title: Influence of lithium cations on prolyl peptide bonds.
abstract: The influence of lithium cations on the cis/trans isomerization of prolyl peptide bonds was investigated in a quantitative manner in trifluoroethanol (TFE) and acetonitrile, employing NMR techniques. The focus was on various environmental and structural aspects, such as lithium cation and water concentrations, the type of the partner amino acid in the prolyl peptide bond, and the peptide sequence length. Comparison of the thermodynamic parameters of the isomerization in LiCl/TFE and TFE shows a lithium cation concentration dependence of the cis/trans ratio, which saturates at cation concentrations >200 mM. A pronounced increase in the cis isomer content in the presence of lithium cations occurs with the exception of peptides with Gly-Pro and Asp-Pro moieties. The cation effect appears already at the dipeptide level. The salt concentration can considerably be reduced in solvents with a lower number of nucleophilic centers like acetonitrile. The lithium cation effect decreases with small amounts of water and disappears at a water concentration of about 5%. The isomerization kinetics under the influence of lithium cations suggests a weak cation interaction with the carbonyl oxygen of the peptide bond.
authors.affiliation: Institut für Biochemie, Fakultät für Biowissenschaften, Pharmazie und Psychologie, Universität Leipzig, Brüderstrasse 34, D-04103 Leipzig, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Kunz
authors.forename: Günther
authors.initials: G
authors.lastname: Jahreis
authors.forename: Robert
authors.initials: R
authors.lastname: Günther
authors.forename: Stefan
authors.initials: S
authors.lastname: Berger
authors.forename: Gunter
authors.initials: G
authors.lastname: Fischer
authors.forename: Hans-Jörg
authors.initials: HJ
authors.lastname: Hofmann
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D000596:Amino Acids / Q000737:chemistry; D002412:Cations / Q000737:chemistry / Q000494:pharmacology; D008094:Lithium / Q000737:chemistry* / Q000494:pharmacology; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000187:drug effects; D013237:Stereoisomerism; D013816:Thermodynamics; D014270:Trifluoroethanol / Q000737:chemistry
chemical_list: D000097:Acetonitriles; D000596:Amino Acids; D002412:Cations; D010455:Peptides; D014270:Trifluoroethanol; D008094:Lithium; C032159:acetonitrile