| Summary: | The present work introduces the solvent exchange procedure as a route for conversion of the Cu<sub>4</sub>I<sub>4</sub>L<sub>2</sub> complex, where the Cu<sub>4</sub>I<sub>4</sub> cluster core is coordinated with two P,N-ligands (L), into an aqueous colloid. The analysis of both colloidal and supernatant phases revealed some losses in CuI going from the initial Cu<sub>4</sub>I<sub>4</sub>L<sub>2</sub> complex to Cu<sub>2</sub>I<sub>2</sub>L<sub>3</sub>-based nanoparticles. The comparative analysis of IR, <sup>31</sup>P NMR spectroscopy, ESI mass-spectrometry and luminescence data argued for a contribution of the “butterfly”-like structures of the Cu<sub>2</sub>I<sub>2</sub> cluster core to Cu<sub>2</sub>I<sub>2</sub>L<sub>3</sub>-based nanoparticles, although the amorphous nature of the latter restricted structure evaluation from the PXRD data. The green luminescence of the colloids revealed their chemical stability under pH variations in the solutions of some amino acids and peptides, and to specify the temperature and concentration conditions triggering the oxidative degradation of the nanoparticles. The spin trap-facilitated ESR study indicated that the oxidative transformations were followed by the generation of reactive oxygen species (ROS). The physiological temperature level (310 K) enhanced the ROS generation by nanoparticles, but the ROS level was suppressed in the solution of GSH at pH = 7.0. The cytotoxicity of nanoparticles was evaluated in the M-HeLa cell line and is discussed in correlation with their cell internalization and intracellular oxidative transformations.
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