The gas phase host–guest chemistry between cucurbit[6]uril (CB[6]) and peptide is investigated using electrospray ionization mass spectrometry (ESI-MS). CB[6] exhibits a high preference to interacting with a Lys residue in a peptide forming a CB[6]–peptide complex. Collisionally activated CB[6] complexes of peptides yield a common highly selective fragment product at m/z 549.2, corresponding to the doubly charged CB[6] complex of 5-iminiopentylammonium (5IPA). The process involves the formation of an internal iminium ion, which results from further fragments to an a-type ion from a y-type ion, and the resulting 5IPA ion threads through CB[6]. Numerous peptides are investigated to test the generality of the observed unique host–guest chemistry of CB[6]. Its potential utility in probing protein structures is demonstrated using CB[6] complexes of ubiquitin. Low-energy collision induced dissociation yields CB[6] complex fragments, and further MSn spectra reveal details of the CB[6] binding sites, which allow us to deduce the protein structure in the solution phase. The mechanisms and energetics of the observed reactions are evaluated using density functional theory calculations.
利用电喷雾质谱法(ESI-MS)研究了葫芦[6]
脲(CB[6])与肽之间的气相主-客
化学反应。CB[6] 对与肽中的赖
氨酸残基相互作用表现出很高的偏好,从而形成 CB[6] - 肽复合物。肽的碰撞活化 CB[6] 复合物在 m/z 549.2 处产生一个共同的高选择性碎片产物,对应于 5-亚
氨基戊基
铵(5IPA)的双电荷 CB[6] 复合物。这一过程包括形成一个内部亚
氨基离子,该亚
氨基离子从一个 y 型离子进一步分裂成一个 a 型离子,由此产生的 5IPA 离子穿过 CB[6] 复合物。研究人员对大量肽进行了研究,以检验所观察到的 CB 独特的主宾
化学反应的普遍性[6]。利用泛素的 CB[6] 复合物证明了它在探测蛋白质结构方面的潜在用途。低能碰撞诱导解离产生了 CB[6] 复合物片段,进一步的 MSn 光谱揭示了 CB[6] 结合位点的细节,使我们能够推断出溶液阶段的蛋白质结构。我们利用密度泛函理论计算对观察到的反应机制和能量进行了评估。