Energy & Fuels 1990,4, 635-639
635
Sedimentary Porphyrins: Correlations with Biological Precursors H. J. Callot,* R. Ocampo, and P. Albrecht URA 31 du CNRS, Dkpartement de Chimie, Universitd Louis Pasteur, 1 rue Blaise Pascal, F-67008 Strasbourg, France Received April 27, 1990. Reuised Manuscript Received July 1 1 , 1990 Over the past 6 years several sedimentary porphyrins (petroporphyrins, geoporphyrins) were correlated for the first time with biological precursors specific for classes of organisms (algae, photosynthetic bacteria (Chlorobiaceae)). This article discusses the various examples of correlations and the methods that led to these conclusions (isolation of pure porphyrins, structure determination using spectroscopic techniques, total synthesis, isotope measurements). The history of porphyrinic biomarkers in geological samples includes two major development phases. The first phase, close to the discovery of the petroporphyrins, was initiated by Treibs's hypothesis' linking these fossil pigments with two classes of biological moleculeschlorophylls and hemes. The improvement of analytical methods in the following years, in particular mass spectrometry, had however a rather negative effect by revealing that Treibs's compounds were in fact complex mixturesF4 The second phase, which started half a century later, is a consequence of the availability of powerful analytical (HPLC)and spectroscopic (FT-NMR) methods, which allowed the isolation and structure determination of pure porphyrin^.^*^ Additional help was provided by the total synthesis of a series of porphyrins, following structural hyp~theses,'~It led to the first correlations between fossil porphyrins and individual biological precursors or limited groups of precursors, these precursors being specific of a given class of living organisms (algae, bacteria).6 A good account of the beginning of this second phase is presented in the ACS Symposium Series Vol. 344 corBecause of responding to the New York 1986 several new developments in the field, it is now time, only 4 years later, to summarize our latest views on the exciting field of petroporphyrin precursor identification. In contrast with most articles and reviews devoted to fossil porphyrins, the following discussion will start with an inventory of "available precursors" presently known and imagine their possible fate and then turn to the geological past and look at their effective remains.
Chart I
Coou
Coou
1 Chlorophyll a R = Phytyl
COOH 4
Chlorophyll b R = Phytyl
Chloroihylls c c1
R = Me. Rs= Et
R = Me. R' I Vinyl c3 R = COzMe. R'= Vlnyl
Q
-
IR H (DPEPI 6 R = COzH
4
Bacteriochlorophyll a Bacterlcchlorophyll b R = Phytyl
Potential Precursors a. Chlorophylls. Chlorophyllsloare the quantitatively I.
(1) Treibs, A. Liebigs Ann. Chem. 1934, 510, 42-62; Angew. Chem.
1936,49,682-686. (2) Baker, E. W.; Palmer, S. E. In The Porphyrins; Dolphin, D., Ed.: Academic Press: New York. 1978: Vol. 1. ChaDter 11. (3) Baker, E. W.; Louda, J. W. In Advances i'n Organic Geochemistry 1981; Bjoroy, M., et al., Eds.; Wiley: Chichester, 1983; pp 401-421. (4) Filby, R. H.;Van Berkel, G. J. In Metal Complexes in Fossil Fueb; Filby, R. H., Branthaver, J. F., Eds.;ACS Symposium Series 344; American Chemical Society: Washington, DC, 1987; pp 2-39. (5) Chicarelli, M.I.; Kaur, S.; Maxwell, J. R. In Metal Complexes in Fossil Fueb; Filby, R. H., Branthaver,J. F., Eda.; ACS Symposium Series 344; American Chemical Society: Washington, DC, 1987; pp 40-67. (6) Ocampo, R.; Callot, H. J.; Albrecht, P. In Metal Complexes in Fossil Fuels; Filby, R. H., Branthaver, J. F., Eds.; ACS Symposium Series 344; American Chemical Society: Washington, DC, 1987; pp 68-73. (7) Verne-Mismer,J.;Ocampo,R.; Callot, H. J.; Albrecht, P. J. Chem. Soc., Chem. Commun. 1987, 1581-1583. (8) Smith, N. W.; Smith, K. M. J . Chem. SOC.,Perkin Trans. 2 1989, 188. (9)Lash, T. D. Org. Geochem. 1989, 24, 213-215.
