Thermal Generation and Mobility of Charge Carriers in Collective Proton Transport in Hydrogen-Bonded Chains

Abstract

The transport of protons in hydrogen-bonded systems is a long standing problem which has not yet obtained a satisfactorily theoretical description. Although this problem was examined first for ice, it is relevant in many systems and in particular in biology for the transport along proteins or for proton conductance across membranes, an essential process in cell life. This broad relevance makes the study of proton conduction very appealing. Since the original work of Bernal and Fowler on ice¹, the idea that the transport occurs through chains of hydrogen bonds has been well accepted. Such “proton wires” were invoked by Nagle and Morowitz² for proton transport across membranes proteins and more recently across lipid bilayers³. In this report, we assume the existence of such an hydrogen-bonded chain and discuss its consequences on the dynamics of the charge carriers. We show that this assumption leads naturally to the idea of soliton transport and we put a special emphasis on the role of the coupling between the protons and heavy ions motions. The model is presented in section II. In section III we show how the coupling affects strongly the dynamics of the charge carriers and in section IV we discuss the role it plays in the thermal generation of carriers. The work presented in section III has been performed in 1986 and 87 with St Pnevmatikos and N. Flytzanis4 and was then completed in collaboration with D. Hochstrasser and H. Bilttner⁵. Therefore the results presented in this part are not new but we think that they are appropriate in the context of this multidisciplinary workshop because they provide a rather complete (and tractable) example of the solition picture for proton conduction.