Proton tunneling in hydrated biological tissues near 200 K.

We measure the protonic conductivity in water clusters adsorbed on intact samples of viable biological samples (corn embryo and endosperm, Artemia cysts, and Typha pollen) below room temperature. In the low-temperature region, the conductivity increases with temperature as exp T6, in agreement with prediction by the theory of dissipative quantum tunneling. We detect the onset of this effect near 180 K, where a glass transition in the hydrated protein matrix is known to take place. Above 220 K other transitions are superimposed onto this simple behavior.