Kinetics of partly diffusion controlled reactions XXII: Competition between long-distance energy transfer and collision quenching — first results

Abstract

In the case of immunological assays, it is possible to use molecular emission spectroscopy techniques based on long-distance electronic energy transfer occurring between different fluorescent donors and acceptors, located in different proteins. Moreover, the same type of transfer can occur with the same protein between identical chromophores, which can modify the sensitivity of the titration. To check that these two types of transfer exist, we have developed a fluorescence quenching technique based on reactions partially controlled by molecular transport phenomena. We have shown that in fact this is the case, and our experimental results are consistent with the kinetics model developed, which is based on coupling between long-distance energy transfer and diffusional quenching. When the quenching of an electronically excited donor occurs through a time-dependent process, the excitation of the donor chromophore by long-distance energy transfer is in fact at the origin of the system re-initialization, which, in the case of diffusion-controlled reactions, implies an apparent increase in the quenching rate. The model we developed takes into account this re-initialization step and has been experimentally checked by adding a variable number of fluorescein molecules to the same protein followed by studying the fluorescence quenching by iodide ions.