Abstract Synthetic polymers prepared by solid-phase processes are often released from the solid support by hydrolysis, leading to an acidic α chain-end which can usefully be employed to perform mass spectrometry experiments in the negative ion mode. This is the case for sequence-defined polyurethanes, which exhibit very simple MS/MS pattern as deprotonated species in great contrast to data obtained in the positive ion mode. Indeed, after deprotonation of their acidic end-group, collision induced dissociation (CID) of these polymers proceeds via competitive cleavages of all carbamate bonds. This leads to a unique series of anionic fragments spaced by the mass of one of the other coding co-monomer, enabling their sequence to be readily deciphered. However, as their size increases, polyurethanes are best ionized in the positive mode but their dissociation pattern is far more complicated, with four to five fragmentation routes depending on the adducted cation. This spectral complexity could however be highly reduced when selecting precursor ions that have experienced H/Na (or any other alkali) exchange in their acidic α end-group: in these conditions, only one reaction is observed and yields pairs of complementary products. Mechanisms could be proposed to explain how, although part of an end-group, the acidic proton had a key role in the dissociation processes of polyurethane chains. Exchange of this proton was then further optimized by proper selection of the X– anion in the NaX salt supplemented to the electrosprayed solution. By allowing simplification of MS/MS data while avoiding signal dilution over multiple ion series, CID of these [M – H + zNa](z–1)+ permitted to envisage reliable decoding of sequence-defined polyurethanes storing large amount of information.

中文翻译：

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促进 ESI 源中的羧酸盐以简化酸封端编码聚氨酯的正模式 MS/MS 测序

摘要 固相法制备的合成聚合物通常通过水解从固相载体上释放出来，形成酸性 α 链端，可用于在负离子模式下进行质谱实验。序列定义的聚氨酯就是这种情况，它表现出非常简单的 MS/MS 模式作为去质子物质，与在正离子模式下获得的数据形成鲜明对比。事实上，在它们的酸性端基去质子化后，这些聚合物的碰撞诱导解离 (CID) 通过所有氨基甲酸酯键的竞争性裂解进行。这导致一系列独特的阴离子片段被其他编码共聚单体之一的质量隔开，使它们的序列易于破译。然而，随着它们的大小增加，聚氨酯最好在正模式下电离，但它们的解离模式要复杂得多，根据加成的阳离子有 4 到 5 条碎裂路线。This spectral complexity could however be highly reduced when selecting precursor ions that have experienced H/Na (or any other alkali) exchange in their acidic α end-group: in these conditions, only one reaction is observed and yields pairs of complementary products. 可以提出机制来解释，尽管是端基的一部分，酸质子如何在聚氨酯链的解离过程中发挥关键作用。Exchange of this proton was then further optimized by proper selection of the X– anion in the NaX salt supplemented to the electrosprayed solution. 通过简化 MS/MS 数据，同时避免多个离子系列的信号稀释，