Indication of a very large proton diffusion in ice i_h. 2. Fluorescence quenching of flavin mononucleotide by protons

A time-resolved emission technique was employed to study the effect of excess protons on the fluorescence quenching process of flavin mononucleotide (FMN) in methanol-doped ice samples. We found that an excess of protons in ice has a very large effect on the fluorescence quenching whereas in liquid water the proton fluorescence quenching is rather small. We analyzed the experimental data using the Smoluchowski diffusion-assisted binary collision model. Under certain assumptions and approximations, the calculated proton diffusion constant in ice in the range of 245-265 K is about 10 times that of water at 295 K.