at (288.15 and 308.15) K, there are in all two invariant points, three univariant solubility curves, and three metastable crystallization regions corresponding to arcanite (i.e., anhydrous potassium sulfate, K2SO4), picromerite (K2SO4⋅MgSO4⋅6H2O) and epsomite (MgSO4⋅7H2O) that are formed in the metastable equilibrium system. A comparison of the stable and metastable phase diagrams at each temperature shows that the metastable regions of magnesium sulfate are obvious, and the crystallizing regions of epsomite and arcanite are much larger than those in the stable phase diagram. The densities of the system changed regularly with the magnesium sulfate content. The resulting information can be used to recover potassium or remove magnesium. The calculated densities using an empirical equation agree well with the experimental results.

Aggregation Behavior of Pyridinium-Based Ionic Liquids in Aqueous Solution

Abstract: Aggregation of the ionic liquids 1-butylpyridinium tetrafluoroborate, 1-butylpyridinium triflate, 1-butyl-2-methylpyridinium tetrafluoroborate, 1-butyl-3-methylpyridinium tetrafluoroborate, 1-butyl-4-methylpyridinium tetrafluoroborate, 1-butyl-3-methylpyridinium dicyanamide, and 1-octyl-3-methylpyridinium tetrafluoroborate in aqueous solution has been characterized at 298.15 K through density, ρ, speed of sound, u, and conductivity, σ, measurements. In addition, apparent molar volumes, Vφ, and isentropic compressibilities, κs, have been calculated from the experimental data. To characterize the formation of aggregates, the critical aggregation concentration of the ionic liquids, cac, the degree of ionization of the aggregates, β, and the standard Gibbs energy of aggregation, \(\Delta G_{\mathrm{m}}^{\circ}\), have been obtained, with good agreement between results derived from the different methods. The dependence on the structural variation of these ions has been analyzed by comparing the results obtained for this series of ionic liquids.

Investigation of the Interactions in Complexes of Low Molecular Weight Chitosan with Ibuprofen

Abstract: Complexation between ibuprofen and low molecular weight chitosan (LMWC) was studied. LMWC was prepared from high molecular weight chitosan using the acid hydrolysis method. The complexes were investigated by using DSC, FT-IR and liquid-state 1H-NMR. Molecular mechanics (MM) calculations were used to give insight into the stoichiometry of the interaction of chitosan with ibuprofen. The results showed that complexation of ibuprofen with LMWC involves ionic interaction between the ammonium group of LMWC and the carboxylate anion of ibuprofen. It was also shown that it is more efficient to prepare the complexes using lower concentration solutions of the polymer. These results were supported by molecular mechanics calculations. The experimental results may explain the discrepancies in the literature where, in many studies, the concentration of chitosan and its low average molecular weight were not considered to be important factors in the complexation process.

On Water Structure in Concentrated Salt Solutions

Abstract: In concentrated salt solutions the average distances between the ions, dav=1.1844⋅(∑νici)−1/3 nm, are commensurate with the sizes of the solvated ions, so that no ‘bulk solvent’ remains. This is illustrated with two saturated aqueous solutions, where 16.67 mol⋅dm−3 CsF at 75 °C has dav(Cs–F)=0.368 nm and 14.54 mol⋅dm−3 LiI at 80 °C has dav(Li–I)=0.385 nm. The minimal distance required for the bare ions (sum of their radii) are 0.303 nm for CsF and 0.289 nm for LiI. Hence no water molecule, diameter 0.276 nm, can be fitted between the ions to form linear or slightly bent hydrogen bonds. Some recent work ignoring such constraints, even in 3–6 mol⋅dm−3 solutions, is criticized on this account.

Density Functional Theory Study of the Ionic Liquid [emim]OH and Complexes [emim]OH(H2O) n (n=1,2)

Abstract: In this work, the structure of the ionic liquid [emim]OH and the influence of water molecules on this ionic liquid were studied by the DFT theory at the B3LYP/6-311++G** level. The calculation results indicate that [emim]OH cannot exist in the form of ion pairs, rather it is inclined to exist the form of water and imidazole carbene. Further studies showed that water mainly influences the anion: it can disperse the negative charge of the O atom of the OH− anion and form hydroxyl–water clusters with the anion. When there are two water molecules in the ionic liquid, the system is most likely to exist in the form of ion-pairs that are composed of hydroxyl–water clusters and cations. Configurations formed near the C2-H fragment of imidazole were favored, and hydrogen bonding interaction plays an important role in the ionic liquid system.

