A CSD search in the Cambridge Crystallographic Database for the substructure N–C_αH–C′(═O)–N gave 24,180 peptide structures for analysis of the pyramidalization of the sp²-hybridized carboxamide group C′(═O)NC_α, which had not been investigated before. The dependence of the pyramidalization θ = O–N–C′–C_α on the rotation angle ψ = O═C′–C_α–N about bond C′–C_α resulted in a curve with three maxima, three minima, and six zero-crossings. Surprisingly, the ψ/θ analysis of the individual amino acid building blocks showed that all of them exhibited similar curves, irrespective of their different R substituents. This unusual behavior is explained by a 3-fold short-range potential set up by the three covalent bonds, emanating from C_α. The tie-up of the rotation angle ψ and the pyramidalization θ in a rigid coupling is remarkable. In the 24,180 peptide structures, subjected to X-ray crystallography, there is no dynamics. For peptides in solution, the rotation/pyramidalization curve ψ/θ_av determines the degree of pyramidalization θ, when the rotation angle ψ runs through a full 360° circle. Density functional theory (DFT) calculations of alaninamide supported the analysis.

中文翻译：

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肽结构中羧酰胺 sp2 中心的金字塔化

CSD 在剑桥晶体学数据库中搜索子结构 N–C _α H–C′(=O)–N 给出了 24,180 个肽结构，用于分析 sp ²杂化甲酰胺基团 C′(=O)NC _{α 的}金字塔化，之前没有研究过。金字塔化 θ = O–N–C′–C _α对关于键 C′–C _α的旋转角 ψ = O=C′–C _α –N的依赖性导致了一条具有三个最大值、三个最小值和六个过零。令人惊讶的是，各个氨基酸结构单元的 ψ/θ 分析表明，无论 R 取代基不同，它们都表现出相似的曲线。这种不寻常的行为可以通过由 C _α发出的三个共价键建立的 3 倍短程电势来解释。刚性耦合中旋转角 ψ 和金字塔化 θ 的结合是显着的。在经过 X 射线晶体学分析的 24,180 个肽结构中，没有动力学。对于溶液中的肽，当旋转角 ψ 穿过完整的 360° 圆时，旋转/金字塔化曲线 ψ/θ _av决定了金字塔化程度 θ。丙氨酰胺的密度泛函理论 (DFT) 计算支持了该分析。