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Previous studies have shown that α-mangostin (α-MG) suppresses intracellular fat accumulation and stimulation of lipolysis in in vitro systems. Together with the relatively high distribution of α-MG in liver and fat, these observations made it possible to propose a plausible hypothesis that an α-MG supplement may regulate hepatic steatosis and obesity. An α-MG supplement (50 mg/kg) reduced the body weight gain (13.8%) and epidymal and retroperitoneal fat mass accumulation (15.0 and 11.3%, respectively), as well as the biochemical serum profiles such as cholesterol [TC (26.9%), LDL-C (39.1%), and HDL-C (15.3%)], glucose (30.2%), triglyceride (29.7%), and fatty acid (30.3%) levels in high-fat fed mice compared with the high-fat diet-treated group, indicating that α-MG may regulate lipid metabolism. In addition, an α-MG supplement up-regulated hepatic AMPK, SirT1, and PPARγ levels compared with the high-fat diet states, suggesting that α-MG regulates hepatic steatosis and obesity through the SirT1-AMPK and PPARγ pathways in high-fat diet-induced obese mice.

Understanding the dynamic surface self-reconstruction of transition metal oxides (TMOs) under operando condition is the key for the rational design of oxygen evolution reaction (OER) electrocatalysts. Herein, we aimed toward spinel Li 2 Co 2 O 4 , as a desirable system because of the pure Co 3+ ions in the as-prepared sample, to clarify the origin of its enhanced activity during in situ evolution. It was discovered that spontaneous extraction of lithium occurs upon the electrochemical condition to generate an amorphous active layer Li 2−x Co 2 O 4−δ (OH) δ (Co 3+ /Co 4+ ), resulting in a progressively increased OER reactivity. Additionally, operando X-ray spectroscopy combined with ex situ techniques unraveled that the appearance of Co 4+ and oxidized oxygen ions (oxygen sites with electronic hole) is tightly accompanied by this surface reconstruction. Finally, density functional theory calculations further suggested a possible reconstruction pathway and addressed the importance of oxidized oxygen ions that are triggered by Co 4+ ions. These new insights are helpful for understanding why high activity occurs in the system with Co 4+ ions and thereby developing efficient OER electrocatalysts.

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