Department of Chemistry, Purdue University, West Lafayette, IN, 47906, USA.
, 1 Makeway Ave #15-03, Singapore, 228598, Singapore.
J Am Soc Mass Spectrom. 2017 Jul;28(7):1392-1405. doi: 10.1007/s13361-017-1655-6. Epub 2017 Apr 29.
The gas-phase reactivity of two aromatic carbon-centered σ,σ-biradicals (meta-benzyne analogs) and a related monoradical towards small oligonucleotides of differing lengths was investigated in a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer coupled with laser-induced acoustic desorption (LIAD). The mono- and biradicals were positively charged to allow for manipulation in the mass spectrometer. The oligonucleotides were evaporated into the gas phase as intact neutral molecules by using LIAD. One of the biradicals was found to be unreactive. The reactive biradical reacts with dinucleoside phosphates and trinucleoside diphosphates mainly by addition to a nucleobase moiety followed by cleavage of the glycosidic bond, leading to a nucleobase radical (e.g., base-H) abstraction. In some instances, after the initial cleavage, the unquenched radical site of the biradical abstracts a hydrogen atom from the neutral fragment, which results in a net nucleobase abstraction. In sharp contrast, the related monoradical mainly undergoes facile hydrogen atom abstraction from the sugar moiety. As the size of the oligonucleotides increases, the rate of hydrogen atom abstraction from the sugar moiety by the monoradical was found to increase due to the presence of more hydrogen atom donor sites, and it is the only reaction observed for tetranucleoside triphosphates. Hence, the monoradical only attacks sugar moieties in these substrates. The biradical also shows significant attack at the sugar moiety for tetranucleoside triphosphates. This drastic change in reactivity indicates that the size of the oligonucleotides plays a key role in the outcome of these reactions. This finding is attributed to more compact conformations in the gas phase for the tetranucleoside triphosphates than for the smaller oligonucleotides, which result from stronger stabilizing interactions between the nucleobases. Graphical Abstract ᅟ.
在傅里叶变换离子回旋共振（FT-ICR）质谱仪中，通过激光诱导声解吸（LIAD）将两种芳基碳中心σ，σ-双自由基（间苯乙炔类似物）和一种相关的单自由基与不同长度的小寡核苷酸进行气相反应性研究。单和双自由基被带正电荷，以便在质谱仪中进行操作。寡核苷酸通过 LIAD 作为完整的中性分子蒸发到气相中。发现一种双自由基没有反应性。反应性双自由基主要通过加成到碱基部分，然后糖苷键断裂，导致碱基自由基（例如，碱基-H）的提取，与二核苷磷酸酯和三核苷二磷酸酯反应。在某些情况下，在初始裂解后，双自由基未被猝灭的自由基位点从中性片段中提取一个氢原子，导致净碱基提取。相比之下，相关的单自由基主要通过糖部分进行容易的氢原子提取。随着寡核苷酸大小的增加，单自由基从糖部分进行氢原子提取的速率由于更多的氢原子供体位点的存在而增加，并且这是仅观察到的四核苷酸三磷酸的反应。因此，单自由基仅在这些底物的糖部分上攻击。双自由基也显示出对四核苷酸三磷酸的糖部分的显著攻击。这种反应性的剧烈变化表明，寡核苷酸的大小在这些反应的结果中起着关键作用。这一发现归因于四核苷酸三磷酸在气相中比较小的寡核苷酸具有更紧凑的构象，这是由于碱基之间更强的稳定相互作用所致。
