NMR studies on dynamic behavior of water molecules in tetraalkylammonium bromide-D2O solutions at 5–25°C+

✍ Scribed by Koichi Fumino; Kenichi Yukiyasu; Akio Shimizu; Yoshihiro Taniguchi

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 510 KB
• Volume: 75
• Category: Article
• ISSN: 0167-7322
• DOI: 10.1016/s0167-7322(97)00020-2

✦ Synopsis

The spin-lattice relaxation times (T1) of D and 170 nuclei of D20 molecules in tetraalkylammonium bromides (R4NBr; R=Me, Et, Pr, Bu), dilute aqueous solutions were measured at the concentration of 0.2 to 1.0 mol/kg and at the temperature of 5 to 25 °C. The relative spin-lattice relaxation rate, R1/RI° (RI=I/T 1) at 25 °C increased linearly with increasing concentration of tetraalkylammonium bromide solutions. But, it varied nonlinearly against the concentration below 20 °C and the deviation increased with decreasing temperature. The dynamic hydration number (nvH N) of D and 170 nuclei ofa D~O molecule in the hydration sphere of tetraalkylammonium ions had good correlation with the molecular size, except for the Bu4N ÷ion. The deviation of nvH N of Bu4 N÷ ion at low temperature reflected the caging effect due to the association through hydrogen bonding among water molecules as the association increases at lower temperature. It was suggested that the rotational anisotropy (x÷~/x÷17o) of water molecules can be used as a new indicator to classify three types of hydration; negative, positive, and hydrophobic hydrations.