Ralf Giernoth

Spiropyrans (SPs) and merocyanines (MCs) are among the most widely used photochromic systems today. Besides solvent polarity and temperature, the electronic properties of the substituents have a significant influence on photochromic behavior. In this work, a comprehensive study on the influences of electron-donating and -withdrawing substituents at the benzopyran as well as the indole moiety of the photochromic system are elucidated. For this purpose, changes in rate constants and the shift of the SP/MC equilibrium are investigated utilizing UV/vis and NMR spectroscopy. Based on DFT calculations, a relationship between these properties and the dipole moments of the molecules is established.

In this study, the efficacy of electron beam irradiation versus chemical coupling for yielding polyethersulfone (PES) membranes with antibacterial properties was investigated. For the surface coating, a recently discovered lead compound, IL-KKA, comprising a short peptide sequence functionalized with imidazolium groups, was used. For better integration within the membrane, several novel variants of IL-KKA were generated. Membrane immobilization was achieved using different doses of electron beam irradiation and NHS/EDC chemical coupling. Physicochemical characterization of the coated membranes was performed by water contact angle measurements, X-ray photoelectron spectroscopy, and scanning electron microscopy. Our results show that electron beam irradiation is as effective and gentle as chemical coupling using the NHS/EDC method. Moreover, it was demonstrated that the obtained membranes exhibit promising antibacterial activity against B. subtilis. In summary, the technique presented herein might be promising as a template for developing future anti-biofilm devices.

We report the very first application of a Transient 1D ¹H{¹⁹F} NOE NMR experiment in neat ionic liquids. In comparison with classical 2D HOESY NMR spectroscopy, a substantial reduction in measurement time is gained with comparable quality and information content of the spectra. In combination with classical X‐ray crystallography, we have applied this technique for the determination of inter‐ionic distances (i.e. probabilities of presence) utilizing an ionic liquid containing a monofluorinated imidazolium cation. Copyright © 2017 John Wiley & Sons, Ltd.

The influence of three sodium salts, covering a wide range of the Hofmeister series, on the conformation of three proline-based peptide models in aqueous solution is examined using a combination of nuclear magnetic resonance spectroscopy and molecular dynamics simulations. The anions preferentially interact with the cis conformers of the peptide models, which is rationalized by the respective electrostatic potential surfaces. These preferred interactions have a strong impact on the thermodynamics of the cis/trans equilibria, leading to a higher population of the cis conformers. In distinct cases, these equilibria are nearly independent of temperature, showing that the salts are also able to stabilize the conformers over wide temperature ranges.

Within the last 25 years ionic liquids have written a tremendous success story, which is documented in a nearly uncountable amount of original research papers, reviews, and numerous applications in research and industry. These days, ionic liquids can be considered as a mature class of compounds for many different applications. Frequently, they are used as neoteric solvents for chemical tansformations, and the number of reviews on this field of research is huge. In this focused review, though, we are trying to evaluate the state of the art of ionic liquid chemistry beyond using them simply as solvents for chemical transformations. It is not meant to be a comprehensive overview on the topic; the choice of emphasis and examples rather refects the authors’ personal view on the field. We are especially highlighting fields in which we believe the most fundamental developments within the next five years will take place: biomass processing, (chiral) ionic liquids from natural sources, biotransformations, and organic synthesis.

Our study presents innovative research dealing with the synthesis and biological evaluation of conjugates out of antimicrobial peptides (AMPs) and imidazolium cations that are derived from ionic liquids. AMPs are considered as promising alternatives to common antibiotics due to their different activity mechanisms. Antibacterial effects have also been described for ionic liquids bearing imidazolium cations . Besides single coupling of carboxy-functionalized imidazolium cations to the peptide N-terminal we also developed conjugates bearing multiple copies of imidazolium cations. The combination of both compounds resulted in synergistic effects that were most pronounced when more imidazolium cations were attached to the peptides. In addition, antibacterial activity even in drug-resistant bacterial strains could be observed. Moreover, the novel compounds showed good selectivity only against bacterial cells, an observation that was further proven by lipid interaction studies using giant unilamellar vesicles.

The oxidation of the conotoxin μ‐SIIIA in different ionic liquids was investigated, and the results were compared with those obtained in [C₂mim][OAc]. Conversion of the reduced precursor into the oxidized product was observed in the protic ILs methyl‐ and ethylammonium formate (MAF and EAf, respectively), whereas choline dihydrogenphosphate and Ammoeng 110 failed to yield folded peptide. However, the quality and yield of the peptide obtained in MAF and EAF were lower than in the case of the product from [C₂mim][OAc]. Reaction conditions (temperature, water content) also had an impact on peptide conversion. A closer look at the activities of μ‐SIIIA versions derived from an up‐scaled synthesis in [C₂mim][OAc] revealed a significant loss of the effect on ion channel Na_V1.4 relative to the buffer‐oxidized peptide, whereas digestion of either μ‐SIIIA product by trypsin was unaffected. This was attributed to adherence of ions from the IL to the peptide, because the disulfide connectivity is basically the same for the differentially oxidized μ‐SIIIA versions.

Parahydrogen-induced dynamic nuclear polarization NMR spectroscopy (PHIP) in ionic liquids leads to weak or no polarization signals, depending on the type of experiment. We demonstrate that the intensity of polarization is directly correlated to the concentration of the ionic liquids. High ion concentration is connected to fast T₁ relaxation, resulting in annihilation of the polarization signals.

During the last decade, ionic liquids (ILs) have revealed promising properties and applications in many research fields, including biotechnology and biological sciences. The focus of this contribution is to give a critical review of the phenomena observed and current knowledge of the interactions occurring on a molecular basis. As opposed to the huge advances made in understanding the properties of proteins in ILs, complementary investigations dealing with interactions between ILs and peptides or oligopeptides are underrepresented and are mostly only of phenomenological nature. However, the field has received more attention in the last few years. This Review features a meta‐analysis of the available data and findings and should, therefore, provide a basis for a scientifically profound understanding of the nature and mechanisms of interactions between ILs and structured or nonstructured peptides. Fundamental aspects of the interactions between different peptides/oligopeptides and ILs are complemented by sections on the experimental (spectroscopy, structural biology) and theoretical (computational chemistry) possibilities to explain the phenomena reported so far in the literature. In effect, this should lead to the development of novel applications and support the understanding of IL–solute interactions in general.