Molecular Interactions of Cooper Complexes with Cell Membranes Models

Victor G. Morgado¹ and Antonio José da Costa Filho¹

¹Department of Physics - FFCLRP, University of São Paulo, São Paulo, SP (email:[email protected]) 

This project investigates, at the molecular level, how two structurally distinct copper complexes—bis(2,9-dimethyl-1,10-phenanthroline)copper(I) ([Cu(Neo)₂]⁺) and bis(1,10-phenanthroline)copper(II) ([Cu(phen)₂]²⁺)—interact with model biological membranes. These coordination compounds exhibit remarkable oncological potential, displaying cytotoxic mechanisms such as DNA cleavage, apoptosis induction in tumor cells, and reactive oxygen species (ROS) generation, with efficacy rivaling conventional drugs like cisplatin. However, their biological performance depends strictly on their ability to cross cellular membranes and interact with lipid structures, directly influencing bioavailability, cellular uptake, and selective toxicity. Obtaining a detailed molecular understanding of these drug-lipid interactions remains a major challenge due to membrane complexity. To address this, this study uses biomimetic membrane models composed of phospholipids, such as DMPC, as well as mixed lipid systems. Molecular interactions are characterized using complementary biophysical techniques, including differential scanning calorimetry (DSC), fluorescence spectroscopy, continuous-wave electron paramagnetic resonance (EPR) with spin-labeled lipids, and optical/fluorescence microscopy. Initial biophysical assays in DMPC model membranes revealed that both complexes interact preferentially with the bilayer interface. Fluorescence quenching of NBD by [Cu(phen)₂]²⁺ confirmed strong interfacial partitioning, while [Cu(Neo)₂]⁺ induced a subtle quenching of Laurdan fluorescence along with an increase in Generalized Polarization (from 0.1446 to 0.2551), indicating decreased interfacial hydration and enhanced lipid packing. Furthermore, EPR spin-labeling (TEMPO, 5-PC, 10-PC, and 16-PC) demonstrated minimal perturbation in the hydrophobic core, confirming that the rigid phenanthroline structure confines the complexes to the membrane surface. These results provide fundamental insights into copper-complex membrane interactions, guiding the rational design of novel metal-based chemotherapeutics with optimized selectivity.

The authors acknowledge the financial support from the National Institute of Science and Technology in Innovative Research in Health Sciences – from Nanotechnology to Artificial Intelligence (INCT PICS) sponsored by CNPq (grant 408417/2024-2), CAPES (grant 88887.197686/2025-00), and FAPESP (grant 2025/26818-7). FAPESP also sponsored the project via grants 2023/04532-9.