Study of the interaction of flavonoids with 3-mercaptopropionic acid modified CdTe quantum dots mediated by cetyltrimethyl ammonium bromide in aqueous medium.

Flavonoids are polyphenols that help the maintenance of health, aiding the prevention of diseases. In this work, CdTe QDs coated with 3-mercaptopropionic acid (3MPA), with an average size of 2.7nm, were used as photoluminescence probe for flavonoids in different conditions. The interaction between 14 flavonoids and QDs was evaluated in aqueous dispersions in the absence and in the presence of cetyltrimethylammonium bromide (CTAB). To establish a relationship between photoluminescence quenching and the concentration of flavonoids, the Stern-Volmer model was used. In the absence of CTAB, the linear ranges for quercetin, morin and rutin were from 5.0×10 ^-6 molL ^-1 to 6.0×10 ^-5 molL ^-1 and from 1.0×10 ^-5 molL ^-1 to 6.0×10 ^-4 molL ^-1 for kaempferol. The sensibility of the Stern-Volmer curves (K _s ) indicated that quercetin interacts more strongly with the probe: K _{s quercetin} >K _{s kaempferol} >K _{s rutin} >K _{s morin} . The conjugation extension in the 3 rings, and the acidic hydroxyl groups (positions 3'and 4') in the B-ring enhanced the interaction with 3MPA-CdTe QDs. The other flavonoids do not interact with the probe at 10 ^-5 molL ^-1 level. In CTAB organized dispersions, K _{s 3-hydroxyflavone} >K _{s 7-hydroxyflavone} >K _{s flavona} >K _{s rutin} in the range from 1.0×10 ^-6 molL ^-1 to 1.2×10 ^-5 molL ^-1 for flavones and of 1.0×10 ^-6 molL ^-1 to 1.0×10 ^-5 molL ^-1 for rutin. Dynamic light scattering, conductometric measurements and microenvironment polarity studies were employed to elucidate the QDs-flavonoids interaction in systems containing CTAB. The quenching can be attributed to the preferential solubility of hydrophobic flavonoid in the palisade layer of the CTAB aggregates adsorbed on the surface of the 3MPA CdTe QDs.
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