Fig. 2: MS2 spectra and fragmentation pattern of four typical archaeal lipids.

A MS2 spectrum of Calditiol-GDGT-4a with the fragmentation pattern highlighted with three regions (I, II, and III). Region I refers to the product ions from the neutral loss of small molecules, Region II contains the characteristic ions of archaeal lipids that concern the neutral loss of one diphytanyl chain and subsequent loss of small molecules, and Region III involves the product ions from the further cleavage of the biphytanyl or phytanyl chains. B GTGT-0, an intermediate compound during the biosynthesis of archaeal tetraether lipids. C PG-Archaeol (20:0_25:0), an intact polar lipid with a phosphoglycerol headgroup. D DGD-PA (20:0_20:0_20:0_20:0), an archaeal cardiolipin analogue. The experimental spectrum is shown at the top (black) and the in silico spectrum at the bottom (red).