A Long-Lived Halogen-Bonding Anion Triple Helicate Accommodates Rapid Guest Exchange

Anion-templated helical structures are emerging as a dynamic and tractable class of supramolecules that exhibit anion-switchable self-assembly. We present the first kinetic studies of an anion helicate by utilizing halogen-bonding m-arylene-ethynylene oligomers. These ligands formed high-fidelity triple helicates in solution with surprisingly long lifetimes on the order of seconds even at elevated temperatures. We propose an associative ligand-exchange mechanism that proceeded slowly on the same timescale. In contrast, intrachannel anion exchange occurred rapidly within milliseconds or faster as determined by stopped-flow visible spectroscopy. Additionally, the helicate accommodated bromide in solution and the solid state, while the thermodynamic stability of the triplex favored larger halide ions (bromide≈iodide≫chloride). Taken together, we elucidate a new class of kinetically stable helicates. These anion-switchable triplexes maintain their architectures while accommodating fast intrachannel guest exchange.

Anti-cancer activity of di- and tri-organotin(IV) compounds with D-(+)-Galacturonic acid on human tumor cells

We have compared the anti-proliferative activity in vitro, of R₂SnGala (1-3) [R = Me, n-Bu, Ph] and novel R₃SnGala (4, 5) [R = Me, n-Bu] with D-(+)-Galacturonic acid [HGala; Gala^q-, q = (2) and (1) for R₂SnGala and R₃SnGala, respectively] compounds, towards human tumor cell lines of intestinal carcinoma (HCT-116) and breast adenocarcinoma (MCF-7). The new synthesized 4 and 5 compounds were characterized, in solution, by ¹H, ¹³C and ¹¹⁹Sn NMR, that showed that HGala acts as monoanionic moiety and evidenced the dynamic behavior of the compounds, due to inter-conversions involving the anomeric carbon atom of the ligand. Cell viability, apoptosis induction and cell cycle distribution were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay and flow cytometry, respectively. The cytotoxicity of the compounds, in the micro-submicromolar range, changed in the order of the organotin(IV) moieties, according to 5 > 3 > 2, while 1 and 4, containing Me_nSn(IV) (n = 2,3) moieties, were ineffective. Compound 5 showed peculiar cytotoxic effects. It did not cause time dependent inhibition of cell growth nor accumulated into the cells. Cell death induced by the active 2, 3, and 5, was shown to be apoptotic by measuring the exposure of phosphatidylserine to the outer membrane and the loss of mitochondrial potential. All the cytotoxic compounds induced an accumulation of cells in the subG0/G1phase, while only 2 and 3 perturbed the cell cycle confining viable cells in G0/G1phase. Finally, none of the compounds investigated affected the viability of normal intestinal or liver cells, indicating selectivity towards tumor cells.