Water-soluble cryptophanes: design and properties

The molecular cages, or host molecules, still play an important role in supramolecular chemistry, where they are at the origin of the most spectacular advances in the field of molecular recognition. In this review we focus on the most significant results developed in recent years in the field of the chemistry of water-soluble host molecules belonging to the family of cryptohanes and hemicryptophanes. Indeed, some recent progress towards biosciences and new approaches in supramolecular catalysis contributed significantly to the development of the domain. The need to work in aqueous media appears evident for biological or biomedical applications and for the design of new catalytic systems to address critical issues of green chemistry, where environmental considerations may require the use of water as solvent. We thus report the new synthetic strategies that have been developed to produce hydrosoluble cages and we discuss their recognition properties toward small neutral molecules, ammonium cations and metal ions. We also describe more specifically the design of water-soluble xenon-cryptophane biosensors potentially usable for biomedical imaging. The inherent chirality of these molecules makes them very selective receptors for chiral substrates and this aspect is also underlined. The potential of hemicryptophanes in supramolecular catalysis in aqueous media has resulted in important and innovative recent results that are reported in this chapter.