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COOR
7
Bacteriochlorophylls d R = Famesyl R = Et, n-Fr. I-Bu. nec-Pentyl R '= Me. Et
8
Bacterlochlorophylls C IR"= Me1 Bacterlochlorophylls e IR"= CHOI R IFamesyt. G-Yl R * Et. n-R. I-Bu.neePentyl R ' Me. Et I
most important tetrapyrroles in the present biomass. This is also true for the "recent" past, after the apparition of photosynthesis. They are a key to the existence of photoautotrophs or plant life and, by consequence, animal life. (10) Vernon, L. P., Seely, G.R., Eds. The Chlorophylls; Academic Press: New York, 1966. Scheer, H., Ed. The Chlorophylls;CRC Press: Boca Raton, FL, in press.
0 1990 American Chemical Society
Callot et al.
636 Energy & Fuels, Vol. 4, No. 6,1990 Scheme I. Rearrangement
+ Diagenesis of Chlorophyll c , I
@ HN /
\'
Chart I1
/
11
9 -
R
i
H. Me, Et
coon
COOH
As for most of the organic matter, the recycling of chlorophylls is an efficient process" and only a minute fraction is trapped in sediments a t the bottom of water bodies. Structurally, the chlorophylls known at present may be separated into two groups (see Chart I). The first is represented by chlorophyll a (1) and the pigments that share the same carbon framework, either intact (chlorophylls b (2) and ~ 1 - 3(3), bacteriochlorophylls a and b (4), but also divinylchlorophyll a, which occurs as a minor biosynthetic intermediate or a major pigment consit ~ e n t ) , ' ~ J or * Jhaving ~ lost the fragile C-15' methyl ester (lowest homologue of bacteriochlorophylls d (7)). The simplest diagenetic route (reductions/aromatization/optional decarboxylation) should lead to one pair of fossil porphyrins, deoxophylloerythroetioporphyrin(DPEP) (5) and the corresponding carboxylic acid 6 having retained the propionic side chain. Additional variations may be introduced by the degradation of fragile groups: cleavage of vinyl, hydroxyethyl, formyl, and alkoxycarbonyl moieties; opening of keto ester (ring E) if present. These last considerations are valid for the rest of the inventory (i.e., vinyl groups of hemes, etc.) and will not be discussed further. However, within this first group, chlorophylls ~ 1 - 3 (3) are unique in possessing a C-17 acrylic side chain, whose rearrangement14 (Scheme I) or cleavage16may produce a C-15,17 five-membered ring or a shortened (2-17 substituent. The second group, containing all the "Chlorobium chlorophylls" 7 + 8 (specific for the family Chlorobiaceae) except the lowest member of the bacteriochlorophylls d (see above), is characterized by the presence of additional carbon atoms either by extension of pyrrolic substituents at positions C-8 and C-12 and/or by methylation of a meso bridge at C-2O.l6 These extended alkyl groups are expected to be stable under diagenetic conditions. In addition to the chlorophylls themselves, a group of compounds, which were isolated from various living organisms (plants and algae, senescent or not; marine and terrestrial grazers) are obvious metabolites of the chlorophylls and, in addition, may cast some light on the first steps of their modifications. The simplest are pheophorbides and pyropheophorbides, corresponding to the loss of magnesium, phytol hydrolysis, and C-15' ester cleavage." Two additional compounds, 9 and 10 (see Chart 11), were isolated from marine animals, a sponge" and a (11) Hendry, G . A. F.; Houghton, J. D.; Brown, S. B. New Phytol. 1987,107, 255-302. (12) Fookes, J. R.; Jeffrey, S. W. J. Chem. SOC.,Chem. Commun. 1989, 1827-1828. (13) Chisholm, S. W.; Olson, R. J.; Zettler, E. R.; Goericke, R.; Waterbury, J. W.; Welschmeyer, N. A. Nature 1988,334, 340-343. (14) Dougherty, R. C.; Strain, H.H.; Swec,W. A.; Uphaus, R. A.; Katz, J. J. J . Am. Chem. SOC.1970,92, 2826-2833. (15) Bonnett, R.; Campion-Smith, I. H.; Page, A. I. J. Chem. SOC., Perkin Trans. 1 1977,68-71. (16) Simpson, D. J.; Smith, K. M. J. A m . Chem. SOC. 1988, 110, 1753-1758 and references cited therein. (17) Karuso, P.; Bergquist, P. R.; Buckelton, P. S.; Cambie, R. C.; Clark, G. R.; Rickard, C. E. F. Tetrahedron Lett. 1986,27, 2177-2178.
c.
