在无溶剂环境中检测异头效应,Nature

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在无溶剂环境中检测异头效应
Nature ( IF 50.5 ) Pub Date : 2011-01-01 , DOI: 10.1038/nature09693
Emilio J Cocinero ₁ , Pierre Carçabal , Timothy D Vaden , John P Simons , Benjamin G Davis

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异头效应是一种化学现象，指的是当六元碳水化合物环在环的 C1 位置包含带负电的取代基时观察到的稳定。这种立体电子效应影响许多生物分子的三维形状。它不仅可以通过这种经典方式表现出来，包括在此类糖中发现的环内氧原子 (O5) 与 C1 取代基的相互作用（内异头效应），而且还可以通过带负电的环外取代基与 O5 的相应相互作用（外-异头效应）。然而，这种现象的潜在物理起源仍不清楚。在这里，我们展示了，结合使用激光光谱和计算分析，截短的肽基序可以在气相中接合分离糖的两个端基异构体，这种环境缺乏可能混淆分析的外来因素。（端基异构体是 C1 上取代基方向不同的异构体。）肽与 d-半乳糖的 α-或 β-端基异构体之间形成的复合物在结构上几乎相同；然而，它们与肽相互作用的极化强度差异很大。自然键序计算支持这一观察结果，并且它们共同揭示了内异头效应之外的外显性。由于吡喃糖环上 C1 和 C2 位置（分别为 O1 和 O2）的氧原子之间的相互作用可以改变碳水化合物的外/内比，我们的结果表明重新评估影响和生物学效应非常重要,

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Sensing the anomeric effect in a solvent-free environment

The anomeric effect is a chemical phenomenon that refers to an observed stabilization of six-membered carbohydrate rings when they contain an electronegative substituent at the C1 position of the ring. This stereoelectronic effect influences the three-dimensional shapes of many biological molecules. It can be manifested not only in this classical manner involving interaction of the endocyclic oxygen atom (O5) found in such sugars with the C1 substituent (endo-anomeric effect) but also through a corresponding interaction of the electronegative exocyclic substituent with O5 (exo-anomeric effect). However, the underlying physical origin(s) of this phenomenon is still not clear. Here we show, using a combination of laser spectroscopy and computational analysis, that a truncated peptide motif can engage the two anomers of an isolated sugar in the gas phase, an environment lacking extraneous factors which could confound the analysis. (Anomers are isomers that differ in the orientation of the substituent at C1.) Complexes formed between the peptide and the α- or β-anomers of d-galactose are nearly identical structurally; however, the strength of the polarization of their interactions with the peptide differs greatly. Natural bond order calculations support this observation, and together they reveal the dominance of the exo- over the endo-anomeric effect. As interactions between oxygen atoms at positions C1 and C2 (O1 and O2, respectively) on the pyranose ring can alter the exo/endo ratio of a carbohydrate, our results suggest that it will be important to re-evaluate the influence, and biological effects, of substituents at position C2 in sugars.

更新日期：2011-01-01

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