Measuring Binding Constants of Cyclodextrin Inclusion Compounds

International audienceThe affinity of cyclodextrins for organic and even inorganic pollutants has led to the development of numerous remediation methods at the laboratory scale. Indeed, the hydrophobic cavity of cyclodextrins constitute a versatile vehicle for the efficient transfer of various pollutants from their initial environmental compartment to the cyclodextrin cavity. This transfer can be applied to any environmental media such as soil, water or atmosphere, because cyclodextrins can be dissolved in water solutions or immobilized on solid supports. Both recovery or destructive processes have thus been designed on the basis of cyclodextrin affinity for the target pollutants. As a consequence, the stability of host-guest edifices is of crucial importance for the efficiency of cyclodextrin applications. Therefore, formation constants of such inclusion compounds have been thoroughly investigated, aiming at the custom design of host-guest couples for a given application. Indeed, the molecular shape of the cavity, and consequently the inclusion compound stability, can be tuned by using cyclodextrins of different size or by taking advantage of chemical modifications on the macrocycle.Nevertheless, the rational design of the perfect cyclodextrin may be hindered by a large uncertainty on the complex stability. Indeed, large discrepancies are observed for a given complex in the cyclodextrin literature. There is a lack of a generalized scheme for the measurement of affinity. Therefore, this chapter reviews the common experimental approaches and proposes a unified framework for measuring binding constants of cyclodextrins inclusion compounds. This unified approach relies on the use of minimization algorithms and is decomposed into major associated concepts, with the description of experimental protocols, equilibriums, analytical methods and data treatments. The chapter discusses the concept of global analysis and the issues of stability accuracy, optimization of experimental conditions and evaluation of thermodynamic parameters. Future research will probably focus on the generalization of algorithmic treatments, global analysis and statistical evaluation