Charge transport and glassy dynamics in ionic liquids

与传统的分子溶剂中的反应相比，离子液体中的反应不仅对转化率，而且对对映体选择性和区域选择性都有明显的影响。这些效应涵盖了广泛的反应类型，主要包括酶促、过渡金属催化甚至非催化反应。目前，有近2600篇关于离子液体的科学出版物，但其中大多数都是专门描述性的，使得离子液体介导的反应的优化成为一项高度经验性的任务。相反，只有很少的贡献提供合理的解释或多或少的分子水平上观察到的宏观effects.In初步研究中，我们评估了离子液体对肽酰化反应的一般影响。因此，离子液体令人惊讶地以高度不均匀的方式影响这些反应，不仅影响肽的转化率，而且同时还影响反应的区域选择性。事实上，适当的离子液体增加了活性酯和具有两个亲核氨基官能团（即N-末端和赖氨酸的N <$-氨基）的寡肽之间的原始非选择性生物素化反应的区域选择性，分别高达75%（N-末端）和（82%赖氨酸侧链）。虽然这种意想不到的区域选择性效应可以使离子液体作为“功能溶剂”非常有用，特别是在未来的肽合成中，甚至可能是蛋白质合成，但目前还没有在分子水平上对这种离子液体效应的连贯解释。在所要求的项目中，应进行物理化学研究，最终目的是为观察到的离子液体效应提供合理的解释，并了解这些特殊溶剂的区域选择性诱导行为的分子原因。自己的初步研究已经表明，离子液体影响乙酸的pKa值。根据Debye-Hückel理论，检测到的pKa位移应对应于介电常数ε。此外，我们可以证明，离子液体调节该系统中的氢键的强度显着。基于这一初步发现，该项目的主要任务是澄清是否有一个合理的相互作用之间已经发现的反应性和区域选择性诱导作用的离子液体一方面和物理化学参数，特别是氢键性质，介电常数，pKa位移和热力学参数（<$RG <$<$、<$RH <$<$、<$RS <$）诱导的离子液体，另一方面。阐明这种因果关系对于合理使用离子液体进行合成具有重要意义。实验上，介电常数应直接通过相应的介电测量来确定，而FT-IR光谱监测amid I键振动提供了相应离子液体和单个肽氨基官能团之间氢键强度的定量数据。根据Eyring方程，通过测定酰化反应速率常数k的温度依赖性，得到了离子液体对热力学活化参数、、的显著影响。最后，应使用优化的FT-IR光谱技术直接测定不同氨基官能团的离子液体介导的pKa位移。

In comparison to reactions in classical molecular solvents, reactions in ionic liquids show pronounced effects not only on the conversion rates, but also on the enantio- and regioselectivities. Those effects cover a broad range of reaction types including mainly enzymatic, transition metal-catalyzed and even non-catalyzed reactions. Presently, there are nearly 2600 scientific publications about ionic liquids, but the majority of them are exclusively descriptive making the optimisation of ionic liquid-mediated reactions a highly empiric task. On the contrary, only a very few contributions provide rational explanations on a more or less molecular level for the macroscopic effects observed.In initial studies we evaluated the general influence of ionic liquids on peptide acylation reactions. Thereby it came out that ionic liquids surprisingly affect these reactions in a highly nonuniform manner influencing not only the conversion rate of the peptide, but simultaneously also the reactions¿ regioselectivity. In fact, proper ionic liquids increased the regioselectivity of an originally non-selective biotinylation reaction between an active ester and an oligopeptide bearing two nucleophilic amino functions, i.e. the N-terminal and lysine¿s N¿-amino group, up to 75% (N-terminus) and (82% lysine side-chain), respectively. Although this unexpected regioselectivity-effect could make ionic liquids highly useful as `functional solvents¿ in particular for peptide and probably even protein synthesis in the future, there is presently no coherent explanation for this ionic liquid-effect on a molecular level. In the project requested, physicochemical studies shall be conducted with the final aim to provide rational explanations of the ionic liquids-effects observed and to understand the molecular reasons of the regioselectivity-inducing behaviour of these special solvents. Own preliminary studies could already show that ionic liquids affect the pKa-value of acetic acid. According to the Debye-Hückel-theory, the pKa-shift detected should correspond to the dielectric permittivity ¿. Furthermore we could prove that ionic liquids modulate the strength of hydrogen bonds in this system significantly. Based on this preliminary findings, the project¿s major task is focused to clarify whether there is a rational interplay between the already found reactivity- and regioselectivity-inducing effect of ionic liquids on the one hand and physicochemical parameters, in particular hydrogen bond properties, dielectric permittivities ¿, pKa-shifts and thermodynamic parameters (¿RG¿, ¿RH¿, ¿RS¿) induced by ionic liquids, on the other hand. Clarification of such causal relationships would be of eminent importance to a rational use of ionic liquids for synthesis. Experimentally, dielectric permittivities shall be determined by respective dielectric measurements directly, while FT-IR spectroscopic monitoring of amid I bond vibrations provides quantitative data to the strength of hydrogen bonds between a respective ionic liquid and individual peptidic amino functions. Access to the distinct influence of ionic liquids on the thermodynamic activation parameters ¿RG¿, ¿RH¿, ¿RS¿ is given according to the Eyring-equation via measuring the temperature-dependency of the rate constant k of the acylation reaction. Finally, optimised FT-IR spectroscopic technologies shall be used to determine ionic liquids-mediated pKa-shifts of distinct amino functionalities directly.