Amphoteric behavior of di-2-pyridyl ketone benzoylhydrazone in ethanol-water mixtures

The ligand di-2-pyridyl ketone benzoylhydrazone (DPKBH) is widely used for the determination of transition metal ions in environmental samples. Due to its low solubility in water it is used in aqueous-ethanol (1:1) solvent and for higher sensitivity the pH must be properly adjusted. The properties of DPKBH solutions must be known at different ethanol-water percentages in order to achieve higher sensitivity and/or selectivity for metal analysis. The acid-base behavior of this reagent in aqueous-ethanol solvent and the dissociation/ionization constants (pK1 and pK2) of DPKBH have been determined in different aqueous-ethanol solvent mixtures (10, 20, 30 and 50 % V/V of ethanol) from potentiometric titrations at 25.0 ± 0.1° C. As the amount of ethanol increases from 10 to 30% the pK1 and pK2 values increased, but they decreased in 50% of the organic solvent. The results are correlated with the medium composition and its effects.

Picosecond Dynamics of Proton Transfer of a 7-Hydroxyflavylium Salt in Aqueous-Organic Solvent Mixtures

The intermediacy of the geminate base proton pair (A*center dot center dot center dot H(+)) in excited-state proton-transfer (ESPT) reactions (two-step mechanism) has been investigated employing the synthetic flavylium salt 7-hydroxy-4-methyl-flavylium chloride (HMF). In aqueous solution, the ESPT mechanism involves solely the excited acid AH* and base A* forms of HMF as indicated by the fluorescence spectra and double-exponential fluorescence decays (two species, two decay times). However, upon addition of either 1,4-dioxane or 1,2-propylene glycol, the decays become triple-exponential with a term consistent with the presence of the geminate base proton pair A*center dot center dot center dot H(+). The geminate pair becomes detectable because of the increase in the recombination rate constant, k(rec), of (A*center dot center dot center dot H(+)) with increasing the mole fraction of added organic cosolvent. Because the two-step ESPT mechanism splits the intrinsic prototropic reaction rates (deprotonation of AH(+)*, k(d), and recombination, k(rec) of A*center dot center dot center dot H(+)) from the diffusion controlled rates (dissociation, k(diss) and formation, k(diff)[H(+)], of A*center dot center dot center dot H+), the experimental detection of the geminate pair provides a wealth of information on the proton-transfer reaction (k(d) and k(rec)) as well as on proton diffusion/migration (k(diss) and k(diff)).

Solution thermodynamics of methocarbamol in some ethanol + water mixtures

Apparent thermodynamic functions, Gibbs energy, enthalpy and entropy of solution and mixing, for methocarbamol in ethanol + water mixtures, were evaluated from solubility data determined at temperatures from 293.15 K to 313.15 K and from calorimetric values of drug fusion. The drug solubility was greatest in the mixtures with 0.70 or 0.80 mass fraction of ethanol and lowest in neat water across all temperatures studied. Non-linear enthalpy-entropy compensation was found for the dissolution processes. Accordingly, solution enthalpy drives the respective processes in almost all the solvent systems analyzed.

Optimization of solvent mixtures for extraction from bark of Schinus terebinthifolius by a statistical mixture-design technique and development of a UV-Vis spectrophotometric method for analysis of total polyphenols in the extract

A statistical mixture-design technique was used to study the effects of different solvents and their mixtures on the yield, total polyphenol content, and antioxidant capacity of the crude extracts from the bark of Schinus terebinthifolius Raddi (Anacardiaceae). The experimental results and their response-surface models showed that ternary mixtures with equal portions of all the three solvents (water, ethanol and acetone) were better than the binary mixtures in generating crude extracts with the highest yield (22.04 ± 0.48%), total polyphenol content (29.39 ± 0.39%), and antioxidant capacity (6.38 ± 0.21). An analytical method was developed and validated for the determination of total polyphenols in the extracts. Optimal conditions for the various parameters in this analytical method, namely, the time for the chromophoric reaction to stabilize, wavelength of the absorption maxima to be monitored, the reference standard and the concentration of sodium carbonate were determined to be 5 min, 780 nm, pyrogallol, and 14.06% w v-1, respectively. UV-Vis spectrophotometric monitoring of the reaction under these conditions proved the method to be linear, specific, precise, accurate, reproducible, robust, and easy to perform.

