A 13C solid-state NMR study of the structure and auto-oxidation process of natural and synthetic melanins

Demonstration of a common indole-based aromatic core in natural and synthetic eumelanins by solid-state NMR

“…7 Both synthetic pigments display aromatic regions (110–160 ppm) similar to CN melanins derived from the obligatory exogenous L-dopa precursor, 20–22 providing preliminary indications of a common heterogeneous amorphous aromatic core structure in the (natural-abundance) synthetic and fungal melanin pigments. 13 C NMR spectra for the isotopically enriched materials are dominated by partially resolved arene (and/or alkene) resonances consistent with proposed indole-based aromatic ring structures, 12,24,26 but additional spectral features are evident from carboxyl groups (168–174 ppm) and open-chain aliphatics (30–60 ppm) as reported for solid fungal melanins 20–23,27 and the polydopamines discussed below. 30 When compared with the L-tyrosine or natural abundance L-dopa starting materials, these polymerized products show 1D 13 C NMR spectra with broad features attributable to superposition of chemically and magnetically similar structural units and also to the presence of stable free radicals.…”

Hydroxide ion-mediated synthesis of monodisperse dopamine–melanin nanospheres

“…The 13 C ssNMR spectrum is comparable with the spectra reported for polydopamine [28,29] and natural melanin [30] in a shape of curve and positions of peaks, as shown in Fig. 4 To further analyze the structure, XPS of dried samples is measured as shown in Fig.…”

Poly(vinyl chloride) and wood flour press mould composites: New bonding strategies

“…35 Carbonyl carbon atoms from PHPA can be identified in the region between 170 and 180 ppm. 35,36 The active chain ends can be identified by the peak at around 17 ppm. 37 The reduction of the peak from PHPA to PVC-PHPA can be explained by the growth of the copolymer molecular weight through reaction of the former active chain ends with VCM.…”