The role of stereochemical factors on the structure and the fragmentation paths of the protonated cyclic dipeptide cyclo histidine–phenylalanine is studied under ion traps conditions by combining tandem mass spectrometry, laser spectroscopy, quantum chemical calculations and chemical dynamics simulations. Vibrational spectroscopy obtained by Infrared Multiple Photon Dissociation (IRMPD) reveals a small difference between the two diastereomers, c-\(\hbox {LLH}^{+}\) and c-\(\hbox {LDH}^{+}\), arising mainly from ancillary CH...\(\uppi \) interactions. In contrast, there is a strong influence of the residues chirality on the collision-induced dissociation (CID) processes. Chemical dynamics simulations rationalize this effect and evidence that proton mobility takes place, allowing isomerization to intermediate cyclic structures that are different for c-\(\hbox {LLH}^{+}\) and c-\(\hbox {LDH}^{+}\), resulting in different barriers to proton mobility. This effect is related to the protonation of the imidazole ring. It contrasts with the minute stereochemical effects observed for other cyclic dipeptides in which the proton is borne by an amide CO.

通过结合串联质谱、激光光谱、量子化学计算和化学动力学模拟，在离子阱条件下研究立体化学因素对质子化环二肽环组氨酸-苯丙氨酸的结构和断裂路径的作用。通过红外多光子解离 (IRMPD) 获得的振动光谱揭示了两种非对映体之间的微小差异，c- \(\hbox {LLH}^{+}\)和 c- \(\hbox {LDH}^{+}\ ) , 主要来自辅助 CH... \(\uppi \)相互作用。相比之下，残基手性对碰撞诱导解离 (CID) 过程有很强的影响。化学动力学模拟使这种效应合理化并证明发生质子迁移，允许异构化为中间环状结构，这些结构对于 c- \(\hbox {LLH}^{+}\)和 c- \(\hbox {LDH}^ {+}\)，导致质子迁移的不同障碍。这种效应与咪唑环的质子化有关。它与在其他环状二肽中观察到的微小立体化学效应形成对比，其中质子由酰胺 CO 承载。