[Protonation of acridine in a hydrated protein matrix]

Fluorescence of polycrystaline acridine in the matrix of solid alpha-chymotrypsin was studied at different humidities of the atmosphere. The fluorescence was not changed when the mixture was extensively dried. At intermediate and high humidities two consecutive processes proceed: 1) the solid-state dissolution of acridine crystals in the protein matrix and 2) the capture of protons by dispersed acridine molecules due to the proton transport through H-bound chains of water molecules from the protein proton-donor groups.