Porous Supramolecular Architectures Based on π-Stacking Interactions between Discrete Metal-Adenine Entities and the Non-DNA Theobromine/Caffeine Nucleobases

Abstract

This work is aimed at the analysis of the π−π stacking interactions as the driving force to develop porous supramolecular metal−organic frameworks (SMOFs) as an alternative to more directional hydrogen bonding interactions. Four compounds based on the interaction between rigid copper/ adenine entities and theobromine/caffeine molecules have been synthesized: [Cu 7 (μ-ade) 4). The blue compound 1 is formed by wheel-shaped cationic heptameric units where the copper atoms are bridged by hydroxide anions, water molecules, and adeninato ligands with a μ-κN3:κN9 coordination mode. The assembly of the heptameric entities and the theobrominate anions takes place mainly through π−π stacking interactions involving the adeninato ligands and theobrominate moieties. Although compound 1 exhibits an open-framework with voids representing 37% of the unit cell, the plasticity of the π−π interactions causes a reversible shrinkage of the porous system upon activation that precludes the adsorption of gas molecules. Dark purple compounds 2−4 contain neutral windmill units in which two copper atoms are bridged by four μ-κN3:κN9 adeninato ligands. Their final crystal structure highly depends on the supramolecular interactions of the theobromine and caffeine molecules. In compound 2, two theobromine molecules are hydrogen bonded to the Hoogsteen face of two trans-arranged adeninato ligands, whereas a third theobromine molecule is joined to the Watson−Crick face of one of the previous adeninato ligands. In compound 3, with a lower amount of theobromine, the Watson−Crick interaction is not present. In both compounds, the three-dimensional (3D) crystal structure requires the additional presence of π−π stacks between the theobromine molecules. In compound 4, as the methyl groups of the caffeine molecule do not allow hydrogen bond interactions, the adeninato ligands are hydrogen bonded among them to generate, together with π-stacking interactions, two-dimensional supramolecular sheets containing rectangular windows in which the caffeine molecules are located. Only compound 4 showed permanent porosity, adsorbing a significant amount of CO 2 (0.88 mmol of CO 2 /g at 5 bar and 273 K). The magnetic characterization of these compounds indicates a ferrimagnetic behavior for 1 and strong intradimeric antiferromagnetic interactions in compounds 2 and 4.

Synergistic Design of Enhanced π–π Interaction and Decarboxylation Cross-Linking of Polyimide Membranes for Natural Gas Separation

“…The two 6FDA-based polyimides were synthesized by a polycondensation reaction as described in our previous publication . The synthesis route for the 6FDA-PABZ:DABA (3:2) polyimide is illustrated in Figure S1.…”

“…The two 6FDA-based polyimides were synthesized by a polycondensation reaction as described in our previous publication. 37 The synthesis route for the 6FDA-PABZ:DABA (3:2) polyimide is illustrated in Figure S1. Briefly, 39.982 g (0.09 mol) of 6FDA dianhydride, 12.110 g (0.054 mol) of PABZ diamine, and 5.477 g (0.036 mol) of DABA diamine monomers with the desired molar ratio (5:3:2) were added into a three-necked flask and further dissolved in 200 mL of NMP under a N 2 atmosphere.…”

“…π–π interaction is a kind of noncovalent interaction that exists between aromatic rings containing π-orbitals. , Due to their facile formation and reversibility, π–π interactions are widely used in research areas such as DNA sequencing, the formation of supramolecules, and controlled drug release. − However, reports on the utilization of π–π interactions to improve the gas separation performance of polymer membranes are rare. Benzimidazole is a heterocyclic compound with rich delocalized electrons, which are conducive to the formation of π–π interactions. , The polymers containing benzimidazole moieties usually have strong π–π interactions and hydrogen bonds, resulting in a narrowed interchain distance and tightened chain packing.…”

An in solution adsorption characterization technique based on the response to an external magnetic field of porous paramagnetic materials: application on supramolecular metal–adenine frameworks containing heterometallic heptameric clusters

“…We have proved that the use of the adenine nucleobase with copper under basic conditions promotes the formation of heptanuclear discrete copper-hydroxido entities capped by the adeninato ligands ([Cu 7 (μadeninato) 6 (μ 3 -OH) 6 (μ-OH 2 ) 6 ] 2+ ). [9][10][11] The coordination environment of the central position with a reduced Jahn-Teller distortion makes it suitable for metal replacement allowing us to obtain a family of heptameric entities: [Cu 6 M(μ-adeninato) 6 (μ 3 -OH) 6 (μ-OH 2 ) 4 ]SO 4 with M II : Cu and Ni, and [Cu 6 M(μadeninato) 6 (μ 3 -OH) 6 (μ-OH 2 ) 6 ](SO 4 ) x with M II (with x = 1): Zn, Co and M III (with x = 1.5): Cr.…”

A biological luminescent metal–organic framework with high fluorescence quantum yield for the selective detection of amino acids and monosaccharides

“…Adenine is one of the most reported nucleobases used in bio-MOFs. [26][27][28][29] With at least five coordination sites, adenine can form multiple binding modes with metal ions, such as paddle wheel cores, 30,31 windmill cores, 32 helical chains, 33 octahedral cages, 34 etc. For example, bio-MOF-1 was a typical bio-MOF with a binding mode of octahedral cages, showing good performance in the storage and release of drugs.…”