The physical significance of the Kamlet–Taft π* parameter of ionic liquids

The Kamlet–Taft dipolarity/polarizability parameters π* for various ionic liquids were determined using 4-tert-butyl-2-((dicyanomethylene)-5-[4-N,N-diethylamino)-benzylidene]-Δ3-thiazoline and 5-(N,N-dimethylamino)-5′-nitro-2,2′-bithiophene as solvatochromic probes.

Using computational chemistry to explore experimental solvent parameters – solvent basicity, acidity and polarity/polarizability

Solvent basicity and polarity/polarizability parameters are analysed using molecular properties of solvents derived from computational chemistry. The results show that Kamlet and Taft’s measure of hydrogen bond basicity, β, is essentially identical to Gutmann’s donor number, a measure of Lewis basicity, both being determined by the charge on the most negative atom of the solvent molecule and the energy of the electron donor orbital. It is also found that, for both parameters, the calculated values for alcohols and N–H containing bases deviate systematically from those for aprotic solvents. This mirrors Kamlet and Taft’s earlier observation that different solvatochromic probes yield different β values in amphiprotic solvents. Reichardt’s ET (30) and Kamlet, Abboud and Taft’s π* both show direct dependences on the dipole moments and quadrupolar amplitudes of the solvent molecules and, surprisingly, an inverse dependence on the molecular polarizability. Additionally, ET (30) has a strong dependence on the charge on the most positive hydrogen atom of the solvent molecule, reflecting its sensitivity to hydrogen bonding. Unexpectedly, π* shows a dependence on the energy of the electron donor orbital. Kammet and Taaft’s hydrogen bond acidity parameter, α, is discussed in light of the results for π* and ET (30).

Quantitative mapping of membrane nanoenvironments through single-molecule imaging of solvatochromic probes

Environmentally-sensitive fluorophores report on their local biochemical or biophysical environments through changes in their emission. We combine the solvatochromic probe di-4-ANEPPDHQ with multi-channel SMLM and quantitative analysis of the resulting marked point patterns to map biophysical environments in the mammalian cell membrane. We show that plasma membrane properties can be mapped with nanoscale resolution, and that partitioning between ordered and disordered regions is observed on length scales below 300 nm.

Understanding the efficiency of ionic liquids–DMSO as solvents for carbohydrates: use of solvatochromic- and related physicochemical properties

The quantification of interactions of solvatochromic probes with ionic liquids/DMSO serves as an expedient approach for predicting the solvent efficiency in dissolving carbohydrates

Cellulose in Ionic Liquids and Alkaline Solutions: Advances in the Mechanisms of Biopolymer Dissolution and Regeneration

This review is focused on assessment of solvents for cellulose dissolution and the mechanism of regeneration of the dissolved biopolymer. The solvents of interest are imidazole-based ionic liquids, quaternary ammonium electrolytes, salts of super-bases, and their binary mixtures with molecular solvents. We briefly discuss the mechanism of cellulose dissolution and address the strategies for assessing solvent efficiency, as inferred from its physico-chemical properties. In addition to the favorable effect of lower cellulose solution rheology, microscopic solvent/solution properties, including empirical polarity, Lewis acidity, Lewis basicity, and dipolarity/polarizability are determinants of cellulose dissolution. We discuss how these microscopic properties are calculated from the UV-Vis spectra of solvatochromic probes, and their use to explain the observed solvent efficiency order. We dwell briefly on use of other techniques, in particular NMR and theoretical calculations for the same purpose. Once dissolved, cellulose is either regenerated in different physical shapes, or derivatized under homogeneous conditions. We discuss the mechanism of, and the steps involved in cellulose regeneration, via formation of mini-sheets, association into “mini-crystals”, and convergence into larger crystalline and amorphous regions. We discuss the use of different techniques, including FTIR, X-ray diffraction, and theoretical calculations to probe the forces involved in cellulose regeneration.