Effect of pH on the Conformation of Inclusion Complexes between β-Lactam Antibiotics and β-Cyclodextrins in Aqueous Solution.

The inclusion complexes of two β-lactam antibiotics, ampicillin (ABPC) and amoxicillin (AMPC), with β-cyclodextrin in aqueous solution has been studied by semi-empirical molecular orbital method. In a strongly acid solution, two different types of complexes with a 1:1 stoichiometry were formed. Complex_Ph, in which the phenyl ring of β-lactam antibiotics was oriented towards the cavity of CD, and Complex_Pe, in which the penam ring was oriented towards the cavity. In neutral or basic solution, only Complex_Ph was formed. These results match the results of microcalorimetry and H NMR spectroscopy. [ABSTRACT FROM AUTHOR]