Department of Chemistry, Miami University, 45056, Oxford, OH.
J Am Soc Mass Spectrom. 1994 Aug;5(8):718-23. doi: 10.1016/1044-0305(94)80003-0.
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.
采用傅里叶变换离子回旋共振质谱仪中的质子转移反应，测定了丝氨酸和甘氨酰-丝氨酸二肽中氨基酸残基的气相碱性。发现 L-丝氨酸的气相碱性（GB）为 205.9 kcal/mol，与最简单的氨基酸甘氨酸（GB = 201.4 kcal/mol）相比，增加一个羟甲基（-CH2OH）基团使碱性增加 4.5 kcal/mol。这归因于分子内氢键、诱导和对称效应的组合。对于二肽，与甘氨酰甘氨酸（GB = 208.0 kcal/mol）的碱性相比，增加羟甲基基团并不导致碱性大幅增加。测定的甘氨酰-L-丝氨酸、L-丝氨酰甘氨酸和 L-丝氨酰-L-丝氨酸的气相碱性分别为 209.3、210.6 和 210.9 kcal/mol。与甘氨酰甘氨酸相比，在 N 末端添加羟甲基基团对碱性的影响大于在 C 末端添加羟甲基基团。这些数据表明，这些二肽的质子化位点是 N 末端的氨基氮。
