Molecular basis for the ability of a calix[4]arene derivative anchored to a silica support to remove herbicide from contaminated wáter

O. E. PIRO; E. E. CASTELLANO; A. F. DANIL DE NAMOR; J. A. ZVIETCIVICH-GUERRA; J. VILLANUEVA SALAS; O. WEBB ; A. EL GAMOUZ

Córdoba

Congreso; I Reunión Latinoamericana de Cristalografía y IX Reunión de la Asociación Argentina de Cristalografía (AACr); 2013

Asociacion Argentina de Cristalografia

The presence in water resources of wasted agricultural herbicides, including phenoxyacids, leads to serious health and environmental problems [1]. Through Supramolecular Physical Chemistry methodology it is possible to engineering receptors with the ability to sequester selectively those armful molecules [2]. Among the many receptors developed, calixarenes [3] have attracted considerable attention due to the possibility of upper and lower rim functionalization, followed by its fixation onto a solid support to act as molecular filters. Here we report the X-ray crystal structure of a complex of partially derivatized and protonated 5,11,17,23-tetra-tert-butyl[25,27-dihydroxy-26,28-bis(diethylamineH)ethoxy] calix[4]arene ligand (LH22+) with a pair of deprotonate herbicide molecules (PhCl2OCH2COO-), LH2(PhCl2OCH2COO)2.H2O. The macro-cycle shows a squashed-cone conformation and a pair of medium to weak O-H?O(pend) bonds in the lower bore. The calix[4]arene derivative binds two negatively charged PhCl2OCH2COO herbicide molecules at the periphery of the hydrophilic cavity through a pair of strong and linear N-H?O bonds. These bonds involve the pendant amide groups and the herbicide carboxylate oxygen atoms [N?O distances of 2.667 and 2.713 Å and N-H?O angles of 171.3 and 178.6°, respectively]. The crystallographic results provide the molecular basis to rationalize the selective sequestering ability of the calix[4]arene towards the herbicide observed both in solution and when anchored to a silica support to become a practical recyclable filter.   [1] Garabrant, D.H., Philbert, M.A., Crit. Rev. Toxicol. 32, 233-257 (2002). [2] Danil de Namor, A.F., Cleverley, R.M., Zapata-Ormachea, M.L., Chem. Rev. 98, 2495-2525 (1998). [3] Gutsche, C.D. Calixarenes. An Introduction, Royal Society of Chemistry (2008).