On Serine Octamer Substitution Reactions.

rationaleMonomeric amino acids substitute into the ionized serine octamer (Ser

methodsThe substitution reactions of several proteogenic AA's (Ala, Leu, isoLeu, Pro, Phe, and Val), along with prebiotically relevant isomers (norVal and isoVal), were investigated using a quadrupole ion trap mass spectrometer to gain insight into the determinants of the chiral behavior. Rather than using isotopically labeled enantiomers, as in previous work, cluster formation was assessed using samples of variable chiral composition and concentration.

resultsSubstitution enantioselectivity was confirmed, though in the case of some double substitutions and the substitution of nonproteogenic isomers, the homochiral preference was decreased or inverted, an observation which is attributed to the disruption of the highly ordered noncovalent contacts of the parent Ser

conclusionsThis investigation illustrates how chiral chemistry using MS must operate through weak but chirality-sensitive forces while avoiding dominance of stronger but chirality-insensitive reaction drivers; namely the propensity of a chiral organic base to acquire the charge of a proton affiliated with other chiral molecules. These results are significant because chiral molecular clusters are fundamentally interesting. Understanding the origins of their enantioselectivity contributes to a general understanding of how small molecules may recognize chirality in reaction partners and accumulate enantiomeric excess.