Analytical Sciences

Abstract − Analytical Sciences, 24(10), 1369 (2008).

NMR Study for Self-aggregation of 1-Butyl-3-methylimidazolium Bromide in Aqueous Solution
Hiroyuki TSUCHIYA,*1 Mamoru IMANARI,*2 Shinji ISHIHARA,*2 Masamichi NAKAKOSHI,*3 Keiko NISHIKAWA,*2 Hiroko SEKI,*4 and Mitsuru TASHIRO*1
*1 Graduate School of Chemistry, Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-8506, Japan
*2 Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan
*3 Chemical Analysis Center, Yokohama National University, 79-1 Tokiwadai, Hodogaya, Yokohama 240-8501, Japan
*4 Chemical Analysis Center, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan
Self-aggregation of 1-butyl-3-methylimidazolium bromide ([bmim]Br) in D2O has been investigated using NMR spectroscopy. The 1H spin-lattice relaxation times (T1) of the [bmim]+ increased with the decrease of concentration in the range of 0.1 - 3.0 mol dm-3 as expected, however, in contrast, the 1H-T1 decreased below 0.1 mol dm-3. The estimated 13C-activation energies indicated that the rotational mobility of the butyl-chain was more restricted than that of the imidazole ring at 0.1 mol dm-3, whereas such a significant difference was not observed at 3.0 mol dm-3. These results suggest that [bmim]+ forms micelle-like aggregations below 0.1 mol dm-3 in D2O.