Theoretical conformational analysis of N–formyl–L–serine–L–alanine–NH₂ dipeptide model was investigated using B3LYP/6-311+G(d,p) and M06-2X/6-311+G(d,p) calculations. In this research, 243 total possible conformations of the dipeptide model were optimized including 87 stable conformers and the other disappeared ones migrated to more stable geometries. Migration pattern suggests more stability of the dipeptide model with the serine (ser) in β_L, γ_L, and γ_D and the alanine (ala) in γ_D and γ_L configurations, along with 26 of the found conformers having β-turn structures. Our calculations reveal that the most stable conformer, γ_L⁺γ_D, is in β-turn region of Ramachandran map; therefore, serine-alanine (ser-ala) dipeptide model should be adopted with a β-turn conformation. The atoms in molecules (AIM) topological analysis was carried out to characterize the nature of the intramolecular hydrogen bonding in β-turn structures. The γ_L⁺γ_D, including three hydrogen bonds, has the highest stability, while α_L^aγ_L as the most unstable β-turn conformer bears two and one hydrogen bonds at the B3LYP/6-311+G(d,p) and M06-2X/6-311+G(d,p) levels of theory, respectively.

Graphical abstract

中文翻译：

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N-甲酰基-L-丝氨酸-L-丙氨酸-NH2二肽的完整构象分析的侦察DFT研究。

使用B3LYP / 6-311 + G（d，p）和M06-2X / 6-311 + G（d，p）研究了N-甲酰基-L-丝氨酸-L-丙氨酸-NH ₂二肽模型的理论构象分析计算。在这项研究中，优化了243个二肽模型的可能构象，包括87个稳定的构象异构体，其他消失的构象迁移到了更稳定的几何结构。迁移模式建议用在丝氨酸（Ser）中，二肽模型的更稳定β_大号，γ_大号，和γ _d和丙氨酸（Ala）在γ _d和γ_大号配置，沿与具有所找到的构象异构体26 β-转结构。我们的计算表明，最稳定的构象，γ_大号⁺ γ _d，是β-德兰地图的转折区; 因此，应采用具有β-转角构象的丝氨酸-丙氨酸（ser-ala）二肽模型。进行了分子中原子（AIM）拓扑分析，以表征β-转弯结构中分子内氢键的性质。的γ_大号⁺ γ _d，其中包括三个氢键，具有最高的稳定性，而α_大号^一个γ_大号作为最不稳定的β-顺式构象异构体分别在B3LYP / 6-311 + G（d，p）和M06-2X / 6-311 + G（d，p）的理论水平上带有两个和一个氢键。

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