Next, precursors were extracted using regular expressions of 41 precursors of interest (full list provided in SI) for each subrecipe. This specific set of precursors was identified by the most frequent precursors within the NER-detected dataset, with a small number of precursors manually added. These include gold source (AuCl - 4 ), capping agents (citrate, CTAB), reducing agents (ascorbic acid, NaBH 4 ), and other additives (AgNO 3 , HCl). This predefined set of precursors is first categorized to one of 54 precursor formulas then normalized to one of 41 precursors using domain knowledge. For instance, 'NaAuCl 4 ', 'gold chloride', 'HAuCl 4 ', and its various hydrates are normalized as 'AuCl - 4 '.