Schwartz B L, McClain R D, Erickson B W, Bursey M M
Department of Chemistry, University of North Carolina, Chapel Hill 27599-3290.
Rapid Commun Mass Spectrom. 1993 May;7(5):339-42. doi: 10.1002/rcm.1290070507.
Low-energy collisionally activated decomposition (CAD) and unimolecular decomposition of the [M+H]+ ions for X-L-Pro-L-Phe, where X is L-Ala, D-Ala, L-Asp, or D-Asp, allow easy differentiation between the LLL and DLL diastereomers. Tandem mass spectrometric (MS/MS) studies of the [M+H]+ ions formed by fast-atom bombardment (FAB) at various ion kinetic energies (Elab values) on a hybrid tandem instrument produced ions of different intensities for the diastereomers. The ratio of NH3 to H2O loss is 0.3 for the L-Ala peptide but 1.7 for the D-Ala isomer at 5 eV. In some L-Ala spectra, the [M+H-NH3]+ ion does not appear at all. The y2 ion is up to twice as abundant in the L-Ala spectra as in the D-Ala, while the b2 ion is somewhat more abundant for CAD of the D-Ala peptide for most collision energies investigated. The D-Asp peptide produces a b2 ion that is more than half-again as abundant as in the case of the L-Asp isomer, and an [M+H-H2O]+ ion that is up to twice as abundant in the D-Asp CAD spectra as in those of the L-Asp. The y1, a2, and phenylalanine immonium ions are each up to twice as abundant in the L-Asp spectra as in those of the D-Asp isomer. The major differences are correlated with force-field calculations on hydrogen-bonded tautomers.
对于X-L-脯氨酸-L-苯丙氨酸（其中X为L-丙氨酸、D-丙氨酸、L-天冬氨酸或D-天冬氨酸）的[M+H]+离子，低能量碰撞活化分解（CAD）和单分子分解使得LLL和DLL非对映异构体易于区分。在一台混合串联仪器上，对通过快速原子轰击（FAB）在各种离子动能（Elab值）下形成的[M+H]+离子进行串联质谱（MS/MS）研究，得到了不同强度的非对映异构体离子。在5 eV时，L-丙氨酸肽的NH3与H2O损失比为0.3，而D-丙氨酸异构体的该比例为1.7。在一些L-丙氨酸光谱中，[M+H-NH3]+离子根本不出现。在L-丙氨酸光谱中，y2离子的丰度高达D-丙氨酸光谱中的两倍，而在大多数研究的碰撞能量下，对于D-丙氨酸肽的CAD，b2离子的丰度略高。D-天冬氨酸肽产生的b2离子丰度比L-天冬氨酸异构体的情况高出一半以上，并且[M+H-H2O]+离子在D-天冬氨酸CAD光谱中的丰度高达L-天冬氨酸光谱中的两倍。y1、a2和苯丙氨酸亚铵离子在L-天冬氨酸光谱中的丰度均高达D-天冬氨酸异构体光谱中的两倍。主要差异与氢键互变异构体的力场计算相关。
