Magnetic non-equivalence and dynamic NMR of N-methylene protons in a Histamine-containing pseudopeptide: Alanyl-Glycyl-Histamine

Add time:07/29/2019    Source:sciencedirect.com

The objective of the present research is to explore the potential of an additional feature of proton 1D-NMR for the study of the properties of peptides in aqueous solution, namely the magnetic non-equivalence of N-methylene protons in linear acyclic peptides induced by an asymmetric carbon atom located nearby. For this exploratory study, we have chosen an l-Alanyl terminal residue adjacent to a Glycyl residue, itself grafted to an optically inactive terminal Histamine unit, i.e., the Histamine-containing pseudopeptide l-Alanyl-Glycyl-Histamine (AGHA). The pH- and temperature-dependence of magnetic non-equivalences of Glycyl and Histamine N-methylene protons was modeled as a weighted mean over four ionization states BH3, BH2, BH, B of AGHA molecules found in the pH range explored: pH −0.78 to 12. In parallel, this research has made it possible to assess the pK's governing the speciation curve, the base- and acid-catalyzed proton exchange rates and the pK's of amide bonds.

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