Densità di spin e dinamica di spin dei complessi di Cu (II). Implicazioni per la sviluppo di sonde diagnostiche per la risonanza magnetica.

Cu(II) coordination chemistry is of significant interest due to copper's widespread applications. Recently the use of paramagnetic Cu(II) coordination compounds has been suggested in the context of the development of novel MRI contrast agents. To this end, one key parameter is the determination of the metal coordination environment and the electronic relaxation properties. This study utilizes Electron Paramagnetic Resonance (EPR) spectroscopy to comprehensively examine how different ligand types -(tris(2aminoethyl)amine (TREN), 1,4,7-triazacyclononane (TACN), and dipicolinate - that coordinate the copper cation, influence coordination and symmetry in solution. Spin Hamiltonian parameters were determined by means of X- and Q-band Continuous Wave (CW) and Pulse EPR and were found to be highly dependent on the type of ligand and on the solution pH, revealing subtle variations in Cu(II) solution coordination chemistry. The temperature dependence, between 5 and 70 K, of electron spin–lattice relaxation and electron coherence measured at Q-band was analysed for a series of copper(II) complexes with varying ligands and geometry, with emphasis on Cu(II) tripodal ligands. The large data set acquired in this study may be of relevance in understanding the effect of the electron spin relaxation on the relaxivities of Cu(II) complexes and the mechanisms that control the efficiency of contrast agents used in diagnostic magnetic resonance imaging (MRI) for the development of alternatives to Gd(II) complexes.