A comparative study of the allomerization reaction of chlorophyll a and bacteriochlorophyll a

Abstract

A combined spectroscopic and chromatographic approach has been employed to study the products of allomerization of chlorophyll a (chl a), bacteriochlorophyll a (bchl a) and bacterioviridin (bvir) under a variety of conditions. Using high-performance liquid chromatography, mass spectrometry (MS), tandem-MS, NMR spectroscopy, UV-VIS absorption spectroscopy and protected surface-enhanced resonance Raman spectroscopy we have 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 hydroxyl in the allomerization reaction and it is firmly established that a C(13 2 )-CO 2 Me group is required for allomerization to occur. Under identical allomerization conditions, bchl a yields a distribution of products that is different from those given by chl a and bvir. This observation 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 conjugated carbonyl functionality that influences the reactivity in ring E.

Synthesis and characterization of chlorophyllaenol derivatives: Chlorophyllatert-butyldimethylsilyl-enol ether and 131-deoxo-131, 132-didehydro-chlorophylla

“…(1) The enol derivatives are important in relation to the theory of electron delocalization and aromacity/antiaromacity in large macrocyclic p-systems [7]. (2) The enolate anion of Chl [8,9] [5,6,[10][11][12][13][14]. (3) It has been suggested that the enol derivatives of Chl may be involved in the primary events of photosynthetic reaction centers [15].…”

[Heavy metal]-Chlorophylls Formed in Vivo During Heavy Metal Stress and Degradation Products Formed During Digestion, Extraction and Storage of Plant Material

“…The results of Kuronen et al (1993) indicate a free radical mechanism. In contrast to Hynninen, however, the study of Woolley et al (1998) suggests that the hydroxyl and methoxyl radicals may not be the active species in the allomerization reaction.…”

“…More evidence has been gathered in the last decade using HPLC coupled to MS and diode array detection (Kuronen et al, 1993;Rahmani et al, 1993;Brereton et al, 1994;Woolley et al, 1998;Gauthier-Jaques et al, 2001). The results of Rahmani et al (1993) suggest that several com peting degradation pathways are involved in allomerization.…”

“…Recent experiments combining HPLC with Raman spectroscopy, UV/VIS spectroscopy and MS (Woolley et al 1998) provided comprehensive evidence for a complete reaction mechanism that accounts for all major allomerization products. These results disprove the mechanism of Brereton et al (1994) and largely confirm that of Hynninen (1991).…”

Synthesis, Reactivity and Structure of Chlorophylls

“…Several analytical studies, mostly employing modern mass spectrometric methods, were aimed at studying the allomerization reaction of Chl (Grese et al, 1990;Rahmani et al, 1993;Brereton et al, 1994;Hyvarinen et al, 1995). A thorough study by Woolley et al (1998) clearly showed that the 13 2 -CO 2 Me group is required for allomerization Scheme 4 to occur and that a double rather than single bond between C7 and C8 (e.g., Chl vs. BChl) exerts a significant influence on the reactivity of ring E: ring E in Chl a is more susceptible to oxidative ring cleavage and lactone formation than in BChl a. Mass spectrometry also played a crucial role in elucidating ring E biosynthesis for (B)Chls from different organisms (Porra and Scheer, 2000).…”