Na⁺‐bound guanine (G)–tetrads possess square planar structures formed solely by noncovalent interactions including multiple hydrogen bonds. Unlike G‐tetrads facilitated by other alkali metal ions, an intriguing behavior in collision‐induced dissociation (CID) has been observed in Na⁺‐bound G‐tetrads, which features a preferential, simultaneous loss of two G ligands in the low energy regime. To understand this unique behavior, we investigated the CID of Na⁺‐bound G‐tetrads with mixed ligands of G and 9‐methylguanine (9mG), [Na·G_m·9mG_n]⁺ (m + n = 4), and [Li·9mG₄]⁺ for comparison. In the CID experiments, the simultaneous losses of two ligands were by far more pronounced than the loss of a single ligand for all five Na⁺‐bound G‐tetrads. However, it appeared that the CID of [Li·9mG₄]⁺ prefers to lose single ligands sequentially. An analysis of the fragment abundances suggested that the generation of Na⁺‐bound dimeric fragments might have occurred with two adjacent ligands. This theoretical study predicted for [Li·9mG₄]⁺ that the loss of a single ligand is more energetically favorable than the production of neutral hydrogen‐bonded fragments by 35.5 kJ/mol (ΔG). This contradicts our previous calculations for [Na·9mG₄]⁺ that a neutral loss of hydrogen‐bonded dimers provides the lowest energy product state of Na⁺‐bound dimeric fragments, which is lower than that of Na⁺‐bound trimeric fragments by 15.6 kJ/mol. From the results, this comparative study suggests that the pronounced generation of Na⁺‐bound dimeric fragments in CID of the G‐tetrads is likely promoted by the dissociation pathway associated with neutral loss of hydrogen‐bonded dimers. It thus demonstrates that multiple hydrogen bonding participating in formation of Na⁺‐bound G‐tetrads may also strongly influence the fate of dissociating complexes of G‐tetrads.

中文翻译：

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氢键影响碰撞诱导的Na +结合鸟嘌呤四联体的解离

Na ⁺结合的鸟嘌呤（G）-四联体具有仅由非共价相互作用（包括多个氢键）形成的方形平面结构。与其他碱金属离子促进的G-tetrads不同，在Na ⁺结合的G-tetrads中观察到了碰撞诱导解离（CID）的有趣行为，其特征是在低能态下优先同时丢失两个G配体。为了理解这种独特的行为，我们研究了Na ⁺结合的G-tetrads与G和9-甲基鸟嘌呤（9mG），[Na·G _m ·9mG _n ] ⁺（m + n = 4）的混合配体的CID。[Li·9mG ₄ ] ⁺进行比较。在CID实验中，对于所有五个与Na ⁺结合的G-tetrads ，两个配体的同时损失远比单个配体的损失更为明显。然而，似乎[Li·9mG ₄ ] ⁺的CID倾向于顺序丢失单个配体。对片段丰度的分析表明，Na ⁺结合的二聚体片段的产生可能与两个相邻的配体一起发生。这项理论研究预测[Li·9mG ₄ ] ⁺，单个配体的损失比产生中性氢键结合片段35.5 kJ / mol（ΔG）更有利。这与我们先前对[Na·9mG₄ ] ⁺氢键结合的二聚体的中性损失提供了Na ⁺结合的二聚体片段的最低能积状态，比Na ⁺结合的三聚体片段的低15.6 kJ / mol。从结果来看，这项比较研究表明，G-tetrads CID中Na ⁺结合的二聚体片段的显着生成可能是由与氢键结合的二聚体的中性损失相关的解离途径促进的。因此，它表明参与形成Na ⁺结合的G-tetrads的多个氢键也可能强烈影响G-tetrads的解离复合物的命运。