Single‐Crystal‐to‐Single‐Crystal Transition in an Enantiopure [7]Helquat Salt: The First Observation of a Reversible Phase Transition in a Helicene‐Like Compound

Here it is reported that crystals of an enantiopure [7]helquat salt undergo reversible thermal solid–solid phase transition at 404 K. Differential scanning calorimetry (DSC), capillary electrophoresis (CE), and X‐ray diffraction analysis were used to unravel the mechanistic details of this process. The single‐crystal‐to‐single‐crystal course enabled direct monitoring of the structural changes by in situ variable‐temperature X‐ray diffraction, thus providing the first direct evidence of a solid phase transition in a helicene‐like compound.     

Standard Koszul standardly stratified algebras

In this paper, we prove that every standard Koszul (not necessarily graded) standardly stratified algebra is also Koszul. This generalizes a similar result of [3 Ágoston, I., Dlab, V., Lukács, E. (2003). Quasi-hereditary extension algebras. Algebras Represent. Theory 6:97–117.[Crossref], [Web of Science ®] , [Google Scholar]] on quasi-hereditary algebras.     

Modification of proteins with cyclodextrins prevents aggregation and surface adsorption and increases thermal stability

This work describes a general approach for preventing protein aggregation and surface adsorption by modifying proteins with β-cyclodextrins (βCD) via an efficient water-driven ligation. As compared to native unmodified proteins, the cyclodextrin-modified proteins (lysozyme and RNase A) exhibit significant reduction in aggregation, surface adsorption and increase in thermal stability. These results reveal a new chemistry for preventing protein aggregation and surface adsorption that is likely of different mechanisms than that by modifying proteins with poly(ethylene glycol).     

Control of surface chemistry, substrate stiffness, and cell function in a novel terpolymer methacrylate library

A focused library of methacrylate terpolymers was synthesized to explore the effects of varying surface chemistry and adhesive peptide ligands on cell function. The chemical diversity of methacrylate monomers enabled construction of a library of polymers in which one can systematically vary the chemical composition to achieve a wide range of contact angle, Young's modulus, and T(g) values. Furthermore, the materials were designed to allow surface immobilization of bioactive peptides. We then examined the effects of these material compositions on protein adsorption and cell attachment, proliferation, and differentiation. We observed that chemical composition of the polymers was an important determinant for NIH 3T3 cell attachment and proliferation, as well as human mesenchymal stem cell differentiation, and correlated directly with the ability of the polymers to adsorb proteins that mediate cell adhesion. Importantly, functionalization of the methacrylate terpolymer library with an adhesive GRGDS peptide normalized cellular responses. RGD-functionalized polymers uniformly exhibited robust attachment, proliferation, and differentiation irrespective of the underlying substrate chemistry. These studies provide a library-based approach to rapidly explore the biological functionality of biomaterials with a wide range of compositions and highlight the importance of cell and protein cell adhesion in predicting their performance.     

NMR cross-correlated relaxation rates reveal ion coordination sites in DNA

In this work, a novel NMR method for the identification of preferential coordination sites between physiologically relevant counterions and nucleic acid bases is demonstrated. In this approach, the NMR cross-correlated relaxation rates between the aromatic carbon chemical shift anisotropy and the proton-carbon dipolar interaction are monitored as a function of increasing Na(+), K(+), and Mg(2+) concentrations. Increasing the counterion concentration modulates the residence times of the counterions at specific sites around the nucleic acid bases. It is demonstrated that the modulation of the counterion concentration leads to sizable variations of the cross-correlated relaxation rates, which can be used to probe the site-specific counterion coordination. In parallel, the very same measurements report on the rotational tumbling of DNA, which, as shown here, depends on the nature of the ion and its concentration. This methodology is highly sensitive and easily implemented. The method can be used to cross-validate and/or complement direct but artifact-prone experimental techniques such as X-ray diffraction, NMR analysis with substitutionary ions, and molecular dynamics simulations. The feasibility of this technique is demonstrated on the extraordinarily stable DNA mini-hairpin d(GCGAAGC).     

