Bioactive Silver–Organic Networks Assembled from 1,3,5-Triaza-7-phosphaadamantane and Flexible Cyclohexanecarboxylate Blocks

Abstract

Three novel bioactive silver-organic networks, namely, the 2D polymer [Ag(μ3-PTA)(chc)]n·n(Hchc)·2nH2O (1), the 3D bioMOF [Ag2(μ3-PTA)2(μ2-chdc)]n·5nH2O (2), and the 2D polymer [Ag2(μ2-PTA)2(μ4-H2chtc)]n·6nH2O (3), were constructed from 1,3,5-triaza-7-phosphaadamantane (PTA) and various flexible cyclohexanecarboxylic acids as building blocks {cyclohexanecarboxylic (Hchc), 1,4-cyclohexanedicarboxylic (H2chdc), and 1,2,4,5-cyclohexanetetracarboxylic (H4chtc) acid, respectively}. The obtained products 1-3 were fully characterized by IR and NMR spectroscopy, ESI-MS(±) spectrometry, elemental and thermogravimetric (TGA) analyses, and single-crystal and powder X-ray diffraction. Their structural diversity originates from distinct coordination modes of cyclohexanecarboxylate moieties as well as from the presence of unconventional N,N,P-tridentate or N,P-bidentate PTA spacers. Topological classification of underlying metal-organic networks was performed, disclosing the hcb, 4,4L28, and a rare fsc-3,4-Pbcn-3 topology in 1, 2, and 3, respectively. Moreover, combination of aqueous solubility (S25°C ≈ 4-6 mg mL(-1)), air stability, and appropriate coordination environments around silver centers favors a release of bioactive Ag(+) ions by 1-3, which thus act as potent antibacterial and antifungal agents against Gram-positive (S. aureus) and Gram-negative (E. coli and P. aeruginosa) bacteria as well as a yeast (C. albicans). The best normalized minimum inhibitory concentrations (normalized MIC) of 10-18 (for bacterial strains) or 57 nmol mL(-1) (for a yeast strain) were achieved. Detailed ESI-MS studies were performed, confirming the relative stability of 1-3 in solution and giving additional insight on the self-assembly formation of polycarboxylate Ag-PTA derivatives and their crystal growth process.