Structures and properties in different media of N,N-(diethylcarbamothioyl)furan-2-carboxamide: A ionophore for sensor membranes

X-ray diffraction, Nuclear Magnetic Resonance and DFT calculations have been used to shed light over the structure and properties of N,N-(diethylcarbamothioyl)furan-2-carboxamide, a non-conventional ionophore for sensor applications. The attention was focused over the molecular conformation in three different phases - i.e. solid state, solution and gas - before and after the interaction with a heavy metal ion, thus simulating the behaviour of the molecule as a ionophore in a typical Ion Selective Electrode membrane. The condensed phase structure, although was not used as a starting guess for the gas phase model, fits one of the two possible conformers suggested for the gas phase. The structure transition solid - liquid - gas with a substantial identity preservation, makes the suggestion of an analogous situation in the liquid phase possible. As a consequence a detailed interaction mechanism between the title compound and the Pb2+ ion in solution has been depicted. Even if this study is confined to the sole molecule, without considering the simultaneous presence of the other ingredients of the membrane cocktail, similarities and differences among the different structures help the understanding of the ionophore behaviour in the electrode with a particular focus on the so called activation procedure, a pre-requisite of any electrochemical analysis performed by means of this type of sensors. (c) 2009 Elsevier B.V. All rights reserved.