We have designed a carbon nanotube that is selectively permeable to monovalent cations, binds divalent cations and rejects anions. The nanotubes, with an effective radius of 4.53 angstrom and length of 36 angstrom, are terminated with hydrogen atoms and are exohydrogenated in two regions near the entrance and exit. Using molecular and stochastic dynamics simulations we examine the free energy, current-voltage-concentration profiles and ion binding sites. The characteristics of this channel are comparable to the antibiotic gramicidin-A, but the potassium current is six times larger. At 40 mM calcium concentration the current is reduced from 26 pA to 4 pA due to a calcium ion binding at the channel entrance. (C) 2010 Elsevier B. V. All rights reserved.