[The reactions between acidic phenolsulfonphthaleins and human serum albumin]

The reactions between HSA and acidic phenolsulfonphthaleins, including phenol red, cresol red, chlorophenol red, bromocresol purple and m-cresol purple, have been investigated by fluorescence spectrometry. The experiments showed that all of the selected acidic phenolsulfonphthaleins strongly quenched the fluorescence produced by HSA, and this fluorescence quenching could be interpreted in terms of statistic quenching. From the calculation results of binding constants K for these dyes at various temperatures, it could be found that the increase in the functional groups numbers of dyes molecules resulted in an increase in K, while the increase in reaction temperature led to a decrease in K. The interactions between dyes and HSA were attributed to static-electricity gravitation, which was confirmed by the calculation results of enthalpy and entropy for these reactions. According to the non-radiation energy transfer theory, the distances and energy transfer efficiencies between dyes and protein at various temperatures were obtained. These results further supported the conclusion that these reactions belonged to the single static quenching caused by the energy transfer.