Abstract
Achieving a precise control of the final structure of metal–organic frameworks (MOFs) is necessary to obtain desired physical properties. Here, we describe how the use of a metalloligand design strategy and a judicious choice of ligands inspired from nature is a versatile approach to succeed in this challenging task. We report a new porous chiral MOF, with the formula Ca5II{CuII10[(S,S)-aspartamox]5}·160H2O (1), constructed from Cu2+ and Ca2+ ions and aspartic acid-decorated ligands, where biometal Cu2+ ions are bridged by the carboxylate groups of aspartic acid moieties. The structure of MOF 1 reveals an infinite network of basket-like cages, built by 10 crystallographically distinct Cu(II) metal ions and five aspartamox ligands acting as bricks of a tubular motif, composed of seven basket-like cages each. The pillared hepta-packed cages generate pseudo-rhombohedral nanosized channels of ca. 0.7 and 0.4 nm along the b and a crystallographic axes. This intricate porous 3D network is anionic and chiral, each cage displaying receptor properties toward three-nuclear [Ca3(μ-H2O)4(H2O)17]6+ entities. 1 represents the first example of an extended porous structure based on essential biometals Cu2+ and Ca2+ ions together with aspartic acid as amino acid. 1 shows good biocompatibility, making it a good candidate to be used as a drug carrier, and hydrolyzes in acid water. The hypothesis has been further supported by an adsorption experiment here reported, as a proof-of-principle study, using dopamine hydrochloride as a model drug to follow the encapsulation process. Results validate the potential ability of 1 to act as a drug carrier. Thus, these make this MOF one of the few examples of biocompatible and degradable porous solid carriers for eventual release of drugs in the stomach stimulated by gastric low pH.
Highlights
Metal−organic frameworks (MOFs)[1−3] have become a hot topic of research during the past decades due to the concomitant presence of atheistically pleasant porous highdimensional structures with intriguing net topologies and thrilling chemical and physical properties
BioMOFs may offer remarkable advantages over traditional MOFs: (i) the possibility to achieve homochiral solids crystallizing in polar space groups in a rational and predictable way with applications in chiral discrimination or separation, due to the enantiopure nature of many biomolecules, (ii) large biocompatibility and feasibility in medical applications, (iii) increased stability in hydrated environments, and (iv) molecular recognition capabilities reminiscent of biological processes
Extending the application of this concept, here we report the synthesis of a novel chiral oxamidato-based bioMOF, of formula Ca5II{CuII10[(S,S)-aspartamox]5}·160H2O (1), (H2Me2-(S,S)aspartamox = bis[(S)-dimethylaspartate]oxalyl diamide, Scheme 1) prepared from a ligand derived from the natural
Summary
Metal−organic frameworks (MOFs)[1−3] have become a hot topic of research during the past decades due to the concomitant presence of atheistically pleasant porous highdimensional structures with intriguing net topologies and thrilling chemical and physical properties. It might explain the large number of water molecules embedded within the structure, together with its capability to exchange them loading dopamine hydrochloride drug, likely stabilized by hydrogen bonds supramolecular interactions. The position of the calcium clusters in the cages of 1 unveils that it occurs through a molecular recognition process, governed by H-bonds involving water molecules surrounding alkaline-earth metal ions and carboxyl and hydroxyl groups of the aspartic acid moieties (Figure 3d). Groups toward Cu(II) (Figure S4b) or Ca(II) ions (Figure S4c) ensures the cohesion of adjacent interlocked {CuII4[(S,S)aspartamox]2} units (Figure 2b,c), self-assembling 10 copper ions unfolding the chiral basket-like cage Not all those free carboxyl terminations coordinate metal ions; a portion of them decorate the two gateways of the cages being stabilized by solvent molecules H-bonded to the cages. This represents only an initial result to place 1 among the valuable candidates for drugs encapsulation and their further release in acidic conditions, without any implication of recovery process or toxic effects, thanks to its biocompatibility
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