Tight binding density functional theory was used to investigate the effects of a water environment on the interaction of amino-acids with a single wall carbon nanotube (SWCNT). We selected four amino acids (Gly, Ser, Arg, and Ile) according to their polarity and hydrophobicity indexes. The changes in the bond distances, in vacuum and water, are seen to be directly related to the amino acids hydrophobicities. The variations in binding energies are seen to be greater for non-polar amino acids. The interaction of the neutral and zwitterionic forms of Gly with the SWCNT in water were also analyzed and discussed. (C) 2011 Elsevier B.V. All rights reserved.