Enantiodifferent Proton Exchange in Alanine and Asparagine in the Presence of H217O
Identifieur interne : 002723 ( Main/Exploration ); précédent : 002722; suivant : 002724Enantiodifferent Proton Exchange in Alanine and Asparagine in the Presence of H217O
Auteurs : Vily Marius Cimpoia U [Roumanie] ; Romulus Ion Scorei [Roumanie] ; Radu Popa [États-Unis]Source :
- Journal of Molecular Evolution [ 0022-2844 ] ; 2010-07-01.
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Abstract
Abstract: Using Time Domain 1H Nuclear Magnetic Resonance with H217O (H217O-TD-1HNMR), we found [H217O]- and pH-controlled chiral differences in proton exchange properties in alanine (Ala) and asparagine (Asn). To minimize and equalize chemical impurities, Asn enantiomers were purified by crystallization from racemic solution. At <0.1 M H217O, a shift in isoelectric pH (pI) occurred, ~1.14 kJ mol−1 l-d-Asn ΔΔG o′ in the 5.91–6.42 pH range. One potential source for this asymmetry is the enantio-different magnetic moments (lμ↑ ≠ dμ↓) produced by neutral ring currents in the chiral center, leading to enantio-different nuclear spin organization and charge distribution in the amino group. At ≥pI, dissimilar interactions may occur in the hydration of the amino group with H217O (NH2/H217O ≠ NH2/H216O; NH3 +/H217O ≠ NH2/H217O; l-*C-NH2/H217O ≠ d-*C-NH2/H217O). As lμ↑ ≠ dμ↓, the l-*C-amino and the d-*C-amino groups are diastereo spin-isomers. The nuclear spin of 17O may be parallel or antiparallel with the ortho-1H1H pair; hence two ortho-H217O molecules exist, also diastereo spin-isomers. As the pK of H217O is different from H216O, dissimilarities between l-*C- and d-*C-amino groups are converted into proton exchange differences. During H217O-TD-1HNMR, the H217O molecule is a “probe” of the state of the amino group. Regarding prebiotic evolution: prebiotic chirality may not require stochastic symmetry breaking or preexisting chiral conditions; chemical chiral effects due to lμ↑ ≠ dμ↓ are small and need chiral amplification to generate an enantiomeric excess significant for prebiotic evolution; and prebiotic symmetry breaking was homochiral because the effect of lμ↑ and dμ↓ on the amino group should be similar in all alpha amino acids.
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DOI: 10.1007/s00239-010-9361-z
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To minimize and equalize chemical impurities, Asn enantiomers were purified by crystallization from racemic solution. At <0.1 M H217O, a shift in isoelectric pH (pI) occurred, ~1.14 kJ mol−1 l-d-Asn ΔΔG o′ in the 5.91–6.42 pH range. One potential source for this asymmetry is the enantio-different magnetic moments (lμ↑ ≠ dμ↓) produced by neutral ring currents in the chiral center, leading to enantio-different nuclear spin organization and charge distribution in the amino group. At ≥pI, dissimilar interactions may occur in the hydration of the amino group with H217O (NH2/H217O ≠ NH2/H216O; NH3 +/H217O ≠ NH2/H217O; l-*C-NH2/H217O ≠ d-*C-NH2/H217O). As lμ↑ ≠ dμ↓, the l-*C-amino and the d-*C-amino groups are diastereo spin-isomers. The nuclear spin of 17O may be parallel or antiparallel with the ortho-1H1H pair; hence two ortho-H217O molecules exist, also diastereo spin-isomers. As the pK of H217O is different from H216O, dissimilarities between l-*C- and d-*C-amino groups are converted into proton exchange differences. During H217O-TD-1HNMR, the H217O molecule is a “probe” of the state of the amino group. Regarding prebiotic evolution: prebiotic chirality may not require stochastic symmetry breaking or preexisting chiral conditions; chemical chiral effects due to lμ↑ ≠ dμ↓ are small and need chiral amplification to generate an enantiomeric excess significant for prebiotic evolution; and prebiotic symmetry breaking was homochiral because the effect of lμ↑ and dμ↓ on the amino group should be similar in all alpha amino acids.</div></front></TEI><affiliations><list><country><li>Roumanie</li><li>États-Unis</li></country></list><tree><country name="Roumanie"><noRegion><name sortKey="Cimpoia U, Vily Marius" sort="Cimpoia U, Vily Marius" uniqKey="Cimpoia U V" first="Vily Marius" last="Cimpoia U">Vily Marius Cimpoia U</name></noRegion><name sortKey="Scorei, Romulus Ion" sort="Scorei, Romulus Ion" uniqKey="Scorei R" first="Romulus Ion" last="Scorei">Romulus Ion Scorei</name></country><country name="États-Unis"><noRegion><name sortKey="Popa, Radu" sort="Popa, Radu" uniqKey="Popa R" first="Radu" last="Popa">Radu Popa</name></noRegion><name sortKey="Popa, Radu" sort="Popa, Radu" uniqKey="Popa R" first="Radu" last="Popa">Radu Popa</name></country></tree></affiliations></record>Pour manipuler ce document sous Unix (Dilib)
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