Structure and interactions in simple solutions

Abstract

Neutron scattering with hydrogen/deuterium isotopic substitution techniques has been used to investigate the full range of structural interactions in a dilute 0.02 mol fraction solution of tertiary butanol in water, both in the absence and in the presence of a small amount of sodium chloride. Emphasis is given to the detailed pictures of the intermolecular interactions that have been derived using the empirical potential structure refinement technique. Analysis has been performed to the level of the spatial density distribution functions that illustrate the orientational dependence of the intermolecular interactions between all combinations of molecular and ionic components. The results show the key structural motifs involved in the interactions between the various components in a complex aqueous system. They underline the structural versatility of the water molecule in accommodating a range of different kinds of interactions while retaining its characteristic first-neighbour interaction geometry. Within this framework, the results highlight the complex interplay between the polar, non-polar and charged molecular interactions that exist in the system.

Conformation and interactions of dopamine hydrochloride in solution

“…The diffuse nature of the aliphatic H alk ···Cl correlations suggests that these are not strong structure directing interactions; the peak at 4 Å for C alk2 ···Cl is due to interaction of the hydrogen on the ammonium group with the chloride ion, as is the peak at 5.4 Å for C alk1 ···Cl. The water-chloride anion pair radial distribution functions and the Cl-O w coordination number are very similar to those documented in the literature for other aqueous systems containing chloride anions, 38,58,59 indicating linear halide-hydrogen bonds between the chloride ions and water molecules.…”

The Structure of a Trimolecular Liquid: tert-Butyl Alcohol:Cyclohexene:Water

“…Figure 4C indicates that when water molecules interact with molecules they have a preference to solvate the plane of the ring structure while Figure 4G shows us very clearly that the water molecule is aligned tangentially to the cyclohexene molecule in the classic hydrophobic hydration geometry where the molecule's H-O-H plane is exposed to the nonpolar surface. 1 Panels F and H of Figure 4 illustrate the most favorable direct interaction between the tert-butyl alcohol and water molecules. As expected, Figure 4F shows that the interactions are dominated by hydrogen bonding between the alcohol molecule's hydroxyl group and the water molecules, where Figure 4H shows us that the alcohol molecule adopts one of the close to tetrahedrally distributed hydrogen bonding sites around the water molecule.…”

“…Recent advances in experimental structure determination of liquids by neutron scattering techniques are increasingly allowing us to look in great detail at the nature of these intermolecular interactions in both a chemically specific and molecular orientation sensitive manner. 1 Central to the establishment of neutron scattering techniques as a particularly powerful means to investigate the structure of liquids has been the development of isotopic substitution methods that allow the labeling of chemically specific atomic sites on a system's constituent atoms and molecules. 2 In particular, for aqueous and organic liquids, the variant of the technique based on neutron diffraction with hydrogen/deuterium substitution has proven exceptionally useful.…”

Adding salt to an aqueous solution of t-butanol: Is hydrophobic association enhanced or reduced?

“…Their main observation is that TBAmolecules form dimers that are connected by hydrogen bonds to a central chloride anion. Salting out appears hence due to solute aggregates, which are formed by anion-bridges between the hydroxyl-groups, increasing the solutes overall hydrophobic surface and thus reducing the solubility of the whole complex [36][37][38]. A straightforward conjecture would suggest that the salting out of proteins could be driven by analogous anion-bridged aggregates.…”

“…Salting out appears hence due to solute aggregates, which are formed by anion bridges between the hydroxyl groups, increasing the solutes' overall hydrophobic surface and thus reducing the solubility of the whole complex. [36][37][38] A straightforward conjecture would suggest that the salting out of proteins could be driven by analogous anion-bridged aggregates. We would like to point out that the proposed mechanism has similarity with the "differential hydrophobicity" concept of Burke et al 39 used to explain the specific protein-aggregation behavior observed in Huntington's disease.…”