Superoxide dismutases (SOD) are a group of enzymes that catalyze the dismutation of superoxide (O) radicals into molecular oxygen (O) and HO as a first line of defense against oxidative stress. Here, we show that glycine-functionalized copper(ii) hydroxide nanoparticles (Gly-Cu(OH) NPs) are functional SOD mimics, whereas bulk Cu(OH) is insoluble in water and catalytically inactive. In contrast, Gly-Cu(OH) NPs form water-dispersible mesocrystals with a SOD-like activity that is larger than that of their natural CuZn enzyme counterpart. Based on this finding, we devised an application where Gly-Cu(OH) NPs were incorporated into cigarette filters. Cigarette smoke contains high concentrations of toxic reactive oxygen species (ROS, >10 molecules per puff) including superoxide and reactive nitrogen species which lead to the development of chronic and degenerative diseases via oxidative damage and subsequent cell death. Embedded in cigarette filters Gly-Cu(OH) NPs efficiently removed ROS from smoke, thereby protecting lung cancer cell lines from cytotoxic effects. Their stability, ease of production and versatility make them a powerful tool for a wide range of applications in environmental chemistry, biotechnology and medicine.
Surface functionalization of nanoparticles (NPs) plays a crucial role in particle solubility and reactivity. It is vital for particle nucleation and growth as well as for catalysis. This raises the quest for functionalization efficiency and new approaches to probe the degree of surface coverage. We present an (in situ) proton nuclear magnetic resonance (H NMR) study on the ligand exchange of oleylamine by 1-octadecanethiol as a function of the particle size and repeated functionalization on Au NPs. Ligand exchange is an equilibrium reaction associated with Nernst distribution, which often leads to incomplete surface functionalization following "standard" literature protocols. Here, we show that the surface coverage with the ligand depends on the (i) repeated exchange reactions with large ligand excess, (ii) size of NPs, that is, the surface curvature and reactivity, and (iii) molecular size of the ligand. As resonance shifts and extensive line broadening during and after the ligand exchange impede the evaluation of H NMR spectra, one- and two-dimensionalF NMR techniques (correlation spectroscopy and diffusion ordered spectroscopy) with 1H,1H,2H,2H-perfluorodecanthiol as the fluorinated thiol ligand were employed to study the reactions. The enhanced resolution associated with the spectral range of the F nucleus allowed carrying out a site-specific study of thiol chemisorption. The widths and shifts of the resonance signals of the different fluorinated carbon moieties were correlated with the distance to the thiol anchor group. In addition, the diffusion analysis revealed that moieties closer to the NP surface are characterized by a broader diffusion coefficient distribution as well as slower diffusion.
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