Nitric Oxide Adsorption and Delivery in Flexible MIL-88(Fe) Metal–Organic Frameworks

Abstract

Adsorption and release of the biologically\nactive nitric oxide\n(NO) was evaluated over a series of highly flexible iron­(III) dicarboxylate\nMOFs of the MIL-88 structure type, bearing fumaric or terephthalic\nspacer functionalized or not by polar groups (NO<sub>2</sub>, 2OH).\nAs evidenced by <i>ex situ</i> X-ray powder diffraction\nand <i>in situ</i> IR spectroscopy, it appears that if the\ncontracted dried forms of MIL-88 do not expand their structures in\nthe presence of NO, the combination of very narrow pores and trimers\nof iron polyhedra leads to the adsorption of significant amounts of\nNO either physisorbed (very narrow pores) and/or chemisorbed [iron­(II)\nor iron­(III) coordinatively unsaturated metal sites (CUS)]. The delivery\nof NO under vapor of water or in simulated body fluid does not exceed\n20% range of the total adsorbed amount probably due to a partial release\nthat occurs between the adsorption/desorption setup and the chemiluminescence\nrelease tests. Some of these solids nevertheless exhibit a significant\nrelease at the biological levels over a long period of time (>16\nh)\nthat make these biocompatible and biodegradable MOFs of interest for\nthe controlled release of NO.