In this study, we investigated the total phenolic and flavonoid contents, antioxidant activity and cellular protective effects against oxidative stress on human skin cells in 50% ethanol extract and its fractions of Calendula officinalis (C. officinalis) flowers. We measured the antioxidant effects of 50% ethanol extract and its fractions of C. officinalis flowers on the free radical scavenging activity (FSC50), the reactive oxygen species (ROS) scavenging activities (OSC50) and the inhibition of intracellular ROS generation in human skin cells. These results showed that the antioxidant effect of the ethyl acetate and aglycone fraction was more than the 50% ethanol extract of C. officinalis flowers. We also investigated the cellular protective activity and the results showed that treatment of the ethyl acetate fraction (0.05 -3.13 µg/mL) protects human skin cells in a concentration-dependent manner when the skin cell damages were induced by treating them with H2O2. In addition, the aglycone fraction (1.56 -3.13 µg/mL) shows cellular protective effects on the UV-induced cell damages in a dose-dependent manner. These results suggest that the fractions of C. officinalis flowers can function as a natural antioxidant agent of cosmetics in human skin cells exposed to oxidative stress by ROS scavenging effects.

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Developing an efficient and sustainable electrocatalyst for facilitating sluggish oxygen reduction reaction (ORR) is a key issue for the realization of metal-air batteries and fuel cells. The platinum deposited carbon (i.e., Pt/C) is the most popular and widely adopted catalyst system for enhancing the ORR kinetics. Unfortunately, the practical use of Pt/C is severely limited by low electrochemical oxidation resistance and subsequent structural collapse of the carbon-based support materials, especially during dynamic cell operations.[1] Recently, alternative inorganic metal oxides (TiO2, WO3, etc.) have been spotlighted as catalyst support due to higher electrochemical robustness than carbon. However, other properties such as electronic conductivity and electrochemical catalyst-support interactions should be considered to perform as a support material for achieving a prominent performance of supported catalyst.[2] Several methods for modulating the properties of metal oxides has been suggested to overcome their intrinsic limitation such as electronic and electrochemical features. Particularly, the off-stoichiometric metal oxides with oxygen-deficient structure have known to exhibit unique surface activity and electrical property. For example, tungsten oxide with low oxidation number, called black WO3-x, can offer several advantages such as (i) high electronic conductivity induced by reduced bandgap, (ii) high surface activity, (iii) improved ion mobility, and (iv) structural flexibility by generating free volumes.[3-7] However, the applicability and feasibility of WO3-x materials as a catalyst support have rarely been reported. In this work, we successfully synthesize the black WO3-x nanofiber (NF) via electrospinning and subsequent reducing thermal treatments, and elucidate their performance as a Pt catalyst support material. Morphological and structural characterizations of the black WO3-x NF are carried out to investigate unique features of the WO3-x NF. It is noted that the Pt catalysts supported on black WO3-x nanofibers (Pt/black WO3-xNF) outperform the Pt/white WO3 NF reference in electrochemical ORR and prolonged cycle tests. We also demonstrate the origin of high durability and catalytic functions of the black WO3-x NF as catalyst support by using various Ex-situ characterizations. [1] Lei Du, Yuyan Shao, Junming Sun, Geping Yin, Jun Liu, and Yong Wang, Nano Energy, 2016, 29, 314-322 [2] P. A. Shinde, S. C. Jun, ChemSusChem 2020, 13, 11. [3] Na-Won Lee, Ji-Won Jung, Jun-Seo Lee, Hye-Yeon Jang, Il-Doo Kim, and Won-Hee Ryu, Electrochimica Acta, 2018, 263, 417-425. [4] Na-Won Lee, Ki Ro Yoon, Jae Yun Lee, Yoonsu Park, Seongji Pyo, Ga-Yoon Kim, Don-Hyung Ha, and Won-Hee Ryu, ACS Applied Energy Materials, 2019, 2, 3513-3522. [5] Won-Hee Ryu, Hope Wilson, Sungwoo Sohn, Jinyang Li, Xiao Tong, Evyatar Shaulsky, Jan Schroers, Menachem Elimelech, André D. Taylor, ACS Nano, 2016, 10, 3, 3257-3266 [6] Ji-Yong Eom, Sung-Jin Lim, Sang-Min Lee, Won-Hee Ryu and Hyuk-Sang Kwon, J. Mater. Chem. A, 2015, 3, 11183-11188 [7] Jiajia Song, Zhen-Feng Huang, Lun Pan, Ji-Jun Zou, Xiangwen Zhang, and Li Wang, ACS Catalysis, 2015, 5, 6594-6599