Understanding solvation

Abstract

The effects of solvents on different chemical phenomena, including reactivity, spectroscopic data, and swelling of biopolymers can be rationalized by use of solvatochromic probes, substances whose UV-vis spectra, absorption, or emission are sensitive to the properties of the medium. Thermo-solvatochromism refers to the effect of temperature on solvatochromism. The study of both phenomena sheds light on the relative importance of the factors that contribute to solvation, namely, properties of the probe, those of the solvent (acidity, basicity, dipolarity/polarizability, and lipophilicity), and the temperature. Solvation in binary solvent mixtures is complex because of "preferential solvation" of the probe by some component of the mixture. A recently introduced solvent exchange model is based on the presence in the binary solvent mixture of the organic component (molecular solvent or ionic liquid), S, water, W, and a 1:1 hydrogen-bonded species (S-W). Solvation by the latter is more efficient than by its precursor solvents, due to probe-solvent hydrogen-bonding and hydrophobic interactions; dimethyl sulfoxide (DMSO)-W is an exception. Solvatochromic data are employed in order to explain apparently disconnected phenomena, namely, medium effect on the pH-independent hydrolysis of esters, 1 H NMR data of water-ionic liquid (IL) mixtures, and the swelling of cellulose.

Extraction of Bioactive Polyphenols with High Antioxidant Activity from Bilberry (Vaccinium myrtillus L.) Processing Waste

“…This increases solvent penetration in the plant matrix, improving the extraction of matrixbound compounds. Due to their small molar volume, high hydrogen bonding capability and large basicity, ethanol and water are effective swelling agents 29 , which suggests that swelling phenomena may play a role in the extraction process.…”

Solvation simplified

“…More discussion on the subject can be found in specialized books, and review articles. [2][3][4][5][6][7][8][9][10][11] The reason for the multi-parameter dependence of chemical phenomena on solvent properties, point (i) above, is that several solutesolvent interactions come into play; their effects should be taken into account. These include both specific and non-specific interactions, e.g., hydrogen-bonding, dipolar-interactions (ion-dipole, dipoledipole, dipole-induced dipole), and dispersion or London interactions.…”

“…19 As an example of the determination of the relative importance of solute-solvent interaction mechanisms, consider the solvation of solvatochromic probes. The procedure in order to extract this information is as follows: 10,11 we determine the effects of a group of solvents on the Uv-vis spectra of one or more probes; we apply Equation 2 in order to calculate E T (probe); we use Equation 3 in order to calculate the regression coefficients (a), (b), (s), and (p). Finally, we draw conclusions about the relative importance of solvent acidity, basicity, etc., from these regression coefficients, after their values are statistically standardized (i.e., from b statistical (regression coefficient)), in order to make them comparable.…”

“…These, after algebraic manipulation, lead to the following solvent exchange equilibria, termed solvent "fractionation factors" j: 10,11 (8) (9) Figure 5. (10) where (m) represents the number of solvent molecules whose exchange in the probe solvation shell affects E T (probe); usually m ≤ 2, Bk refers to bulk solvent, and the concentrations of the solvent species are "effective" not analytical ones.…”

“…Our results have shown that the magnitude of this energy is sizeable (e.g., range from 2.1 to 3.7 kcal mol -1 over a 50 o C range for WB in aqueous alcohols) relative to the activation enthalpies of many organic reactions. 10,11 …”