Conformation-specific pathways of beta-alanine: a vacuum ultraviolet photoionization and theoretical study.
Conformation-specific pathways of beta-alanine: a vacuum ultraviolet photoionization and theoretical study.
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DOI：
10.1021/jp9002565
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发表时间：
2009-04
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通讯作者：
Lidong Zhang;Yang Pan;Huijun Guo;Taichang Zhang;Liu-si Sheng;F. Qi;Po-Kam Lo;K. Lau
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文献类型：
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作者：
Lidong Zhang;Yang Pan;Huijun Guo;Taichang Zhang;Liu-si Sheng;F. Qi;Po-Kam Lo;K. Lau
本文报道了用红外激光解吸结合同步辐射真空紫外光电离质谱研究β-丙氨酸的光电离和离解光电离。由光电离产生的m/z = 45、44、43和30的片段分别归属于NH（3）CH（2）CH（2）（+）、NH（2）CHCH（3）（+）、NH（2）CHCH（2）（+）和NH（2）CH（2）（+）。通过从头计算G3 B3方法和光电离效率（PIE）谱的测量，建立并确定了一些新的构象特异性解离通道和相应的解离能.理论值与实验结果相当一致。用G3 B3方法研究了β-丙氨酸阳离子的三种低位构象，包括两种偏位构象G1+、G2+和一种反位构象A+。构象G1+（分子内氢键N-H…OC）是形成NH（3）CH（2）CH（2）（+）离子的另一个前体，这与先前报道的仅与构象体G2+（分子内氢键O-H.的形成途径是互补的。N）。NH（2）CHCH（2）（+）可能来自于G1+、G2+和A+通过不同的解离途径的贡献。最丰富的碎片离子NH（2）CH（2）（+）由直接C-C键断裂形成。分子内氢转移过程主导了β-丙氨酸阳离子的大多数断裂途径。
We report a photoionization and dissociative photoionization study of beta-alanine using IR laser desorption combined with synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry. Fragments at m/z = 45, 44, 43, and 30 yielded from photoionization are assigned to NH(3)CH(2)CH(2)(+), NH(2)CHCH(3)(+), NH(2)CHCH(2)(+), and NH(2)CH(2)(+), respectively. Some new conformation-specific dissociation channels and corresponding dissociation energies for the observed fragments are established and determined with the help of ab initio G3B3 calculations and measurements of photoionization efficiency (PIE) spectra. The theoretical values are in fair agreement with the experimental results. Three low-lying conformers of the beta-alanine cation, including two gauche conformers G1+, G2+ and one anti conformer A+ are investigated by G3B3 calculations. The conformer G1+ (intramolecular hydrogen bonding N-H...OC) is found to be another precursor in forming the NH(3)CH(2)CH(2)(+) ion, which is complementary to the previously reported formation pathway that only occurs with the conformer G2+ (intramolecular hydrogen bonding O-H...N). Species NH(2)CHCH(2)(+) may come from the contributions of G1+, G2+, and A+ via different dissociation pathways. The most abundant fragment ion, NH(2)CH(2)(+), is formed from a direct C-C bond cleavage. Intramolecular hydrogen transfer processes dominate most of the fragmentation pathways of the beta-alanine cation.