Porphyrins fractionation

PTLC may be also applied to obtain very narrow organic compoimd groups such as petroporphyrins. The most simple approach to isolate nickel and vanadyl porphyrin fractions is to use sihca gel TLC plates and hexane-dichloromethane (1 1 v v) or toluene-chloroform (3 1 v v) as a developer. The Rf values for nickel and vanadyl porphyrins are 0.40 to 0.85 and 0.05 to 0.40, respectively [106-109]. 

Fig. 11. Vanadium elution profiles from SEC-HCLP with element selective detection (a) Morichal crude, (b) residual oil, (c) porphyrin fraction (Biggs et al., 1985).

Vanadyl salen provides a model of mixed heteroatom metal coordination characteristic of Ni and VO in the maltenes and asphaltenes. Approximately 50-90% of the metals in petroleum are not contained in the free porphyrin fraction. Yen (1975, 1978) has postulated that these metals exist in a variety of environments such as highly aromatic bound porphyrins, complexed to tetradentates of mixed N, S, and O ligands, or defect sites in large aromatic sheets. Analytical work by Fish et al. (1984) has indicated the presence of metals complexed to salen-type ligands in petroleum. 

Methods for porphyrin fractionation are complex and time consuming and not available in every laboratory. For this reason, simple qualitative screening tests are often used to exclude the majority of specimens that do not require further investigation from the few that justify fractionation of the individual porphyrins. Screening tests in which extracts of urine or feces are examined visually for typical red-pink fluorescence of porphyrins lack sensitivity and should not be used. Methods based on spectrophoto-metric scanning of acidified urine or fecal extracts for the presence of the Soret band are recommended and yield semiquantitative information. Quantitative fluorometric methods are also available. ... 

For diagnostic purposes, quantification of individual porphyrins is rarely necessary, particularly if the concentrations are clearly elevated. Table 32-5 shows expected findings in. the various types of porphyria, and reference values for individual porphyrin fractions are given in Table 32-3. There is considerable variation in the reference values quoted in the hterature/ probably a consequence of the difficulties in calibration. 

The separation of the extract into polycyclic hydrocarbons, and nickel and vanadium porphyrin fractions was accomplished using CCl /CHClo chromatography with Kieselgel (Merck). The vanadium porpnyrin fraction was then further separated into seven major fractions using a variety of column chromatography procedures. Demetallation of the porphyrin fractions was carried out with methanesulphonic acid (Merck) using published procedures (6). 

Although there are obvious differences in the concentrations of the organic vanadium complexes found in the shallow and deep drill cores, the nature of the vanadium complexes present appeared to be virtually identical, as shown by high pressure liquid chromatography (C18 column, methanol solvent at 3 cc/min) of the vanadium porphyrin fractions extracted from core samples taken at depths of 90-92 m and 29-31 m. It would clearly be desirable to extend such studies to samples taken from much greater depths in the Toolebuc formation. 

Figure 2. Typical absorption spectra of the various porphyrin fractions determined in...

Key a, spectrum ofnickel porphyrin fraction b, spectrum typical of Samples 3,61,421, and 441 and identified as vanadyl porphyrins c, spectrum typical of Samples 422 and 4422, tentatively identified as vanadyl phylloerythrin derivatives and d, spectrum of Sample 630 possibly a vanadyl-chlorin complex. This sample contained some vanadyl porphyrin impurities as shown by the absorption peaks at 407, 575, and533 nm. 

Figure 3. Insertion probe mass spectra (electron ionization) of various porphyrin fractions. Key a, Sample 3 b, Sample 61 c, Sample 441 d, Sample 421 e, Sample 422 andf...

Figure 4. Fast atom bombardment spectra (electron ionization) of various porphyrin fractions. Key a,...

Attempts to demetallate the various porphyrin fractions appeared partly successful only in the case of the nickel porphyrins and for sample 3, while demetallation of samples 630, 422 and 4422 yielded no porphyrin type compounds at all. HPLC runs on the demetallated nickel porphyrins and the vanadium porphyrins from fraction 3 showed these to be significantly different. Similar observations have been made previously (12) and may explain why the nickel and vanadium porphyrins appear to have different distributions in the drill cores. However,... 

A green porphyrin fraction, which exhibited 590 nm in the visible spectrum, has been isolated from petroleum. This fraction has been demonstrated to be a ring-containing porphyrin. ... 

Urine 24 h All porphyrin fractions (uro-, heptac.-, hexac., pentac.-, copra-porphyrin) significantly elevated 4 4... 

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