Hypercarbonic Chiral Propagation
From Wikinfo
Hypercarbonic Chiral Propagation
The chirality propagation mechanism here shown for racemic aminoacids is a minimally stripped down version of the possible equilibrium forms in the hypercarbonic medium. Accordingly, N-carboxylation and protonation of the main-chain carboxyl are essential, but the actual reactive species may involve the addition of CO2 or H2S to the peptidic material, with the use the corresponding aminodiacids and thioacid derivatives. Although modern organisms use optically active aminoacids, this mechanism is otherwise fully congruent with present-day biochemistry.
In the hypercarbonic medium, aminoacids are deprived of their zwitterion properties. The nucleophilic attack of the carboxylated amino group on the protonated carboxyl proceeds easily, generating an adduct which contains a resonance stabilised carbanion. The asymmetric recombination with the proton is oriented by the aminoacid residue added in the previous cycle. Since initiation may occur through acylation by an achiral carboxylic acid, the first aminoacid of the chain can be any of the two enantiomers. It will determine, however, the chiral orientation of all its subsequents, giving rise to homochiral polypeptides. Another important aspect is that the acylation of the amino group of the aminoacid residue raises the pka of the carboxyl group thereby increasing the proportion of protonated carboxyls and favouring chain elongation rather than the attack of monomers. The mechanistic theory for the origin of chirality in the biological world is an integral part of the ecopoesis model [1] for the origin of life.
As of 29 Jan 2008 this page is an authorized abridged copy of the official Ecopoesis website [2]
