Structural Studies and Cytotoxicity of Trimethyl(ferrocenylmethyl)ammonium Iodide Encapsulated in β-Cyclodextrin

Inclusion complexes that comprise beta-cyclodextrin (beta-CD) and trimethyl(ferrocenylmethyl)ammonium iodide (1) have been prepared by codissolution of the host and guest in ethanol/water, accompanied by either conventional heating at 40 degrees C for 26 h (to give 2) or microwave-assisted heating for 30 min (to give 3). Solids were isolated and characterized by elemental and thermogravimetric analyses, powder X-ray diffraction (XRD), and IR, Raman, and C-13{H-1} CP/MAS NMR spectroscopy. Powder XRD indicated the presence of microcrystalline inclusion compounds with supramolecular structures that comprise beta-CD head-to-head dimers arranged into infinite channels. A small crop of single crystals of the inclusion compound 2 were obtained and analyzed by XRD. Despite diffraction being very poor above a resolution of around 1 angstrom, the data could be indexed to the space group P1 (in agreement with powder XRD) and a reasonable structural model could be achieved when the asymmetric unit was composed of two directly located beta-CD hosts, 1.4 iron atoms, and a small fraction of iodide anions. By using these data as a starting point, DFT calculations were carried out and led to a model of the crystal structure that comprised 2:1 (host/guest) and 2:2 adducts. The cytotoxic and antiproliferative activities of 1 and 2 were tested against the breast adenocarcinoma MDA-MB-231 and osteosarcoma MG-63 cell lines. Results indicate that both 1 and 2 are cytotoxic against the MDA-MB- 231 line but exhibit negligible activity on the MG-63 line.