Chemical shifts as a novel measure of interactions between two binding sites of symmetric dialkyldimethylammonium bromides to α-cyclodextrin

Abstract Complex formation of α-cyclodextrin (α-CD) with decyltrimethylammonium (DeTAB), N , N -dioctyldimethylammonium (DOAB), and N , N -didecyldimethylammonium bromides (DDeAB) was investigated by proton NMR spectroscopy. Analysis of chemical shifts yielded macroscopic 1:1 and 1:2 binding constants ( K 1 and K 2 ) and chemical shift differences (Δ δ SD and Δ δ SD2 ) for the 1:1 and 1:2 complexes of DeTAB, DOAB, and DDeAB with α-CD. The K 1 and K 2 values of DDeAB were quantitatively explained on the basis of the assumption that the microscopic 1:1 binding constant of DDeAB is identical to the observed K 1 value of DeTAB. The K 2 value of DDeAB was also explained in terms of its observed K 1 value and the independent binding of two alkyl chains. Furthermore, the Δ δ SD and Δ δ SD2 values for protons of DDeAB and α-CD were quantitatively explained on the basis of the assumption that the geometry of the decyl group of DDeAB in an α-CD cavity is identical to that of DeTAB. The Δ δ SD value was also explicable on the basis of the same geometric assumption and the observed Δ δ SD2 value for this system. Similar results were obtained for the 1:1 and 1:2 DOAB–α-CD complexes.