In the past year progress in the study of cationic species has been ma
de, particularly in our understanding of the factors which control the
selective recognition of biologically important cations such as ammon
ium, alkali and alkaline earth metal ions, and of metal ions used in b
iomedicine such as lanthanides and iron(III). Based on this knowledge,
several new hosts with improved transport, photophysical and biologic
al properties have been designed.