Redistribution reaction on a six-fold coordinated Sn(IV) atom and reactions towards axially unsymmetric substituted Sn(IV) porphyrins

Abstract Investigations of the Kocheshkov redistribution reaction were performed on the six fold coordinated tin(IV) atom using the axially coordinated Sn(IV) meso-tetra-phenylporphyrin system with axially trans di-chloro and trans di-acetylido substituted derivatives. The immobile four dentate porphyrin ligand enables the detailed investigation of these typically complex reaction systems on higher coordinated tin(IV) species. The thermally activated reaction displays an equilibrium. Further on, a series of axial unsymmetrically substituted Sn(IV) porphyrins are selectively synthesized and described

Evidence from Studies with Heat-Stressed Caco-2 Cells, C. elegans and Growing Broilers

Climatic changes and heat stress have become a great challenge in the livestock industry, negatively affecting, in particular, poultry feed intake and intestinal barrier malfunction. Recently, phytogenic feed additives were applied to reduce heat stress effects on animal farming. Here, we investigated the effects of ginseng extract using various in vitro and in vivo experiments. Quantitative real-time PCR, transepithelial electrical resistance measurements and survival assays under heat stress conditions were carried out in various model systems, including Caco-2 cells, Caenorhabditis elegans and jejunum samples of broilers. Under heat stress conditions, ginseng treatment lowered the expression of HSPA1A (Caco-2) and the heat shock protein genes hsp-1 and hsp-16.2 (both in C. elegans), while all three of the tested genes encoding tight junction proteins, CLDN3, OCLN and CLDN1 (Caco-2), were upregulated. In addition, we observed prolonged survival under heat stress in Caenorhabditis elegans, and a better performance of growing ginseng-fed broilers by the increased gene expression of selected heat shock and tight junction proteins. The presence of ginseng extract resulted in a reduced decrease in transepithelial resistance under heat shock conditions. Finally, LC-MS analysis was performed to quantitate the most prominent ginsenosides in the extract used for this study, being Re, Rg1, Rc, Rb2 and Rd. In conclusion, ginseng extract was found to be a suitable feed additive in animal nutrition to reduce the negative physiological effects caused by heat stress. View Full-Tex

