Giubertoni Giulia, Sofronov Oleksandr O, Bakker Huib J
AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands.
Commun Chem. 2020 Jun 30;3(1):84. doi: 10.1038/s42004-020-0329-7.
The molecular conformation of the carboxyl group can be crucial for its chemical properties and intermolecular interactions, especially in complex molecular environments such as polypeptides. Here, we study the conformational behaviour of the model amino acid N-acetylproline in solution at room temperature with two-dimensional infrared spectroscopy. We find that the carboxyl group of N-acetylproline adopts two distinct conformations, syn- and anti-. In the syn-conformer the O-H group is oriented at ~60 with respect to the C=O and in the anti-conformer the O-H is anti-parallel to the C=O. In hydrogen-bond accepting solvents such as dimethyl sulfoxide or water, we observe that, similar to simple carboxylic acids, around 20% of the -COOH groups adopt an anti-conformation. However, when N-acetylproline is dissolved in a weakly hydrogen-bond accepting solvent (acetonitrile), we observe the formation of a strong intramolecular hydrogen bond between the carboxyl group in the anti-conformation and the amide group, which stabilizes the anti-conformer, increasing its relative abundance to ~60%.
羧基的分子构象对其化学性质和分子间相互作用可能至关重要，尤其是在诸如多肽等复杂分子环境中。在此，我们利用二维红外光谱研究了模型氨基酸N - 乙酰脯氨酸在室温溶液中的构象行为。我们发现，N - 乙酰脯氨酸的羧基呈现两种不同的构象，顺式和反式。在顺式构象中，O - H基团相对于C = O呈约60°的取向，而在反式构象中，O - H与C = O反平行。在诸如二甲基亚砜或水等氢键接受溶剂中，我们观察到，与简单羧酸类似，约20%的 - COOH基团采取反式构象。然而，当N - 乙酰脯氨酸溶解在弱氢键接受溶剂（乙腈）中时，我们观察到反式构象的羧基与酰胺基团之间形成了强分子内氢键，这使反式构象得以稳定，将其相对丰度提高到约60%。
