Rhenium(I) complexes featuring naphthalimide ligands: chemical properties and interactions with biomolecules

• Compounds fac -[Re(CO) 3 (py-NI) 2 Cl] 1 and fac -[Re(CO) 3 (py-NI-Br) 2 Cl] 2 are presented • 1 and 2 have spectroscopic behaviour dominated by the naphthalimide characteristics • The solvatochromic profile of compounds 1 and 2 is depicted • Experimental and in silico data unraveled their interaction profile with DNA • Experimental and in silico data unraveled their interaction profile with HSA This work reports on two novel bis -naphthalimide Re I complexes of general formula fac -[Re(CO) 3 (py-NI-R) 2 Cl] (NI-py = N-(4-pyridyl)-1,8-naphthalimide; R = H ( 1 ) or Br ( 2 )). IL (intraligand) and MLCT (metal-to-ligand charge transfer) transitions dominate their absorption spectra. Photoluminescence data revealed that the lower energy state, responsible for their photoluminescence, has an IL character, matching the photoluminescence behavior of the free ligands. The solvatochromic profile, employed to help understand the intermolecular interaction of the complexes in solution, showed that hydrogen bonding and π-stacking are the principal factors that keep the solute-solvent interactions. The interaction showed that there is a competition between the complexes intercalation (K b ( 1 ) = 4.87±0.03·10 4 M −1 ; K b ( 2 ) = 3.95±0.05·10 4 M −1 ) and minor groove binding (K b ( 1 ) = 7.25±0.01·10 4 M −1 ; K b ( 2 ) = 5.15±0.05·10 4 M −1 ), probably due to the relative positioning of the two coordinated naphthalimide ligand, as indicated by in silico calculations. As the complexes retain the electronic characteristics of the ligands, with short-lived and relative high-energy 1 IL excited states, no DNA photocleavage was observed. With the HSA, we have obtained higher association constants for both complexes (K α ( 1 ) = 0.26±0.01·10 5 M −1 ; K α ( 2 ) = 0.45±0.05·10 5 M −1 ) due to hydrophobic interactions and hydrogen bonds between the complex and the protein.