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件。作为黄素蛋白和蓝光感受器中的辅酶，它们在涉及一个和两个电子传递过程的众多生化氧化还原反应和其他光化学现象中发挥着重要作用。黄素令人印象深刻的生物化学多样性依赖于它们丰富的光化学，而光化学是基于它们共同的异四氧嘧啶发色团。黄素家族最基本的成员是光色素、光黄素、核黄素(维生素B2)和黄素单核苷酸(FMN)，它们只是不同于异四氧嘧啶环的取代基(侧链)。大量的理论研究和溶液实验表明，黄素的光物理性质强烈地依赖于它们的氧化、质子化和金属化状态、侧链和溶剂。然而，对气相中分离的黄素进行实验研究，从而从分子水平上了解光学活性物种的光化学性质，是完全缺乏的。为此，本项目旨在对气相中必需的黄素离子进行光谱和量子化学表征，其中我们可以控制地改变氧化、质子化和金属化状态，以及微溶剂化的类型和程度。后者将单独揭示溶剂的影响，并弥合与凝聚相性质之间的差距。该实验战略涉及在一台新型低温离子陷阱质谱仪(4-300K)中对黄素离子进行最先进的振动(红外)和电子(光学)激光光谱分析，该质谱仪与上一个资助期建造的电喷雾电离源相耦合。通过适当的量子化学计算对得到的光谱进行了分析，得到了基本参数，如几何结构和电子结构，质子化和金属化位置和结合亲和力，以及在极性和非极性溶剂中逐步微溶剂化的影响作为氧化还原态的函数。最终目标是在分子水平上描述和基本了解黄素的光化学性质和反应性以及它们的溶剂化效应。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级和动力学。

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.