Self-assembled monolayers of metal complexes attached to gold electrodes

• Main Author: Calatayud Sanz, Maria Pilar
• Published: University of Edinburgh 2009
• Subjects: 541.37
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.642311

In this thesis, ten different ligands were designed and synthesized in such a way as to provide metal containing SAMs. The metal binding sites of these ligands are derivatives of the tripodal ligand tris(2-pyridylmethyl)amine (TPA) and the tridentate amine bis(2-pyridylmethyl)amine (BPA), which have good molecular recognition properties in solution. As interface separating the electrode from the metal binding site and gold anchor group we have chosen a thiophenyl, thioethyl and thioctic acid groups. Electrochemical studies with [Fe(CN)₆]^3-/4- as redox probe in solution were carried out on SAMs of the TPA thioctic acid derivative L4  and its complexes Cu-L4, Zn-L4 and Fe-L4. Monolayers containing redox active Cu(II/I) ions accelerated the electron-transfer reaction (<i>k</i>_app= 2.78 x 10^-2 cm/s) more than those containing Zn(II) (<i>k</i>_app = 1.51 x 10^-4 cm/s) and Fe(II) (<i>k</i>_app= 1.40 x 10^-3 cm/s) ions. This is consistent with a mechanism for electron-transfer in which the Cu ions exit in different coordination environments and with different redox potentials, and are rapidly undergoing interconversion. The ability of this system to facilitate the electron-transfer process to the redox probe was used to develop a new cyanide sensor. Addition of cyanide ions increases the blocking behaviour of the SAM, suggesting the elimination of Cu from the SAM to form [Cu(CN)_n]^(n-1)-complexes. The cyanide detection limit was found to be 1 nM. Electrodes modified with the binucleating ligand 2,6-bis[bis(2-pyridylmethyl)amino-methyl]phenol thioctic acid derivative (bearing two BPA arms) L7 were also investigated. Metal containing SAMs can influence the electron-transfer process through the SAM to a solution containing a redox probe. This property can be used to develop new anion sensors in aqueous system.