Department of Chemistry, Iowa State University, Ames, Iowa 50011-3111, USA.
J Phys Chem B. 2011 Sep 15;115(36):10707-14. doi: 10.1021/jp200080s. Epub 2011 Aug 24.
The photophysical properties of cyclocurcumin in various solvents are studied for the first time to shed light on the nonradiative processes of the parent compound, curcumin, which has a range of medicinal properties. Steady-state fluorescence and fluorescence-excitation spectra of cyclocurcumin in polar aprotic solvents are strongly dependent on excitation (λ(ex)) and emission (λ(em)) wavelength, respectively. The fluorescence quantum yield also depends on λ(ex) and increases with the viscosity of the medium. Time-resolved studies show nonexponential fluorescence decay in all solvents studied. The two fluorescence decay components of cyclocurcumin in alcohols exhibit a strong dependence on viscosity and temperature. NMR spectroscopy indicates that cyclocurcumin is entirely in the trans form with respect to the C6-C7 double bond in methanol, chloroform, and acetone. It is suggested that at least two conformational isomers about another single bond (C5-C6 or C7-C1″ or both) and that trans-to-cis isomerization about the C6-C7 double bond of these isomers provide the most likely means of rationalizing the steady-state spectra and the nonradiative decay mechanisms in both protic and aprotic polar solvents.
首次研究了环巴库林在各种溶剂中的光物理性质，以期阐明母体化合物姜黄素的非辐射过程，姜黄素具有多种药用特性。在极性非质子溶剂中，环巴库林的稳态荧光和荧光激发光谱分别强烈依赖于激发（λ（ex））和发射（λ（em））波长。荧光量子产率也取决于λ（ex），并随介质粘度的增加而增加。时间分辨研究表明，在所有研究的溶剂中，荧光衰减均非指数衰减。在醇中，环巴库林的两个荧光衰减分量强烈依赖于粘度和温度。NMR 光谱表明，在甲醇、氯仿和丙酮中环巴库林在 C6-C7 双键处完全为反式。据推测，至少有两个构象异构体关于另一个单键（C5-C6 或 C7-C1″或两者），并且这些异构体的 C6-C7 双键的顺式-反式异构化提供了合理化在质子和非质子极性溶剂中的稳态光谱和非辐射衰减机制的最可能的方法。