Lamellar Liquid Crystals of Brij 97 Aqueous Solutions Containing Different Additives

Abstract: Lamellar liquid crystals of Brij 97 aqueous solutions were investigated by means of rheological techniques and SAXS at 25 °C, in the presence of various additives including isopropyl myristate, oleic acid, ionic liquid bmim-PF6 and bmim-BF4. The lamellar phases show high elasticity as indicated by their mechanical and discrete relaxation spectra, which is expected to be an advantage when they are used as drug delivery vehicles. It is noted that in comparison with other systems, the lamellar phase formed in the Brij 97/water/IPM system has the lowest storage and loss moduli, implying that it has a weak network strength and less stable internal structure. The Brij 97/water/oleic acid system is the most shear resistance, whereas the Brij 97/water/bmim-PF6 system exhibits fluid-like viscoelastic properties to some extent. These differences are analyzed through SAXS data for the different location of the additive in the lamellar phase.

Complexation of Eu(III), Am(III) and Cm(III) with Dicarboxylates: Thermodynamics and Structural Aspects of the Binary and Ternary Complexes

Abstract: The complexation of Eu(III), Am(III) and Cm(III) with dicarboxylate anions with O, N or S donor groups was measured in I=6.60 mol⋅kg−1 (NaClO4) at temperatures of 0–60 °C by potentiometry and solvent extraction. The complexation thermodynamics of these complexes show that their stability is due to highly favorable complexation entropies because the complexation enthalpies are endothermic. Luminescence studies with Eu(III) and Cm(III) were used to measure the hydration numbers of the complexes. NMR spectra of 1H and 13C were used to determine the binding modes of La(III) with the ligands. The formation of 1:1:1 ternary complexes of M(EDTA)− with the dicarboxylate ligands was studied to determine changes in coordination of the metal cation with formation of the ternary species. The complexation of ternary complexes changes from bidentate to monodentate as the chain length between the binding sites of the dicarboxylates increases from 1 (malonate) to 4 (adipate). DFT computations were used to confirm the structural aspects of the interaction of these complexes.

Acoustic and Thermodynamic Properties of Binary Liquid Mixtures of Benzaldehyde in Hexane and Cyclohexane

Abstract: Densities and ultrasonic speeds of binary mixtures of benzaldehyde with n-hexane and cyclohexane at 30 °C were measured over the entire composition range. From these experimental data, the adiabatic compressibility (K S ), intermolecular free length (L f), acoustic impedance (Z), relative association (R a) and relaxation strength (r) were calculated. Also, the excess adiabatic compressibility (K E ), intermolecular free length (L f E ), acoustic impedance (Z E), and ultrasonic velocity (U E) were calculated. The observed variation of these parameters helps in understanding the nature of interactions in these mixtures. Further, theoretical values of the ultrasonic speed were evaluated using theories and empirical relations. The relative merits of these theories and relations were discussed.

Reverse Schreinemakers Method for Experimental Analysis of Mixed-Solvent Electrolyte Systems

Abstract: A method based on Schreinemakers’s tie-line theory of 1893 is derived for determining the composition and phase amounts in solubility experiments for multi-solvent electrolyte systems. The method uses the lever rule in reverse compared to Schreinemakers’s wet residue method, and is therefore called the reverse Schreinemakers (RS) method. The method is based on simple mass balance principles similar to the wet residues method. It allows for accurate determination of the mixed-solvent phase composition even though part of the solvent may precipitate as complexes between solvent and salt. Discrepancies from determining the composition of salt mixtures by pH titration are discussed, and the derived method significantly improves the obtained result from titration. Furthermore, the method reduces the required experimental work needed for analysis of phase composition. The method is applicable to multi-solvent systems and may be used for the determination of solid-phase compositions, similar to Schreinemakers’s original “rest” method. An example calculation is presented for the Na2CO3-NaHCO3-MEG-H2O system.

