Dipartimento di Chimica, Università degli Studi di Milano, via Golgi 19, 20133 Milano, Italy.
J Chem Phys. 2022 Apr 28;156(16):164303. doi: 10.1063/5.0089720.
Proline, a 17-atom amino acid with a closed-ring side chain, has a complex potential energy surface characterized by several minima. Its IR experimental spectrum, reported in the literature, is of difficult and controversial assignment. In particular, the experimental signal at 3559 cm associated with the OH stretch is interesting because it is inconsistent with the global minimum, trans-proline conformer. This suggests the possibility that multiple conformers may contribute to the IR spectrum. The same conclusion is obtained by investigating the splitting of the CO stretch at 1766 and 1789 cm and other, more complex spectroscopic features involving CH stretches and COH/CNH bendings. In this work, we perform full-dimensional, on-the-fly adiabatically switched semiclassical initial value representation simulations employing the ab initio dft-d3-B3LYP level of theory with aug-cc-pVDZ basis set. We reconstruct the experimental spectrum of proline in its main features by studying the vibrational features of trans-proline and cis1-proline and provide a new assignment for the OH stretch of trans-proline.
脯氨酸是一种含有 17 个原子的氨基酸，具有封闭的侧链环，其势能表面具有几个稳定点。其红外实验光谱在文献中有报道，但其归属存在困难和争议。特别是与 OH 伸缩振动相关的实验信号 3559cm-1 很有趣，因为它与全局最小的反式脯氨酸构象不一致。这表明可能存在多种构象共同贡献于红外光谱。通过研究 1766 和 1789cm-1 处的 CO 伸缩振动的分裂以及其他涉及 CH 伸缩和 COH/CNH 弯曲的更复杂的光谱特征，也可以得到相同的结论。在这项工作中，我们采用 ab initio dft-d3-B3LYP 理论水平和 aug-cc-pVDZ 基组，进行全维、在线绝热切换半经典初始值表示模拟。我们通过研究反式脯氨酸和顺式 1-脯氨酸的振动特征，重建了脯氨酸的实验光谱的主要特征，并对反式脯氨酸的 OH 伸缩振动进行了新的归属。
