Soapy SeparationsChromatography: Detergent film preferentially transports one enantiomer of a small molecule
Soap films cut grease with ease, but with just a dash of the ring-shaped polysaccharide cyclodextrinthey can do even more: separate one mirror image of a small molecule from a mixture containing both (J. Am. Chem. Soc., DOI: 10.1021/ja109461r). Soap bubbles could become useful for chiralseparations, which are important for purifying molecules such as drugs, pesticides, and their precursors. Purnendu K. Dasgupta and colleagues at the University of Texas, Arlington, had previously found a way tomake normally evanescent soap bubbles last for tens of minutes and detect low levels of gases (Anal. Chem., DOI: 10.1021/ac052198h). While investigating how small molecules permeate their soapstructures, they doped films of the detergent Triton-X100 with α-cyclodextrin, a common player in chromatography. The researchers found that, by a factor of 1.6, more α(+)-pinene crossed the soap membranethan did its enantiomer. This happens because, compared to α(+)-pinene, α(-)-pinene gets held up longer in the soap film by binding to the cyclodextrin, the team says.
The soap membrane's 1.6-foldselectivity leaves room for improvement, says Mathias Ulbricht, who studies membranes as tools for separations at the University of DuisburgEssen, in Germany. He suggests that the researchers couldmodify the species doped into the soap film as a chiral selector. Chromatography expert Apryll M. Stalcup at the University of Cincinnati welcomes the new technique. Existing chiral separation...