PORPHYRINS IN COAL

The background to recent developments in investigations on coal porphy rins is reviewed. Essentially all the work of the past ten years has b een with lignites and coals of the humic series. The concentrations of porphyrins and metalloporphyrins are low (0-ca. 10 mu g g(-1)), which makes for difficulties in isolation and analysis. The preferred metho ds of isolation and analysis are summarised. The coal porphyrins diffe r from the porphyrins from crude oil, oil shale and related deposits i n a variety of ways which are discussed. The major differences are the predominance of the etio series over the cycloetio series (DPEP serie s), the presence of Fe and Ga porphyrins (rather than Ni and VO porphy rins), and the presence of mesoporphyrin IX in lignite. Recent results tend to support Treibs' original idea (1935) that, for the coal porph yrins, both chlorophyll and iron porphyrin (haem) sources are importan t. The application of a weighted mean molecular mass of the porphyrins present as a biological marker in determining coal rank (Porphyrin In dex of Coalification) is illustrated Current activity is directed to t he isolation and identification of individual iron complexes, and here a combination of thin layer chromatography and paramagnetically shift ed H-1-NMR spectroscopy (of dicyanoferrihaems), together with direct c omparison with authentic haems especially synthesised for the purpose, has been rewarding.