Some thoughts on the existence of ion and water channels in highly dense and well-ordered CH3-terminated alkanethiol self-assembled monolayers on gold

Through extensive and systematic reviewing of literatures, this paper presents some thoughts on the existence of ion and water channels in highly dense and well-ordered CH3-terminated alkanethiol self-assembled monolayers (CnSH-SAMs) on gold: (1) based on the combinational effect of “the van der Waals interaction between the neighbor hydrocarbon chains”, “the framework size of CnSH molecule” and “the surface lattice structure of CnSH-SAMs on gold”, a simple ideal model of the close-packed CnSH-SAMs is proposed for the first time. The channel with an appropriate diameter of about 3 Å (∼3 Å) existing in SAMs on Au is deduced, which is found large enough for ions and water molecules to permeate; (2) through summarizing the literature reports for various experiments (e.g. scan microscopy techniques and electrochemical methods, etc.), the existence of the ion and water channels (∼3 Å) in close-packed CnSH-SAMs is verified; (3) furthermore, the effect of the ions and water molecules permeation on the studies of the SAMs’ electron tunneling process is discussed. This simple ideal model of the close-packed CnSH-SAMs established by us may clarify the controversies about the permeation mechanism of ions and water molecules in CnSH-SAMs.