I
I
COOH
I
I COOH
COOH 13
12
Heme
Mesoporphyrln
IX
I
I
R' 14 R I H. R ICOOH 15 R = COOH. R = H
-I
I
I
COOH
COOH 18
Bonellln
17
COOH
I
I
COOM 18
R = Farnesyl. R ICHO
Coralllsun A
21
20
V l t a m h BIZ
Slrohydrochlorln
R = CH2-CONHz
R = CHz-COOH
coon
F430
R = CH2-COOH. R
I
CHz-CONzH
clam,18and have in common a C-13 to C-17 bicyclic fragment corresponding to the condensation of the propionic chain with E ring. This new ring system may survive as such or suffer a retrocondensation of the diketone, the strained five-membered ring being expected to open. Indeed "nonspecific" porphyrins having the same ring system as 9 and 10, as well as compounds like 11, were isolated from several source^.^^ b. Hemes. Hemes (12) have a wider distribution than chlorophylls but contribute to a minor fraction, in terms of biomass, of the biological tetrapyrroles. In addition, they are also heavily represented in land animals whose organic remains are less likely to be fossilized. Heme structures are based on the protoporphyrin carbon framework, a fact that suggests a rather uniform structural pattern for the correspondingfossil porphyrins, viz.,simple "etioporphyrins" (in the general sense of meso-unsubstituted polyalkylporphyrins) or the corresponding mono(C-13 and C-17) and dicarboxylic acids (mesoporphyrin (13) and its decarboxylation products 14 and 15). (18) Sakata, K.; Yamamoto, K.; Ishikawa, H.; Yagi, A.; Etoh, H.; h a ,
K. Tetrahedron Lett. 1990,31, 1165-1168.
Sedimentary Porphyrins
Energy & Fuels, Vol. 4, No. 6,1990 637
Some marine pigments like bonellin (l6)l9or corallistin A (17pwhich lack an E ring may produce porphyrins of the "etio" series during diagenesis. A few compounds depart from the basic pattern, i.e., the heme 18 from cytochrome c oxidase, the C-3 side chain of which is extended by a farnesyl chain.z1 c. Miscellaneous Tetrapyrroles. This vague title covers a range of tetrapyrrolic structures, mostly of bacterial origin, vitamin Blz (19),sirohemes (20),factor F430 (21),etc.,2zwhich share in common the property of being highly modified, as compared to the "simple" porphyrins discussed above. These changes involve loss of aromaticity, additional methylations of pyrrolic positions, and loss of one bridge carbon. Many of these compounds retain several carboxylated side chains and are thus very polar as compared to chlorophylb and even hemes. It is difficult, at present, to appreciate the chances of survival of such structures in sediments. In any case one would expect a higher risk of degradation (absence of aromaticity) and possibly a different history due to the polar substituents (participation in the formation of insoluble material?). The field of "exotic" tetrapyrroles is growing rapidly and a porphyrin geochemist should always remain aware that new compounds may provide new interpretations for the presence of "unexpected" fossil molecules.
Correlations The general imagez3given by the 78 petroporphyrins known to the authors at the time of writing of this review (March 1990) fits quite well with the above presentation. These porphyrins belong to 49 basic carbon frameworks, the variations involving the metal (Ni, V=O, Cu, Ga, Fe), and/or the oxidation level (porphyrins/chlorins, presence of hydroxyl group, etc). Most of the expected diagenetic possibilities are illustrated in the fossil record: partial or total loss of fragile groups (vinyl cleavage, decarboxylations, etc.), rearrangements, condensations leading to sevenmembered rings from chlorophylls, et^.^^^ Structural correlations have been drawn between 17 petroporphyrins (12 carbon frameworks) and chlorophylls specific for a class of organisms (algae, bacteria). Additional information, restricted to samples in which specific internal standards are present, could be obtained from isotope measurements. The case of heme-derived porphyrins is more complex, although both structural (five compounds, four carbon frameworks) and isotopic evidence has been presented. a. Algal Chlorophylls. The most spectacular correlations involve chlorophylls ~ 1 - 3and their fossil counterparts. These three porphyrins, typical for certain groups of algae, share in common an acrylic side chain instead of the classical propionic acid.14 An acid-catalyzed rearrangement of the "southern half" of the molecule is known14to lead to a new five-membered ring attached to carbons 15 and 17. A series of porphyrins 22-27 (see Chart 111), which show this modified ring system and thus must be correlated with the "c" series, was found, first in Messel ~
(19) Kennedy, G. Y. Ann.
