Hydrophobic Complexation Promotes Enzymatic Surfactant Synthesis from Alkyl Glucoside/Cyclodextrin Mixtures

The unique ability of cyclodextrin glycosyltransferase to form and utilize the cyclic maltooligosaccharide cyclodextrin (CD) makes this enzyme an attractive catalyst for the synthesis of alkyl glycosides. Here, we characterize the sugar headgroup elongation of alkyl glucosides (acceptor) via two transglycosylation reactions from either a linear (maltohexose) or a cyclic (CD) glycosyl donor. Inclusion complex formation overcomes both poor substrate solubility and aggregation. We have used pure alkyl glucosides and alpha CD as model compounds. The complex between CD and alkyl glucoside was efficiently used as a substrate. Kinetic and thermodynamic measurements allow the prediction of the optimal synthesis conditions. This optimum corresponds to the transition between a donor-limiting and an acceptor-limiting regime. The resulting rational design should lead to the practical development of a cost-efficient industrial synthesis. Our findings with respect to the importance of complexation should also readily apply to other enzymatic systems

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