A COMPARATIVE-STUDY OF THE ALLOMERIZATION REACTION OF CHLOROPHYLL-A AND BACTERIOCHLOROPHYLL A

A combined spectroscopic and chromatographic approach has been employe d to study the products of allomerization of chlorophyll a (chl a),bac teriochlorophyll a (bchl a) and bacterioviridin (bvir) under a variety of conditions. Using high-performance liquid chromatography, mass spe ctrometry (MS), tandem-MS, NMR spectroscopy, UV-VIS absorption spectro scopy and protected surface-enhanced resonance Raman spectroscopy we h ave identified the allomers formed under all the conditions. Analysis of the different product distributions enables us to reach conclusions about the reaction mechanism. Water is identified as the source of hy droxyl in the allomerization reaction and it is firmly established tha t a C(13(2))-CO2Me group is required for allomerization to occur. Unde r identical allomerization conditions, bchl a yields a distribution of products that is different from those given by chi a and bvir. This o bservation has allowed us to demonstrate that it is the bonding at the C(7)-C(8) position of chlorophylls and not the presence of a conjugat ed carbonyl functionality that influences the reactivity in ring E.