Naslov
On the Specificity of a-Cyclodextrin Complexes with Aliphatic Dicarboxylic Acids Detected by Electrospray Mass Spectrometry

Autori
Galic, Nives ; Gabelica, V. ; De Pauw, E.

Izvornik
Journal of the American Society for Mass Spectrometry (1044-0305) 13 (2002); 946-953

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Cyclodextrins ; Aliphatic Dicarboxylic Acids ; Electrospray Mass Spectrometry

Sažetak
Cyclodextrins (CD’ s) are torus-like macro-rings built up from glucopyranose units. The exterior of the cavity is hydrophilic, making the molecule water-soluble, whether the interior is semi-polar. The most probable mode of binding involves the insertions of the less polar part of the guest molecule into the cavity, while the more polar group of the guest is exposed to the bulk solvent just outside the wider opening of the cavity. As a general rule, the complex is strong when there is a size complementarity between the guest and the cavity of the CD. Molecules containing aliphatic chains can fit into the a-CD (6 glucose units), whether molecules containing phenyl groups fit better into b-CD (7 glucose units). We have chosen to investigate the complexes between a-CD and aliphatic a, w-dicarboxylic acids -OOC– (CH2)n– COO-. In solution, the binding constant increases when the aliphatic chain length increases, and this is attributed to the hydrophobic effect. Experiments were carried out on a Micromass Q-TOF2 instrument equipped with the Z-spray source. Samples were all prepared in an aqueous basic solution (pH = 9), to ensure that the diacid is doubly deprotonated in solution. The full scan mass spectra show for all complexes a large peak corresponding to the (1:1)2- complex, as well as a smaller peak corresponding to 2 cyclodextrins bound to 1 diacid: (2:1)2-. The relative intensity of the 1:1 complex does not change dramatically with the chain length, although more complex is supposed to be present in solution as the chains length increases. This suggests that the complexes observed by ES-MS are not all specific. Comparisons have been made with maltohexaose, which is the linear analog of a-CD, and which is not supposed to make specific complexes. A significant amount of 1:1 and 2:1 complex is nevertheless observed. After correcting for the different response factors of maltohexaose and a- CD, we could estimate the proportion of specific and nonspecific complexes observed. It has been found that the proportion of specific complex increases with the chain length, which is in agreement with the solution phase data.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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