L-抗坏血酸与稀土离子作用的NMR研究

NMR STUDY OF THE INTERACTION BETWEEN L-ASCORBIC ACID AND LANTHANIDE CATIONS

利用稀土诱导位移方法研究了水溶液中L-抗坏血酸(Vc)与三价稀土离子的配位作用。在弱酸性条件下二者形成1:1的配合物,稳定常数为8.0M^(-1)。抗坏血酸通过内脂环3位碳上的羟基氧与稀土离子配位,RE^(3+)-O键长为2.0,内脂基和其他碳上的羟基不与稀土离子配位。在配合物中C(3)-C(4)-C(5)-C(6)成反式构象。C(5)-C(6)键与配合物的零偶极位移锥面交叉。

The coordination between L-ascorbic acid(V_c) and the trivalent lanthanide cations is studied in aqueous sotutions by means of the lanthanide-induced-shift method. The 1:1 complex is formed in the solution of weak acid with the stability constant 8.0 M^(-1). The lanthanide cation coordinates to L-ascorbic acid through its oxygen anion bonded to C(3) in lactone ring. The RE^(3+)-O bond distance is 2.0 and C(3)-C(4)-C(5)-C(6) is in anti-form conformation in this complex. The inner-ester radical and hydroxyl linked with other carbon atoms do not coordinate to rare earth ions. The C(5)-C(6) bond is located respectively at outer and inner side of the cone suface on which the dipolar shift is zero.