Responses of polar organic compounds to different ionic environments in aqueous media are interrelated

Abstract

Solubilities of 17 polar organic compounds in aqueous solutions of Na2SO4, NaCl, NaClO4, and NaSCN at the salt concentrations of up to 1.0-2.0 M were determined and the Setschenow constant, ksalt, values were estimated. It was found that NaClO4 may display both salting-in and salting-out effects depending on the particular compound structure. The Setschenow constant values for all the polar compounds examined in different salt solutions are found to be interrelated. Similar relationships were observed for partition coefficients of nonionic organic compounds in aqueous polyethylene glycol-sodium sulfate two-phase systems in the presence of different salt additives reported previously [Ferreira et al., J. Chromatogr. A, 2011, 1218, 5031], and for the effects of different salts on optical rotation of amino acids reported by Rossi et al. [J. Phys. Chem. B, 2007, 111, 10510]. In order to explain the observed relationships it is suggested that all the effects observed originate as responses of the compounds to the presence of a given ionic environment and its interaction with the compounds by forming direct or solvent-separated ionic pairs. The response is compound-specific and its strength is determined by the compound structure and the type (and concentration) of ions inducing the response.

Cooperativity between various types of polar solute–solvent interactions in aqueous media

“…This finding agrees with the aforementioned interrelationship between the solute specific responses of different polar compounds to various ionic environments reported previously [18][19][20][21] and confirmed above. The electrostatic nature of dipole-dipole and hydrogen bonding interactions [32][33][34] explains why the relative intensities of these solute-water interactions may vary with the ionic composition of the media.…”

“…The limited experimental data obtained so far prevent any general conclusion. It was suggested earlier [18][19][20][21] that the aforementioned relationships imply that the abilities of various solutes to participate in each type of solute-solvent interactions in the presence of different salt additives are also interrelated.…”

“…It has been reported recently [19] that different properties of organic compounds in aqueous media with different salt additives, such as salting-out and salting-in coefficients, optical rotation, partition coefficients in PEG-sodium sulfate ATPS with different salt additives, are linearly interrelated as described by Eq. (2).…”

“…These results led us to suggest [18][19][20][21][22] that different solutes respond to different ionic composition by changes in the solute-solvent interactions in the solute structure specific manner. The purpose of the present work was to explore if and to what extent the intensities of the different types of solute-solvent interactions change in the presence of different salts in aqueous solution.…”

“…Recent studies [18][19][20][21][22] suggested that the solute properties in aqueous solutions of different ionic composition are linearly interrelated according to: SP salt-1 = k 1 + k 2 × SP salt-2 + k 3 × SP salt-3 (2) where SP is the solute property (logarithm of partition coefficient in octanol-water system [21], in polymer-polymer or polymer-salt ATPSs [18,20], solubility [19], optical rotation [23]); k 1 , k 2 , and k 3 are constant coefficients dependent on the solute property and salt compositions. These results led us to suggest [18][19][20][21][22] that different solutes respond to different ionic composition by changes in the solute-solvent interactions in the solute structure specific manner.…”