New [4.4]cyclophanes: molecular parallelograms, triangles, rhombuses, pentagons, and supramolecular constructions

The fair or good yield synthesis of new [(4.4)(n)]cyclophanes (n = 1-5), starting from 1,4-bis(2-hydroxymethyl-5,5-dimethyl-1,3-dioxan-2-yl)benzene and several diacid-dichlorides, based on monomer and oligomer formation reactions (from 1 + 1 to 5 + 5), is reported. The structure and the complex architectures of the lattices for these cyclophanes are revealed by the X-ray molecular structure for five compounds, NMR investigations, and mass spectrometry measurements. Intramolecular and intermolecular CH-pi, p-pi, and pi-pi interactions are observed, both in solid state and solution.     

Tautomerism in drug discovery

The influence of tautomerism on the precise structure of drugs and thus of their potential to interact with biological systems is discussed from thermodynamic and kinetic aspects. The types of tautomerism encountered in the structure of drugs in current use are surveyed together with the effect of pH, solvent polarity, and temperature.     

SERS approach for Zn(II) detection in contaminated soil

Soil contamination by metals is a common problem encountered in many industrialized countries. In this work we present a new approach for heavy metals detection by using surface-enhanced Raman scattering (SERS) spectroscopy. Zn(II) can be clearly determined by SERS in contaminated soil by using 4-(2-pyridylazo) resorcinol (PAR) as chelating molecule for the metal ion. The SERS spectra of PAR, of its metal chelates and of the soil extract-PAR mixture were recorded using a hydroxylamine reduced silver colloid. An excellent match of the PAR-contaminated soil extracts SERS spectrum to the Zn(PAR)₂ SERS spectrum can be observed, demonstrating the presence of Zn(II) in the soil probes. Density functional theory (DFT) based calculations were also performed for a reliable assignment of SERS spectra.     

Studies of irreversible heat denaturation of green fluorescent protein by differential scanning microcalorimetry

Heat denaturation of green fluorescent protein (the GFP-cycle3 mutant) was studied by the method of differential scanning microcalorimetry. Activation energy values for two stages of GFP unfolding were calculated from the calorimetric data using the model of irreversible denaturation. Dependences of activation energy and denaturation enthalpy on the temperature of the maxima of corresponding stages of denaturation were obtained, which allow estimating the corresponding increments of heat capacity. Based on the known correlations of the structure and energy parameters, it was concluded that the first transition state is close to the native state, whereas the second transition state is close to the denatured state, judging by the exposure of hydrophobic groups to the solvent.     

Molecular docking performance evaluated on the D3R Grand Challenge 2015 drug-like ligand datasets

The D3R Grand Challenge 2015 was focused on two protein targets: Heat Shock Protein 90 (HSP90) and Mitogen-Activated Protein Kinase Kinase Kinase Kinase 4 (MAP4K4). We used a protocol involving a preliminary analysis of the available data in PDB and PubChem BioAssay, and then a docking/scoring step using more computationally demanding parameters that were required to provide more reliable predictions. We could evidence that different docking software and scoring functions can behave differently on individual ligand datasets, and that the flexibility of specific binding site residues is a crucial element to provide good predictions.     

Deactivation of a mixed oxide catalyst of Mo–V–Te–Nb–O composition in the reaction of oxidative ethane dehydrogenation

The operational stability of a mixed oxide catalyst of Mo–V–Te–Nb–O composition in the oxidative dehydrogenation of ethane (ratio of C₂H₆: O₂ = 3: 1) is studied in a flow reactor at temperatures of 340–400°C, a pressure of 1 atm, and a WHSV of the feed mixture of 800 h^?1. It is found that the selectivity toward ethylene is 98% at 340°C, but the conversion of ethane at this temperature is only 6%; when the temperature is raised to 400°C, the conversion of ethane is increased to 37%, while the selectivity toward ethylene is reduced to 85%. Using physical and chemical means (XPS, SEM), it is found that the lack of oxidant in the reaction mixture leads to irreversible changes in the catalyst, i.e., reduced selectivity and activity. Raising the reaction temperature to 400°C allows the reduction of tellurium by ethane, from the +6 oxidation state to the zerovalent state, with its subsequent sublimation and the destruction of the catalytically active and selective phase; in its characteristics, the catalyst becomes similar to the Mo–V–Nb–O system containing no tellurium.     

Reduction of carbon dioxide by hydrogen on metal–carbon catalysts under supercritical conditions

The reduction of carbon dioxide with hydrogen on metal–carbon (Ru, Rh, Ir) catalysts is investigated under supercritical conditions for the first time. High selectivity (close to 100%) toward methanation with good stability of catalytic activity is observed for Ru- and Rh-containing catalyst, while the preferred reduction to CO is observed for Ir/C catalyst.     

Halogen aggregation in chlorobenzene-<Emphasis Type="Italic">o</Emphasis>-dichlorobenzene solutions

The chlorobenzene (CB)–o-dichlorobenzene (o-DCB) liquid system has been studied by classical molecular dynamics simulation over the entire range of concentrations. The structure of the solutions is characterized by using radial angular distribution functions for the distances between the planes of benzene rings and the angle between them, using radial distribution functions for the distances between chlorine atoms, and by calculating the self-diffusion coefficients and local dipole moments. Halogen aggregation in the pure components and solutions is analyzed. It is found that in pure CB, chlorine aggregates consisting of four to ten molecules are most likely to form. The sizes of chlorine aggregates increase with increasing o-DCB concentration, and at a o-DCB concentration of 0.50-1.00 ppm, an extended system of chlorine–chlorine contacts is formed. In pure o-DCB, the chlorine aggregation system includes 99% of the molecules of the simulated system. The agglomeration of solute molecules in the range of dilute solutions (x < 0.1 ppm) is investigated.