1 NP 4-hydroxy-3-nitrophenylacetyl-epsilon-aminocaproic acid 1.000 2 NPC 4-hydroxy-3-nitrophenylacetyl-epsilon-aminocaproic acid anion 1.000 3 NIP 4-hydroxy-5-iodo-3-nitrophenylacetyl-epsilon-aminocaproic acid anion 0.957