FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein, The Netherlands.
J Am Soc Mass Spectrom. 2010 May;21(5):698-706. doi: 10.1016/j.jasms.2010.01.004. Epub 2010 Jan 22.
We present the first infrared spectra of a mass-selected deprotonated peptide anion (AlaAlaAla) and its decarboxylated fragment anion formed by collision induced dissociation. Spectra are obtained by IRMPD spectroscopy using an FTICR mass spectrometer in combination with the free electron laser FELIX. Spectra have been recorded over the 800-1800 cm(-1) spectral range and compared with density functional theory calculated spectra at the B3LYP/6-31++G(d,p) level for different isomeric structures. These experiments suggest a carboxylate anion for M-H and an amide deprotonated (amidate) structure for the a(3) fragment anion M-H-CO(2). The frequency for the amidate carbonyl stretch occurring around 1555 +/- 5 cm(-1) has been confirmed by additional spectroscopic studies of the conjugated base of N-methylacetamide, which serves as a simple model system for the deprotonated amide linkage in a peptide anion.
我们呈现了第一个通过碰撞诱导解离形成的质量选择的去质子化肽阴离子（AlaAlaAla）及其脱羧片段阴离子的红外光谱。通过 FTICR 质谱仪与自由电子激光 FELIX 联用的 IRMPD 光谱获得了光谱。光谱记录在 800-1800 cm(-1) 的光谱范围内，并与不同异构体结构的 B3LYP/6-31++G(d,p) 水平的密度泛函理论计算光谱进行了比较。这些实验表明，M-H为羧酸根阴离子，而 a(3) 片段阴离子M-H-CO(2)为酰胺去质子化（酰胺基）结构。酰胺羰基伸缩的频率约为 1555 +/- 5 cm(-1)，通过 N-甲基乙酰胺的共轭碱的附加光谱研究得到了证实，N-甲基乙酰胺作为肽阴离子中去质子化酰胺键的简单模型体系。
