The Mixing of K⁺, (nBu₄)N⁺, Mg²⁺, and Ca²⁺ with Guanidinium Cation in Water:  Ionic Interactions from a Thermodynamic Study

Abstract

Ionic interactions have been determined from the experimental osmotic coefficients, densities, and sound speeds for the mixing of guanidinium cation (Gn+) with K+, tetra-n-butylammonium cation (nBu4)N+, Mg2+, and Ca2+ in aqueous solutions containing Cl- at several ionic strengths. As Mg2+ and Ca2+ are more hydrophilic than K+, and (nBu4)N+ is a strong hydrophobic cation, their mixing with another strong hydrophobic species, that is, Gn+, throws light on the importance of binary and ternary interactions involving two cations and one common anion. The excess free energy of mixing, Δm G E, volumes, Δm V E, and compressibility, Δm K E calculated from independent osmotic coefficient, density, and sound speed measurements indicate strong binary interactions as a result of mixing of K+−Gn+ and (nBu4)N+−Gn+ cation pairs. The mixing of Mg2+ with Gn+ and Ca2+ with Gn+ suggests the neutralization of opposing effects produced by the hydrophilic and hydrophobic cations. This situation, which is similar to that noted in an earlier study (Kumar, A. J. Phys. Chem. B 2000, 104, 9505) on the mixing of Na+ and Gn+, offers important information on the binary and ternary interactions present on the mixing of one hydrophilic or hydrophobic cation with another hydrophobic cationic species.

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

“…The Scatchard-Rush-Johnson equations provide a more accurate description of thermodynamics of electrolytes at the expense of a large number of parameters. 1,2,16,17 In the Pitzer theory, a combination of the Debye-Huckel and virial coefficient terms is used to describe the thermodynamic properties of electrolyte solutions. Earlier, we summarized the Pitzer equations applicable to the mixtures of 1:1 electrolytes with a common ion.…”

“…Recently, we have investigated the ionic interactions in the aqueous mixtures of guanidinium chloride (GnCl) with NaCl, KCl, MgCl 2 , CaCl 2 and tetrabutylammonium chloride (TBAC). 1,2 GnCl being a potential denaturant of proteins and DNA duplex is also known to inhibit the reaction rates. 3 We observed interesting changes in the excess free energies, volumes, and compressibilities of mixing in these cases, as Na + , Mg 2+ , and Ca 2+ are the hydrophilic cations and TBA + and Gn + the hydrophobic ones.…”

“…To obtain deeper insights into the ionic interactions and their role in biological molecules and reactivities in organic systems, we in this investigation raise the following questions: (1) What are the types of interactions operating in the above ionic mixtures and how do they vary with the mixture compositions and ionic strengths? (2) In view of the opposite nature of Na + and Gn + species, how do these different types of interactions of Na + with Gn + containing Ac -, NO 3 -, ClO 4and SO 4 2species compete with each other to yield the total excess free energy of mixing? The orientations of water molecules by cations will be affected by anions of different types.…”

DABCO‐Catalyzed Double Cascade Cycloaddition of Maleimides with Bisarylhydrazones: Access to Fused Pyrazolo[5,1‐c][1,2,4]triazole Derivatives

“…Hydrazones, equipped with multiple reactive sites, have considered as valuable building blocks in cycloaddition reaction . Indeed, a large number of privileged N‐heterocycles, such as pyrazolines,, pyrazoles, triazoles, tetrazoles have been smoothly synthesized using hydrazones as the annulation reaction precursors (Scheme a–1c). However, these methods have the disadvantages of requiring either transition metal, tedious workup or harsh reaction conditions.…”

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.…”