Electron Spin Relaxation Studies of Polydopamine Radicals

Abstract

We present a thoroughgoing electron paramagnetic resonance investigation of polydopamine (PDA) radicals using multiple electron paramagnetic resonance techniques at the W-band (94 GHz), electron nuclear double resonance at the Q-band (34 GHz), spin relaxation, and continuous wave measurements at the X-band (9 GHz). The analysis proves the existence of two distinct paramagnetic species in the PDA structure. One of the two radical species is characterized by a long spin–lattice T 1 relaxation time equal to 46.9 ms at 5 K and is assigned to the radical center on oxygen. The obtained data revealed that the paramagnetic species exhibit different electron spin relaxation behaviors due to different couplings to local phonons, which confirm spatial distancing between two radical types. Our results shed new light on the radical structure of PDA, which is of great importance in the application of PDA in materials science and biomedicine and allows us to better understand the properties of these materials and predict their future applications.

Expanding the spectrum of polydopamine antioxidant activity by nitroxide conjugation

“…EPR characterization. X-band Electron paramagnetic resonance (EPR) spectra of PDAn showed a weak signal, attributed to a semiquinone radical formed by the comproportionation of catechol and quinone groups, 19 whose concentration was 6.6 mol/g, in agreement with previous reports. 12,19 In the case of PDAnT an intense spectrum typical of a nitroxide in the slowmotion regime, characterized by broadened lines with uneven height, 15 was detected (Figure 1c).…”

Surface engineering for cellulose as a boosted Layer-by-Layer assembly: Excellent flame retardancy and improved durability with introduction of bio-based “molecular glue”

“…S5, the curves of pristine cotton didn't show any signal under magnetic field. By contrast, PDA-cotton show a slightly asymmetrical signal with g value of 2.004, which is in accordance with reports [70,71].…”

“…The second radical is located in the benzene ring of PDA. The dominant radical that contributes to that signal is reported to aromatic ring π-radical [70]. After incorporating PHA with PDA cover (PDA-C-PHA), the signal disappeared in Fig.…”

Polymer Grafting to Polydopamine Free Radicals for Universal Surface Functionalization

“…Despite the widespread exploration of PDA for surface engineering, existing routes to post-modify PDA have chiefly addressed the backbone amine and catechol groups for functionalization, limiting the diversity of attachable polymers. , Little attention has been directed at the ubiquitous free radicals present in the 5,6-dihydroxyindole backbone of PDA as a reactive handle for post-modification. − The presence of stable paramagnetic species within the macrostructure of PDA is a characteristic feature shared with natural melanins, which has been implicated in the conductive and antioxidant properties of melanin-like materials. ,− Two key radical species have been identified in melanin systems: an intrinsic, carbon-centered radical (CCR) associated with the oxidative propagation of catecholamine polymerization and an extrinsic semiquinone radical (SQR) resulting from the comproportionation reaction of hydroquinone and quinone in the 5,6-dihydroxyindole backbone. − …”