Phenolation is one of the effective strategies to synthesize lignin-based polyphenols, improve lignin's properties, and extend its value-added applications in biological, medicinal and cosmetic fields. Herein, by taking the structural feature advantage of lignin, an effective and green strategy was developed to molecularly engineer lignin into a robust lignin-3-(2-hydroxyphenyl)propionate ester (LPPE) derivative via a transesterification reaction between 3,4-dihydrocoumarin (DHC) and the aliphatic hydroxyls in lignin under organocatalysis. The strategy is optimized and the novel derivative was systematically characterized by 1 H, 13 C and 31 P nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopy. The findings indicated that the successful introduction of 3-(2-hydroxyphenyl)propionate groups using a OH groups/DHC/organic base molar ratio of 1꞉1꞉0.3 at 120 °C for 6 h increased the content of phenolic hydroxyl groups from 1.793 1 to 3.017 9 mmol/g, and the LPPE exhibited excellent ultraviolet-absorbing and antioxidant performance with up to 90% free radical scavenging activity within 20 min using 5 mg/mL of LPPE. In addition, good biocompatibility and a high Sun protection factor (SPF) value of 40.9 were achieved at 5% ( w ) dosage of LPPE in the cream, indicating its significant application potential in sunscreen.
Jikang Wang,Yanqi Xu,Jiaxin Li,Xiaodong Ma,Si-Min Xu,Rui Gao,Yufei Zhao,Yu-Fei Song
Dihydroxybenzenes (DHB) are one of the most important fine chemicals used as raw materials or intermediates in industries. One-step selective phenol hydroxylation using a photo-Fenton system is an attractive and challenging strategy, especially under long-wavelength irradiation. Herein, we report that a highly selective photo-driven Fenton hydroxylation reaction of phenol to DHB can be achieved over NiFe-layered double hydroxide nanosheets (NiFe-NS) under visible-light irradiation with 70% phenol conversion and ∼99% DHB selectivity. A more interesting finding is that a high phenol conversion (∼40%) activity can be maintained even under monochromatic irradiation at 550 nm. The superior photocatalytic activity was attributed to the abundant defects in NiFe-NS, which facilitated the adsorption of hydrogen peroxide (H2O2) onto the catalyst surface and promoted the transfer efficiency of photoinduced electrons from the catalyst to H2O2, generating ˙OH radicals to participate in the hydroxylation of phenol.
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