Calorimetric Measurement of the CH/ Interaction Involved in the Molecular Recognition of Saccharides by Aromatic Compounds

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• 作者：Lorena Bautista-Ibá ; ñ ; ez ; Karla Ramí ; rez-Gualito ; Beatriz Quiroz-Garcí ; a ; Aaró ; n Rojas-Aguilar ; Gabriel Cuevas
• 刊名：Journal of Organic Chemistry
• 出版年：2008
• 出版时间：February 1, 2008
• 年：2008
• 卷：73
• 期：3
• 页码：849 - 857
• 全文大小：210K
• 年卷期：v.73,no.3(February 1, 2008)
• ISSN：1520-6904

文摘

Can a benzene molecule differentiate between two isomeric carbohydrates? It is generally accepted thattwo factors govern molecular recognition: complementarity and preorganization. Preorganization requiresthe presence of cavities for positioning the host's groups of complementary nature to those of the guest.This study shows that, in fact, groups should be complementary to recognize each other (for the casepresented here, it is controlled by the CH/ interaction) but preorganization is not essential. Since weakinteractions have their origin in dispersion forces, they also have impact on the enthalpic term of the freeenergy, so it was considered that their participation can be demonstrated by measuring the energy involved.For recognition to happen, two conditions must be satisfied: specificity and associated stabilizing energy.In this study we evaluated the heat of dissolution of different carbohydrates such as methyl 2,3,4,6-tetra-O-methyl--D-mannopyranoside and methyl 2,3,4,6-tetra-O-methyl--D-galactopyranoside usingdifferent aromatic solvents. The solvation enthalpies in benzene were -78.8 ± 3.9 and -88.7 ± 5.5 kJmol^-1 for each carbohydrate, respectively; and these values yielded a CH/ energy of interaction of 9.9kJ mol^-1. In addition, NMR studies of the effect of the addition of benzene to chloroform solutions ofthe two carbohydrates showed that benzene specifically interacts with the hydrogen atoms of the pyranosering at positions 3, 4, and 5 located on the face of the methyl--galactoside, so it is, in fact, able torecognize it. Thus, the interactions between carbohydrates and the aromatic residues of proteins occur inthe absence of the confinement generated by the protein structure. By experimentally measuring theenergy associated with this interaction and comparing it to theoretical calculations, it was also possibleto unequivocally determine the existence of CH/ interactions between carbohydrates and proteins.