On the Origin of Microheterogeneity:  Mass Spectrometric Studies of Acetonitrile−Water and Dimethyl Sulfoxide−Water Binary Mixtures (Part 2)

Abstract

The microscopic structures of acetonitrile-water and DMSO-water binary mixed solvents and their influence on the solvation for solutes (some alcohols and phenol) have been studied on the basis of the cluster structures observed through a specially designed mass spectrometer. In acetonitrile-water mixtures, the water clusters were observed at water mole fractions: X w > 0.2; on the other hand, in DMSO-water mixtures, the water clusters were observed only at much higher water mole fractions: X w > 0.93. In the mixing processes, the water clusters were stabilized in the acetonitrile-water mixtures, whereas the DMSO clusters were stabilized in the DMSO-water mixtures. It is demonstrated that these microscopic structures directly affect the solvation for alcohols and phenol in these binary mixed solvents.

Ultrafast Excited-State Dynamics of Kynurenine, a UV Filter of the Human Eye

“…It has been recently shown that compounds such as 2-butanol, cyclopentanol, cyclohexane, and phenol in H 2 O/ DMSO are predominantly solvated by water clusters at H 2 O > 0.9 and predominantly by DMSO clusters at H 2 O < 0.9. 43 The experimental results presented in Figure 8 reveal that KN is not predominantly solvated by DMSO clusters in the range 0 < H 2 O < 0.7, otherwise the fluorescence and triplet yields would remain unchanged in this region. This might be due to intermolecular hydrogen-bond interactions between KN and water molecules.…”

Density Functional Theory Study of Acetonitrile -Water Clusters: Structures and Infrared Frequency Shifts

“…Since the focus in this work is on the interactions between different kinds of "solvent" molecules in the mixed clusters, our calculated results may help elucidate the structures and the nature of interactions in the mixed clusters to probe the structure of the solution phase. 22 We calculate a variety of conformers, either of σ-type (-OH and -CN binding linearly) or π-type (-OH and -CN binding perpendicularly). We calculate that the IR frequency of the proton-accepting C≡N stretching mode red-shifts in the π-type clusters and blueshifts in σ-type conformers.…”

Density functional study of hydrogen‐bonded acetonitrile–water complex

“…There are several experimental studies [8 -19] of acetonitrile-water mixtures using NMR and IR spectroscopy [8 -14], mass spectroscopy [15], and dielectric spectroscopy [16,17]. Acetonitrile-water complex was also studied theoretically using ab initio methods [20,21] and molecular dynamics simulations [22][23][24].…”