A new series of steryl chlorin esters: pheophorbide a steryl esters in an oxic surface sediment

Investigation of chlorins in the oxic surface sediment of a small eutrophic alpine lake (Motte lake) revealed the presence of a new series of steryl c hlorin esters containing the pheophorbide a nucleus. together with their py ropheophorbide a steryl ester counterparts previously observed in the anoxi c surface sediment of the same lake, Identification of the pheophorbide tr steryl esters was based on comparison of spectroscopic, chromatographic and mass spectrometric characteristics of the compounds with those of a synthe tic standard and of pyropheophorbide a steryl esters. Combined liquid chrom atography-mass spectrometry analysis confirmed the absence of pheophorbide a steryl esters in the anoxic sediment but allowed their detection in tract s in the water column. indicating that pheophorbide a steryl esters are, li ke their pyropheophorbide a analogs, formed in the water column. The distri bution of sterols released by hydrolysis of the pheophorbide a steryl ester s shows close similarities to that of the free sterols in the water column and of the sterols of the pyropheophorbide a steryl esters. It appears that , like their pyropheophorbide a counterparts, pheophorbide a steryl esters incorporate mainly sterols of phytoplanktonic origin. Their formation proba bly involves the same mechanism as for pyropheophorbide a steryl ester form ation. i.e. metabolism by zoo-plankton grazing on phytoplankton. The presen ce of pheophorbide it steryl esters in the oxic sediment and their absence from the anoxic sediment is probably due to a lower stability of compounds containing a carbomethoxy substituent in the anoxic environment. (C) 2000 E lsevier Science Ltd, All rights reserved.