Bicyclic diironcryptates with mobile guest cations: A new class of solid ionic conductors

Polycrystalline bicyclic diironcryptates with different mobile guest cations were synthesized and characterized by XRD analysis, IR spectroscopy, FAB-mass spectroscopy, elemental analysis, electrical conductivity spectroscopy and ion exchange experiments. We find strong indication that the guest cations exhibit a long-range mobility and that their mobility is governed by their size relative to the size of the cryptand molecules. On the other hand, the valence of the guest cations seems to play a minor role for the mobility. These results are discussed in comparison to the properties of conventional solid cationic conductors.     

Critical aspects of analysis of Micrococcus luteus, Neisseria cinerea, and Pseudomonas fluorescens by means of capillary electrophoresis

Within the frame of our study we investigated Microccocus luteus, Neisseria cinerea, and Pseudomonas fluorescens by means of capillary zone electrophoresis (CZE). They form chains and clusters on a different scale, which can be reflected in the electropherograms. A low buffer concentration of Tris-borate and Na2EDTA containing a polymeric matrix of 0.0125% poly(ethylene) oxide (PEO) was used. Key factors were the standardization and optimization of CE conditions, buffer solution, and pretreatment of bacterial samples, which are not transferable to different bacterial strains, in general. The different compositions of the cell wall of on the one hand Gram-positive (M. luteus) and Gram-negative (N. cinerea) cocci and on the other hand Gram-negative, rod-shaped bacteria (P. fluorescens), are probably responsible for the different pretreatment conditions.     

Randomizing the Unfolded State of Peptides (and Proteins) by Nearest Neighbor Interactions between Unlike Residues

To explore the influence of nearest neighbors on conformational biases in unfolded peptides, we combined vibrational and 2D NMR spectroscopy to obtain the conformational distributions of selected “GxyG” host–guest peptides in aqueous solution: GDyG, GSyG, GxLG, GxVG, where x/y=A, K, L, V. Large changes of conformational propensities were observed due to nearest‐neighbor interactions, at variance with the isolated pair hypothesis. We found that protonated aspartic acid and serine lose their above‐the‐average preference for turn‐like structures in favor of polyproline II (pPII) populations in the presence of neighbors with bulky side chains. Such residues also decrease the above‐the‐average pPII preference of alanine. These observations suggest that the underlying mechanism involves a disruption of the hydration shell. Thermodynamic analysis of ³J(H^N,H^α) (T) data for each x,y residue reveals that modest changes in the conformational ensemble masks larger changes of enthalpy and entropy governing the pPII?β equilibrium indicating a significant residue dependent temperature dependence of the peptides’ conformational ensembles. These results suggest that nearest‐neighbor interactions between unlike residues act as conformational randomizers close to the enthalpy–entropy compensation temperature, eliminating intrinsic biases in favor of largely balanced pPII/β dominated ensembles at physiological temperatures.     

Multivalent Siderophore–DOTAM Conjugates as Theranostics for Imaging and Treatment of Bacterial Infections

There is a strong need to better diagnose infections at deep body sites through noninvasive molecular imaging methods. Herein, we describe the synthesis and characterization of probes based on siderophore conjugates with catechol moieties and a central DOTAM scaffold. The probes can accommodate a metal ion as well as an antibiotic moiety and are therefore suited for theranostic purposes. The translocation of the conjugates across the outer and inner cell membranes of E. coli was confirmed by growth recovery experiments with enterobactin-deficient strains, by the antibacterial activity of ampicillin conjugates, and by confocal imaging using a fluorogen-activating protein–malachite green system adapted to E. coli. The suitability of the probes for in vivo imaging was demonstrated with a Cy5.5 conjugate in mice infected with P. aeruginosa.