New Visions in Clay Science
June 11-14, 2018 – University of Illinois at Urbana-Champaign
Session Role of Clay Minerals in the Events Leading to the Origin of Life
« Conspiration of minerals and organic in origins of life »
Francisco de Assis Rodriguez, Thomas Georgelin, Jean-François Lambert, and Maguy Jaber
The condensation of oligomers (amino acids, nucleotides) into the corresponding biopolymers on mineral surfaces, with or without activators, is a part of many prebiotic scenarii [1,2,3]. While it has long been evidenced experimentally, a satisfactory physico-chemical description is still lacking, and would constitute a prerequisite to determine the likelihood of “surface scenarii”. The corresponding polymerization reactionsin aqueous solutions are endergonic and therefore do not occur spontaneously.
What makes them thermodynamically allowed on surfaces is simply the possibility of working in conditionsofverylowwateractivity,as allreportedsuccessfulinstancesofpolymerizationinvolvedrying steps. Since these condensation reactions result in the production of one water molecule (R-COO–+ R’-NH3+= R-CO-NH-R’ + H2O), simple thermodynamic arguments (Lechâtelier’s principle) ensure that decreasing water activity will favor condensation. This is of course not a catalytic effect since catalysis cannot change the thermodynamics.
The same argument holds for several reactions of fundamental importance in current bioenergetics, such as the formation of ATP (P-O-P from P-OH condensation) or various phosphorylations (C-O-P from C-OH and P-OH).
Therefore we have compared on the same supports the dimerization of the simple amino acid with the formation of ATP from ADP and inorganic phosphate, and with the formation of an inorganic activated molecule (pyro- and/or metaphosphates from orthophosphate). The investigated systems are characterizedboth macroscopically, from thermogravimetric analysis, and at the molecular level with 13C,31P solid-state NMR, transmission IR and Raman spectroscopy of the dried powders in order to unequivocally identify the formation of so-called “high-energy” bonds (P-O-P, C-O-P bust also amide bonds).
Not all mineral surfaces are efficient to promote endothermic condensations, although the thermodynamicargument should be the same for all of them. Some surfaces provide an intermediate strength interaction with the adsorbed biomolecules, probably by H-bonding, and in this way open new reaction pathwayswith lower activation energy, resulting in condensation at measurable rates for moderate temperatures (100-200°C).