LC-ESI-MS-MS Method for Monitoring Dopamine,Serotonin and Their Metabolites in Brain Tissue

A rapid and precise LC-ESI-MS-MS method for the parallel identification and quantification of dopamine, serotonin and their metabolites (homovanillic acid, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindolacetic acid) from rat brain tissue without any pre-analysis adjustment of the sample such as pre-concentration or derivatization has been developed. In particular, the reaction-monitoring mode was selected for its extremely high degree of selectivity and the stable-isotope-dilution assay for its high precision of quantification. Alternation the ionization polarity in the course of mass spectrometry detection enabled to determine substances susceptible to various ionization modes in only one analysis run. This fact, in combination with an easy pre-treatment step, constitutes the method straightforward and time undemanding. The developed method was characterized with a high precision (≤19.5%, determined as RSD), an acceptable accuracy (≥82.0%, determined as recovery), a low limit of detection (≤0.40 ng/100 mg brain tissue) and a low limit of quantification (≤0.42 ng/100 mg brain tissue). The method has been applied in a recent animal study. The levels of the studied neurotransmitters have been determined in the rat brain hippocampus, prefrontal cortex, and striatum in an animal model of schizophrenia induced by an acute dose of a dizocilpine.     

From realistic to simple models of fluids. III. Primitive models of carbon dioxide,hydrogen sulphide and acetone,and their properties

Recently developed methodology to construct primitive models of associating fluids as direct descendants of complex realistic intermolecular potential functions [L. Vl?ek, I. Nezbeda. Molec. Phys., 102, 485 (2004).] is extended to polar fluids and applied to three substances of practical importance: quadrupolar carbon dioxide, and dipolar hydrogen sulphide and acetone. It is shown that the structural properties (in terms of the site–site correlation functions) of the primitive models of polar fluids reproduce very well those of their parent realistic models but, nonetheless, they perform worse than in the case of associating fluids. A number of thermodynamic properties of the developed models obtained by computer simulations is also reported (for their later use in theoretical investigation) and discussed.     

Simulation of the electric field in Earth’s ionosphere during a geomagnetic storm

Previously, a global self-consistent model of the thermosphere, ionosphere, and protonosphere (GSM TIP) was used to study the ionospheric effects of geomagnetic storms in 2005, 2006, 2010, and 2011. In these studies, the input parameters of the model were specified using different dependences of variations of the potential difference across the polar caps and of the spatial distribution of Region 2 field-aligned currents during geomagnetic storms on the geomagnetic activity indices, solar wind parameters, and interplanetary magnetic field parameters. In the present work, we have tried to examine how correct was the choice of these relationships and how faithful are the obtained global distributions of the electric field in the ionosphere. For this, we present the results of a comparative analysis of the electric field in the ionosphere during geomagnetic storms of May 2–3, 2010, obtained using two models (GSM TIP and LC06) based on different approaches to solving this problem.     

Reaction of Tertiary 2-Chloroketones with Cyanide Ions: Application to 3-Chloroquinolinediones

3-Chloroquinoline-2,4-diones react with cyanide ions in dimethyl formamide to give 3-cyanoquinoline-2,4-diones in small yields due to the strong hindrance of the substituent at the C-3 atom. Good yields can be achieved if the substituent at this position is the methyl group. In the methanol solution, the reaction proceeds by an addition mechanism to form 2-oxo-1a,2,3,7b-tetrahydrooxireno[2,3-c]quinoline-7b-carbonitriles, from which 4-hydroxy-3-methoxy-2-oxo-1,2,3,4-tetrahydroquinoline-4-carbonitriles are subsequently formed by opening of the epoxide ring with methanol. Some minor products of these reactions have also been isolated. The ¹H, ¹³C and ¹⁵N NMR spectra of the prepared compounds were measured, and all resonances were assigned using appropriate two-dimensional spectra.     

New Approaches to the Creation of Nanocomposite Anode Materials Based on PbO2: A Review

Theoretical and Experimental Chemistry - An original approach to the creation of new nanocomposite anode materials based on PbO2 and to the processes of composite formation due to the influence of...