The gas-phase interactions of uracil (Ura) with dimethyltin(IV) were studied by a combined experimental and theoretical approach. Positive-ion electrospray spectra show that the interaction of dimethyltin(IV) with Ura results in the formation of the [(CH₃)₂Sn(Ura-H)]⁺ ion. The tandem mass spectrometry spectrum of this complex is characterized by numerous fragmentation processes, notably associated with elimination of H,N,C,O and C₃,H₃,N,O moieties, as well as the unusual loss of C₂H₆ leading to the [Sn(Ura-H)]⁺ complex. In turn, the [Sn(Ura-H)]⁺ complex fragments according to pathways already observed for the [Pb(Ura-H)]⁺ analogue. Sequential losses of ·CH₃ radicals are also observed from the [(CH₃)₂Sn(N,C,O)]⁺ species (m/z 192). Comparison between density functional theory-computed vibrational spectra and the infrared multiple photon dissociation spectrum recorded between 1000 and 1900 cm^–1 shows a good agreement as far as the global minimum is concerned. This comparison points to a bidentate interaction with a deprotonated canonical diketo form of uracil, involving both the N3 and O4 electronegative centers. This binding scheme has been already reported for the Pb/uracil system. The bidentate form characterized by the interaction between dimethyltin with N3 and O2 centers is slightly less stable. Interconversion between the two structures is associated with a small activation barrier (56 kJ/mol). The potential energy surfaces were explored to account for the main fragmentations observed upon collision-induced dissociation.

中文翻译：

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气相研究二甲基锡（IV）与尿嘧啶的相互作用

通过实验和理论相结合的方法研究了尿嘧啶（Ura）与二甲基锡（IV）的气相相互作用。正离子电喷雾光谱表明，二甲基锡（IV）与Ura相互作用导致形成[（CH ₃）₂ Sn（Ura-H）] ⁺离子。该络合物的串联质谱图的特征在于众多的碎片化过程，特别是与消除H，N，C，O和C ₃，H ₃，N，O部分以及异常的C ₂ H ₆损失有关。导致[Sn（Ura-H）] ⁺络合物。反过来，[Sn（Ura-H）] ⁺根据已经观察到的[Pb（Ura-H）] ⁺类似物的途径选择复杂的片段。还从[（CH ₃）₂ Sn（N，C，O）] ⁺物种（m / z 192）中观察到·CH ₃自由基的顺序损失。密度泛函理论计算的振动光谱与记录在1000和1900 cm ^–1之间的红外多光子解离光谱之间的比较就全球最低要求而言，它显示出良好的协议。该比较表明与去质子化的经典二酮形式的尿嘧啶发生双齿相互作用，涉及N3和O4负电中心。对于Pb /尿嘧啶系统已经报道了这种结合方案。以二甲基锡与N3和O2中心之间的相互作用为特征的双齿形式的稳定性稍差。两种结构之间的相互转化与较小的活化势垒（56 kJ / mol）有关。探索了势能表面，以解释碰撞诱导的离解过程中观察到的主要碎裂现象。