~~
N.Y.Acad. Sci. 1975,244,662-673. Bal-
lantine, J. A.; Psaila, A. F.; Pelter, A.; Murray-Rust, P.; Ferrito, V.; Schembri, P.; Jaccarini, V. J. Chem. SOC., Perkin Trans. 2 1980,
1080-1089. (20) D'Ambrosio, M.; Guerriero, A.; Debitus, C.; Ribes, 0.;Richer de Forges, B.; Pietra, F. Helu. Chim. Acta 1989, 72, 1451-1454. (21) Battersby, A. R.; Cardwell, K. S.; Leeper, F. J. J. Chem. SOC., Perkin Trans. 2 1986, 1565-1580. (22) Leeper, F. J. Natural Products Reports, 1985,19-47. Battersby, A. R. Acc. Chem. Res. 1986,19,147-152. Pfaltz, A.; Jann, B.; Fiissler, A.; Eschenmoser, A. Helu. Chim.Acta 1982, 65, 828-865. (23) Callot, H. J. Unpublished compilation.
Chart 111
R'
2 2 R Et. R = H 23R=Et,R=COOH 24 R. n. R = n
28
25 R = Et 26 R = Me 27R.H
coon 29 R = H.R = Et 30 R = Me. R' = Et 31 R = H.R' = n
as
32 R = Et 33 R = n-Pr 34 R = i-Bu
36 Etloporphyrln 111
oil shale (lacustrine; Eocene; West GermanyP4 and then in other sediments like Oulad Abdoun and Timahdit oil shales (marine; Maastrichtian; M o r o c c ~ ) . ~ "An ~ ~interesting structural variation is shown by porphyrins 25-27 which lack a substituent at C-7,n suggesting a more specific precursor like chlorophyll c3 (methyl ester at C-7)28or a 7-formylchlorophyllc, by an analogy with the chlorophyll b/chlorophyll a pair.z5*z6The corresponding DPEP (7nor-DPEP) (28)isolated from Serpiano (marine; Triassic; Switzerland)Band Oulad Abdoun oil shales may arise both from chlorophyll b, as earlier suggested,= and from chlorophyll c3.27 Also starting with a chlorophyll c precursor an independent route can lead to a group of pigments 29-31 modified at C-17, after decarboxylation of the free acrylic chain and cleavage of the resulting vinyl group. Indeed they were isolated from most porphyrin fractions of marine origin: Siberian the above Moroccan oil shales,25 (24) Ocampo, R.; Callot, H. J.; Albrecht, P.; Kintzinger, J. P. Tetrahedron Lett. 1984, %, 2589-2592. Ocampo, R.; Callot, H. J.; Albrecht, P. J . Chem. Soc., Chem. Commun. 1985,198-200. (25) Verne-Mismer, J. Th&e de Doctorat, Universit4 Louis Pasteur, Strasbourg, France, 1988. (26) Veme-Mismer, J.; Ocampo,R.; Bauder, C.; Callot, H. J.; Albrecht, P. Abstracts of Papers, 197th ACS National Meeting, Dallas, TX, April 9-14, 1989; American Chemical Society: Washington, DC, 1989, Abstr. PRTR - - - - - nm - --. (27) Verne-Mismer, J.; Ocampo, R.; Callot, H. J.; Albrecht, P. Tetrahedron Lett. 1990, 32, 1751-1754. (28) Fookes, C. J. R.: Jeffrey, S. W. J. Chem. SOC., Chem. Commun. 1989, 1827-1828. (29) Chicarelli. M. I.: Maxwell. J. R. Tetrahedron Lett. 1984, 25, 4701-4704.