Volumetric Study of Aqueous Solutions of Polyethylene Glycol as a Function of the Polymer Molar Mass in the Temperature Range 283.15 to 313.15 K and 0.1 MPa

Abstract: Density measurements were made for binary aqueous solutions of polyethylene glycol at seven temperatures: 28315, 28815, 29315, 29815, 30315, 30815, and 31315 K Polyethylene glycol samples with nominal average molar masses of 3000 g⋅mol−1 (PEG 3000), 6000 g⋅mol−1 (PEG 6000), 10000 g⋅mol−1 (PEG 10000) and 20000 g⋅mol−1 (PEG 20000) were used These results were used to determine the specific volumes of solutions with solute-to-solvent mass ratios (mass of the solute/mass of the solvent) in the range 00546 to 14932 for PEG 3000, from 00553 to 14986 for PEG 6000, from 00552 to 12241 for PEG 10000, and from 00530 to 12264 for PEG 20000 The differences between the specific volume of a solution and the specific volume of the pure solvent, at a given temperature, were represented by a virial-type equation in terms of solute concentration The first-order coefficient of the expansion is the partial specific volume of the solute at infinite dilution The higher-order coefficients are related to the contribution of pairs, triplets, and higher-order solute aggregates, according to the Constant-Pressure Solution Theory The functional dependence of the virial coefficients upon temperature is discussed in terms of solute-solute and solute-solvent interactions The effect of the PEG molar mass on the partial specific volume of solute at infinite dilution, as well as the contributions of pairs of solute molecules to the solution volume, are also investigated The apparent specific volume, apparent specific expansibility, apparent specific expansibility at infinite dilution and virial coefficients of the apparent specific expansibility are also presented

Interaction Between Trans-resveratrol and Serum Albumin in Aqueous Solution

Abstract: The interaction between trans-resveratrol (TR) with bovine serum albumin (BSA) in aqueous solution was investigated by means of fluorescence, synchronous fluorescence and infrared spectroscopy. The fluorescence of BSA can be quenched remarkably by TR in aqueous solution. A notable red-shift of the maximum emission of BSA from 340 to 353 nm together with appearance of an isoemissive point at 395 nm were observed. The results indicate that TR binds to BSA, forming a TR–BSA complex. The TR–BSA binding distance was determined to be less than 7 nm, suggesting that energy transfer from BSA to TR may occur. The interaction process is spontaneous. Based on the obtained thermodynamic parameters, electrostatic forces may play a major role in this process. Both synchronous fluorescence and FT-IR spectra confirmed the interaction, and indicate the conformational changes of BSA.

In Vitro Binding of Furadan to Bovine Serum Albumin

Abstract: Under physiological conditions, the interaction between furadan (FRD) and bovine serum albumin (BSA) was investigated by spectroscopy including fluorescence emission, UV-visible absorption, scattering, circular dichroism (CD) spectra, synchronous and three-dimensional fluorescence spectra The observed binding constant Kb and the number of binding sites n were determined by the fluorescence quenching method The distance r between donor (BSA) and acceptor (FRD) was obtained according to the Forster theory of non-radiation energy transfer The enthalpy change (ΔHθ), Gibbs energy change (ΔGθ) and entropy change (ΔSθ) at four different temperatures were calculated The process of binding was proposed to be a spontaneous process since the ΔGθ values were negative The positive ΔSθ and ΔHθ values indicated that the interaction of FRD and BSA was driven mainly by hydrophobic interactions The addition of FRD to BSA solutions leads to enhancement in scattering intensity, exhibiting the formation of an aggregate in solution CD spectra, synchronous and three-dimensional fluorescence spectra were used to measure the structural change of BSA molecules with FRD present

Interaction Between Levamisole Hydrochloride and Bovine Serum Albumin and the Influence of Alcohol: Spectra

Abstract: The interaction between levamisole hydrochloride (LH) and bovine serum albumin, BSA, has been studied by a spectral method under physiological conditions. For 1:n complexes, the relationship between fluorescence quenching intensity and concentration of the quenchers can be deduced on the basis of the modified Stern–Volmer equation. The binding constants and corresponding thermodynamic parameters ΔHm, ΔGm and ΔSm at different temperatures were calculated. The experimental results demonstrated that the combination reaction of LH and BSA was a static quenching process because a 1:1 complex was formed, and the main dominant binding forces were hydrogen bonding and van der Waals forces. Meanwhile, the polarity of the tyrosine residue (Tyr) or tryptophan residue (Trp) micro-region was not obviously affected by the interaction. Furthermore, the binding constant increase when alcohol was added.