Mercuric Chloride Catalysed Solvolysis of Benzyl Chloride in Water & Highly Aqueous Organic Solvent Systems

Kinetics of mercuric chloride catalysed solvolysis of benzyl chloride have been studied in water. 10% aq. ethanol, 10,20 and 30% aq. acetone and 20% aq. DMSO. The results confirm the operation of a mass law effect.

Singlet oxygen reactivity in water-rich solvent mixtures

The 3-methylindole (3MI) oxygenation sensitized by psoralen (PSO) has been investigated in 100%, 20% and 5% O2-saturated water/dioxane (H2O/Dx) mixtures. The lowering of the ¹O2* chemical rate when water (k chem∆3MI = 1.4 × 109 M-1 s-1) is replaced by deuterated water (k chem∆3MI = 1.9 × 108 M-1 s-1) suggests that hydrogen abstraction is involved in the rate determining step. A high dependence of the chemical rate constant on water concentration in H2O/Dx mixtures was found showing that water molecules are absolutely essential for the success of the 3MI substrate oxidation by ¹O2* in water-rich solvent mixtures.

Thermodynamic study of the solubility of sodium naproxen in some ethanol + water mixtures

By using the van't Hoff and Gibbs equations the apparent thermodynamic functions Gibbs energy, enthalpy, and entropy of solution for sodium naproxen in ethanol + water cosolvent mixtures, were evaluated from solubility data determined at temperatures from (278.15 to 308.15) K. The drug solubility was greatest in neat water and lowest in neat ethanol at all the temperatures studied. By means of non-linear enthalpy-entropy compensation analysis, it follows that the dissolution process of this drug in ethanol-rich mixtures is entropy-driven, whereas, in water-rich mixtures the process is enthalpy-driven.

Aqueous gels of mixtures of ionic surfactant SDS with pluronic copolymers P123 or F127

Gel diagrams based on tube inversion and oscillatory rheometry are reported for Pluronic copolymers F127 (E98P67E98) and P123 (E21P67E21) in mixtures with anionic surfactant sodium dodecyl sulfate (SDS). Total concentrations (e, SDS+copolymer) were as high as 50 wt% with mole ratios SDS/copolymer (mr) in the ranges 1-5 (F127) a lid 1-7 (PI 23). Temperatures were its high as 90 degrees C. Determination of the temperature dependences of the dynamic moduli served to confirm the gel boundaries from tube inversion and to reveal the high elastic moduli of the gels, e.g., compared at corn parable positions in the gel phase, a 50 wt% SDS/P123 wit h mr = 7 had G' three times that of a corresponding gel of P123 alone. Sin all-angle X-ray scattering (SAX S) was used to show that the structures of all the SDS/F127 gels were bee and that the structures of the SDS/P123 gels with mr = I were either fcc(c = 30 wt%) or hex (c = 40 wt%). Assignment of structures to SDS/P123 gels with values of mr in the range 3-7 was more difficult, as high-order scattering peaks Could be very weak, and at the higher values of c and mr, the SAXS peaks included multiple reflections.

Tailored Media for Homogeneous Cellulose Chemistry: Ionic Liquid/Co-Solvent Mixtures

Co-solvents can minimize two of the major problems associated with the use of ionic liquids (ILs) as solvents for homogeneous derivatization of cellulose: high viscosity and limited miscibility with non-polar reagents or reaction products. Thus, the effects of 18 solvents and 3 binary solvent mixtures on cellulose solutions in three ILs were systematically studied with respect to the solution phase behavior. The applicable limits of these mixtures were evaluated and general guidelines for the use of co-solvents in cellulose chemistry could be advanced: Appropriate co-solvents should have EN T values (normalized empirical polarity) > 0.3, very low ``acidity`` (alpha < 0.5), and relatively high ""basicity`` (beta >= 0.4). Moreover, novel promising co-solvents and binary co-solvent mixtures were identified.

Rapid determination of desorption efficiency, and analysis of solvent mixtures for occupational exposure studies

An analytical procedure has been developed for simultaneous determination of solvent mixture vapors to enable evaluation of occupational exposure. To determine the desorption efficiency the volatile components of the solvent mixtures were generated from a glass tube filled with glass wool. This device is easy to prepare and use. These vapors were then collected in activated charcoal tubes and analyzed by capillary gas chromatography. The method was tested with a mixture of 22 solvents, including aliphatic and aromatic hydrocarbons, alcohols, ethers, esters, and ketones, oil at low concentrations. All the components were defected. When a 99: 1 mixture of carbon disulfide-dimethylformamide was used for desorption the efficiency was > 75% for most of the solvents.

