Tao W A, Zhang D, Wang F, Thomas P D, Cooks R G
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907.
Anal Chem. 1999 Oct 1;71(19):4427-9. doi: 10.1021/ac990530h.
Chiral recognition of d- and l-amino acids is achieved in the gas phase on the basis of the kinetics of competitive fragmentations of trimeric Cu(II)-bound complexes. The singly charged copper(II)-amino acid trimeric cluster ions A(2)BCu(II) - H dissociate to form A(2)Cu(II) - H and ABCu(II) - H upon collision-induced dissociation (CID) in a quadrupole ion trap. The abundance ratios of these fragments depend strongly on the stereochemistry of the ligands in the A(2)BCu(II) - H complex ion. The kinetic method was used to calculate relative Cu ion affinities (ΔCu(II)') for homo- and heterochiral copper(II)-bound dimeric cluster ions as the indicator of chiral discrimination. Six amino acids of four different types showed chiral distinctions which ranged from 0 to 6.5 kJ/mol in terms of values of ΔCu(II)' with abundance ratios, referenced to the other enantiomer, ranging from 1 to 9.2. Amino acids with aromatic substituents displayed the largest chiral distinction, which correlates well with reported chromatographic results. The methodology presented here provides a sensitive means to study enantiomers by mass spectrometry, and initial results show that it is applicable to measurement of enantiomeric excess.
基于三聚体铜（II）结合配合物的竞争碎片化动力学，在气相中实现了对d-和l-氨基酸的手性识别。单电荷铜（II）-氨基酸三聚体簇离子[A₂BCu（II） - H]⁺在四极杆离子阱中发生碰撞诱导解离（CID）时，会解离形成[A₂Cu（II） - H]⁺和[ABCu（II） - H]⁺。这些碎片的丰度比强烈依赖于[A₂BCu（II） - H]⁺复合离子中配体的立体化学。动力学方法被用于计算同手性和异手性铜（II）结合二聚体簇离子的相对铜离子亲和力（ΔCu（II）'），作为手性识别的指标。四种不同类型的六种氨基酸表现出手性差异，以ΔCu（II）'值衡量，范围为0至6.5 kJ/mol，相对于另一种对映体的丰度比范围为1至9.2。带有芳香取代基的氨基酸表现出最大的手性差异，这与报道的色谱结果良好相关。本文介绍的方法提供了一种通过质谱研究对映体的灵敏手段，初步结果表明它适用于对映体过量的测量。