Callot et al.
638 Energy & Fuels, Vol. 4, No. 6,1990
Monterey crude oil (Miocene; Calif~rnia),~~ etc. In parallel to these specific fossil porphyrins, chlorophylls c may contribute to a whole range of information-poor “classical” DPEP and DPEP-related structures. b. Bacterial Chlorophylls. Again, the first evidence for bacterial chlorophyll precursors came from lacustrine Messel shale.32 A series of three carboxylic acids 32-34 showed the expected specific substitution pattern: extended side chains a t C-12 (ethyl) and C-8 (propyl and isobutyl). These compounds are only compatible with bacteriochlorophylls d specific of Chlorobiaceae. An additional indication was obtained from Oulad Abdoun oil shale,25which yielded structure 35 (postulated; total synthesis in progress33). Such a C-20 methylated porphyrin may arise from either bacteriochlorophylls c or e (methyl or reducible aldehyde a t C-7). Correlations of petroporphyrins with chlorophylls from photosynthetic bacteria are important since they imply the existence of anoxic layers below the oxygenated waters suitable for algal growth. c. Correlations from Isotope Measurements. The presence of fossil pigments specific for a given class of organisms, which can be used as “internal standards” of origin, allowed a different type of correlations. If one assumes that all porphyrins produced by a given class of organisms should have a similar 13C/12C(=6(13C))ratio, then the relative contribution from various groups of organisms can be estimated by comparing the 8(l3C)of one or several “internal standards” and the 6(13C) measured for the remaining porphyrins of lower structural information content. Such an evaluation of the relative contribution of algae and bacteria to the major porphyrin fractions from Messel shale has been done.34 d. Heme-DerivedPetroporphyrins. Strong evidence for the involvement of hemes or related structures in the formation of petroporphyrins was obtained when mesoporphyrin (13) was isolated from coal.35 The presence of one of its monodecarboxylated products 14 or 15 was also suggested. Isotope measurements on the porphyrins of Julia Creek oil shale (Cretaceous; Australia) added weight to this proposal. Two s t u d i e ~ showed ~ v ~ ~ that all porphyrins that could be clearly related to chlorophylls (“DPEP”s,“etioporphyrins” modified a t C-13, etc.) fall within a rather narrow V 3 C ) range, whereas etioporphyrin I11 (36) itself showed a significantly different 6(13C)value. This result was verified for both nickel and vanadium complexes. Independently, reinvestigation of the composition of Messel oil shale porphyrins permitted the isolation of the nickel complexes of mesoporphyrin (13) (M = Ni) and of its two monodecarboxylationproducts 14 and 15 (M = Ni), which were compared and identified with synthetic samples (NMR, HPLC).= Etioporphyrin I11 (36) itself could ~
~~
~
(30) Serebrennikova, 0.V.;Mozzhelina, T. K.; Shul’ga, A. M. Geokhimiya 1987, 1494-1496. (31) Ocampo, R. Unpublished results. (32) Ocampo, R.; Callot, H. J.; Albrecht, P. J. Chem. SOC.,Chem. Commun. 1985, 200-201. (33) Jeandon, C.; Callot, H. J. Unpublished results. (34) Hayes, J. R.; Takigiku, R.; Ocampo, R.; Callot, H. J.; Albrecht, P. Nature 1987,329, 48-51. (35) Bonnett, R.; Burke, P. J.; Czechowski, F.; Reszka, A. Org, Geochem. 1984, 6, 177-182. Bonnett, R.; Burke, P. J.; Czechowski, F. In Metal Complexes in Fossil Fuels; Filby, R. H.; Branthaver, J. F., Eds.; ACS Symposium Series 344; American Chemical Society: Washington, DC, 1987; pp 173-187. Bonnett, R.; Burke, P. J.; Reszka, A. Fuel 1987, 66, 515-520. (36) Ocampo, R.; Callot, H. J.; Albrecht, P.; Popp, B. N.; Horowitz, M. R.; Hayes, J. M. Naturwissenschaften 1989, 76, 419-421. (37) Boreham, C. J.; Fookes, C. J. R.; Popp, B. N.; Hayes, J. R. Ceochim. Cosmochrm. Acta 1989,53, 2451-2455.
