Issue 21, 2011

Molecular recognition probes of solvation thermodynamics in solvent mixtures

Abstract

High-throughput UV-Vis experiments using four molecular recognition-based probes, made by the combination of two hydrogen bond acceptors, tri-n-butylphosphine oxide and N,Nā€²-bis(2-ethylhexyl)acetamide, and two hydrogen bond donors, 4-phenylazophenol and 4-nitrophenol, were performed. The association constants for the 1ā€†:ā€†1 H-bond interaction involved in each probe system were measured in mixtures of a polar and non-polar solvent, di-n-hexyl ether and n-octane, respectively. Similar behaviour was observed for all four systems. When the concentration of the polar solvent was low, the association constant was identical to that observed in pure n-octane. However, once the concentration of the polar solvent exceeded a threshold, the association constant decreased linearly with the concentration of di-n-hexyl ether. Selective solvation in mixtures can be understood based on the competition between the multiple competing equilibria in the system. In this case, solvation thermodynamics are dominated by competition of the ether for solvation of H-bond donors. For the more polar solute, 4-nitrophenol, the selective solvation starts at lower concentrations of the polar solvent compared with the less polar solute, 4-phenylazophenol. Thus the speciation and hence the properties of systems containing multiple solutes and multiple solvents can be estimated from the H-bond properties and the concentrations of the individual functional groups.

Graphical abstract: Molecular recognition probes of solvation thermodynamics in solvent mixtures

Article information

Article type
Paper
Submitted
05 Jul 2011
Accepted
15 Aug 2011
First published
23 Sep 2011

Org. Biomol. Chem., 2011,9, 7571-7578

Molecular recognition probes of solvation thermodynamics in solvent mixtures

V. Amenta, J. L. Cook, C. A. Hunter, C. M. R. Low and J. G. Vinter, Org. Biomol. Chem., 2011, 9, 7571 DOI: 10.1039/C1OB06083J

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