Coordination chemistry in molecular recognition

Reversible coordinative binding of Lewis basic donors to iminodiacetato (IDA) and nitrilotriacetato (NTA) metal complexes is widely used for the design of synthetic receptors binding to peptides, proteins or enzymes at physiological conditions. However, no data on the affinity of M(II)-NTA (M = Cu, Ni, Zn) to a single histidine or imidazole moiety are available. We herein report (chapter 1) the investigation of the binding affinity and thermodynamics of copper(II), nickel(II) and zinc(II) NTA complexes to histidine, imidazole and hen egg white lysozyme, bearing a single surface exposed histidine unit, by isothermal titration calorimetry at physiological conditions. Further, we describe a peptide-metal complex hybrid approach to enhance the binding affinity of Cu(II)-NTA to lysozyme. In the second part of this work (chapter 2) the rationally design of a selective peptide receptor is described. The combination of copper(II)nitrilotriacetato (NTA) complex with an ammonium-ion sensitive and luminescent benzocrown ether revealed a peptide receptor with a micromolar affinity and selectivity for glycine and histidine containing peptide sequences. This affinity closely resembles that of copper(II) ion peptide binding: The two free coordination sites of the copper(II) NTA complex bind to imidazole and amido nitrogen atoms, retracing the initial coordination steps of non-complexed copper(II) ions. The benzocrown ether recognizes intramolecularly the N-terminal amino moiety and the significantly increased emission intensity signals the binding event, as only if prior coordination of the peptide has taken place, the intramolecular ammonium ion � benzocrown ether interaction is of sufficient strength in water to trigger an emission signal. Intermolecular ammonium ion � benzocrown ether binding is not observed. Isothermal titration calorimetry confirmed the binding constants derived from emission titrations. Thus, as deduced from peptide coordination studies, the combination of a truncated copper(II) coordination sphere and a luminescent benzocrown ether allows for the more rational design of sequence selective peptide receptor. Suitable combinations of an affinity tag and an artificial probe are useful for non-covalent protein labelling. Several of such peptide tag � probe pairs have been developed and reported in the literature. The most prominent example is the His-tag � Ni(II)-NTA (nitrilotriacetic acid) pair. Recently, the Hamachi group reported a genetically encodable oligo-aspartate sequence (D4-tag) and a corresponding oligonuclear Zn(II) dipicolyl¬amine (Zn(II)-Dpa) complex as new peptide tag � probe pair, which is orthogonal to the His-tag � Ni(II)-NTA pair. We describe in the third part of this work (chapter 3) the preparation of fluorescent 1,4,7,10-tetraazacyclododecane (cyclen) Zn(II) complexes and their application as an alternative artificial probe for the D4-tag system. The binding affinities of the new complexes to the affinity tags were investigated by emission and UV-vis titration. Tetranuclear Zn(II)-cyclen complexes respond to the presence of oligo-aspartate, oligo-glutamate and oligo-aspartate dimers in aqueous solution at micromolar concentrations by a strong spectroscopic change. Based on the high binding affinities due to strong electrostatic interactions and Job´s plot analysis, we propose the formation of receptor�peptide tag aggregates. The results clearly show the potential of Zn(II)-cyclen complexes for applications as non-covalent protein markers, although their optical properties require further optimization for practical use. The fourth part of this work (chapter 4) deals with the syntheses of new amphiphilic 1,4,7,10-tetraazacyclododecane Zn(II) complexes for a template guided cooperative self-assembly of nucleotides at interfaces fabricated by combination of self-assembly monolayer technique (SAM) and Langmuir Blodgett technique (LB). Three amphiphilic Zn(II)-cyclen complexes were synthesized as binding sites at interfaces prepared by a combination of SAM and LB film approaches or in vesicles. Detailed investigations of the binding properties of surfaces incorporating the new amphiphilic complexes are in progress. The fifth part of this work (chapter 5) deals with the preparation of self assembled vesicular polydiacetylene (PDA) particles with embedded metal complex receptor sites. The particles respond to the presence of ATP and PPi (pyrophosphate) in buffered aqueous solution by visible changes of their color and emission properties. Blue PDA vesicles of uniform size were obtained upon UV irradiation from mono- and dinuclear zinc(II)-cyclen and iminodiacetato copper [Cu(II)-IDA] modified diacetylenes, embedded in amphiphilic diacetylene monomers. Addition of ATP and PPi to the PDA vesicle solution induces a color change from blue to red observable by the naked eye. The binding of ATP and PPi changes the emission intensity. Other anions like ADP, AMP, H2PO4¯, CH3COO¯, F¯, Cl¯, Br¯ and I¯ failed to induce any spectral changes. The zinc(II)-cyclen nanoparticles are useful for the facile detection of PPi and ATP in millimolar concentrations in neutral aqueous solutions, while Cu(II)-IDA modified vesicular PDA receptors are able to selectively discriminate between ATP and PPi. In the sixth chapter (chapter 6) we report a new methodology for the preparation of a artificial phosphate receptors. Phosphate anion probes typically consist of a binding site and a luminescent reporter group. The luminescent moiety is either part of the chemosensor in close proximity of the analyte binding site or in indicator displacement assays non-covalently bound to the binding site and displaced by the analyte. We report here the preparation and binding properties of 80 nm vesicular synthetic receptors, which contain amphiphilic 1,4,7,10-tetraazacyclododecane (cyclen) Zn(II) complexes as phosphate anion binding sites and amphiphilic coumarin derivatives as fluorescent reporter groups. By colocalization of binding sites and reporter groups in the vesicle they respond to the presence of phosphate anions in aqueous solution at micromolar concentrations by a strong emission decrease. The technique avoids the covalent synthesis of labelled analyte binding sites and allows the rapid and versatile preparation of luminescent nanometer size synthetic receptors. In the last part of this work (chapter 7) the syntheses of new non-fluorescent and fluorescent amphiphilic Lewis acidic metal complexes (metal chelating artificial lipids) based on 1,4,7,10-tetraazacyclododecane Zn(II) complexes, dipicolylamine (Dpa) complexes and a nitrilotriacetato acid (NTA) complex are described. The prepared metal chelating artificial lipids will be used for fabrication of complex self-assembled supramolecular surfaces by one or more different chemosensors for molecular recognition at interfaces