Chart IV
37 R Et 38R.H E
39
40
R = H. Me Et
not be detected in this sediment of very low maturity. An origin from heme is probable for the three acids, thus extending the presence of heme fossils from coals to oil shales. e. ”Correlations”with Hypothetical Precursors. The presence in the fossil porphyrin assemblages of compounds rich in information but which cannot, a t present, be correlated with known natural products, forces us to figure out structures for hypothetical precursors. For a short molecules like 25-27 illustrated this situation, until chlorophyll c3 (3) (R’ = COOMe; R” = vinyl) was discovered%and acted as a plausible precursor.27 37-39 It is still the case for tetrahydrobenzoporphyrin~~ and rhodoporphyrins (40)39 (see Chart IV), their dehydrogenated counterpart. If one considers the “southern half” of some of these fossil porphyrins, it is tempting to draw a chlorophyll c like structure for the precursor. On the other hand, the six-membered ring attached to porphyrin ring B suggests a condensation of an acetic and a propionic side chaina The resulting product may retain either a keto ester, or a ketone, or some other oxygenated function. A more fundamental problem is the fact that such a biosynthetic route does not involve protoporphyrin as for all known chlorophylls. It is also interesting to note that the carbon isotope composition of one of these tetrahydrobenzoporphyrins, from Julia Creek oil shale, was measured and did not fit with the 6(13C) of both etioporphyrin I11 and “classical” chlorophyll derived petroporphyrins, suggesting an independent origin.36
Conclusion The above results illustrate how a very simple approach of porphyrin geochemistry, viz., isolation of pure compounds followed by careful structure determination, gave a spectacular impulse to the whole field. However, one should always remember that this approach was made possible by the recent improvement of analytical, spectroscopic, and synthetic methods. Correlations with natural precursors was the immediate consequence and in some favorable cases, like Messel shale, allowed a reconstruction of the paleoenvironment to be proposed and extensions like isotope-based quantitative estimation of the respective contributions of algae and bacteria to the porphyrin fractions. The existence of several independent diagenetic routes from the same biological precursor(s), as illustrated by the products from chlorophyll c, is another promising feature and should find use in differentiating maturity parameters of various sediments. Demonstration of the contribution of hemes or heme-like molecules is the most recent achievement in the field, and the existence of several still uncorrelated, but information-rich petroporphyrins suggests further developments. (38) Bauder, C.; Ocampo, R.; Callot, H. J.; Albrecht, P. Naturwissenschaften 1990, 77, 378-379. (39) Kaur, S.; Chicarelli, M. I.; Maxwell, J. R. J.Am. Chem. SOC.1986, 108, 1347-1348. (40) Clezy, P.S.; Mirza, A. H. Aust. J. Chem. 1982,35, 197-209.
Energy & Fuels 1990,4, 639-643
639
The knowledge of porphyrin biomarkers has now reached maturity and their use as biomarkers in oil-related studies, as are hopanes, steranes, etc., can be envisaged. Studies of detailed structural variations of porphyrins as a function of depth41or of structural correlations between
Acknowledgment. We thank the CNRS and the doofthe Petroleum Research Fund, administered bY the American Chemical Society, for financial support.
(41) Ocampo,R.; Callot, H. J.;Albrecht, P. Abstracts of Papers, 199th ACS National Meeting, Boston, April 22-27,1990; American Chemical Society: Washington, DC, 1990; Abstr. GEOC 074.
(42) Ocampo, R.; Riva, A.; Callot, H. J.; Albrecht, P. Abstracts of Papers, 199th ACS National Meeting, Boston, April 22-27, 1990; American Chemical Society: Washington, DC, 1990; Abstr. GEOC 069.
