| Since the development of soft ionization techniques such as matrix assisted laser desorption ionization (MALDI), and electrospray ionization (ESI), in the 1980s, the use of mass spectrometry (MS) as a bioanalytical tool has increased exponentially. Although the number of studies of noncovalent interactions by MS is increasing, the question of how they relate to solution chemistry is under discussion. In order to routinely use mass spectrometric methods to solve bioanalytical problems, the correlation between solution-phase and gas-phase chemistry of biomolecules must be understood.; The formation of micelles by bile acids and related surfactants was the model system used in this research for the study of noncovalent interactions by mass spectrometry. Few studies of noncovalent interactions concerning molecules other than proteins, peptides, and oligonucleotides have been reported, but the door for the development of this novel area of study has been opened.; Micelles are noncovalent aggregates formed by amphiphilic molecules. Bile acids are digestive biosurfactants that form micelles in order to aid in the degradation of lipids. Substances present in food, such as saponins (steroid glycosides of plant origin), have the ability to form mixed micelles with bile acids and steroids. Those interactions have been linked to an anti-hypercholesterolaemic effect of dietary saponins, because they may interfere with cholesterol absorption and bile acids metabolism.; This research was directed toward a method to characterize such complexes, with a focus in the basic concepts involved in the observation of noncovalent interactions of biomolecules by mass spectrometry. Using a quadrupole ion trap instrument, spectra of bile acids and surfactants were obtained. The spectra presented a regular pattern, where multiply charged ions corresponding to large aggregates were identified. The interpretation of the spectra is discussed in terms of a new parameter, n/z, where n is the number of molecules in the multimer ion and z is the charge of the ion. The solution conditions and instrumental parameters required to observe noncovalent interactions were addressed in this work. |
