Enthalpic Nature of the CH/π Interaction Involved in the Recognition of Carbohydrates by Aromatic Compounds, Confirmed by a Novel Interplay of NMR, Calorimetry, and Theoretical Calculations
Enthalpic Nature of the CH/π Interaction Involved in the Recognition of Carbohydrates by Aromatic Compounds, Confirmed by a Novel Interplay of NMR, Calorimetry, and Theoretical Calculations
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DOI：
10.1021/ja903950t
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发表时间：
2009-12-23
影响因子：
15
通讯作者：
Cuevas, Gabriel
中科院分区：
文献类型：
--
作者：
Ramirez-Gualito, Karla;Alonso-Rios, Rosa;Cuevas, Gabriel
分子之间的特定相互作用，包括由给定溶质产生的分子和周围溶剂之间的特定相互作用，对于驱动分子识别过程是必不可少的。一个简单的分子，如苯，能够识别和区分非常相似的实体，如甲基2，3，4，6-四-O-甲基-α-D-吡喃半乳糖苷（alpha-Me（5）Gal），methyl 2，3，4，6-tetra-O-methyl-beta-D-galactopyranoside（β-Me（5）Gal）、1，2，3，4，6-五-O-乙酰基-β-D-吡喃半乳糖（β-Ac（5）Gal）和甲基2，3，4，6-四-O-甲基-α-D-吡喃甘露糖苷（α-Me（5）Man）。为了确定这些复合物是否形成，使用Calvet微量热法测定苯与不同碳水化合物之间的相互作用能作为溶剂化焓。四种络合物的焓值分别为-89.0 +/- 2.0、-88.7 +/- 5.5、-132.5 +/- 6.2和-78.8 +/- 3.9 kJ mol（-1）。通过建立使用NMR发生相互作用的分子区域来完成不同复合物的表征。确定β-Me（5）Gal通过α面上碳水化合物的非极性区域产生的CH/pi相互作用而稳定。相比之下，α-Me（5）Man不被苯特异性地溶剂化，并且不存在任何堆积相互作用。虽然α-Me（5）Man的几何结构与其差向异构体相似，但获得的NMR数据似乎表明，异头位置的轴向甲氧基增加了苯分子与吡喃糖环的距离。甲氧基被乙酸酯部分取代，如在β-Ac（5）Gal中，排除了苯产生CH/pi的途径。互动事实上，β-Ac（5）Gal的升高的稳定化能可能是由于苯与乙酰基的甲基之间的相互作用。因此，甲氧基和乙酰基取代基对吡喃糖环的质子具有不同的影响。
Specific interactions between molecules, including those produced by a given solute, and the surrounding solvent are essential to drive molecular recognition processes. A simple molecule such as benzene is capable of recognizing and differentiating among very similar entities, such as methyl 2,3,4,6-tetra-O-methyl-alpha-D-galactopyranoside (alpha-Me(5)Gal), methyl 2,3,4,6-tetra-O-methyl-beta-D-galactopyranoside (beta-Me(5)Gal), 1,2,3,4,6-penta-O-acetyl-beta-D-galactopyranose (beta-Ac(5)Gal), and methyl 2,3,4,6-tetra-O-methyl-alpha-D-mannopyranoside (alpha-Me(5)Man). In order to determine if these complexes are formed, the interaction energy between benzene and the different carbohydrates was determined, using Calvet microcalorimetry, as the enthalpy of solvation. These enthalpy values were -89.0 +/- 2.0, -88.7 +/- 5.5, -132.5 +/- 6.2, and -78.8 +/- 3.9 kJ mol(-1) for the four complexes, respectively. Characterization of the different complexes was completed by establishing the molecular region where the interaction takes place using NMR. It was determined that beta-Me(5)Gal is stabilized by the CH/pi interaction produced by the nonpolar region of the carbohydrate on the a face. In contrast, alpha-Me(5)Man is not specifically solvated by benzene and does not present any stacking interaction. Although alpha-Me(5)Man has a geometry similar to that of its epimer, the obtained NMR data seem to indicate that the axial methoxy group at the anomeric position increases the distance of the benzene molecules from the pyranose ring. Substitution of the methoxy groups by acetate moieties, as in beta-Ac(5)Gal, precludes the approach of benzene to produce the CH/pi. interaction. In fact, the elevated stabilization energy of beta-Ac(5)Gal is probably due to the interaction between benzene and the methyl groups of the acetyls. Therefore, methoxy and acetyl substituents have different effects on the protons of the pyranose ring.