Distinguishing aggregation from random mixing in aqueous t-butyl alcohol solutions

Abstract

Raman spectroscopic measurements are combined with various multivariate curve resolution (Raman-MCR) strategies, to characterize the aggregation of t-butyl alcohol (TBA) in aqueous solutions. The resulting TBA solute-correlated (SC) spectra reveal perturbed water OH features arising from the hydration-shell of TBA as well as shifts in the TBA CH vibrational frequency arising from TBA-TBA interactions. Our results indicate that at low concentrations (below approximately 0.5 M), there is virtually no TBA aggregation. The first aggregates formed above 0.5 M remain highly hydrated, while those formed above approximately 2 M are significantly less hydrated. Comparisons with predictions pertaining to a randomly mixed (non-aggregating) solution indicate that below approximately 1 M there are fewer TBA-TBA contacts than would be present in a random mixture, thus implying that the thermodynamic stability of the first hydration-shell of TBA suppresses the formation of direct contact aggregates at low TBA concentrations. Our results further suggest that microheterogeneous domains containing many water-separated TBA-TBA contacts form near a TBA concentration of approximately 1 M, while at higher concentrations the TBA-rich domain size distribution may resemble that in a non-aggregating random mixture.

Depolarized light scattering and dielectric response of a peptide dissolved in water

“…90,91,116,117 When solutes provide specific binding sites, water molecules bound to solutes demonstrate relaxation times specific to the solute motions. 118 Once sites for specific binding are not available, as is the case with NALMA studied here and with somewhat similar on the hydrophobicity scale t-butyl alcohol studied elsewhere, 119 there is little perturbation of the water dynamics caused by the solute. For instance, recent simulations of electrolyte solutions 91 have shown no slowing down of water dynamics around chloride ions, but significantly slower dynamics around stronger solvating magnesium ions, all in the same electrolyte solution.…”

Ratiometric detection of Raman hydration shell spectra

“…A single hydration spectrum was obtained in such low concentration regions. Recently, the MCR was developed to much higher concentration region, and it was used to deduce the concentration dependent spectra of hydration shell. These spectra were used to reflect the aggregation of solutes in higher concentration region.…”

Microstructure and concentration fluctuations in alcohol–Toluene and alcohol-Cyclohexane binary liquids: A small angle neutron scattering study

“…Water -Tert-butanol (TBA) mixture is one of the systems that are the most debated currently, being considered as the prototypical system to advance our understanding of hydrotrope solubility in aqueous solution [5,8,9,15,16,17,18,19]. Analogous interest arises from studies on non-aqueous solvent -TBA mixtures.…”