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Fig. 2. a) Part of the 400 MHz HR-MAS TOCSY spectrum of AEPF dissolved in 70%[EMIM][Et 2 PO 4 ]/30% D 2 O(v/v), 303 K, spinning rate 6 kHz. b) 1 H NMR chemical shiftdifferences of the peptide AAPF dissolved in [EMIM][Et 2 PO 4 ] (white), [MMIM][Me 2 PO 4 ](black) and [EMIM][CF 3 CO 2 ](grey).* could not be assigned. # no Δδ.As a result, a large quantity of proton chemical shift differences has been obtainedindicating that the peptides strongly interact with ILs. For the ionic liquids, we found smallΔδ what might be connected to the large excess of the ILs in the mixtures with ratios of upto 40:1. However, the data agree with the reported fact that chemical shifts of imidazoliumring protons depend on the IL concentration as well as anion structure [3]. In Figure 2b, Δδvalues are presented graphically for one example peptide, AAPF. In the bar graphs, Δδ isshown for each proton of each amino acid in the peptide sequence. Since Δδ values areindicators of the interaction between ILs and peptides, the strength of the interactionscorrelates with the bar height. We can conclude that the strength of the interaction dependson the IL chosen as well as on the position of the proton in the peptide sequence. Thestrongest effects for all peptides occur with [EMIM][CF 3 CO 2 ] pointing to a specific role ofthe ionic liquid anions for IL/peptide interactions. Furthermore, most amide protons of eachsingle amino acid shifted considerably downfield displaying that the interactions with theILs are fairly strong along the peptide backbone and may be caused by hydrogen bondingwith the solvent anions [4]. Upfield shifts for Pro and Phe aromatic side chain protons wereobtained (see Figure 2b) likely arising from ring stacking with imidazolium ring protons.We also found an influence of ILs on the cis/trans equilibrium of Xaa-Pro peptidebonds what is in agreement with solvent jump experiment data mentioned above. Thecis/trans equilibrium seems to depend on the nature of the amino acid in position Xaa.Compared to water, ionic liquids favour the trans isomer. It is of special interest thatdifferent Δδ values between the two conformers cis and trans were obtained, particularly atposition Xaa. Summarizing, these results clearly show that the remarkable impact of ILs onthe cis/trans equilibrium relies on direct conformer-specific IL/peptide interactions.From our future work we can expect detailed insights into the molecular reasons forinteractions of ionic liquids with peptidic structures that may help to explain effects alreadyfound in protein folding or enzyme catalysis.AcknowledgmentsWe acknowledge financial support by the Deutsche Forschungsgemeinschaft (DFG) within the priorityprogram SPP 1191, grant BO 1770/4-1.References1. Wehofsky, N., Wespe, C., et al. ChemBioChem 9, 1493-1499 (2008).2. Wespe, C., Ph.D. thesis, Martin-Luther-University Halle-Wittenberg, Halle, 2009.3. Bonhôte, P., Dias, A.-P., et al. Inorg. Chem. 35, 1168-1178 (1996).4. Hesse, M., Spektroskopische Methoden in der organischen Chemie. 2 nd ed., Thieme Verlag,Stuttgart, 1984.17