NMR studies on selectivity of beta-cyclodextrin to fluorinated/hydrogenated surfactant mixtures

The interactions between beta-cyclodextrin (beta-CD) and the equimolar/nonequimolar mixtures of sodium perfluorooctanoate (C7F15COONa, SPFO) and sodium alkyl sulfate (CnH2n+1SO4Na, CnSO4, n = 8, 10, 12) were investigated by H-1 and F-19 NMR. It showed that beta-CD preferentially included the fluorinated surfactant when exposed to mixtures of hydrogenated (CnSO4) and fluorinated (SPFO) surfactants, notwithstanding whether the hydrogenated surfactant CnSO4 was more or less hydrophobic than the SPFO. Such preferential inclusion of the fluorinated surfactant continued to a certain concentration of beta-CD at which time the CnSO4 was then observed to be included. The longer the hydrocarbon chain of CnSO4 the lower the concentration of beta-CD at which the hydrogenated surfactants began to show inclusion. The inclusion process can be qualitatively divided into three stages: first, formation of 1:1 beta-CD/SPFO complexes; second, formation of 1:1 beta-CD/CnSO4 complexes; and finally, formation of 2:1 beta-CD/SPFO complexes upon further increase of beta-CD concentration. In the concentration range studied, during the last stage of inclusion both 2:1 beta-CD/C12SO4 and 2:1 beta-CD/SPFO complexes appear to be simultaneously formed in the system of beta-CD/SPFO/C12SO4 but not in either the systems of beta-CD/SPFO/C8SO4 or beta-CD/SPFO/C10SO4. The selective inclusion of the shorter fluorocarbon chain surfactant might be attributed to the greater rigidity and size of the fluorocarbon chains, compared to those of the hydrocarbon chains, which provide for a tighter fit and better interaction between the host and guest. This latter effect appears to dominate the increase in hydrophobic character as the carbon chain length increases in the hydrogenated series.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000247966300024&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Chemistry, PhysicalSCI(E)EIPubMed29ARTICLE288089-809511