Interaction between carboplatin and cucurbit[7]uril studied by means of multinuclear NMR spectroscopy and DFT calculations

Encapsulation of platinum-based antitumor drugs into host molecules is a rapidly growing field, as it provides the potential to reduce the toxicity and overcome tumor resistance issues, with cucurbit[n]uril family being a very promising class of potential hosts. Although, previously it was reported that carboplatin, a second generation platinum-based antitumor drug, did not interact with cucurbit[7]uril, in this work, we have observed such an interaction by means of multinuclear NMR spectroscopy. Apparently, upon the interaction with cucurbit[7]uril in aqueous solution, carboplatin decomposes into 1,1-cyclobutane dicarboxylic acid and some cis-PtL₂(NH₃)₂ (L = H₂O or OH⁻) which forms a relatively stable inclusion complex with cucurbit[7]uril. DFT calculations of the geometry of hypothetical complexes and NMR shielding of ¹H, ¹³C, and ¹⁹⁵Pt nuclei help with interpretation of the experimental NMR results.