Gas-phase basicities of serine and dipeptides of serine and glycine

✍ Scribed by John W. McKiernan; Christina E.A. Beltrame; Carolyn J. Cassady

• Book ID: 103995802
• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 588 KB
• Volume: 5
• Category: Article
• ISSN: 1044-0305
• DOI: 10.1016/1044-0305(94)80003-0

✦ Synopsis

The gas-phase basicities of serine and dipeptides containing amino acid residues of serine and glycine were determined by proton transfer reactions in a Fourier transform ion cyclotron resonance mass spectrometer. The gas-phase basicity (GB) of L-serine was found to be 205.9 kcal/mol, with addition of a hydroxymethyl group (-CH2OH) increasing the basicity by 4.5 kcal/mol relative to the simplest amino acid glycine (GB = 201.4 kcal/mol). This is attributed to a combination of intramolecular hydrogen bonding, induction, and symmetry effects. For the dipeptides, addition of a hydroxymethyl group does not result in a large increase in basicity relative to the basicity of glycylglycine (GB = 208.0 kcal/mol). The gas-phase basicities determined for glycyl-L-serine, L-serylglycine, and L-sery-L-serine are 209.3,210.6, and 210.9 kcal/mol, respectively. In comparison to glycylglycine, addition of the hydroxymethyl group at the N terminus has a greater impact on basicity than its placement at the C terminus. These data suggest that the protonation site for these dipeptides is the N-terminal amino nitrogen.