Methyl radicals interacting with silica gel surfaces have been investigated by means of DFT and direct ab-initio molecular dynamics (MD) methods using cluster models. Four typical binding sites of CH3 on the cluster models were found in the geometry optimization from several initial geometries of CH3 around the silica gel clusters. These were two silanol Si-OH sites and two siloxane Si-O-Si sites. In both sites, magnitude of hyperfine coupling constants of the methyl radical (a(H)) was smaller than that of free CH3 (a(H) = 23.04 G). Temperature effects on aH of the methyl radical were investigated by means of the direct ab-initio MD method. The hyperfine coupling constant of CH3 interacting with the SiOH group decreased with increasing temperature. The methyl radical interacting with alkali metal supported silica gel was also investigated for comparison. The electronic states of methyl radicals on silica gel were discussed on the basis of theoretical results. (C) 2009 Elsevier B.V. All rights reserved.