Synthesis of substituted pyrimidine hydrazine acids (PHA) and their use in peptide recognition

Substituted pyrimidine-hydrazine-acids (PHA) were prepared from orotic acid in five synthetic steps and high yields. Their geometry of hydrogen bond acceptor and donor sites make them suitable for the molecular recognition of peptide β-sheets. In non-protic solvents the PHA unit emits at around 420 nm after irradiation at 281 nm. The emission intensity decreases upon peptide binding and signals the binding event. Peptides consisting of PHAs and natural amino acids or a turn structure motif were prepared. The investigation of the intramolecular binding pattern by NMR spectroscopy revealed the expected interaction of the PHA and peptide β-sheet

Dynamic Interface Imprinting: High-Affinity Peptide Binding Sites Assembled by Analyte-Induced Recruiting of Membrane Receptors

Dynamic molecular recognition events at biological membrane receptors play a key role in cell signaling. Artificial membranes have been prepared with embedded synthetic receptors which dynamically arrange and selectively respond to external stimuli like small peptide ligands

Detection of protein phosphorylation on SDS-PAGE using probes with a phosphate-sensitive emmision response

Fluorescent probes for the detection of protein phosphorylation on SDS-PAGE are presented. The probes were designed using a dinuclear metal-chelate phosphate recognition unit and an environmentally sensitive fluorophore. The specificity of the probes is determined by their binding site selectivity toward phosphate ions and the emission response induced by the change in the electrostatic environment of the fluorophore upon binding to a phosphorylated amino acid residue. The staining is fully reversible due to the noncovalent binding of the probe. Gel bands with less than 100 ng of phosphorylated R-casein are detectable with the new probes on a normal UV-table without specialized equipment like a laser-based gel scanner or a cooled camera detecto

Organo–Phosphorus–Sulfur Heterocycles by Reactions of Phenylphosphine with Ketones

<div><p></p><p>The reaction of phenylphosphine (PhPH₂) with ketones showed conversion into a 5-membered heterocyclic ring of the type P₂SOC if 2–2.5 equivalents of sulfur (S₈) were used. X-Ray data and ³¹P, ¹³C, ¹H NMR spectra proved the formation of the (Z) diastereomer of 1,3,2,4-oxathiadiphospholane <b>1</b> ((PhPS)₂SOCMe₂) if acetone is used. Mechanistic studies displayed that small changes in the reaction pathway lead toward the formation and characterization of intermediates including 1,3,2,4,5-dithiatriphospholane, 2,4,5-triphenyl-2-sulfide (PhP)₃S₃ and 1,3,2,4-oxathiadiphospholane, and 5,5-dimethyl-2,4-diphenyl-2-sulfide ((PhPS)(PhP)SOCMe₂), which undergo reactions with acetone, subsequently yielding the abovementioned heterocyclic ring.</p></div

O2 supplementation disambiguation in clinical narratives to support retrospective COVID-19 studies

Abstract Background Oxygen saturation, a key indicator of COVID-19 severity, poses challenges, especially in cases of silent hypoxemia. Electronic health records (EHRs) often contain supplemental oxygen information within clinical narratives. Streamlining patient identification based on oxygen levels is crucial for COVID-19 research, underscoring the need for automated classifiers in discharge summaries to ease the manual review burden on physicians. Method We analysed text lines extracted from anonymised COVID-19 patient discharge summaries in German to perform a binary classification task, differentiating patients who received oxygen supplementation and those who did not. Various machine learning (ML) algorithms, including classical ML to deep learning (DL) models, were compared. Classifier decisions were explained using Local Interpretable Model-agnostic Explanations (LIME), which visualize the model decisions. Result Classical ML to DL models achieved comparable performance in classification, with an F-measure varying between 0.942 and 0.955, whereas the classical ML approaches were faster. Visualisation of embedding representation of input data reveals notable variations in the encoding patterns between classic and DL encoders. Furthermore, LIME explanations provide insights into the most relevant features at token level that contribute to these observed differences. Conclusion Despite a general tendency towards deep learning, these use cases show that classical approaches yield comparable results at lower computational cost. Model prediction explanations using LIME in textual and visual layouts provided a qualitative explanation for the model performance