Spectroscopic studies of the structure and reactivity of isolated and microsolvated flavins in a cryogenic ion trap

与DNA碱基和氨基酸类似，黄素是生命化学中丰富的关键分子构建块。作为黄素蛋白和蓝光光感受器中的辅酶，它们在许多涉及一个和两个电子转移过程和其他光化学现象的生物化学氧化还原反应中发挥重要作用。黄素令人印象深刻的生物化学多功能性依赖于它们丰富的光化学，这是基于它们共同的异咯嗪发色团。黄素家族中最基本的成员是光色素、光黄素、核黄素（维生素B2）和黄素单甘肽（FMN），它们的区别仅在于异咯嗪环的取代基（侧链）。大量的理论研究和溶液中的实验表明，黄素的物理化学性质强烈依赖于它们的氧化，质子化和金属化状态，侧链和溶剂。然而，在气相中分离的黄素的实验研究，以获得分子水平的光化学性质的光学活性物种的理解是完全缺乏的。为此，该项目旨在对气相中的基本黄素离子进行光谱和量子化学表征，其中我们可以以可控的方式改变氧化，质子化和金属化状态，以及微溶剂化的类型和程度。后者将分别揭示溶剂的影响和桥梁的差距差距的凝聚相性质。实验策略涉及最先进的振动（红外）和电子（光学）的黄素离子的激光光谱在一个新的低温离子阱质谱仪（4-300 K）耦合到一个电喷雾电离源在以前的资助期间。衍生的光谱进行了分析，通过适当的量子化学计算和产量的基本参数，如几何和电子结构，质子化和金属化位点和结合亲和力，和逐步微溶剂化在极性和非极性溶剂的氧化还原状态的函数的影响。最终目标是在分子水平上描述和基本理解黄素的光化学性质和反应性及其溶剂化效应。高精度的气相光谱数据也将作为测试和开发理论方法的有价值的基准，以描述黄素在基态和激发电子态的能量学和动力学。

Similar to DNA bases and amino acids, flavins are abundant key molecular building blocks in life chemistry. As co-enzymes in flavoproteins and blue-light photoreceptors, they play a fundamental role in numerous biochemical redox reactions involving one and two electron transfer processes and other photochemical phenomena. The impressive biochemical versatility of flavins relies on their rich photochemistry, which is based on their common isoalloxazine chromophore. The most basic members of the flavin familiy are lumichrome, lumiflavine, riboflavine (vitamin B2), and flavin mononucleotide (FMN), which just differ by the substituent (side chain) of the isoalloxazine ring. A plethora of theoretical studies and experiments in solution demonstrate that the photophysical properties of flavins strongly depend on their oxidation, protonation and metalation state, the side chain, and the solvent. However, experimental studies of flavins isolated in the gas phase to derive a molecular-level understanding of the photochemical properties of the optically active species are completely lacking. To this end, this project aims at the spectroscopic and quantum chemical characterization of essential flavin ions in the gas phase, in which we can vary in a controlled fashion the oxidation, protonation and metalation state, as well as the type and degree of microsolvation. The latter will separately reveal the effects of the solvent and bridge the gap to the condensed phase properties. The experimental strategy involves state-of-the-art vibrational (infrared) and electronic (optical) laser spectroscopy of flavin ions in a novel cryogenic ion trap mass spectrometer (4-300 K) coupled to an electrospray ionization source constructed in the previous funding period. The derived spectra are analyzed by appropriate quantum chemical calculations and yield fundamental parameters, such as geometric and electronic structure, protonation and metalation sites and binding affinities, and effects of stepwise microsolvation in polar and nonpolar solvents as a function of the redox state. The ultimate goal is a description and fundamental understanding of the photochemical properties and reactivity of the flavins and their solvation effects at the molecular level. The high-precision gas-phase spectroscopic data will also serve as valuable benchmark for testing and developing theoretical approaches to describe the energetics and dynamics of flavins in their ground and excited electronic states.