The ability of macrocycles to adapt their apparent polarity to that of the surroundings by conformational change has been termed chameleonicity , with cyclosporine A being the most thoroughly investigated example . In an apolar environment (such as the interior of a cell membrane), the polar groups are shielded from the surroundings through intramolecular hydrogen bonds. Chameleonicity significantly increases the passive membrane permeability of a compound in the presence of a relatively large number of hydrogen-bond donors and acceptors, which are required for good solubility and target binding . Note that chameleonicity is not limited to macrocycles, it can occur in any sufficiently flexible molecule and several non-macrocyclic examples exist .