SEDIMENTARY PURPURINS - OXIDATIVE TRANSFORMATION PRODUCTS OF CHLOROPHYLLS

Examination of sediments from three contemporary lakes (Priest Pot, Lo ch Ness and Lake Baikal) reveals the presence of oxidative transformat ion products of chlorophyll a in two of the settings. Purpurin-18 phyt yl ester, not previously reported in sediments, occurs in the two lake s that have deep water columns. The free acid counterpart, purpurin-18 , occurs in only one of the samples, that from Loch Ness. Although, wh ere present, the abundance of purpurin-18 phytyl ester is similar to t hat of individual chlorin steryl esters there appears not to be a corr elation between their abundances in the sediments, suggesting that for mation of the purpurins is not mediated by herbivory. The presence of oxidative transformation products of chlorophyll in contemporary lake bottom sediments indicates their formation during the earliest stages in chlorophyll degradation. Their preservation in sediments demonstrat es that oxidative transformation reactions in the aquatic environment lead not only to destruction of the chlorophyll macrocycle, but also t o structures modified in ring E. This lends support to the view that s edimentary aetioporphyrins originate mainly, though not exclusively, f rom transformations of chlorophylls that involve oxidative cleavage of the five-membered exocyclic ring. (C) 1998 Elsevier Science Ltd. All rights reserved.