Spectroscopic studies on the interaction of BSA and 5-spiro-3′-piperidine-2″-spiro-3″-indole-4′,2″-diones

The interaction of 5-spiro-3′-piperidine-2″-spiro-3″-indole-4′,2″-diones (SPSDs), an anti-tumor drug, to bovine serum albumin (BSA) in aqueous solution has been investigated by fluorescence spectra and ultraviolet–visible (UV–vis) spectra at pH 7.40. We have studied the effect of four substituents on the SPSD for the first time. The results of fluorescence titration indicated that SPSD can quench the intrinsic fluorescence of BSA and the quenching mechanism has been analyzed. The binding sites number (n), the binding constant (KA) and the spatial-distance (r) of SPSD with BSA without or with substituents on the benzene ring at 302 and 310 K have been calculated. The results show that the presence of the substituents increased the binding constant and changed the binding distance between the acceptor and the donor, which possibly results from the formation of SPSD–BSA complex. We have investigated the possible sub-domain on BSA where bind SPSD by displacement experiments. The effect of SPSD on the conformation of BSA has also been analyzed using synchronous fluorescence under experimental conditions.

The interaction between 5-spiro-3′-piperidine-2″-spiro-3″-indole-4′,2″-diones (SPSDs) and bovine serum albumin (BSA) was studied by fluorescence and UV–vis spectroscopy. The quenching mechanism, binding constants, and binding distance were determined. Conformation change of BSA was observed from synchronous fluorescence spectra. The comparison of binding potency of SPSD and BSA suggested that the substituents on the benzene ring influence the binding affinity of SPSD and BSA.Figure optionsDownload as PowerPoint slideHighlights
► We explored the interaction between BSA and SPSD by spectroscopic methods.
► The fluorescence quenching mechanism is combined quenching.
► The binding constants and binding sites were calculated.
► The conformation of BSA was changed affected by SPSD.
► The four substituents influenced the binding affinity of SPSD and BSA.