Abiotic ester formation

Several of the more common commodity polymers like the polyolefins are susceptible to photo-oxidation. For a polymer like polyethylene, photo-oxidation leads to increasing amounts of carbonyl compounds. In-chain ketone groups act as sensitisers by UV light absorption. Through the well-known Norrish type I and II degradations radicals, end-vinyl and ketone groups are formed. Other products often observed in photo-oxidised low-density polyethylene (LDPE) are esters [5]. Scheme 1 shows one mechanism for abiotic ester formation. By Norrish type I cleavage the radical formed can react with an alkoxyl radical on the polyethylene (PE) chain. 

Scheme L Abiotic ester formation in polyethylene (see also G. Scott, Polymer Age 6 (3), 54 (1975), Biological Recycling of Polymers)...

The thioester hypothesis can be summed up as follows the formation of thiols was possible, for example, in volcanic environments (either above ground or submarine). Carboxylic acids and their derivatives were either formed in abiotic syntheses or arrived on Earth from outer space. The carboxylic acids reacted under favourable conditions with thiols (i.e., Fe redox processes due to the sun s influence, at optimal temperatures and pH values) to give energy-rich thioesters, from which polymers were formed these in turn (in part) formed membranes. Some of the thioesters then reacted with inorganic phosphate (Pi) to give diphosphate (PPi). Transphosphorylations led to various phosphate esters. AMP and other nucleoside monophosphates reacted with diphosphate to give the nucleoside triphosphates, and thus the RNA world (de Duve, 1998). In contrast to Gilbert s RNA world, the de Duve model represents an RNA world which was either supported by the thioester world, or even only made possible by it. 

Evidence of the formation of mono-M-octylphthalatc and phthalate ester metabolites has been shown in in vitro studies. The appearance of mono-w-octylphthalatc was observed with preparations of human small intestine, rat liver and intestine, ferret liver and intestine, and baboon liver and intestine (Lake et al. 1977). However, the amount of phthalic acid and other metabolites in these preparations was either minimal or not detected. The study authors concluded that di-ra-octylphthalate is probably absorbed primarily as mono- -octylphthalate (Lake et al. 1977). An in vitro study reported the formation of five keto acids and two diols when metabolic oxidation of the alkyl groups of di-ra-octylphthalate was simulated abiotically (Brodsky et al. 1986). Therefore, the in vivo and in vitro data indicate that major oxidation may occur in the remaining alkyl chain after di-ra-octylphthalate has been hydrolyzed to the... 

It is assumed that polypeptides were formed by self condensation of abiotically produced amino acids, and polynucleotides by self condensation of abiotically produced nucleotides Several mechanisms are possible for the promotion of such condensations In particular, it is known that polyphosphates or polyphosphate esters act as dehydrating agents for the formation of peptides from amino acids when heated or irradiated with UV-light. Such polyphosphates, which are strong candidate forerutmers of ATP, could have arisen from phosphate minerals by the action of cyanoacetylene or cyanogua-nidine, or under the influence of high temperatures (e. g. near to volcanoes). For the development of a true... 

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