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Classical molecular dynamics simulations combined with adaptive biasing force samplings have been performed to investigate the dynamic behaviors and transport properties of ethanol molecules through transmembrane cyclic peptide nanotubes(CPNTs)with various radii,i.e.,8×(WL-)3,4,5/POPE.The results show that ethanol molecules fill spontaneously the octa-and deca-CPNTs except for the hexa-CPNT.In the octa-CPNT,ethanol molecules are trapped at dividual gaps with their carbon skeletons perpendicular to the tube axis,forming a broken single-file ethanol chain.As the channel radius increases,ethanol molecules inside the deca-CPNT tend to form a tubular layer and the hydroxyl groups mainly stretch towards the tube axis.Computations of diffusion coefficients indicate that ethanol molecules in the deca-CPNT diffuse~4.5 times as fast as in a(8,8)SWNT with a similar tube diameter.The osmotic(pf)and diffusion permeability(pd)of the deca-CPNT transporting ethanol reach 25.84 and 4.29(A)3 ns-1,respectively.The distributions of the gauche and trans conformers of ethanol molecules in the octa-and deca-CPNTs are quite similar,both with about 57%gauche conformers.The profiles of potential of mean force(PMF)can well explain the movement behaviors of ethanol molecules in these two CPNTs.The results uncover interesting and comprehensive mechanisms underlying the diffusing characteristics of ethanol in a CPNT.