Background Iron (Fe)-induced oxidative stress leads to reactive oxygen species that damage biomembranes, with this mechanism being involved in the activity of some anti-cancer chemotherapeutics. Methods Herein, we compared the effect of the ligand, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT), or the potential ligand, Emodin, on Fe-catalyzed lipid peroxidation in cell membrane models (micelles and bicelles). These studies were performed in the presence of hydrogen peroxide (H 2 O 2 ) and the absence or presence of ascorbate. Results In the absence of ascorbate, Fe(II)/Emodin mixtures incubated with H 2 O 2 demonstrated slight pro-oxidant properties on micelles versus Fe(II) alone, while the Fe(III)-Dp44mT complex exhibited marked antioxidant properties. Examining more physiologically relevant phospholipid-containing bicelles, the Fe(II)- and Fe(III)-Dp44mT complexes demonstrated antioxidant activity without ascorbate. Upon adding ascorbate, there was a significant increase in the peroxidation of micelles and bicelles in the presence of unchelated Fe(II) and H 2 O 2 . The addition of ascorbate to Fe(III)-Dp44mT substantially increased the peroxidation of micelles and bicelles, with the Fe(III)-Dp44mT complex being reduced by ascorbate to the Fe(II) state, explaining the increased reactivity. Electron paramagnetic resonance spectroscopy demonstrated ascorbyl radical anion generation after mixing ascorbate and Emodin, with signal intensity being enhanced by H 2 O 2 . This finding suggested Emodin semiquinone radical formation that could play a role in its reactivity via ascorbate-driven redox cycling. Examining cultured melanoma cells in vitro , ascorbate at pharmacological levels enhanced the anti-proliferative activity of Dp44mT and Emodin. Conclusions and general significance Ascorbate-driven redox cycling of Dp44mT and Emodin promotes their anti-proliferative activity.
Crystallization of vivianite-phosphorus is a promising method to recover phosphate as a vital resource from sewage sludge hydrothermal carbonization (HTC) products. This study reveals the in-situ recrystallization mechanism of vivianite-phosphorus (Fe 3 (PO 4 ) 2 ·8H 2 O) regulated by FeCl 3 -assisted HTC in depth. The key finding includes the decipherment that phosphorus is mainly enriched in hydrochar (72.7 ± 2.9 %wt ∼ 84.4 ± 3.31 %wt). Further identified by HRTEM and XRD, dominant phosphorus is profiled as vivianite (Fe 3 (PO 4 ) 2 ·8H 2 O) with very few calcium phosphate crystals (Ca 3 (PO 4 ) 2 ) formation in hydrochar at near-neutral condition. Under acidic conditions, HMF oxidation triggers reductive dissolution of surface-bound Fe(III)-phosphate complexes, releasing Fe 2+ , HPO 4 2− , and PO 4 3− . The anoxic, reducing conditions at circumneutral pH created by HTC, combining with favorable Fe: P ratio (1.72) and lower calcium concentration (532 mg L −1 ), comprehensively drives the crystallization of Fe 3 (PO 4 ) 2 ·8H 2 O. This demonstration-of-practice study provides deep insights into dual organic waste resource and energy valorization.
Methods allowing the oxidation of graphite to graphene oxide (GO) are vital important for the production of graphene from GO. This oxidation reaction has mainly relied on strong acid strategy for 174 years, which circumvents issues associated with toxicity of reagent and product, complex post-treatment, high cost and waste generation. Here, we report a green route for performing this oxidization reaction via a ferro-induced strategy, with use of water, potassium ferrate (Fe(VI)) and hydrogen peroxide (H 2 O 2 ) as reagents, to produce about 65% yield of GO (vs. 40% for Hummers’ method, the most commonly used concentrated acid strategy) and non-toxic by-products. Moreover, GO produced from this new method shows equivalent performance to those reported previously. This H 2 SO 4 -free strategy makes it possible to process graphite into GO in a safe, low-cost, time-saving, energy-efficient and eco-friendly pathway, opening a promising avenue for the large-scale production of GO and GO-based materials.
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