A Possible Prebiotic Origin on Volcanic Islands of Oligopyrrole-Type Photopigments and Electron Transfer Cofactors

Abstract

Tetrapyrroles are essential to basic biochemical processes such as electron transfer and photosynthesis. However, it is not known whether these evolutionary old molecules have a prebiotic origin. We have serendipitously obtained pyrroles, which are the corresponding monomers, in laboratory experiments that simulated the interaction of amino acid-containing seawater with molten lava. The thermal pyrrole formation from amino acids, which so far has only been reported for special cases, can be explained by the observation that the amino acids become metal bonded, for example in (CaCl2)3(Hala)2·6H2O (Hala=DL-alanine), when the seawater evaporates. At a few hundred degrees Celsius, sea salt crusts also release hydrochloric acid (HCl). On primordial volcanic islands, the volatile pyrroles and HCl must have condensed at cooler locations, for example, in rock pools. There, pyrrole oligomerization may have occurred. To study this possibility, we added formaldehyde and nitrite, two species for which plausible prebiotic sources are known, to 2,4-diethylpyrrole and HCl. We found that even at high dilution conjugated (oxidized) oligomers, including octaethylporphyrin and other cyclic and open-chain tetrapyrroles, were formed. All experiments were conducted under rigorously oxygen-free conditions. Our results suggest that primitive versions of present-day biological cofactors such as chlorophylls, bilins, and heme were spontaneously abiotically synthesized on primordial volcanic islands and thus may have been available to the first protocells.

Hypercondensation of an Amino Acid: Synthesis and Characterization of a Black Glycine Polymer

“…The thermolysis apparatus used has been described elsewhere. [70] Further experimental details are given in the Supporting Information.…”

The Emergence of Life

“…The genetic code of the thermophilic LUCA likely arose in such a setting; Weiss et al (2016) suggest that life arose in a single hydrothermal vent rather than different components being produced in different environments. Whether or not this was really the case (indeed, cells could have emerged in a number of environments around the globe), it is possible that various prebiotic molecules could have been formed in a variety of environments, ranging from subaerial springs (Damer and Deamer 2015), to coastal volcanic splash pools (Fox and Strasdeit 2013), to pumice rafts (Brasier et al 2011), or submarine hydrothermal sediments. Dass et al (2016) and Westall et al (2018) reviewed the advantages and disadvantages of the various scenarios proposed for the emergence of life (as documented in Table 1) in terms of production of organic molecules, presence of complementary elements of relevance for catalyzing primitive metabolisms, availability of chemical energy for fueling reactions, availability of reactive mineral surfaces, potential for concentrating organic molecules, suitability of temperature for molecular complexification, temperature, pH and redox gradients, influence of fluid dynamics, plausibility of distribution on the Hadean Earth, and protection from impacts, radiation, etc.…”

The Landscape of the Emergence of Life

“…The last products are exceptionally important in that they can transport electrons and harness light, an inexhaustible supply of energy; in modern organisms, these functions are also carried out by cytochromes and chlorophylls respectively. Moreover, porphyrin-type cofactors could have played an important role in the chemical evolution of life by aiding in the formation of important molecules such as peptides and RNA and then eventually DNA [39]. The central tenet of the metabolism first hypothesis is that, initially, protoenzymes were made of amino acids.…”