Ionic Interactions from the Mixing of NaCl with the Acetate, Nitrate, Perchlorate, and Sulfate Salts of Guanidinium in Water

Abstract

Ionic interactions have been investigated from the experimental isopiestic osmotic coefficient measurements on the mixing of NaCl with several guanidinium (Gn) salts, like CH 3 COOGn, GnNO 3 , GnClO 4 , and Gn 2 SO 4 , up to high ionic strengths. Analysis of osmotic coefficient data by the Pitzer theory offers valuable information on the mixing of ions of like and unlike charges of hydrophilic and hydrophobic nature. The mixing effects arising out of symmetrical and unsymmetrical mixing of ions are computed by the Pitzer theory in these systems. The excess Gibbs free energies of mixing, ∆ m G E have been analyzed by the Friedman theory of cluster integral expansion. The ∆ m G E values display very interesting features with respect to the ionic strength fraction of the acetate, nitrate, and perchlorate salts of guanidinium. The minima in the ∆ m G E values are noted in the NaCl-rich mixtures, and the addition of these guanidinium salts slowly enhances ∆ m G E , passing through zero to positive values. The mixing of NaCl with Gn 2 SO 4 offers negative ∆ m G E throughout the mixture composition. Although binary interactions are nearly absent in the NaCl-CH 3 COOGn mixtures, the ternary and quaternary interactions are noted to be important in the mixtures of NaCl with other guanidinium salts. The ∆ m G E values of the mixture containing Na + , Gn + , Cl -, and SO 4 2ions (where binary interactions are important) can be estimated by Young's cross square rule (YCSR) with confidence. The YCSR is not obeyed when NaCl is mixed with CH 3 COOGn, GnNO 3 and GnClO 4 , where ternary and quaternary interactions are dominant over the binary interactions.

New tricks for old dogs: improving the accuracy of biomolecular force fields by pair-specific corrections to non-bonded interactions

“…The osmotic pressure computed using the standard CHARMM36 force field (red marks in Fig. 5A) was significantly lower than prescribed by experiment 89 . For example, 139 bar was measured in experiment at 2 m concentration whereas the simulated osmotic pressure was only 18 bar.…”

“…Calibration of the guanidinium–acetate interaction using the osmotic pressure method. (A) Osmotic pressure of the guanidinium–acetate solution as a function of the solution molality obtained using the CHARMM36 force field with the specified value of the NBFIX correction (colored symbols) and experiment 89 (black symbols). Gray dashed line shows the dependence of an ideal 1:1 solution.…”

Reassessment of the Binary, Ternary, and Quaternary Interactions in Mixed Electrolytes from Thermodynamic Quantities: The Systems with Uncommon Ions Containing Hydrophobic Character

“…As discussed above, first, the theory does not account for quaternary and higher-order multiplet interactions that are important in the mixtures containing hydrophobic ionic species such as guanidinium (Gn + ) and the clathrate-forming and strong hydrophobic quaternary ammonium electrolytes. In these mixtures, the quaternary interactions have been recognized in several reports. − These interactions are absent in the mixtures of simple strong electrolytes. The evidence obtained from the ultrasonic absorption spectra of the clathrate-forming quaternary ammonium salts and GnCl indicates the formation of large clusters owing to the association of ions. , The effect of these clusters has also been observed in many solution properties such as viscosity, activity coefficient, and density .…”

“…In such systems, the contributions to Δ m G E , excess volumes of mixing, Δ m V E , and excess compressibilities of mixing, Δ m K E , were estimated in terms of binary and ternary interactions as determined by FCIET and PSIIT. In a very recent contribution from this laboratory, we compared the roles of different interactions in determining the Δ m G E values for several mixed electrolytes with uncommon ions, in which one strong hydrophobic and hydrophilic cation or anion were present . The mixtures studied included NaCl, CH 3 COOGn (henceforth abbreviated as GnAc), GnNO 3 , GnClO 4 , and Gn 2 SO 4 in full composition range up to high ionic strengths.…”

Cation Effect on the Water Activity of Ternary (S)-Aminobutanedioic Acid Magnesium Salt Solutions at 298.15 and 310.15 K

“…Further, osmotic coefficients of some other aminomethanamidine halides in aqueous binary mixtures are presented in the literature at 298.15 K, and also some for aqueous solutions containing other salts, e.g., GndmNO 3 , GndmClO 4 , GndmBz, and GndmPr . Activity of water in ternary aqueous mixtures with Gndm + salts at 298.15 K was investigated by Kumar − for mixtures cotaining GndmCl + NaCl, GndmCl + KCl, GndmCl + MgCl 2 , GndmCl + (C 4 H 9 ) 4 NCl, GndmNO 3 + NaCl, and GndmClO 4 + NaCl. Ternary mixtures of GndmCl with amino acids (glycine, l -leucine) and peptides (diglycine, triglycine, glycyl- l -leucine, l -leucyl- l -leucine) were investigated by Vesnaver et al Vapor-pressure osmometry was used to derive ratios of activity coefficients.…”