“…[16][17][18][19][20] When including additionally to the 2,3-dihydroxybenzaldehyde, the 4-aminobenzoic acid functionality, the total number of studies is far smaller. [8,12,[21][22][23][24][25] Some of them provide two carboxylic acid functions and vary in the location of the two phenolic OH group for building up hydrogen bonding networks. [8,9,12,14,21] The deprotonated function of such 2,3-dihydroxybenzaldehyde-4aminobenzoic acid derivatives was previously used for coordination of metals, [8,12] and contain the biologically important catechol (benzene-1,2-diol) unit.…”