Chipuk Joseph E, Brodbelt Jennifer S
Department of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station A5300, Austin, Texas 78712.
Int J Mass Spectrom. 2009 Oct 15;287(1-3):87-95. doi: 10.1016/j.ijms.2008.09.011.
Gas-phase hydrogen/deuterium (H/D) exchange reactions of four deprotonated dinucleotides (dAA, dAG, dGA, dGG) and their 5'-monophosphate analogs (5'-dAA, 5'-dAG, 5'-dGA, 5'-dGG) with D(2)O were performed in a quadrupole ion trap mass spectrometer. Significant differences in the rates and extents of exchange were found when the 5'-hydroxyl group of the dinucleotides was replaced by a phosphate functionality. Extensive and nucleobase-dependent exchange occurred for the deprotonated 5'-monophosphate dinucleotides, whereas the dinucleotides all exhibited essentially the same limited exchange. Results for the isomeric 5'-monophosphates, 5'-dAG and 5'-dGA, were remarkably different, indicating that the H/D exchange reaction was sequence dependent. An elaborate array of computations was performed to investigate the gas-phase structures of the ions individually and also as participants in ion-molecule complexes with D(2)O. Integration of the experimental and theoretical results supports a relay exchange mechanism and suggests that the exchange behavior depends highly on the identity and sequence of the nucleobases as well as their ability to interact with the deprotonation site. Finally, a shuttling mechanism is proposed to possibly account for the bimodal H/D exchange behavior observed for deprotonated 5'P-dGA. In this case, hydrogen bonding between the nucleobases in concert with interaction from the deuterating agent creates an ion-molecule complex in which hydrogen and deuterium atoms may be shuttled amongst the hydrogen bonded participants.
在四极杆离子阱质谱仪中进行了四种去质子化二核苷酸（dAA、dAG、dGA、dGG）及其5'-单磷酸类似物（5'-dAA、5'-dAG、5'-dGA、5'-dGG）与D₂O的气相氢/氘（H/D）交换反应。当二核苷酸的5'-羟基被磷酸官能团取代时，发现交换速率和程度存在显著差异。去质子化的5'-单磷酸二核苷酸发生了广泛的、依赖于核碱基的交换，而二核苷酸都表现出基本相同的有限交换。异构体5'-单磷酸酯5'-dAG和5'-dGA的结果明显不同，表明H/D交换反应是序列依赖性的。进行了一系列精细的计算，以单独研究离子的气相结构，以及它们作为与D₂O形成离子-分子复合物的参与者的结构。实验和理论结果的整合支持了一种接力交换机制，并表明交换行为高度依赖于核碱基的身份和序列以及它们与去质子化位点相互作用的能力。最后，提出了一种穿梭机制，以解释去质子化的5'P-dGA观察到的双峰H/D交换行为。在这种情况下，核碱基之间的氢键与氘化剂的相互作用共同形成了一种离子-分子复合物，其中氢原子和氘原子可能在氢键参与者之间穿梭。
