Geometric Origin of the Photosynthetic Macrocycle: Dual-Chrysene Cage Rearrangement, 18 pi-Electron Conservation, and the 1.1 Ga Geoporphyrin Record

Abstract

The oldest secure molecular fossils of chlorophyll—nickel and vanadyl geoporphyrins of the Etio and DPEP series recovered from 1.1 Ga black shales of the Taoudeni Basin—occupy a narrow carbon-number window (C28-C34) and retain an 18 pi-electron aromatic core. Under the Identification Hypothesis the dual-chrysene metal cage of the Chrysene Formalism supplies a carbon-parsimonious geometric precursor for these molecules. One tetrasubstituted chrysene unit (18 carbons, 18 pi-electrons), together with its four substituent arms, rearranges into a metal-coordinated macrocycle whose carbon count falls inside the observed C26-C34 interval. The second chrysene opens into a linear C18 chain whose step-defect carbons are pre-positioned for isoprenoid-type methylation, thereby generating the geometric scaffold of a phytol-like tail. Phosphorus-centred linkers hold the metal in the initial cage and are competent to evolve into the N4 coordination sphere of chlorophyll and of the geological Ni- and VO-porphyrins. The same architecture that accounts for the co-production of membrane lipids and nucleic-acid components therefore also accounts for the core structural features of the photosynthetic macrocycle. The 1.1 Ga geoporphyrin record constitutes a direct empirical test of this pathway and supplies a second, independent geometric fossil of the metamaterial in the pre-Cambrian sedimentary archive.