Caffeic acid 3 4 dihydroxycinnamic acid

All experiments have been performed using analytical-grade chemicals. Folin-Ciocalteu solution, gallic acid, sodium carbonate, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid 114 (Trolox), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) and all HPLC Standards of gallic acid (3,4,5-Trihydroxybenzoic acid), p-Hydroxybenzoic acid, (+)-catechin hydrate, protocatechuic, rutin hydrate, quercetin (3,3’,4’,5,7-Pentahydroxyflavone), chlorogenic acid, p-coumaric acid, caffeic acid (3,4-Dihydroxycinnamic acid), trans-cinnamic acid, ellagic acid, resveratrol, and sinapic acid (3,5-Dimethoxy-4-hydroxycinnamic acid) were obtained from Sigma-Aldrich (Darmstadt, Germany). All assay kits for FRAP, CUPRAC, and proanthocyanin were purchased from Bioquochem (Asturias, Spain). As for the solvents, aqua and O-Phosphoric Acid 85% extra pure were provided by Fisher Scientific (Janssen Pharmaceuticalaan, Belgium), and Acetonitrile was provided by LiChrosolv^® (Darmstadt, Germany). Polyoxyethylene-20 (Tween 20) was obtained from Biotech (Markham, ON, Canada). A basic cream formula and two commercial exfoliating scrubs were purchased from a local store (Beirut, Lebanon) and used as positive controls, one containing 5% sugar and the other containing 5% raspberry seed powder and Argania spinosa shell powder.

Caffeic acid (3,4-Dihydroxycinnamic acid) was acquired from Sigma-Aldrich, St. Louis, MO, and used as received without further purification. The molecular structure of caffeic acid in non-hydrolyzed form is illustrated in Table 1. Iron (II) sulfate heptahydrate (FeSO₄•7H₂O) was acquired from Panreac, Barcelona, Spain, and hydrogen peroxide (H₂O₂ 30% w/w) and titanium (IV) oxysulfate solution 1.9–2.1%, for determination of hydrogen peroxide, were acquired from Sigma-Aldrich, St. Louis, MO, USA. Sodium sulfite anhydrous (Na₂SO₃) was acquired from Merk, Darmstadt, Germany. Trifluoroacetic acid (HPLC grade, ≥99.0%) was acquired from Riedel-de Haën, Seelze, Germany, and acetonitrile (HPLC grade, ≥99.9%) was acquired from Chem-Lab, Zedelgem, Belgium. For pH adjustment, sodium hydroxide (NaOH) from Labkem, Barcelona, Spain, it was used, along with sulfuric acid (H₂SO₄, 95%) from Scharlau, Barcelona, Spain. Deionized water was used to prepare the respective solutions.