The State Key Laboratory of Physical Chemistry of Solid Surfaces, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, China.
J Am Chem Soc. 2011 Aug 31;133(34):13731-6. doi: 10.1021/ja205613x. Epub 2011 Aug 10.
The anomeric effect plays a central role in carbohydrate chemistry, but its origin is controversial, and both the hyperconjugation model and the electrostatic model have been proposed to explain this phenomenon. Recently, Cocinero et al. designed a peptide sensor, which can bind to a sugar molecule methyl D-galactose, and claimed that the anomeric effect can be sensed by the spectral changes from the β- to the α-complex, which are ultimately attributed to the lone pair electron density change on the endocyclic oxygen atom [Nature 2011, 469, 76; J. Am. Chem. Soc. 2011, 133, 4548]. Here, we provide strong computational evidence showing that the observed spectral changes simply come from the conformational differences between the α- and β-anomers, as the replacement of the endocyclic oxygen atom with a methylene group, which disables both the endo- and the exo-anomeric effects in methyl D-galactose, leads to similar spectral shifts. In other words, the "sensor" cannot probe the anomeric effect as claimed. We further conducted detailed energetic and structural analyses to support our arguments.
端基效应在碳水化合物化学中起着核心作用，但它的起源存在争议，超共轭模型和静电模型都被提出来解释这一现象。最近，Cocinero 等人设计了一种肽传感器，它可以与糖分子甲基 D-半乳糖结合，并声称可以通过从β-到α-复合物的光谱变化来感知端基效应，而这些变化最终归因于环内氧原子上孤对电子密度的变化[《自然》2011，469，76；《美国化学会志》2011，133，4548]。在这里，我们提供了强有力的计算证据，表明观察到的光谱变化仅仅来自于α-和β-端基异构体之间的构象差异，因为用亚甲基取代环内氧原子会同时使甲基 D-半乳糖的内端基和外端基效应失活，导致类似的光谱位移。换句话说，所谓的“传感器”并不能探测端基效应。我们进一步进行了详细的能量和结构分析来支持我们的论点。
