Table 2.

Compound identifications of the C₁ to C₆ alkylpyrroles

Compound	LRIa	Mass spectral Characteristics	Distb Cave 1	Quantb 249-01	Quantb 2552-02	Isbistb DL715	Isbistb DL5119	Isbistb DL5838	Mont42,c kerogen	Bili42	Chlor a42
1. 2-methylpyrrole	841	81(70), 80(100), 53(60)	√	√	√	√	√	√		√	√
2. 3-methylpyrrole	850	81(70), 80(100), 53(50)	√	√	√	√	√	√	√	√	√
3. 2,5-dimethylpyrrole	-		-	-	-	-	-	-		(√)	-
4. 2,4-dimethylpyrrole	930	95(62), 94(100), 80(50)	√	√	√	√	√	√	√	√	√
5. 2,3-dimethylpyrrole	939	95(75), 94(100), 80(40)	√	√	√	√	√	√	√	√	√
6. 3,4-dimethylpyrrole	953	95(60), 94(100), 80(30)	-	√	√	√	√	√	√	√	√
7. 2-ethyl-4(?)-methylpyrrole	1007	109(30), 108(3), 94(100)	√	√	√	√	√	√		(√)	(√)
8. 2-ethyl-3(?)-methylpyrrole	1010	109(40), 108(5), 94(100)	√	√	√	√	√	√		√	√
9. 4-ethyl-2-methylpyrrole	1016	109(37), 108(5), 94(100)	√	√	√	√	√	√		(√)	(√)
10. 2,3,5-trimethylpyrrole	1020	109(62), 108(100), 94(37)	√	√	√	√	√	√	√	√	√
11. 3-ethyl-4-methylpyrrole	1024	109(48), 108(7), 94(100)	-	-	-	√	√	√	√	√	√
12. 2,3,4-trimethylpyrrole	1041	109(68), 108(100), 94(33)	-	-	-	√	√	√	√	√	√
13. ethyldimethylpyrrole	1091	123(40), 108(100), 94(20)	-	-	√	-	√	√		(√)	(√)
14. ethyldimethylpyrrole	1099	123(35), 108(100), 94(5)	-	-	tr.	tr.	-	tr.		(√)	(√)
15. 4-ethyl-2,3-dimethylpyrrole	1103	123(37), 108(100), 93(6)	√	√	√	√	√	√	√	√	√
16. 3-ethyl-2,4-dimethylpyrrole	1109	123(40),122(30),108(100)	√	√	√	√	-	√	√	√	√
17. 2,3-diethyl-4-methylpyrrole	1181	137(30),122(100),107(50)	-	-	-	-	-	tr.		√	(√)
18. 3-ethyl-2,4,5-trimethyl- pyrrole	1199	137(35),122(100),107(15)	tr.	-	-	-	tr.	tr.	√	√	√
19. 3-methyl-4-isobutyl- pyrroled	1130	137(10),122(10),94(100)	tr.	tr.	tr.	-	-	tr.	n/a	-	-
20. 2,3-dimethyl-4-n-propyl-pyrroled	1185	137(25),122(35),108(100)	-	-	-	tr.	-	tr.	n/a	-	-
21. 3-ethyl-4-isobutyl- pyrroled	1239	151(5),136(35),121(70), 109(55),94(100)	tr.	-	tr.	-	-	tr.	n/a	-	-
22. 3-methyl-4-neopentyl- pyrroled	1258	151(5),94(100)	-	-	-	tr.	-	tr.	n/a	-	-
23. 2-methyl-3-ethyl-4-n-propylpyrroled	1258	151(5),122(100),108(90)	-	-	-	-	-	tr.	n/a	-	-

√ = present; - = absent/not detected; (√) = present, but only as a minor component (<1%); tr. = compounds identified as trace constituents (based on retention times and mass spectra) from those samples with C₁ to C₅₊ alkylpyrroles thermolytically-derived by pyrolysis-gas chromatography mass spectrometry at 610 °C (following thermal desorption/extraction of free compounds at 310 °C) and comparisons with alkylpyrroles from pyrolysed Monterey kerogen and tetrapyrrole model compounds⁴².

Mont kerogen Monterey kerogen, Bili bilirubin (an animal-derived tetrapyrrole pigment), chlor a chlorophyll a (a plant, algae and cyanobacteria-derived tetrapyrrole pigment), n/a not applicable.

^aLRI = linear retention index.

^bCalculus samples: Distillery Cave 1; Quanterness samples 249-01 and 2552-02; Isbister samples DL715, DL5119 and DL5838.

^cOnly major alkylpyrroles reported in the original publication⁴².

^dAlkylpyrroles in bold derive from the C8 side chain in bacteriochlorophylls c and d found in green bacteria such as Chloroflexus sp⁴⁵. and known to naturally occur in association with red seaweeds such as Porphyra umbilicali^4,46,47.