High-pressure Raman studies on aqueous protonated thiazole: presence of charge-enhanced C-H...O hydrogen bonds.
Close interactions of the charge-enhanced C-H...O type have been analyzed both experimentally and computationally in the protonated thiazole-water system. The formation of a weak hydrogen bond was directly evidenced by a low-frequency shift of the hydrogen-bonded aromatic C-H stretch in the protonated thiazole moiety. For pure thiazole, the pressure dependence of the C-H bands yielded blue frequency shifts. The peak frequency of the aromatic C-H stretch band of protonated thiazole in a dilute D2O solution possesses an unusual nonmonotonic pressure dependence, which indicates enhanced C-H...O hydrogen-bond formation at high pressure. We performed density functional theory calculations to predict the frequency shift of the C-H stretching vibrations. The reorganization of the hydrogen-bonded network may be one of the factors to induce the blue frequency shift to the red frequency shift.
Chang
Hai-Chou
HC
Department of Chemistry, National Dong Hwa University, Shoufeng, Hualien 974, Taiwan. hcchang@mail.ndhu.edu.tw
Jiang
Jyh-Chiang
JC
Lai
Wen-Wei
WW
Lin
Jui-San
JS
Chen
Guan-Ciao
GC
Tsai
Wei-Cheng
WC
Lin
Sheng Hsien
SH