多肽是廣泛應用於催化、藥物傳遞等生物醫學領域的生物聚合物。特別是多肽的自發形成被認為是理解早期地球生命起源的關鍵。最近，研究顯示在深共熔溶劑（DESs）中進行的酯肽交換反應之胜肽合成能夠降低酯和肽序列混合的高多樣性，從而產生高產率的目標多肽。然而，DES對肽合成的機制及其影響仍然不清楚。在此，我們利用分子動力學（MD）模擬和密度泛函理論（DFT）計算來確定酯肽交換反應之胜肽合成的機制，該機制包含乙醇酸和甘氨酸的寡聚化以及酯-醯胺交換和酯延長的兩個競爭反應。通過DFT計算，我們發現了反應的途徑及其相應的中間體。利用反應物的最高佔據分子軌道（HOMO）和最低未佔分子軌道（LUMO），酯-醯胺交換和酯延長的相對反應性與實驗數據一致。此外，我們研究了DES對反應途徑中自由能和活化能的影響。MD模擬有助於識別共熔和非共熔系統中反應物空間分佈的差異，顯示出DES立體效應的重要性。綜合結果表明，DES可以抑制酯鍵的形成，促進醯胺延長和酯-醯胺交換反應，從而實現高產率的寡肽。此外，由於與氯的相互作用，DES顯著降低了每個反應的質子化。最終，上述結果為深共熔溶劑中多肽合成的新設計提供了重要的見解。

Polypeptides are biopolymers widely applied in biomedical fields related to biocatalysis, drug delivery, and so on. Particularly, the spontaneous formation of polypeptides is regarded as the key to understand the origin of life on the early Earth. Recently, ester-mediated peptide synthesis in deep eutectic solvents (DESs) has been shown to attenuate the high diversity of the mixing sequences of esters and peptides to produce desired polypeptides with high yields. Nevertheless, the mechanism and the effects of DES on peptide synthesis remain unclear. Here, we utilized both molecular dynamics (MD) simulations and density functional theory (DFT) calculations to determine the mechanism of ester-mediated peptide synthesis, including the oligomerization of glycolic acid and glycine, and two competitive reactions: the ester-amide exchange and the side reaction of ester elongation. Using DFT calculations, we discovered the pathways and the corresponding intermediates of the reaction. Using the HOMO and LUMO of the reactants, the relative reactivities of the ester-amide exchange and the ester elongations were consistent with experimental data. Furthermore, we examined the effects of DES on the free energies and the activation energies along the reaction pathway. MD simulations helped identify the differences in spatial distributions of reactants in the eutectic and non-eutectic systems, showing the importance of the DES steric effects. The combined results demonstrated that DES could inhibit the formation of ester bonds and promote the amide elongation and ester-amide exchange reactions, leading to a high yield of oligopeptides. Moreover, DES significantly decreased the protonation of each reaction because of the interaction with chloride ions. Eventually, these results provide important insights into the novel designs of polypeptide synthesis in deep eutectic solvents.

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