Ramírez-Galicia Guillermo, Garduño-Juárez Ramón, Gabriela Vargas M
Instituto de Ciencias Físicas, UNAM, PO Box 48-3, 62251, Cuernavaca Morelos, México.
Photochem Photobiol Sci. 2007 Jan;6(1):110-8. doi: 10.1039/b614107b. Epub 2006 Nov 24.
In order to explain the observed fluorescence enhancement of Aflatoxin B1 (AFB1) when forming AFB1:beta-cyclodextrin (AFB1:beta-CD) inclusion complexes, we have performed a theoretical (quantum chemistry calculations) study of AFB1 and AFB1:beta-CD in vacuum and in the presence of aqueous solvent. The AM1 method was used to calculate the absorption and emission wavelengths of these molecules. With the help of density functional theory (DFT) and time-dependent DFT (TDDFT) vibrational frequencies and related excitation energies of AFB1 and AFB1.(H2O)m = 4,5,6,11 were calculated. On the basis of these calculations we propose a plausible mechanism for the fluorescence enhancement of AFB1 in the presence of beta-CD: (1) before photoexcitation of AFB1 to its S1 excited state, there is a vibrational coupling between the vibrational modes involving the AFB1 carbonyl groups and the bending modes of the nearby water molecules (CG + WM); (2) these interactions allow a thermal relaxation of the excited AFB1 molecules that results in fluorescence quenching; (3) when the AFB1 molecules form inclusion complexes with beta-CD the CG + WM interaction decreases; and (4) this gives rise to a fluorescence enhancement.
为了解释黄曲霉毒素B1（AFB1）形成AFB1:β-环糊精（AFB1:β-CD）包合物时观察到的荧光增强现象，我们对AFB1以及AFB1:β-CD在真空和存在水溶剂的情况下进行了理论（量子化学计算）研究。采用AM1方法计算这些分子的吸收和发射波长。借助密度泛函理论（DFT）和含时密度泛函理论（TDDFT）计算了AFB1以及AFB1·(H2O)m（m = 4、5、6、11）的振动频率和相关激发能。基于这些计算结果，我们提出了一种在β-环糊精存在下AFB1荧光增强的合理机制：（1）在AFB1光激发至其S1激发态之前，涉及AFB1羰基的振动模式与附近水分子的弯曲模式之间存在振动耦合（CG + WM）；（2）这些相互作用使激发态的AFB1分子发生热弛豫，导致荧光猝灭；（3）当AFB1分子与β-环糊精形成包合物时，CG + WM相互作用减弱；（4）这导致荧光增强。
