Determination of the Binding Constant for the Complexation Reaction of PGE1 and a-Cyclodextrin by Capillary Electrophoresis, NMR, and Conductometry
Schipper, Benjamin R.
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Three different techniques were used to determine the binding constant for the complexation reaction ofPGE 1 with a-cyclodextrin (a-CD). The three techniques used were capillary electrophoresis (CE), NMR, and conductivity. CE utilized a change in the electrophoretic mobility depending on the amount of complexed material. NMR measured a change in the chemical shift of the C20 methyl proton& which is also directly related to the fraction ofPGE 1 complexed with a-CD. Conductivity relied on changes in conductivity measurements and, once again, these measurements were dependent on the percentage of complexed compound. In all cases a binding curve was generated by plotting the above mentioned changes against the concentration of a-CD. From that curve the binding constant was extracted. By CE the values obtained ranged from 518 M-l to 708 M-l. The variations in results are mostly due to runs conducted at different temperatures with higher temperatures resulting in higher values for the binding constant. NMR yielded a result of 1117 M-l in a buffered experiment and 393 M-l for an experiment run in the presence of benzyl alcohol. Conductivity results were unusable for the set of experiments using batch solutions but the experiments that involved titration were much better behaved. They gave a mean value for the binding constant of710 M -l.