title: Effect of water molecules on the fluorescence enhancement of Aflatoxin B1 mediated by Aflatoxin B1:beta-cyclodextrin complexes. A theoretical study.
abstract: 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.
authors.affiliation: Instituto de Ciencias Físicas, UNAM, PO Box 48-3, 62251, Cuernavaca Morelos, México. grg@fis.unam.mx
authors.forename: Guillermo
authors.initials: G
authors.lastname: Ramírez-Galicia
authors.forename: Ramón
authors.initials: R
authors.lastname: Garduño-Juárez
authors.forename: M
authors.initials: M
authors.lastname: Gabriela Vargas
mesh_terms: D016604:Aflatoxin B1 / Q000737:chemistry* / Q000378:metabolism; D005453:Fluorescence; D046911:Macromolecular Substances / Q000737:chemistry; D015394:Molecular Structure; D011789:Quantum Theory; D014867:Water / Q000737:chemistry*; D047392:beta-Cyclodextrins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D047392:beta-Cyclodextrins; D014867:Water; D016604:Aflatoxin B1