PECULIARITIES OF COMPLEX FORMATION IN THE SULFOBUTYL ETHER-β-CYCLODEXTRIN - IONIC LIQUID SYSTEM

Abstract

The inclusion complexation of sulfobutyl ether-β-cyclodextrin sodium salt (SBECD) - ionic liquid (IL) has been investigated by a series of appropriate methods. The stability constant of the complex of SBECD-IL (K = 72.4 m-1) was determined by the method of Higuchi and Connors. An increase in the surface tension of solutions with different SBECD’s content was recorded by using the method of Wilhelm's plate, which could serve as an additional evidence of the formation of inclusion complex between SBECD and IL. Analysis of the TGA results provided for the initial IL and SBECD, their mechanical mixture and the complex elaborated allows us to conclude that the "guest-host" type complexation is emerged. Differential scanning calorimetry (DSC) data also confirmed the formation of inclusion complex between SBECD and IL. While the guest molecule is incorporated into cyclodextrin cavity, its thermal properties are changed. So, the loss of physically bonded water in the complex is equal to 5% by weight, indicating the IL’s molecule being located in the SBECD’s hydrophobic cavity. The thermogram of inclusion complex demonstrates just one endothermic peak at 74 oC. The complex is formed by entering the long alkyl chain of ionic liquid into the hydrophobic cavity of SBECD. Since the bonds of sulfo groups and β-СD’s glucopyran cycles become weaker, this may testify an additional interactions between SBECD and IL. With  thermograviometric analysis (TGA) of the original IR and SB-β-CD, their mechanical mixture and the test compound fixed the formation of not a classical complex, but an associated complex of inclusion type "guest-host", which is formed by entering a long alkyl chain IR in the hydrophobic cavity SB-β-CD.