Mixed Alcohol-water Solvent Research Articles

A ferrocene-based multiple-stimuli responsive organometallogel

Three new ferrocene-peptide compounds were designed and prepared. We investigated their gelling abilities and found that two of them were capable of gelling various organic solvents, especially alcohols. Gels also formed in mixed alcohol-water solvents, which decreased the critical gelation concentration (CGC) of the gels. Compound 1, comprised of a dipeptide (Phe-Phe) and ferrocene, acted as a novel low-molecular-weight gelator in the formation of metallogel 1 in isopropanol-water (v/v = 1 : 1). This gelation was found to be reversible under redox stimuli; changing of the redox state of ferrocene induced a reversible gel-sol phase transition. Additionally, gel 1 responded to β-CD as a result of host-guest interactions between this compound and ferrocene. With the addition of β-CD, the gel network gradually broke down, as demonstrated by SEM.

Surface-induced electrolytic dissociation of oxalic and phosphoric acid in mixed alcohol–water solvents

The electric conductance of solutions of oxalic, phosphoric and sulfuric acid (up to 0.025 M) in ethanol, methanol, and mixed alcohol–water solvents has been studied in the presence and absence of TiO 2 (1–10% by mass). TiO 2 enhanced the conductance of solutions of oxalic and phosphoric acid in anhydrous alcohol and in alcohol-rich mixed solvents. In water-rich mixed solvents “normal” behavior was observed, that is, TiO 2 depressed the conductance of electrolyte solutions. The enhanced conductance is interpreted in terms of surface-induced electrolytic dissociation. In nonaqueous solvents, oxalic and phosphoric acid occur chiefly in molecular form, even in very dilute solutions. TiO 2 binds the hydrogen oxalate or dihydrogen phosphate anions (which originate from neutral acid molecules) and the protons remain in solution in form of solvated cations. The lyonium cations have a substantially higher molar conductance than other ions due to the Grotthuss mechanism. This is why the enhancement of conductance is more substantial in solutions of weak acids than in solutions of other electrolytes.

Synthesis and Characterization of Mesoporous Cerium Oxide Prepared Using an Organic Base and a Templating Agent

This paper discusses the effect on the surface properties of precipitated cerium oxide of using a mixed alcohol–water solvent as well as an organic base instead of the ammonia solution used hitherto. It further discusses the influence of the presence of a templating agent, such as CTAB, on the pore structure of ceria. It was found that the use of a template leads to a more well-defined pore system. Furthermore, in addition to any mesopores, an interesting network of secondary macropores was developed.

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.

Chemical force spectroscopy in heterogeneous systems: intermolecular interactions involving epoxy polymer, mixed monolayers, and polar solvents.

We used chemical force microscopy (CFM) to study adhesive forces between surfaces of epoxy resin and self-assembled monolayers (SAMs) capable of hydrogen bonding to different extents. The influence of the liquid medium in which the experiments were carried out was also examined systematically. The molecular character of the tip, polymer, and liquid all influenced the adhesion. Complementary macroscopic contact angle measurements were used to assist in the quantitative interpretation of the CFM data. A direct correlation between surface free energy and adhesion forces was observed in mixed alcohol-water solvents. An increase in surface energy from 2 to 50 mJ/m(2) resulted in an increase in adhesion from 4-8 nN to 150-300 nN for tips with radii of 50-150 nm. The interfacial surface energy for identical nonpolar surface groups of SAMs was found not to exceed 2 mJ/m(2). An analysis of adhesion data suggests that the solvent was fully excluded from the zone of contact between functional groups on the tip and sample. With a nonpolar SAM, the force of adhesion increased monotonically in mixed solvents of higher water content; whereas, with a polar SAM (one having a hydrogen bonding component), higher water content led to decreased adhesion. The intermolecular force components theory was used for the interpretation of adhesion force measurements in polar solvents. Competition between hydrogen bonding within the solvent and hydrogen bonding of surface groups and the solvent was shown to provide the main contribution to adhesion forces. We demonstrate how the trends in the magnitude of the adhesion forces for chemically heterogeneous systems (solvents and surfaces) measured with CFM can be quantitatively rationalized using the surface tension components approach. For epoxy polymer, inelastic deformations also contributed heavily to measured adhesion forces.

The effect of end-group substitutions and use of a mixed solvent system on β-diketones and their iron complexes

The protonation constants and the Fe(II) and Fe(III) binding constants have been determined potentiometrically in a solvent consisting of 75% ethanol and 25% water (vol./vol.) for the anions derived from four β-diketones: acetylacetone, benzoylacetone, 1, 1, 1-trifluoro-2, 4-pentanedione, and 1-phenyl-4, 4, 4-trifluoro-1, 3-butanedione. Replacement of a methyl group by a phenyl group results in a small increase in basicity and small increases of the stability constants of the Fe(II) and the Fe(III) chelates. Replacement of a methyl group by trifluoromethyl results in considerable reduction in the basicity of the ligand and considerable decreases in the stabilities of the Fe(II) and Fe(III) chelates. The metal ions are found to form successively 1:1, 1:2 and 1:3 metal-ligand chelates as the pH is increased. Protonation constants of the ligands and the stability constants of the 1:1 Fe(III) chelates are also determined spectrophotometrically. The use of the mixed alcohol-water solvent, required to increase the solubility of the chelates formed, results in increases in the protonation constants and the stability constants of the metal chelates, compared with the values of these constants obtained in water.

Spectrophotometric determination of water in lower alcohols

The reduction of iodate ion by iodide ion in the presence of acid in mixed alcohol-water solvents depends upon the amount of water present over a limited aqueous range. Absorbance values, measured at 360 nm, of tri-iodide ion formed from the reaction are quantitatively related to the volume percent water in ethanol and propanol from 3.0 to 7.0 % v/v water. Ten replicate samples each containing 5.0 % v/v water in ethanol gave a mean absorbance value of 0.334 with a standard deviation of ±0.013. The procedure is a simple and rapid alternative to Karl Fisher titration in measuring the water content of commercial, 95% v/v, ethanol.