Tuning the nitric oxide release behavior of amino functionalized HKUST-1 Katharina Peikert a, b , Laura J. McCormick b , Damiano Cattaneo b , Morven J. Duncan b , Frank Hoffmann a , Arafat H. Khan c , Marko Bertmer c , Russell E. Morris b , Michael Fr € oba a, * a Department of Chemistry, Institute of Inorganic and Applied Chemistry, University of Hamburg, Martin-Luther-King Platz 6, D-20146 Hamburg, Germany b EaSTChem School of Chemistry, University of St. Andrews, Purdie Building, St. Andrews KY16 9ST, United Kingdom c Physics and Earth Sciences, Institute of Experimental Physics II, Leipzig University, Linn estraße 5, 04103 Leipzig, Germany article info Article history: Received 3 December 2014 Received in revised form 12 June 2015 Accepted 15 June 2015 Available online 25 June 2015 Keywords: Metal-organic framework HKUST-1 Amino functionalized HKUST-1 Nitric oxide release NONOate abstract Four new secondary amino functionalized trimesic acid ligands (H 3 RNHbtc, R ¼ Me, Et, n Pr, and i Pr) were synthesized. When used in combination with H 3 btc these ligands lead to four new mixed-linker metal- organic frameworks (MOFs) which we call UHM-36, UHM-37, UHM-38, and UHM-39. All MOFs are isostructural to HKUST-1. We tested these MOFs as nitric oxide storage and release materials and investigate the influence of the amine groups on the NO storage capacity of the MOFs. The results were compared to the unfunctionalized HKUST-1, i.e. Cu 3 (btc) 2. © 2015 Elsevier Inc. All rights reserved. 1. Introduction Nitric oxide (NO) is a colorless, diatomic gas and a radical with one unpaired electron. For a long time this molecule had primarily been known as a toxic gas which contributes to acid rain, and is contained in smog and tobacco smoke [1]. However, since Furch- gott, Ignarro, Murad, and Moncada investigated the crucial role of NO in the cardiovascular system in the late 1980s [2e4] the interest in this small compound has steadily grown. NO is now known as an extremely important biological protective, regulatory, and signaling molecule which plays a key role in many physiological processes, such as regulation of blood pressure and clotting, neurotransmission, vasodilation, inflammation, immune response, pulmonary hypertension, penile erection, anti-tumor activity, and wound healing [5e11]. The concentrations of NO that are needed for physiological processes are estimated to vary between 100 pM and 5 nM [12]. The required amount of NO is normally regulated and well balanced by the endothelial enzyme nitric oxide synthase (NOS). However, excessive NO can lead to dangerously low blood pressure and interaction with transition metals, heme-containing proteins, and thiol groups, which results in the oxidation and damage of func- tional groups on proteins and DNA. On the other hand, a lack of NO will lead to serious health problems, such as unwanted clot formation, erectile dysfunction, and respiratory distress [1,13,14]. When using exogenous NO for therapeutic applications it is there- fore important to develop compounds, which allow a controlled release and targeted delivery of NO to specific sites in the body [1]. During the last decades a lot of research has been done in developing appropriate NO storage and release systems: NO can be released from organic nitrates, nitrites, metal-NO complexes, ni- trosamines, N-diazeniumdiolates (NONOates), and S-nitrosothiols (RSNOs) [15]. NO release systems based on these functionalities include amino functionalized polymers [16,17] and silica particles [18,19], in which the NO is stored as NONOates, as well as metal exchanged zeolites [20] and metal-organic frameworks (MOFs), in which the NO is bound directly to the metal centers [21]. MOFs are solid state inorganic-organic materials, which have attracted much attention during the past decade as they have shown excellent performance in applications like gas storage and separation [22,23], catalysis [24], sensing [25,26], and drug delivery [27]. * Corresponding author. E-mail address: froeba@chemie.uni-hamburg.de (M. Fr€ oba). Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso http://dx.doi.org/10.1016/j.micromeso.2015.06.020 1387-1811/© 2015 Elsevier Inc. All rights reserved. Microporous and Mesoporous Materials 216 (2015) 118e126