Electronic structure of biomolecules in aqueous solutions: Photo/Auger-electron spectroscopy from a water microjet using synchrotron light

我们对水溶液中电子-结构相互作用的后续液体喷射光电子能谱研究将越来越多地探索生物相关分子与周围溶剂水分子之间的电荷和能量转移。来自BESSY同步辐射装置的软X射线(&lt；1600 eV)用于电离和/或激发。核能级激发和随后的核空穴超快填充导致俄歇类电子的发射。通常，电子弛豫不是局部的，而是涉及溶质和水溶剂之间的电荷或能量转移。这可以通过二次(或自动电离)过程来识别，并将在这里进行研究。在最近的研究中，我们为纯净的液态水和几种水溶液开辟了这些路线，包括OH-(AQ)和过渡金属(AQ)。给定溶质-水(壳)相互作用的强度定义了轨道重叠的程度，也定义了溶剂化构型，这共同决定了局部激发后电子弛豫路径的细节。我们的研究主要集中在旁观者俄歇衰变、分子间库仑衰变(ICD)和共振光电子能谱(RPE)，目前首次将其应用于DNA组分和其他生物相关分子，包括水中含金属的分子络合物。互补的非共振PE研究提供了芯级和价电子能量(特别是最低电离)，后者对于更好地了解水溶液的化学反应活性至关重要。此外，核心能级能量变化揭示了与环境的化学变化相关的准确的原子位置能量变化，例如由pH值变化引起的变化。

Our follow-up liquid-jet photoelectron (PE) spectroscopy studies of the electronic-structure interactions in aqueous solutions will increasingly explore charge and energy transfers between biologically relevant molecules and the surrounding solvent water molecules. Soft X-rays (<1600 eV) from the BESSY synchrotron-radiation facility are used for ionization and/or excitation. Core-level excitation and the subsequent ultrafast refill of the core hole leads to emission of Auger-type electrons. Often, electronic relaxation will not be local but rather involves charge or energy transfer between solute and water solvent. This can be identified through secondary (or autoionization) processes, and will be investigated here. In recent studies we have pioneered these routes for neat liquid water and for several aqueous solutions, including OH-(aq) and transition metals(aq). The strength of a given solute – water(shell) interaction defines the extent of orbital overlap and also defines the solvation configuration, and together this determines the details of the electronic relaxation pathway following local excitation. Our studies specifically focus on spectator Auger decay, intermolecular Coulombic decay (ICD), and resonant photoemission (RPE) spectroscopy, now for the first time applied to DNA components and other biologically relevant molecules, including metal-containing molecular complexes in water. Complementary non-resonant PE studies provide core-level and valence electron energies (specifically lowest ionization), the latter being crucial for a better understanding of aqueous solution chemical reactivity. In addition, core-level energy shifts reveal accurate atomic-site energy changes associated with chemical changes of the environment, induced for instance by change of pH value.