Zirconium Dioxide Solubility in High Temperature Aqueous Solutions

Abstract: The heat transport purification system of CANDU nuclear reactors is used to remove particulates and dissolved impurities from the heat transport coolant. Zirconium dioxide shows some potential as a high-temperature ion-exchange medium for cationic and anionic impurities found in the CANDU heat transport system (HTS). Zirconium in the reactor core can be neutron activated, and potentially can be dissolved and transported to out-of-core locations in the HTS. However, the solubility of zirconium dioxide in high-temperature aqueous solutions has rarely been reported. This paper reports the solubility of zirconium dioxide in 10−4 mol⋅kg−1 LiOH solution, determined between 298 and 573 K, using a static autoclave. Over this temperature range, the measured solubility of zirconium dioxide is between 0.9 and 12×10−8 mol⋅kg−1, with a minimum solubility around 523 K. This low solubility suggests that its use as a high-temperature ion-exchanger would not introduce significant concentrations of contaminants into the system. A thermodynamic analysis of the solubility data suggests that Zr(OH)40 likely is the dominant species over a wide pH region at elevated temperatures. The calculated Gibbs energies of formation of Zr(OH)40(aq) and Zr(OH)4(am) at 298.15 K are −1472.6 kJ⋅mol−1 and −1514.2 kJ⋅mol−1, respectively. The enthalpy of formation of Zr(OH)40 has a value of −1695±11 kJ⋅mol−1 at 298.15 K.

Thermodynamic Protonation Parameters of some Sulfur-Containing Anions in NaClaq and (CH3)4NClaq at t=25 °C

Abstract: Protonation constants of one thiocarboxylate (thioacetate) and four sulfur-containing carboxylates (2-methylthioacetate, thiolactate, thiomalate, 3-mercaptopropionate) were determined by potentiometric measurements in a wide ionic strength range [0≤I≤5 mol⋅L−1 in NaCl and 0 ≤I≤3 mol⋅L−1 in (CH3)4NCl] at t=25 °C. For two of these ligands (2-methylthioacetate and thiolactate), the protonation enthalpies were also determined by calorimetric measurements in NaCl ionic medium [0 ≤I≤5 mol⋅L−1] at t=25 °C. Individual UV spectra of the protonated and unprotonated 3-mercaptopropionate species, together with values of the protonation constants, were obtained by spectrophotometric titrations. Results were analyzed in terms of their dependence on the ionic medium by using different thermodynamic models [Debye-Huckel type, SIT (Specific ion Interaction Theory) and Pitzer’s equations]. Differences among protonation constants obtained in different media were also interpreted in terms of weak complex formation.

Speciation of Phytate Ion in Aqueous Solution. Thermodynamic Parameters for Zinc(II) Sequestration at Different Ionic Strengths and Temperatures

Abstract: Results of an investigation on phytate interactions with zinc(II) cation in NaNO3aq at different ionic strengths (0.1≤I/mol⋅L−1≤1.0) are reported. Stability constants of various Zn i H j Phy(12−2i−j)− species were determined by potentiometry (ISE-H+ glass electrode) and the corresponding formation enthalpies by direct calorimetric titrations. Data obtained were used to provide an exhaustive speciation scheme of zinc(II) in the presence of phytate, as well as a comprehensive representation of the binding ability of phytate toward zinc(II) in different conditions. Different pL50 values [an empirical parameter already proposed, expressed as the −log 10 C Phy, where C Phy is the total phytate concentration necessary to bind 50% zinc(II)] were calculated in several conditions, and equations were formulated to model its dependence on different variables, such as ionic strength, temperature and pH. Other empirical predictive relationships are also proposed.

