Effects of Tetramethyl-
and Tetraethylammonium Chloride
on H<sub>2</sub>O: Calorimetric and Near-Infrared Spectroscopic Study
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Abstract
The effect of tetraethylammonium chloride (TEAC) on H<sub>2</sub>O was investigated by the 1-propanol (1P) probing thermodynamic
methodology
developed by us earlier. It was found that TEAC is an amphiphile with
a small hydrophobic and a dominant hydrophilic contribution. An earlier
application of the same 1P-probing methodology to tetramethylammonium
chloride (TMAC) indicated that the latter is as hydrophilic as urea
without any hydrophobic contribution. The hydrophilic effect of TEAC
was found to be about twice stronger than that of TMAC. To investigate
further these surprising findings, we applied a new analysis method
using the concept of the excess partial molar absorptivity of the
solute on the ν<sub>2</sub> + ν<sub>3</sub> combination
band of H<sub>2</sub>O in the near-infrared (NIR) range of their aqueous
solutions. The results confirmed that both salts are indeed strongly
hydrophilic toward H<sub>2</sub>O which manifests itself in the 5123
cm<sup>–1</sup> chromophore of the NIR band of H<sub>2</sub>O. Furthermore, we suggest from the behavior of the 5263 cm<sup>–1</sup> band that both solutes might form small aggregates in the H<sub>2</sub>O-rich region of the respective aqueous solutions