The UV absorption of the 1:1 complex of Pb(II) with caffeate in aqueous solution has been studied theoretically. From different possible structures of complexes, the calculated optical electronic transitions with a polarizable continuum model using the time-dependent density functional theory (B3LYP) show that Pb(II) coordinates with the carboxylate function. Moreover, the theoretical spectral changes observed according to the number of water molecules coordinated to Pb(II) suggest the formation of [Pb(H(2)CA)(H2O)(4)](+), a monodentate complex with a pentacoordinated metal in a hemidirected arrangement. (c) 2007 Elsevier B.V. All rights reserved.