Epicatechin

Vinyl pyrrolidone (VP), iron (III) chloride hexahydrate (FeCl₃·6H₂O), sodium acetate, malonic acid (MA), and molybdenum disulfide (MoS₂) were purchased from Sigma Chemical Co. (St. Louis, MO, USA). Acetic acid and ethylene glycol were procured from Duskan Pure Chemical (Kyungki-do, Korea). Methanol and ethanol were acquired from Fisher Scientific (Seoul, Korea). Ammonium persulfate (APS), 3-methacryloxypropyltrimethoxysilane (MPS), Ethylene glycol dimethacrylate (EGDMA), and 2-methylpropionitrile (AIBN) were purchased from Daejung Chemicals & Metals (Gyonggido, Korea). The standard chemicals of (+)-catechin (C, ≥98%), (−)-epicatechin (EC, ≥90%), (−)-epigallocatechin (EGC, ≥95%), (−)-epicatechin gallate (ECG, ≥95%), and (−)-epigallocatechin gallate (EGCG, ≥98%) were supplied by Tokyo Chemical Industry (Tokyo, Japan). All other solvents used in the experiment were either of HPLC or analytical grade.

The flavan-3-ol fraction (FL) was provided by Meiji Co., Ltd (Tokyo, Japan) and was prepared from cocoa powder using a method described in a previous report [24] (link). In brief, the cocoa powder was defatted with n-hexane and the residue was extracted with acetone. The n-butanol-dissolved fraction of the extract was subsequently applied to a Diaion HP2MG column (Mitsubishi Kasei Co. Ltd., Tokyo, Japan). The fraction eluted with 80% ethanol was collected, freeze-dried, and used in the experiments. The concentration of catechins and procyanidins was determined by the method of high-performance liquid chromatography (HPLC). FL contained 4.56% (+)-catechin, 6.43% of (−)-Epicatechin, 3.93% of procyanidin B2, 2.36% of procyanidin C1, and 1.45% cinnamtannin A2. (−)-Epicatechin was purchased from Tokyo Chemical Industry (Tokyo, Japan).

HPLC-grade acetonitrile and methanol were obtained from ECHO Chemical Co. Ltd. (Miaoli, Taiwan). Pronase (catalog number: PRON-RO), 1-phenyl-2-thiourea (PTU), and molecular biology-grade DMSO were purchased from Sigma-Aldrich (St. Louis, MO, USA). Catechin and epiCatechin were obtained from Tokyo Chemical Industry Co. Ltd. (Tokyo, Japan). Quercetin was purchased from Alfa Aesar (Ward Hill, MA, USA). Catechu (dried evaporated decoction from Uncaria gambir Roxb) was obtained from Hing Zong Co., Ltd. (Kaohsiung, Taiwan) (batch number: 213N-107-02). Raw materials were imported from Singapore (Figure 1).