Variational multirate integration in multi-body dynamics

For systems that contain slow and fast dynamics, variational multirate integration schemes are used. These schemes split the system into parts which are simulated using two time grids consisting of micro and macro nodes. This formulation can be extended for multi-body systems. The rigid multi-body system is described by the so called director formulation and constraints describing the joints connecting the bodies. With the Lagrange multiplier method, the constraints are introduced into the equations of motion. A way to implement the null space method into the variational multirate framework is shown and the influence on the number of unknowns is investigated. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Alkali metal and ammonium cation–arene interactions with tetraphenylborate anion

Sodium, potassium, rubidium, caesium, ammonium and tetramethylammonium tetraphenylborates were studied by both positive and negative ion electrospray mass spectrometry. An affinity order of Cs⁺ > Rb⁺ > K⁺ ～ Na⁺ was obtained. The results obtained were compared with both calculations and solid-state structures, where available. The previously reported high affinity of caesium for tetraphenylborate concluded from NMR experiments was confirmed for the gas phase. The affinity does not appear to result from steric effects and a cation–pi interaction seems likely. In the positive ion mode, a unique acetonitrile complex of NaBPh₄ was observed.     

Comparison of copper labeling followed by liquid chromatography-inductively coupled plasma mass spectrometry and immunochemical assays for serum hepcidin-25 determination

Hepcidin-25 has been defined as the key biomarker in iron metabolism. This peptide binds to the iron transporter ferroportin to cause its degradation. Therefore, the need for specific, accurate and precise methods for the quantification of hepcidin-25 in biological fluids is dramatically increasing. In this regard, the use of rapid immunochemical methods that provide low limit of quantification is desired for routine clinical use. However, such fast methodologies should be first analytically evaluated and compared with alternative strategies to check for their advantages and limitations. Here we compare the use of a commercial immunochemical assay for hepcidin determination with a novel analytical approach based on Cu-labeling of the peptide followed by Cu determination using liquid chromatography (HPLC) and plasma mass spectrometry (ICP-MS). The figures of merit of both systems reveal similar analytical characteristics and both seem to be adequate for the determination of the peptide at biologically relevant concentrations in human serum samples. The analysis of a larger number of samples (n = 50) by both techniques showed a good agreement in the concentrations found. Such finding permits to address the hepcidin recovery in the sample preparation procedure necessary for the HPLC-ICP-MS analysis in human serum that turn out to be 76–85%. Additionally, limitations due to cross-reactivity issues of the ELISA method could be addressed in some of the samples by using LC-ICP-MS and were confirmed by LC-Electrospray-MS.     

Synthesis and characterization of novel carbene complexes of phosphorus(V) fluorides with potential liquid-crystalline properties

A series of novel push–pushI and push–pullII carbene-stabilized complexes of phosphorus(V) fluorides bearing substituents with liquid-crystalline properties were synthesized by the oxidative addition of difluoroamines to phosphorus(III) halides. These octahedral complexes were characterized by NMR spectroscopy and X-ray analysis.     

Annelated Pyridines as Highly Nucleophilic and Lewis Basic Catalysts for Acylation Reactions

New heterocyclic derivatives of 9‐azajulolidine have been synthesized and characterized with respect to their nucleophilicity and Lewis basicity. The Lewis basicity of these bases as quantified through their theoretically calculated methyl‐cation affinities correlate well with the experimentally measured reaction rates for addition to benzhydryl cations. All newly synthesized pyridines show exceptional catalytic activities in benchmark acylation reactions, which correlate only poorly with Lewis basicity or nucleophilicity parameters. A combination of Lewis basicity with charge and geometric parameters in the framework of a three‐component quantitative structure–activity relationship (QSAR) model is, however, highly predictive.     

Integration of the 1,2,3‐Triazole “Click” Motif as a Potent Signalling Element in Metal Ion Responsive Fluorescent Probes

In a systematic approach we synthesized a new series of fluorescent probes incorporating donor–acceptor (D‐A) substituted 1,2,3‐triazoles as conjugative π‐linkers between the alkali metal ion receptor N‐phenylaza‐[18]crown‐6 and different fluorophoric groups with different electron‐acceptor properties (4‐naphthalimide, meso‐phenyl‐BODIPY and 9‐anthracene) and investigated their performance in organic and aqueous environments (physiological conditions). In the charge‐transfer (CT) type probes 1 , 2 and 7 , the fluorescence is almost completely quenched by intramolecular CT (ICT) processes involving charge‐separated states. In the presence of Na⁺ and K⁺ ICT is interrupted, which resulted in a lighting‐up of the fluorescence in acetonitrile. Among the investigated fluoroionophores, compound 7 , which contains a 9‐anthracenyl moiety as the electron‐accepting fluorophore, is the only probe which retains light‐up features in water and works as a highly K⁺/Na⁺‐selective probe under simulated physiological conditions. Virtually decoupled BODIPY‐based 6 and photoinduced electron transfer (PET) type probes 3 – 5 , where the 10‐substituted anthracen‐9‐yl fluorophores are connected to the 1,2,3‐triazole through a methylene spacer, show strong ion‐induced fluorescence enhancement in acetonitrile, but not under physiological conditions. Electrochemical studies and theoretical calculations were used to assess and support the underlying mechanisms for the new ICT and PET 1,2,3‐triazole fluoroionophores.     

pH‐Dependent Coordination of AgI Ions by Histidine: Experiment,Theory, and a Model for SilE

Artificial implants and biomaterials lack the natural defense system of our body and, thus, have to be protected from bacterial adhesion and biofilm formation. In addition to the increasing number of implanted objects, the resistance of bacteria is also an important problem. Silver ions are well‐known for their antimicrobial properties, yet not a lot is known about their mode of action. Silver is expected to interact on many levels, thus the development of silver resistance is very difficult. Nevertheless, some bacteria are able to resist silver, even at higher concentrations. One such defense mechanism of bacteria against heavy‐metal intoxication includes an efflux system. SilE, a periplasmic silver‐binding protein that is involved in this defense mechanism, has been shown to possess numerous histidine functions, which strongly bind to silver atoms, as demonstrated by ourselves previously. Herein, we address the question of how histidine binds to silver ions as a function of pH value. This property is important because the local proton concentration in cells varies. Thus, we solved the crystal structures of histidine–silver complexes at different pH values and also investigated the influence of the amino‐acid configuration. These results were completed by DFT calculations on the binding strength and packing effects and led to the development of a model for the mode of action of SilE.