Thermochemistry and structures of Na+ coordinated mono- and disaccharide stereoisomers
Thermochemistry and structures of Na+ coordinated mono- and disaccharide stereoisomers
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DOI：
10.1016/s1387-3806(99)00085-8
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发表时间：
1999-08-11
影响因子：
1.8
通讯作者：
Wesdemiotis, C
中科院分区：
文献类型：
--
作者：
Cerda, BA;Wesdemiotis, C
几种单糖和双糖立体异构体的Na+亲和在气相中根据Na+结合异二聚体[糖+ B-i]Na+的解离来确定，其中B-i代表已知Na+亲和的参考碱（动力学方法）。所研究的化合物包括戊糖、阿拉伯糖、木糖和核糖；己糖葡萄糖、半乳糖和甘露糖；还有二糖蜜二糖，生二糖和乳糖。[糖+ B-i]Na+的分解作为内能的函数进行评估，从而获得Na+的绝对亲和和Na+附着的相对熵。测定的Na+亲和与钠离子通过糖的氧位进行多齿配位是一致的。一般来说，己糖比戊糖结合Na+的能力更强，这表明羟基甲基取代基使己糖具有更大的构象灵活性和更大的络合Na+的诱导效应。后一种性质在双糖中进一步增强，双糖也携带更多的碱性取代基；因此，双糖与Na+形成更强的键。发现Na+的附着熵按照戊糖<己糖<双糖的顺序上升，表明Na+附着后旋转柔韧性的损失在这个方向上增加。计算预测的有利的[单糖+ Na]（+）结构包含椅子或船形的pyranose环，允许三齿或四齿Na+配位和羟基配体之间的氢键；最稳定的双糖配合物是四齿的，具有椅状结构。在计算的结构中，吡喃糖O原子和羟甲基普遍参与Na+结合，与实验趋势一致。糖立体化学的微小变化改变了Na+的最佳配位，从而改变了Na+的亲和力；因此，后一种热化学性质非常适合于立体异构糖的区分。（intj质谱189 (1999)189-204）O 1999 Elsevier Science B.V.
The Na+ affinities of several mono- and disaccharide stereoisomers are determined in the gas phase based on the dissociations of Na+-bound heterodimers [saccharide + B-i]Na+, where B-i represents a reference base of known Na+ affinity (kinetic method). The compounds investigated include the pentoses arabinose, xylose, and ribose; the hexoses glucose, galactose, and mannose; and the disaccharides melibiose, gentiobiose, and lactose. The decompositions of [saccharide + B-i]Na+ are assessed as a function of internal energy, to thereby obtain both absolute Na+ affinities as well as relative entropies of Na+ attachment. The Na+ affinities measured are consistent with multidentate coordination of sodium ion by the oxygen sites of the saccharides. In general, hexoses bind Na+ stronger than pentoses, suggesting that the hydroxymethyl substituent equips them with more conformational flexibility and larger inductive effects for complexing Na+. The latter properties are further enhanced in the disaccharides, which also carry more basic substituents; as a result, disaccharides form even stronger bonds to Na+. The entropies of Na+ attachment are found to rise in the order pentose < hexose < disaccharide, pointing to an increase in this direction of the rotational flexibility lost after attachment of Na+. The favored [monosaccharide + Na](+) structures predicted computationally contain pyranose rings in chair or boat conformations that permit tri- or tetradentate Na+ coordination and hydrogen bonds between the hydroxyl ligands; the most stable disaccharide complexes are tetradentate and involve chair forms. In the calculated structures, the pyranose O atom and the hydroxymethyl group(s) generally participate in the Na+ binding, in agreement with the experimental trends. Small changes in the saccharide stereochemistry alter the optimum Na+ coordination possible and, therefore, the Na+ affinity; as a result, the latter thermochemical property is ideally suitable for the distinction of stereoisomeric saccharides. (Int J Mass Spectrom 189 (1999) 189-204) O 1999 Elsevier Science B.V.