oil and source rocks42are in progress. nOrS
Structural Comparison of Nickel, Vanadyl, Copper, and Free Base Porphyrins from Oulad Abdoun Oil Shale (Maastrichtian, Morocco) J. Verne-Mismer, R. Ocampo, C. Bauder, H. J. Callot,* and P. Albrecht* URA 31, Dgpartement de Chimie, Universitg Louis Pasteur, 1 rue Blaise Pascal, F-67008 Strasbourg, France Received April 27, 1990. Revised Manuscript Received June 15, 1990 Twenty-eight individual alkylporphyrins have been identified complexed by nickel, vanadyl, or copper in the Moroccan bituminous marl of Ouland Abdoun. A structural comparison of the composition of the nickel and vanadyl porphyrin fractions has shown substantial differences. The nickel porphyrins are strongly enriched in a whole variety of yet unidentified "etio" compounds, in cycloheptano components, and in rearranged products derived from algal chlorophyll c. The vanadyl fraction is enriched in 17-nor-DPEP (DPEP = deoxophylloerythioetioporphyrin),presumably also derived from chlorophyll c , relative to classical C,-DPEP, which is major in the nickel fraction. A free base porphyrin fraction has been tentatively characterized and seems to be restricted to a mixture of "etioporphyrins". The reasons for these differences are still unelucidated; they may arise from a selective availability of metals at various stages of sedimentation or from a structure-dependent selectivity in metal insertion. The isolation of pure porphyrins from various geological sources, followed by unequivocal structure assignment, represents the only reliable method for reconstructing the identity and fate of the chlorophyll precursors and their depositional conditions. In addition, the knowledge of the structures of all quantitatively significant porphyrins present in a sediment allows comparisons between various porphyrin assemblages like fractions from different sediments or porphyrins complexed by different The present study was first devoted to the structure determination of the extractable porphyrins present in the Moroccan Oulad Abdoun bituminous marl (Maastrichtian; 65 Myr ago), which has been deposited in an area of intense marine sedimentation due to active upwelling events. The primary organic matter is mainly of algal origin and has been well preserved due to limited bacterial reworking. I t turned out that the extract contained four groups of alkylporphyrins either present as free bases or metalated by nickel, vanadium (as vanadyl), and copper. This paper will comment on the variations of porphyrin composition ~~
~~~
~
(1) Chicarelli, M. I.; Kaur, S.; Maxwell, J. R. In Metal Complexes in
Fossil Fuels;Filby, R. H., Branthaver, J. F., Ede.; ACS Symposium Series 344; American Chemical Society: Washington, DC, 1987; pp 40-67. (2) Ocampo, R.; Callot, H. J.; Albrecht, P. In Metal Complexes in Fossil Fuels; Filby, R. H., Branthaver, J. F., Ed.;ACS Symposium Series 3&, American Chemical Society: Washington, DC, 1987; pp 68-73. (3) Filby, R. H.; Van Berkel, G. J. In Metal Complexes in Fossil Fuels; Filby, R. H., Branthaver, J. F., Eds.; ACS Symposium Series 344; American Chemical Society: Washingon, DC, 1987; pp 2-39.
0887-0624/90/ 2504-0639$02.50/0
as a function of the complexed metal.
Isolation, Purification, and Structure Determination of Individual Porphyrins The bituminous marl was collected in the Oulad Abdoun ~ phosphate basin (100 km south of Rabat, M o r ~ c o ) .The sample used for the study contained 14.5% organic C and 4.4% P ~ 0 5 . ~ The extraction and separation of the porphyrin fractions from the marl6produced two major groups of compounds: nickel (7 mg/kg marl) and vanadium alkylporphyrins (19 mg/kg marl). In addition, three minor fractions were observed copper alkylporphyrins which coeluted (on silica gel, but not under HPLC conditions) with the nickel compounds, a "zinc" porphyrin fraction (2 mg/kg marl) which proved to be produced by artifactual metalation of free bases during the chromatographic separations, and a vanadyl porphyrin acid fraction which will not be discussed here. The vanadyl and zinc porphyrin fractions were transmetalated into nickel complexes before being separated (HPLC) into individual compounds, in order to work within homogeneous series. The copper porphyrins were separated along with the nickel complexes and then individually transmetalated into nickel complexes. The (4) Rauacher, R.; Schuler, M.; Benalioulhaj, N. Doc. Bur. Rech. Ceol. Min. 1984, 110, 127-139. (5) Meunier-Christmann, C. These de Doctorat de l'Universit.6 Louis Pasteur, Strasbourg, 1988.
1990 American Chemical Society
