Abstract
Carbon nanodots (CNDs) have shown good antioxidant capabilities by scavenging oxidant free radicals such as diphenyl-1-picrylhydrazyl radical (DPPH•) and reactive oxygen species. While some studies suggest that the antioxidation activities associate to the proton donor role of surface active groups like carboxyl groups (–COOH), it is unclear how exactly the extent of oxidant scavenging potential and its related mechanisms are influenced by functional groups on CNDs’ surfaces. In this work, carboxyl and the amino functional groups on CNDs’ surfaces are modified to investigate the individual influence of intermolecular interactions with DPPH• free radical by UV-Vis spectroscopy and electrochemistry. The results suggest that both the carboxyl and the amino groups contribute to the antioxidation activity of CNDs through either a direct or indirect hydrogen atom transfer reaction with DPPH•.
Highlights
Carbon nanodots (CNDs) have been explored for applications in biomedicine, sensors, optoelectronics and catalysis [1,2,3,4], owing to discovered superior biocompatibility and outstanding optoelectronic properties [5,6]
Taking all the results together, we have proved that both carboxyl groups and amino groups
Taking all the results together, we have proved that both carboxyl groups and amino groups participate in the antioxidation process of CNDs based on a DPPH reduction assay
Summary
Carbon nanodots (CNDs) have been explored for applications in biomedicine, sensors, optoelectronics and catalysis [1,2,3,4], owing to discovered superior biocompatibility and outstanding optoelectronic properties [5,6]. CNDs were reported as good antioxidant agents in free radical scavenging [18]. CNDs’ properties as electron donors or electron acceptors endow them with potential applications in antioxidants or prooxidants [20], depending on the activities of the unpaired valence electrons. In order to test the hypothesis regarding functional groups, the carboxyl groups (–COOH) and amino groups(–NH2 ) of CNDs in DPPH radical scavenging, an idea was proposed to explore the roles of –COOH and –NH2 , respectively, in the process of antioxidation by blocking one of them using organic chemistry methodology. Carboxyl groups and amino groups on the CNDs were blocked by a modified EDC/NHS reaction and citraconic anhydride method, respectively. The antioxidation capability of the CNDs before and after blocking was evaluated by UV-Vis spectroscopic and electrochemical assays
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