Copper Coordination Compounds Conjugated to Gold Nanoparticles as Innovative Anticancer Drugs: Structural Investigation Carried Out by Synchrotron Radiation-Induced Techniques.

In recent years, the biomedical research of new metal-based anticancer drugs alternative to Pt(II) based complexes, has been extended to Au, Ru, and Cu metals. In particular, novel Cu-based antitumor agents have been studied according to the view that endogenous metals may be less toxic toward normal cells with respect to cancer ones. The synthesis strategy utilizes ligands having soft donor atoms such as aromatic sp2 hybridized nitrogen of pyrazolyl derivatives but these coordination compounds have low solubility in aqueous medium, making necessary to design specific approach for drug delivery. Conjugating the copper complexes with hydrophilic gold nanoparticles appears a promising way, suitable to improve their solubility and stability in water, and consequently raising their bioavailability. Furthermore, these complexes seem to provide slow and controlled release of copper complexes, making them suitable for targeted therapies. In this context, we investigated the molecular and electronic structure of a selection of Cu(II)-coordination compounds as pristine or bonded to Au NPs, exploiting SR-XPS and Cu-K edge XAFS spectroscopy in order to understand the electronic state and local coordination chemistry around Cu as a function of molecular complexes. The Cu K-edge XAFS data were analysed in the near edge (XANES) and extended (EXAFS) regions. The pristine ligands were also studied for sake of comparison. The combined use of complementary probes (XPS, XANES, EXAFS) is providing an accurate and reliable understanding of local coordination chemistry and electronic structure of Cu(II)-coordination compounds which appear elementary building blocks suitable to realize nanoassemblies by conjugation with hydrophilic AuNPs, along the route already successfully tested by some of us on model systems. Here the results of multidisciplinary characterization of Cu(II)-coordination compounds and preliminary results on coordination compound/AuNPs interactions will be presented, discussing the further steps for the research.