Competition of Viscosity Correlation Equations in Isobutyric Acid + Water Binary Mixtures Near and Far Away from the Critical Temperature

Abstract: Shear viscosity deviations Δη have been investigated by using density (ρ) and kinematic viscosity (ν) measurements for isobutyric acid + water (IBA + W) mixtures over the entire range of mole fractions at atmospheric pressure and at two temperatures (301.15 and 315.15 K). This study extends the temperature range from the five other temperatures investigated in a previous work, 1.055 K≤(T−Tc)≤14.055 K, both far from and close to the critical temperature. This system exhibits very large positive values of Δη due to increased hydrogen bonding interactions and the correlation length between unlike molecules in the critical region, and to very large differences between the molar volumes of the pure components at low temperatures. The results were also fitted with the Redlich–Kister polynomial equations and the recently proposed Herraez correlation equation. Comparisons between the two models at different temperatures and number of parameters are discussed. We note that, in this system where the shear viscosity η as a function of mole fraction (x1) of IBA presents a maximum, experimental data are in agreement with the two correlation models when more than three parameters are employed, especially for temperatures far from the critical temperature.

Effects of Temperature and Common Ions on Binding of Puerarin to BSA

Abstract: The effects of temperature and common ions on binding of puerarin to bovine serum albumin (BSA) are investigated. The binding constants (Ka) between puerarin and BSA are 1.13×104 L⋅mol−1 (20 °C) and 1.54×104 L⋅mol−1 (30 °C), and the number of binding sites (n) is (0.95±0.02). However, at a higher temperature (40 °C) the stability of the puerarin–BSA system decreases, which results in a lower binding constant (1.58×103 L⋅mol−1) and number of binding sites (n=0.73) of the puerarin–BSA system. However, the presence of Cu2+ and Fe3+ ions increases the binding constants and the number of binding sites in the puerarin–BSA complex.

Isothermal Titration Calorimetry and Theoretical Studies on Host-guest Interaction of Ibuprofen with α-, β- and γ-Cyclodextrin

Abstract: Thermodynamic parameters for formation of the inclusion complexes of α-, β- and γ-cyclodextrin (α-, β- and γ-CD) with ibuprofen (BF) in Tris-HCl buffer solutions (pH=7.0) have been determined by isothermal titration calorimetry (ITC) with nanowatt sensitivity, and the inclusion structures have been investigated by using 1H-NMR spectra at 298.15 K. A theoretical study on the inclusion processes between BF and CDs has been performed with the B3LYP/6-31G*//PM3 method in order to investigate the formation mechanism of the inclusion complexes. An analysis of the thermodynamic data indicates that the stoichiometries of α-, β- and γ-CD with BF are all 1:1 and formation of the inclusion complexes α-CD⋅BF and β-CD⋅BF are driven by enthalpy and entropy, whereas formation of γ-CD⋅BF is an entropy driven process. The 1H-NMR spectra provide clear evidence for the inclusion phenomenon, and show that the isobutyl group and aromatic ring of the guest molecule are trapped inside the cavity of the CDs. Theoretical calculations suggest that the complex formed by the BF molecule entering into the cavity of the CD molecule from the wide side is more stable than that from the narrow side.

Spectroscopic Studies on the Molecular Complex of the Drug Atenolol with Iodine

Abstract: Spectroscopic and spectrofluorimetric studies were made of the interaction between the drug atenolol and iodine. The interaction was found to proceed through the initial formation of a charge transfer (CT) complex as an intermediate species. The product of this interaction has been isolated and characterized using UV-Vis, FT-IR and Raman spectroscopic techniques. Formation of the triodide $\mathrm{I}_{3}^{-}$ species was confirmed by its electronic and Raman spectra. Peaks appeared in Raman spectrum of the isolated product at 153, 102 and 85 cm−1 that are assigned to ν as(I-I), ν s(I-I) and $\delta(\mathrm{I}_{3}^{-})$ respectively, which confirmed the presence of the $\mathrm{I}_{3}^{-}$ ion. The stoichiometry of the complex was found to be 1:2. The rate of their reaction has been measured as a function of time and solvent. Pseudo-first-order rate constants for the reaction were measured at various temperatures and the thermodynamic activation parameters (ΔG #,ΔS # and ΔH #) were computed. Preliminary fluorescence quenching studies indicated that the interaction between atenolol and iodine is spontaneous and proceeds through a CT complex, and the quenching of fluorescence of atenolol by iodine increases as the extent of such complexation increases