The First Quantitative Synthesis of a Closed Three-Link Chain (613) Using Coordination and Noncovalent Interactions-Driven Self-Assembly.

Engineering of supramolecular topologies offers potential opportunities for tailoring their properties to various function and applications. However, the synthesis of interlocked or intertwined compounds, catenanes, links or knots, is a challenge. Previously, we used coordination-driven self-assembly and noncovalent interactions (NCIs) between metal-based acceptors and multipyridyl donors to create supramolecular topologies with increasing complexity. Self-assembling components of fixed length and geometry have been utilized for the production of topologies such as Borromean rings, Solomon links, Hopf's link, "rectangle in rectangle", and an 818 molecular knot. However, recent synthesis of a linear [3]catenane by us witnessed the importance of flexible ligands along with coordination-driven self-assembly and NCIs in self-assembling units. This flexibility provides distinctive angularity for the recognition of various NCIs and thus offers tremendous possibilities for realizing complex supramolecular topologies. This study proposed a selective and quantitative synthesis, and also the first X-ray characterization of a closed three-link chain (a prime link of [3]catenane with 6 crossings) via two component coordination-driven self-assembly. The experiments based upon concentration, guest template, and solvent effects were systematically presented. Furthermore, the experimental finding was supported by density functional theory calculations, which highlighted the necessity of the multiple NCIs along with appropriate geometry of the [2 + 2] rings.

Heterometallic BODIPY-Based Molecular Squares Obtained by Self-Assembly: Synthesis and Biological Activities.

Metal-based multinuclear supramolecules with different functionalities designed by self-assembly represent a growing area of research due to their versatile applications, particularly as anticancer agents. Four novel boron dipyrromethene (BODIPY)-based octacationic heterometallic molecular squares, 3-6 were synthesized by self-assembly via reaction of dipyridyl BODIPY ligands with suitable 90° palladium and platinum acceptors. The formation of the as-synthesized molecular squares was confirmed by multinuclear NMR spectroscopy, elemental analysis, high resolution electrospray mass spectrometry, UV-vis spectroscopy, and fluorescence spectroscopy. The square molecular structures of 4 and 6 were further rationalized theoretically using the PM7 semi-empirical method. The activities of the supramolecules against cancer cells were tested using cell lines of various malignant and nonmalignant origins. Complexes 3-6 showed high cytotoxicity toward cancer cells but 7.0 to 15.2 times lower cytotoxic effects were observed against nonmalignant human kidney epithelial cells (HEK-293). Particularly, complexes 3-6 provided 2.1-6.0 times lower IC50 values as compared to cisplatin in HCT116 cells. Interestingly, BDP ligand-containing complexes (3 and 4) induced cytotoxicity through apoptosis, whereas BDPCC-based complexes (5 and 6) induced cell death by necrosis. This study presents a novel series of iron-based heteroatomic palladium and platinum complexes that exhibit substantial potential as drug candidates for anticancer therapy.

Selective and quantitative synthesis of a linear [3]catenane by two component coordination-driven self-assembly.

Here we report the synthesis of a linear [3]catenane comprised of three interlocking rings, by coordination-driven self-assembly. Naphthalene-based acceptor A1 and triazole-based donor L1 were utilized for the self-assembly reaction, which facilitated the formation of linear [3]catenane topology through synergistic non-covalent intercycler interactions (π-π, CH-π and CH-N).