A copper(II) thiosemicarbazone complex built on gold for the immobilization of lipase and laccase

A self-assembled monolayer (SAM) of imidazole-2-carbaldehyde thiosemicarbazone (H(2)ImTSC) on gold was formed and characterized by ATR-FTIR, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS). The self-assembly of the ligand through its thioenolate group was confirmed by ToF-SIMS and the presence of XPS peaks at 161.9 (S(2p1/2)) and 163.1 eV (S(2p3/2)). The two nitrogen donor atoms of self-assembled HImTSC were able to coordinate (kappa(2)-N,N) copper(II) when set to interact with a CuCl(2) solution upon a second deprotonation of the ligand. This way, two types of modified gold sheets for the immobilization of lipase and laccase were obtained: (a) SAM of the ligand on gold (Au-HImTSC), and (b) SAM of HImTSC with a second monolayer of copper(II) (Au-ImTSC-Cu(II)). The highest immobilization of enzyme was achieved for laccase on Au-ImTSC-Cu(II) according to XPS and enzymatic activity determinations. Copper(II) played a an important recognition role through coordination to the enzyme and/or electrostatic interactions. Nevertheless, the positively charged surface of Au-ImTSC-Cu(II) affected the activity of laccase. (C) 2010 Elsevier Inc. All rights reserved.