Charge conductivity in peptides: Dynamic simulations of a bifunctional model supporting experimental data

Our previous finding and the given mechanism of charge and electron transfe r in polypeptides are here integrated in a bifunctional model involving ele ctronic charge transfer coupled to special internal rotations. Present mole cular dynamics simulations that describe these motions in the chain result in the mean first passage times for the hopping process of an individual st ep. This "rest and fire" mechanism is formulated in detail-i.e., individual amino acids are weakly coupled and must first undergo alignment to reach t he special strong coupling. This bifunctional model contains the essential features demanded by our prior experiments, The molecular dynamics results yield a mean first passage time distribution peaked at about 140 fs, in clo se agreement with our direct femtosecond measurements. In logic gate langua ge this is a strongly conducting ON state resulting from small firing energ ies, the system otherwise being a quiescent OFF state. The observed time sc ale of about 200 fs provides confirmation of our simulations of transport, a model of extreme transduction efficiency. It explains the high efficiency of charge transport observed in polypeptides. We contend that the moderate speed of weak coupling is required in our model by the bifunctionality of peptides. This bifunctional mechanism agrees with our data and contains val uable features for a general model of long-range conductivity, final reacti vity, and binding at a long distance.