Studies on the non-covalent interactions between cyclodextrins and aryl alkanol piperazine derivatives by mass spectrometry and fluorescence spectroscopy

The non-covalent complexes of alpha- and beta-cyclodextrins (alpha-, beta-CDs) with two aryl alkanol piperazine derivatives (Pipe I and Pipe II) have been studied by electrospray ionization mass spectrometry (ESI-MS) and fluorescence spectroscopy. The ESI-MS experimental results demonstrated that Pipe I can conjugate to beta-CD and form 1:1 or 1:2 stoichiometric non-covalent complexes, and Pipe II can only form 1:1 complexes with alpha- or beta-CD. Fluorescence spectra indicated that the fluorescence intensities of Pipe I and Pipe II can be enhanced by increasing the content of beta-CD. The mass spectrometric titration experiments showed that the dissociation constants K-d1 were 5.77 and 9.52 x 10(-4) mol L-1 for the complexes of alpha-CD with Pipe I and Pipe II, respectively, revealing that the binding of alpha-CD-Pipe I was stronger than alpha-CD-Pipe II. The K-d1 and K-d2 values were 9.81 x 10(-4) mol L-1 and 1.11 x 10(-7) (mol L-1)(2) for 1:1 and 1:2 complexes of Pipe I with beta-CD, respectively. The K-d values obtained from fluorescence spectroscopy were in agreement with those from ESI-MS titration. Copyright (C) 2010 John Wiley & Sons, Ltd.