Figure 1: The structures of matrices used in this study. (A) a-cyano-4- hydroxycinnamic acid (CHCA), (B) 2,5-dihydroxybenzoic acid (DHB), (C) 9H-pyrido[3,4-b] indole (Norharman), (D) 6-aza-2-thiothymin (6-AZA).