分离稀土诱导位移的双稀土混合方法

稀土顺磁性诱导位移包含接触位移和偶极位移两种成份,如果把z>或D符号相反的两种稀土离子以适当的浓度比混合于同一溶液中。则实验上观测到的顺磁位移仅含一种成份,另外一种位移成份将被抵消。双稀土混合分离诱导位移技术要求底物分子与稀土离子间的的配位过程满足快速交换平衡条件且形成的稀土-底物配合物具有轴对称性或有效轴对称性。与其它分离诱导位移的方法相比,双稀土混合方法具有简单明确的特点。本文将这一方法应用于L-抗坏血酸¹³C稀土诱导位移的分离验证了其可行性。

SEPARATION OF LANTHANIDE-INDUCED SHIFT BY MIXED-COUPLE METHOD

By using lanthanide couple with different signs of spin expectation value or magnetic constant D as shift reagent, the contact shift or the dipolar shift could be canceled out and the experimentally observed NMR paramagnetic shift would contain only one of the components. The treatment assumes that the coordinating process of the substrate fo lanthanide ion is in the fast exchange equilibrium and the substrate-lanthanide complex isof effective axial symmetry. The lanthanide couple technique provides an easy method to separate the individual components of lanthanide-induced shift (LIS) and to testify the validity of separation by other methods. The feasibility of this method is confirmed by application to L-ascorbic acid for the analysis of 13C LIS.