Fig. 2: Chemical structures of compounds investigated in this study.

a Benzene derivatives; b amino acid derivatives and peptides; c polycyclic aromatic and heterocyclic compounds; d pesticides, insecticides, fungicides, herbicides, and antibiotics; e drugs; and f vitamin B1 as well as selected non-aromatic compounds, for which the alternative dye-displacement strategy was adopted (see the Supplementary Information). The compounds are represented in their predominant charge state at pH 7. Color code; green: rapidly permeable, black: slowly permeable, and red: impermeable.