Estudo espectroscópico da interação entre análogos da α-lapachona e albumina sérica humana

Abstract

The interaction between human serum albumin (HSA) and 1,4-naphthoquinone derivatives ( LP LP4Cl , LP4Me , LP4F , LF , LF4Me , LF4Br , LF4Cl ), in buffered solution (PBS, pH = 7.4), was studied by spectroscopic methods such as ultraviolet-visible (UV -Vis), circular dichroism (CD) and steady-state and time resolved fluorescence emission. The values obtained for the quenching rate constant of the fluorescence emission of HSA (kq  1012 L/mol.s) suggest a static mechanism for the quenching process. The values of r, the distance between donor and acceptor, calculated by the theory of radiative energy transfer of Förster (r   to  nm) are smaller than 7 nm, which indicate the occurrence of a HSA/naphthoquinone strong interaction, which is independent of temperature. Through the use of fluorescence emission spectroscopy it was possible to verify that in the interaction HSA/naphthoquinones, the Tryptophan residue of HSA is located in a more hydrophobic environment when compared to free HSA. The values obtained for Ho and So are dependent on the substituent contained in the naphthoquinone, thus demonstrating that there is an influence of the naphthoquinone structure on its interaction with HSA. For positive values of Ho (endothermic process), the interaction occurred primarily by Van der Waals forces, in connection with the hydrophobic character. The negative values of Go (-24 to -30 kJ/mol) demonstrated the spontaneity of the interaction between naphthoquinones and HSA. The main interaction is resulting from a hydrophobic contact, but an electrostatic interaction cannot be excluded. Studies by circular dichroism spectroscopy revealed a decrease on the % of  -helix of HSA at 208 nm and 222 nm, as a function of increasing concentration of naphthoquinones. These effects can be attributed to the association of HSA/naphthoquinone which may induce conformational changes in HSA