Influence of Solvent Polarity on Preferential Solvation of Molecular Recognition Probes in Solvent Mixtures

Abstract

The association constants for formation of 1:1 complexes between a H-bond acceptor, tri-n-butylphosphine oxide, and a H-bond donor, 4-phenylazophenol, have been measured in a range of different solvent mixtures. Binary mixtures of n-octane and a more polar solvent (ether, ester, ketone, nitrile, sulfoxide, tertiary amide, and halogenated and aromatic solvents) have been investigated. Similar behavior was observed in all cases. When the concentration of the more polar solvent is low, the association constant is identical to that observed in pure n-octane. Once a threshold concentration of the more polar solvent in reached, the logarithm of the association constant decreases in direct proportion to the logarithm of the concentration of the more polar solvent. This indicates that one of the two solutes is preferentially solvated by the more polar solvent, and it is competition with this solvation equilibrium that determines the observed association constant. The concentration of the more polar solvent at which the onset of preferential solvation takes place depends on solvent polarity: 700 mM for toluene, 60 mM for 1,1,2,2-tetrachloroethane, 20 mM for the ether, ester, ketone, and nitrile, 0.2 mM for the tertiary amide, and 0.1 mM for the sulfoxide solvents. The results can be explained by a simple model that considers only pairwise interactions between specific sites on the surfaces of the solutes and solvents, which implies that the bulk properties of the solvent have little impact on solvation thermodynamics.

Sorbent Mass Variation Method: A New Possibility for the Determination of Binding Isotherms

“…However, such selective binding of one of the components of a mixture by a third component (sorbent) may frequently occur not only at different types of interfaces but inside homogeneous molecular systems like in electrolyte 913 , nonelectrolyte 14,15 and polymer 1620 solutions, too.…”

Fluorescent and colorimetric molecular recognition probe for hydrogen bond acceptors

“…Titrations were carried out using a Cary 3 Bio UV/vis spectrophotometer, using standard titration protocols. 15 A 10 mL sample of the host, 1-naphthol (1) was prepared at a known concentration (typically between 0.16 mM and 0.20 mM in CHCl 3 , between 0.14 mM and 0.21 mM in CH 2 Cl 2 and between 0.10 mM and 0.14 mM in CCl 4 ). 2 mL of this solution was removed and added to a quartz cuvette and the UV-Vis spectrum was recorded.…”

“…1). A variety of UV/vis and NMR spectroscopic molecular recognition probes [14][15][16] have been employed to understand the influence of solvent on solution equilibria but these probes can only be used with a single spectroscopic technique. Dual probes hold distinct advantages over single output systems as they provide orthogonal spectroscopic techniques by which to validate data but dual molecular recognition probes are yet to Fig.…”

Functional group interaction profiles: a general treatment of solvent effects on non-covalent interactions

“…11 across the entire composition range for THF-chloroform mixtures (see ESI † for details). 27,29,30,[32][33][34][35] These experimental measurements can be compared with the solvation energies DG S calculated using the SSIMPLE approach as follows.…”

“…21 The validity of eqn (1) has been experimentally demonstrated for formation of 1 : 1 complexes between a wide variety of different solutes in a range of different solvents. 20,[22][23][24][25][26][27][28][29][30][31][32][33][34][35] The constant c in eqn (1) is related to the fact that organic solvents typically have a concentration of about 10 M, whereas the standard state for solutes is 1 M. 36 The origin of the value c will be discussed in more detail below, but the focus of this paper is the development of a computational method for calculation of the rst term in eqn (1) for any solvent environment. The rst term in eqn (1) represents the free energy change associated with the exchange of polar interactions between solutes and solvent.…”