Reduced cytotoxicity and boosted antibacterial activity of a hydrophilic nano-architecture magnetic nitrogen-rich copper-based MOF

A new category of antibacterial compounds is copper-based metal-organic frameworks which suffer from cyto-toxicity caused by the fast release of copper ions and low hydrophilicity. Their post-synthetic modification with nitrogen-rich dendrimers is suggested to resolve the problems. We synthesized a magnetic nitrogen-rich N-doped copper-based metal-organic framework as a post-synthetically modified metal-organic framework through four steps:1) synthesize the third generation of magnetic polyamidoamine dendrimer containing the core of iron oxide nanoparticles and amine branches, 2) synthesize N-doped copper-based metal-organic framework through polyvinylpyrrolidone-assisted strategy, 3) modification of the framework with L-cysteine, and 4) post-synthetic modification of L-cysteine modified metal-organic framework by as-prepared magnetic dendrimer. All of the synthesis steps were studied with Powder X-ray diffraction, Fourier-transform infrared spectroscopy, zeta -potential, ultraviolet-visible spectroscopy, field emission scanning electron microscopy/energy-dispersive X-ray spectroscopy, and CHNS elemental analysis. The water contact angles of 60o for N-doped copper-based metal -organic framework, 38o for L-cysteine modified metal-organic framework, and 35o for the framework which was modified with both L-cysteine and dendrimer confirmed increasing hydrophilicity of the metal-organic frame-work after the post-synthetic modifications. Reduced cytotoxicity (57.5% of cell viability within 24 h), controlled release of copper ions (1.7 mu g. mL-1 within 96 h), and boosted antibacterial activity (inhibition zone diameter of 11 mm on E. coli and 14 mm on S. aureus) were observed for the N-doped copper-based metal-organic framework modified with both L-cysteine and magnetic dendrimer compared to the N-doped copper-based metal-organic framework that was only modified with L-cysteine which can be attributed to the presence of nitrogen-rich dendrimer.