Gouvion C, Mazeau K, Heyraud A, Taravel F R, Tvaroska I
Centre de Recherches sur les Macromolécules Végétales, CNRS, Grenoble, France.
Carbohydr Res. 1994 Aug 17;261(2):187-202. doi: 10.1016/0008-6215(94)84016-4.
The solution conformation of digalacturonic acid and its sodium salt have been analyzed using nuclear magnetic resonance data and molecular mechanics calculations. The flexibility around the glycosidic linkage was characterized by calculation of the relaxed (phi, psi) potential surfaces for the isolated molecule, and also for dimethyl sulfoxide and aqueous solutions using the CHARMM and SOLVOL programs. The one-bond and three-bond proton-carbon couplings were measured and H-1'-H-4 distances were estimated from NOESY experiments. The calculated potential surfaces were used to determine theoretical ensemble averages of NMR data. The agreement between the experimental and theoretical data is very satisfactory. The calculations show a strong effect of solvent on the solution behavior of both compounds. The vacuum lowest energy conformer of digalacturonic acid is stabilized by solvation, while for sodium digalacturonate the solvent induces a conformational change. An extrapolation of the stable conformers to polysaccharide chains implies that poly(galacturonic acid) occurs in solution as a three-fold helix and sodium poly(galacturonate) as a two-fold helix.
已利用核磁共振数据和分子力学计算分析了二半乳糖醛酸及其钠盐的溶液构象。通过使用CHARMM和SOLVOL程序计算分离分子以及二甲基亚砜和水溶液的松弛（φ，ψ）势能面，对糖苷键周围的柔韧性进行了表征。测量了一键和三键质子-碳耦合，并通过NOESY实验估算了H-1'-H-4距离。计算得到的势能面用于确定NMR数据的理论系综平均值。实验数据与理论数据之间的一致性非常令人满意。计算结果表明溶剂对两种化合物的溶液行为有很强的影响。二半乳糖醛酸的真空最低能量构象异构体通过溶剂化作用得以稳定，而对于二半乳糖醛酸钠，溶剂会诱导构象变化。将稳定构象异构体外推至多糖链意味着聚半乳糖醛酸在溶液中以三股螺旋形式存在，而聚半乳糖醛酸钠以双股螺旋形式存在。
