Does the "C-3 Effect" Offset the Delta 2 Effect, as Regards the Solution Flexibility of Aldoses?

作者：Morris Mallory J; Striegel Andre M^*

来源：Biopolymers, 2014, 101(7): 703-711.

DOI：10.1002/bip.22446

• solution conformational entropy
• size-exclusion chromatography
• aldohexoses
• aldopentoses
• 2 effect
• " C-3 effect&quot

The solution flexibility of carbohydrates influences a variety of molecular recognition and regulatory processes. For aldoses and other monosaccharides, this flexibility is dictated by the orientations of the various hydroxyl (OH) groups present, which influences conformer and anomer ratios, interactions among these OH groups, and interactions between them and the surrounding solvent. Depending on the number and position of axial OH groups, a variety of structures can coexist in solutions at equilibrium. In 1950, as part of his pioneering studies on the shape of pyranoside rings, Reeves described the 2 effect, the greater destabilization of the pyranose ring conformation when the OH group on carbon 2 (C-2) is in the axial position. It was later proposed by Angyal that the 2 effect could be cancelled by the presence of an axial OH on C-3, termed here the C-3 effect. Employing size-exclusion chromatography, an entropically-controlled separation technique, we have investigated whether or not the C-3 and 2 effects indeed do compensate for one another with respect to their influence on the solution flexibility of select aldohexoses and aldopentoses. As will be seen, while qualitatively and semiquantitatively this mutual cancellation of effects does occur in aldohexoses, it does not appear to do so in aldopentoses. An explanation for the latter appears to lie in the variety of anomers and conformers present in equilibrium solutions of those aldopentoses studied and in the relative entropic contribution of individual conformers or anomers to the total solution flexibility.

• 出版日期2014-7