Uncaria tomentosa Aqueous-ethanol Extract Triggers an Immunomodulation toward a Th2 Cytokine Profile

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Theoretical study of the absorption and nonradiative deactivation of 1-nitronaphthalene in the low-lying singlet and triplet excited states including methanol and ethanol solvent effects

The photophysics of the 1-nitronaphthalene molecular system, after the absorption transition to the first singlet excited state, is theoretically studied for investigating the ultrafast multiplicity change to the triplet manifold. The consecutive transient absorption spectra experimentally observed in this molecular system are also studied. To identify the electronic states involved in the nonradiative decay, the minimum energy path of the first singlet excited state is obtained using the complete active space self-consistent field//configurational second-order perturbation approach. A near degeneracy region was found between the first singlet and the second triplet excited states with large spin-orbit coupling between them. The intersystem crossing rate was also evaluated. To support the proposed deactivation model the transient absorption spectra observed in the experiments were also considered. For this, computer simulations using sequential quantum mechanic-molecular mechanic methodology was used to consider the solvent effect in the ground and excited states for proper comparison with the experimental results. The absorption transitions from the second triplet excited state in the relaxed geometry permit to describe the transient absorption band experimentally observed around 200 fs after the absorption transition. This indicates that the T-2 electronic state is populated through the intersystem crossing presented here. The two transient absorption bands experimentally observed between 2 and 45 ps after the absorption transition are described here as the T-1 -> T-3 and T-1 -> T-5 transitions, supporting that the intermediate triplet state (T-2) decays by internal conversion to T-1. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4738757]

Soft solution processing of cerium hydroxysulfate powders with different morphologies

Polycrystalline cerium hydroxysulfate powders have been prepared by soft solution processing using various basic solvents. The crystals prepared have varying morphologies, spherical and flaky, depending on the solvent used. The crystals obtained from distilled water-pyridine and aqueous ammonia solvent mixtures are spherical, whereas those obtained from mixtures of distilled water and ethylenediamine or hydrazine hydrate are flaky. All the crystalline cerium hydroxysulfate samples display luminescence properties. It was found that the flaky crystals generally show a much stronger luminescence than their spherical counterparts.

First study on the thermo-solvatochromism in aqueous 1-(1-butyl)-3-methylimidazolium tetrafluoroborate: A comparison between the solvation by an ionic liquid and by aqueous alcohols

The thermo-solvatochrornic behaviors of 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl) phenolate, RB; 2,6-dichloro-4-(2,4,6-triphenyloyridinium-1-yl) phenolate, WB; 2,6-dibromo-4-[(E)-2-(1-methylpyridinium-4-yl)ethenyl] phenolate, MePMBr(2); 2,6-dibromo-4-[(E)-2-(1-n-octylpyridinium-4-yl)ethenyl] phenolate, OcPMBr(2), have been investigated in binary mixtures of the ionic liquid, IL, 1-(1-butyl)-3-methylimidazolium tetrafluorborate, [BuMeIm][BF(4)], and water (W), in the temperature range from 10 to 60 degrees C. Plots of the empirical solvent polarities, ET (probe) in kcal mol(-1), versus the mole fraction of water in the binary mixture, chi(w) showed nonlinear, i.e., nonideal behavior. Solvation by these IL-W mixtures shows the following similarities to that by aqueous aliphatic alcohols: The same solvation model can be conveniently employed to treat the data obtained; it is based on the presence in the system-bulk medium and probe solvation shell of IL, W, and the ""complex"" solvent 1:1 IL-W. The origin of the nonideal solvation behavior appears to be the same, preferential solvation of the probe, in particular by the complex solvent. The strength of association of the IL-W complex, and the polarity of the IL are situated between the corresponding values of aqueous methanol and aqueous ethanol. Temperature increase causes a gradual desolvation of all probes employed. A difference between solvation by IL-W and aqueous alcohols is that probe-solvent hydrophobic interactions appear to play a minor role in case of the former mixture, probably because solvation is dominated by hydrogen-bonding and Coulombic interactions between the ions of the IL and the zwitterionic probes.