Solvation and Rotational Dynamics of Coumarin-153 in Ethylammonium Nitrate Containing γ-Cyclodextrin

摘要

Carbohydrates are known to serve as an abundant, diverse, and reusable source of carbon, but their derivatization for industrial applications is still a challenging task because of their low solubility in solvents other than water; they are only sparingly soluble in common organic solvents as well as in weakly coordinating ionic liquids, such as l-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4). In this manuscript, we have shown that the solubility of cyclodextrins (CDs) in ethylammonium nitrate (EAN), at 298 K is comparable to that in water. This combination of EAN and γ-CD can be useful in many ways: (i) combination of both γ-CD and EAN can provide selectivity and resolution for separations that otherwise are not possible (vide infra); (ii) the combination of these two can find interesting applications in protein-detergent systems (vide infra), and (iii) they can improve chiral resolutions in simultaneous enantioseparation by capillary electrophoresis method (vide infra). In this study, we have characterized thissystem using the following techniques: By the use of the competitive fluorescence method we have shown that there is no inclusion complex formation between EAN and γ-CD. Using the Benesi Hildebrand equation, we have shown the variation of binding constant of the C- 153/γ-CD complex with temperature. The negative entropy and enthalpy changes indicated that the formation of the above C-153/γ-CD complex is entropically unfavorable and enthalpy-driven. We have also investigated the effect of temperature on the fluorescence anisotropy decays and the solvation dynamics of coumarin-153 (C-153) using picosecond time-resolved spectroscopy. Finally, we have shown that the aggregation behavior of γ-CD in EAN is entirely different from that in water, and the increase in average solvation time on going from neat EAN to EAN containing γ-CD is very small compared to the increase in solvation time on going from pure water to water containing γ-CD.