Molecular recognition of amidines in water

[structure: see text] Tetraphosphonates of the general structure shown above are biomimetic hosts for bisamidinium cations in drugs such as pentamidine and DAPI. Similar to their insertion into DNA's minor groove, these drugs are often sandwiched by two tetraphosphonate hosts (2:1). The alternative binding mode (1:2) produces extremely high association constants in water of approximately 10(8) M(-)(2) ( approximately 12 kcal/mol), which can compete with the biological process.