Polydopamine Nanoparticles Prepared Using Redox-Active Transition Metals

Abstract

Autoxidation of dopamine to polydopamine by dissolved oxygen is a slow process that requires highly alkaline conditions. Polydopamine can be formed rapidly also in mildly acidic and neutral solutions by using redox-active transition-metal ions. We present a comparative study of polydopamine nanoparticles formed by autoxidation and aerobic or anaerobic oxidation in the presence of Ce(IV), Fe(III), Cu(II), and Mn(VII). The UV–vis spectra of the purified nanoparticles are similar, and dopaminechrome is an early intermediate species. At low pH, Cu(II) requires the presence of oxygen and chloride ions to produce polydopamine at a reasonable rate. The changes in dispersibility and surface charge take place at around pH 4, which indicates the presence of ionizable groups, especially carboxylic acids, on their surface. X-ray photoelectron spectroscopy shows the presence of three different classes of carbons, and the carbonyl/carboxylate carbons amount to 5–15 atom %. The N 1s spectra show the presence of protonated free amino groups, suggesting that these groups may interact with the π-electrons of the intact aromatic dihydroxyindole moieties, especially in the metal-induced samples. The autoxidized and Mn(VII)-induced samples do not contain metals, but the metal content is 1–2 atom % in samples prepared with Ce(IV) or Cu(II), and ca. 20 atom % in polydopamine prepared in the presence of Fe(III). These differences in the metal content can be explained by the oxidation and complexation properties of the metals using the general model developed. In addition, the nitrogen content is lower in the metal-induced samples. All of the metal oxidants studied can be used to rapidly prepare polydopamine at room temperature, but the possible influence of the metal content and nitrogen loss should be taken into account.

Catalytic Enhancement of Inductively Heated Fe3O4 Nanoparticles by Removal of Surface Ligands

“…To elucidate the difference in performance between the two phase transfer processes, a series of surface characterizations (TGA, FTIR, neutron scattering, and XPS) were performed. TGA can quantify the extent of the phase transfer since it is known that hydrophilic films can be deposited around colloidal NPs for certain phase transfer agents, such as polydopamine [29] . The TGA results are shown in Table 2 and Figure S6 for the as‐synthesized and phase transferred samples.…”

Polydopamine as a stable and functional nanomaterial

“…Adding boric acid to dopamine solutions after a given oxidation and self-assembly duration allows to stop the growth of the PDA based nanoparticles to a controlled and reproducible size provided the boric acid/dopamine ratio is higher than 5 [47]. A recent study showed that a vast repertoire of oxidants can be used to rapidly prepare polydopamine under aerobic or anaerobic conditions, also in mildly acidic aqueous solutions, and at room temperature [48]. Also, the use of strong oxidants such as sodium periodate leads to PDA formation in a much shorter time [49].…”

Strategic Advances in Spatiotemporal Control of Bioinspired Phenolic Chemistries in Materials Science

“…As a prominent example, Mun et al reported that, by using the atmospheric pressure plasma and DA mist, a ≈536 nm thick polymer film could be deposited in 60 s. [29] The inclusion of unique reagents is also a valuable approach to regulate the polymerization of DA, aimed at altered deposition dynamics and tailored structures and properties of PDA. [25,[106][107][108][109][110][111] On the one hand, many oxidants, such as Cu 2+…”

“…It was reported that the formal potential of the Cu 2+ / Cu + could be positively shifted to +0.53 V in the presence of 0.1 m Cl − . [108,184] Likewise, reactive oxygen species generated from UV irradiation can accelerate PDA deposition (curve 6). [27,100] Du et al investigated the polymerization of DA under pH 7.0 and 8.5, with/without UV irradiation.…”

“…The inclusion of unique reagents is also a valuable approach to regulate the polymerization of DA, aimed at altered deposition dynamics and tailored structures and properties of PDA. [ 25,106–111 ] On the one hand, many oxidants, such as Cu 2+ , ClO 3 − , S 2 O 8 2− , and IO 4 − , have shown an impact on PDA deposition (Figure 4C, a). [ 25,111 ] Especially, Cu 2+ not only helps oxidize DA to DA quinone and trigger subsequent polymerization, [ 107 ] it also favors the selective formation of 2,2′ dimers of DHI.…”