Excited-StateProton Transfer of Photoacids Adsorbedon Biomaterials.

Theinteraction between a photoacid (8-hydroxy-1,3,6-pyrenetrisulfonate,HPTS) and the surfaces of biomaterials and the diffusion of protonsalong the biomaterial surfaces were examined by following the excited-stateproton transfer (ESPT) from the photoacid, adsorbed on the surfaces,to water molecules next to it. We chose two different types of biomaterialsurfaces, hydrophobic insulin amyloid fibrils and hydrophilic cellulosesurfaces. With the help of steady-state and time-resolved fluorescencetechniques, we found that the rate of ESPT from HPTS on insulin fibrilsto adjacent water molecules is about 1/10thatin bulk water. However, the proton geminate recombination takes placewith an efficiency similar to that in bulk water. ESPT from HPTS inwet cellulose to water depends on the weight percentage of water adsorbedby the cellulose. In a semidry sample (<100% weight percentageof water), the ESPT rate is rather low and thus the quantum efficiencyof the ESPT is also low within the excited-state lifetime. When thewater content is higher, the ESPT rate is almost that of bulk water.We explain these results by the existence of pools of water in celluloseof high water content, in which the triple-negatively charged HPTSmolecules desorb from the cellulose surface to these pools. The useof HPTS has allowed us to examine the biological surface and its interactionwith water molecules, while obtaining important information regardingthe hydration state of the surface that otherwise could not have beenobtained. The model that we propose here for the use of photoacids to followthe hydrated state of a given surface is a promising new method ofexamining the interaction of water molecules with biological surfaces. [ABSTRACT FROM AUTHOR]