Important Effects of Lithium Carbonate on Stoichiometry and Property of the Inclusion Complexes of Polypropylene Glycol and β-Cyclodextrin

The present work reveals a significant influence of lithium carbonate (Li2CO3) on stoichiometry, yield, spectral property, and thermal behavior of the inclusion complex formed by polypropylene glycol (PPG) and beta-cyclodextrin (CD). First, the presence of Li2CO3 in aqueous solution leads to the formation of an inclusion complex PPG-(beta-CD)(6), which is completely different from that precipitated from pure water. This finding is supported by the result of a similar experiment in the case of lithium chloride, demonstrating that the self-assembling behavior of PPG, a flexible oligomer, and beta-CD, a rigid oligomer, in solution can be mediated by additions of the lithium salts. Second, powder X-ray diffraction patterns indicate that the lithium salts in solution play a considerable role in fabricating three-dimensional structures of the complex. Third, the difference in stoichiometry and microstructure of the complexes precipitated from different media is reflected by the difference of their thermal properties. Finally, the results of viscosity, surface tension, and conductivity measurements provide positive support on the effect of the lithium salts on the physical property of PPG solution. Taken together, these observations provide a novel framework for understanding functions of inorganic salts in designing and constructing supramolecules.