Alpha-cyclodextrin complexes with linear alpha,omega-dicarboxylic acids were investigated
by electrospray mass spectrometry. These hydrophobic complexes are known to have an
equilibrium binding constant that increases with the diacid chain length. However,
the electrospray mass spectrometry (ES-MS) spectra showed that the relative intensity
of the complex did not vary significantly with chain length. This contradiction is
caused by a contribution of nonspecific adducts to the signal of the complex in ES-MS.
In order to estimate the contribution of nonspecific adducts to the total intensity
of the complexes with alpha-cyclodextrin, the comparison was made between alpha-cyclodextrin
and maltohexaose, the latter being incapable of making inclusion complexes in solution.
The signal observed for complexes between diacids and maltohexaose can only result
from nonspecific electrostatic aggregation, and is found to be more favorable with
the shorter diacids. This is also supported by MS/MS experiments. A procedure is described
which allows estimation of the contribution of the nonspecific complex in the spectra
of the complexes with alpha-cyclodextrin by using the relative intensity of the complex
with maltohexaose. The contribution of the specific complex to the total signal intensity
is found to increase with the diacid chain length, which is in agreement with solution