Hydration and association in solutions of tetraalkylammonium iodides

Abstract

Conductivity, self-diffusion coefficient and viscosity were measured at 298 K for tetraalkylammonium iodides in aqueous solutions, 0.5 M urea solutions and mixtures of water with tert-butanol. The molar conductivity was analysed via the Fuoss-Hsia equation. The limiting molar conductivity, the separation of ions forming the ion pairs and the association constants were determined. In all studied systems the association of opposite ions was weak, but contact ion pairs were present. The hydrodynamic radii of ions, determined from the self-diffusion coefficients, were used to compute the dynamic hydration numbers. As expected, the dynamic hydration numbers were noticeably smaller than the static numbers, because they represented the water molecules located inside the R 4 N + ions, between the alkyl chains. Addition of tert-butanol reduced the hydration of Me 4 N + and, probably, Bu 4 N + ions, but induced aggregation of Bu 4 N + cations only.

Ion association in aqueous and non-aqueous solutions probed by diffusion and electrophoretic NMR

“…58 In particular, we note that the divalent sulphate ion does not seem to associate with the TMA + ion to any larger extent than the monovalent anions. In addition, the lack of association in aqueous solutions is a general phenomenon for tetraalkylammonium ions irrespective of the alkyl chain length (also in agreement with previous studies 57,58 ); the data in Fig. 4 show that it is the non-specific ion-ion interaction term that dominates the observed behavior in water.…”

“…52,56 For water, this result is expected as ion association is known to be weak in aqueous solutions. 1,57 For example, a recently reported value of the association constant from conductivity measurements is K = 2.0 for TMABr. 58 In particular, we note that the divalent sulphate ion does not seem to associate with the TMA + ion to any larger extent than the monovalent anions.…”

Effect of surfactant head group size on polyelectrolyte–surfactant interactions: steady-state and time-resolved fluorescence study

“…In our previous research [21], the area per molecule of absorbed C 12 NB at the air-liquid interface is smaller than that calculated on geometric considerations. In fact, it is known that the tetrabutylammonium cations themselves can self associate in water to form clusters [22,23]. These may support our hypotheses.…”

Raman Spectroscopic Study on the Hydration Structures of Tetraethylammonium Cation in Water

“…Hydrophobic hydration plays an important role in the thermodynamic and solution properties of aqueous apolar solutes and the stabilization of proteins in aqueous solution. − Tetraalkylammonium halides have long been considered as model systems to investigate the nature of hydrophobic hydration because of their good solubility in aqueous solution and their nonpolar surface which increases with increasing alkyl-chain length within the series of homologues. − These compounds also provide a suitable candidate for investigating the competing influence of the Coulombic effect of the charge density and the hydrophobic effect of the nonpolar surface. , …”

“…[1][2][3][4] Tetraalkylammonium halides have long been considered as model systems to investigate the nature of hydrophobic hydration because of their good solubility in aqueous solution and their nonpolar surface which increases with increasing alkyl-chain length within the series of homologues. [5][6][7][8][9][10][11][12][13][14][15][16][17] These compounds also provide a suitable candidate for investigating the competing influence of the Coulombic effect of the charge density and the hydrophobic effect of the nonpolar surface. 18,19 There have been some reports on the effect of R 4 NX on the structural stability of proteins.…”