Mass Spectrometric Structural Investigations of Chlorophyll a and Chlorophyll b Derivatives Including the Willstätter Allomerization Products

Objective: This mini-review highlights the highly sensitive ¨soft¨ ionization mass spectrometric methods applied to chlorophyll chemistry. Method: This is a first-hand review of the important developments made over the mass spectrometry of chlorophyll a and chlorophyll b derivatives. Results: The review covers the capacity of the mass spectrometric techniques to solve problems, e.g., assignment of stereochemical configuration at a chiral center, determination of the structures of the chlorophyll b allomers, which are difficult to prepare and purify in larger amounts, and elucidation of the mechanism of Willstatter's allomerization of chlorophylls. Only one example, in which the conventional electron impact mass spectrometry was used, is provided by the characterization of the chlorophyll derivatives found as retinal pigments in the eyes of the remarkable deep-sea fish Malacosteus niger. Other mass spectrometric investigations, dealing with structural properties of chlorophylls, are considered briefly in an end paragraph of this review. Conclusion: Different mass spectrometric techniques have been shown to be very useful in the structural assignments of chlorophyll derivatives.