Li Hongbao, Jiang Jun, Luo Yi
Hefei National Laboratory for Physical Sciences at the Microscale, School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230026, China.
Phys Chem Chem Phys. 2017 Jun 14;19(23):15030-15038. doi: 10.1039/c7cp01997a.
Extensive ab initio investigations have been performed to characterize stable conformers of protonated triglycine (GGGH) in the gas phase. Calculations using the composite CBS-QB3 method confirmed that the most favorable site of protonation on triglycine at 298 K is still the traditional amino nitrogen, rather than the more-recently reported amide oxygen. Furthermore, a non-proline cis-peptide bond conformer is identified for the first time as the global minimum of GGGH. Further transition state calculations considering the temperature effects explained why the previous experimental infrared multiple photon dissociation (IRMPD) spectrum contains a combination of two local minima, rather than a global one. First-principles simulations have been performed for near-edge X-ray absorption fine-structure (NEXAFS) spectra and X-ray photoelectron spectra (XPS) at the C, N and O K-edges to identify the notable spectral differences that enable the unambiguous identification of different protonated forms. The calculated proton affinity (PA) and gas basicity (GB) of triglycine are in excellent agreement with the experimental values. Our study thus provides valuable insights into the protonation of short peptides and illustrates the competition between cis and trans peptide bonds.
已经进行了广泛的从头算研究，以表征气相中质子化三甘氨酸（GGGH）的稳定构象异构体。使用复合CBS-QB3方法进行的计算证实，在298K下三甘氨酸上最有利的质子化位点仍然是传统的氨基氮，而不是最近报道的酰胺氧。此外，首次鉴定出一种非脯氨酸顺式肽键构象异构体是GGGH的全局最小值。考虑温度效应的进一步过渡态计算解释了为什么先前的实验红外多光子解离（IRMPD）光谱包含两个局部最小值的组合，而不是一个全局最小值。已经对C、N和O K边的近边X射线吸收精细结构（NEXAFS）光谱和X射线光电子能谱（XPS）进行了第一性原理模拟，以识别能够明确识别不同质子化形式的显著光谱差异。计算得到的三甘氨酸的质子亲和力（PA）和气相碱度（GB）与实验值非常吻合。因此，我们的研究为短肽的质子化提供了有价值的见解，并说明了顺式和反式肽键之间的竞争。
