气相中环糊精与甘氨酰-苯丙氨酰-苯丙氨酸和甘氨酸三肽非共价复合物的质谱研究

摘要

为了探索环糊精和寡肽的非共价相互作用,一定化学计量比的a-,β-,γ-环糊精(CD)分别和甘氨酸三肽(GGG)、甘氨酰-苯丙氨酰-苯丙氨酸三肽(GFF)在室温下反应达到平衡并用正离子模式质谱检测.实验结果显示GGG,GFF均可以和α-,β-,γ-CD生成1∶1配合比的非共价复合物.碰撞诱导解离实验进一步验证了α-,β-,γ-CD与GGG,GFF非共价复合物的形成.质谱滴定法测得的结合常数结果表明环糊精和两种三肽形成非共价复合物的结合强度均按照γ-,β-,α-CD的次序逐渐增大.GGG和α-,β-,γ-CD复合物的结合常数分别为2799.96,2528.73,1697.11L·mol-1,GFF和α-,β-,γ-CD复合物的结合常数分别为2773.94,2134.03,1330.68 L·mol-1对于α-,β-或γ-CD,含有苯基的GFF+ CD复合物的结合强度要小于相应的脂肪族的GGG+ CD复合物,表明虽然在气相GFF+CD复合物的构象与溶液中的构象有所变化,但是苯基仍然参与和环糊精疏水腔体的键合作用.%To investigate the non-covalent interaction between α-, β-, y-cyclodextrins and peptides, a stoichiometry of α-, β-, y-cyclodextrins (CD) with GGG (Gly-Gly-Gly) or GFF (Gly-Phe-Phe) was mixed respectively, and then incubated at room temperature for 12 h to reach the equilibrium. In positive mode, the electrospray ionization mass spectrometry (ESI-MS) results indicated that α-, β-, γ-CD with GGG or GFF could form non-covalent complexes, respectively. The binding of cyclodextrins with GGG or GFF was further confirmed by collision induced dissociation (CID) in a tandem mass spectrometer. The formation constants of six complexes (GGG+CD and GFF+CD) were determined by mass spectrometric titration. The results showed the formation constants for both GGG's and GFF's complexes increased according to the order γ-CD, β-CD, α-CD. The formation constants Kst values for GGG complexes with α-CD, β-CD or γ-CD are 2799.96, 2528.73, 1697.11 L·mol-1, respectively. While the formation constants Kst values for GFF complexes with α-CD, β-CD or γ-CD are 2773.94, 2134.03, 1330.68 L·mol-1 respectively. For α-CD, β-CD or γ-CD, the Kst values of GFF complexes containing aromatic group are smaller than those of GGG complexes only containing aliphatic group. The main reason is that in gas phase, with the weakening of hydrophobic force, Van der Waals force plays an important role in the conjugation process of GFF with CD, the coordinating group of GFF is still phenyl group. While in GGG's complexes, the hydrogen bond dominates in the conjugation process. Our convincing results from the formation constants provides a new evidence, indicating that although the conformations for GFF+CD complexes change slightly when the analysts transfer from solution to gas phase, the phenyl group still takes part in coordinating.