A very stable complex of a modified marine cyclopeptide with chloroform.

Noncovalent interactions play a pivotal role in molecular recognition. These interactions can be subdivided into hydrogen bonds, cation-π interactions, ion pair interactions and London dispersion forces. The latter are considered to be weak molecular interactions and increase with the size of the interacting moieties. Here we show that even the small chloroform molecule forms a very stable complex with a modified marine cyclopeptide. By means of high-level quantum chemical calculations, the size of the dispersive interactions is calculated; the dispersion energy (approximately -40 kcal mol⁻¹) is approximately as high as if the four outer atoms of the guest form four strong hydrogen bonds with the host. This strong binding of chloroform to a modified marine cyclopeptide allows the speculation that the azole-containing cyclopeptides-haloform interaction may play some biological role in marine organisms such as algae.