Conformational Analyses of Physiological Binary and Ternary Copper(II) Complexes with l-Asparagine and l-Histidine; Study of Tridentate Binding of Copper(II) in Aqueous Solution

This study explores the structural properties and energy landscapes of the physiologically important bis(l -asparaginato)copper(II) [Cu(l -Asn)₂] and (l -histidinato)(l -asparaginato)copper(II) [Cu(l -His)(l -Asn)]. The conformational analyses in the gas phase and implicitly modeled water medium, and magnetic parameters of electron paramagnetic resonance spectra were attained using density functional theory calculations. The apical Cu^II coordination and hydrogen bonding were analyzed. Predicted lower-energy structures enabled the confirmation and, for apical bonding, also the refinement of structural proposals from literature. Available experimental results were indecisive regarding the amido-group binding in the Cu^II equatorial plane in solutions, but the examination of the relative stability of Cu(l -Asn)₂ conformers in 30 binding modes confirms the glycine-like mode as the most stable one. Previously reported experimental results for Cu(l -His)(l -Asn) were interpreted for l -His to have a tridentate histamine-like mode. However, the aqueous conformers with l -His in the glycinato mode are also predicted to have low energies, which does not contradict the tridentate l -His binding. The predicted magnetic parameters of conformers with an apical oxygen atom (intramolecular or from a water molecule) can reproduce the experimental data. An extent of conformational flexibility and abundance of l -His-containing ternary copper(II) amino acid complexes under physiological conditions may be related.     

The Michael-Type Addition Reaction: A Stereocontrolled Construction of a New Quaternary Chiral Center at C(2) of 2-(4-Hydroxybenzyl)cyclohexanone Derivatives

The Michael-type addition reaction was used as a convenient method for the stereocontrolled construction of a new quaternary C-center at position 2 of 2-substituted cyclohexanones (Scheme) with the aim to study the effect of an additional substituent at C(2) in a series of biologically active compounds bearing generally a 2-substituted cyclohexanone moiety. Thus, a new series of compounds consisting of a racemate (RS)- 12 and its enantiomers (S)- and (R)- 12 (ee ≥96% for both enantiomers) was obtained. The Michael adduct derivatives (S)-, (R)-, and (RS)- 12 were subjected to a biological screening using several non-related insect species.     

Sol-Gel Synthesis of Ceria-Zirconia-Based High-Entropy Oxides as High-Promotion Catalysts for the Synthesis of 1,2-Diketones from Aldehyde

Efficient Lewis-acid-catalyzed direct conversion of aldehydes to 1,2-diketones in the liquid phase was enabled by using newly designed and developed ceria–zirconia-based high-entropy oxides (HEOs) as the actual catalysts. The synergistic effect of various cations incorporated in the same oxide structure (framework) was partially responsible for the efficiency of multicationic materials compared to the corresponding single-cation oxide forms. Furthermore, a clear, linear relationship between the Lewis acidity and the catalytic activity of the HEOs was observed. Due to the developed strategy, exclusively diketone-selective, recyclable, versatile heterogeneous catalytic transformation of aldehydes can be realized under mild reaction conditions.     

ATP bioluminescence method: tool for rapid screening of organic and microbial contaminants on deteriorated mural paintings

Abstract

The extent of the microbial contamination of the seventeenth-century wall paintings in the nave of the old Church of the Holy Ascension (Veliki Kr?imir, Serbia) was evaluated via newly implemented ATP bioluminescence method, and traditional cultivation-based method, utilising commercially available dip slides. To assess the validity of ATP, as a biomarker for rapid detection of mural surface contamination, obtained zones of cleanliness values, in range from 1.0 to 5.3, were compared to documented total microbial counts, ranging between seven and 247 CFU/cm². Small coefficients of determination, 0.0106–0.0385, suggest poor correlation between microbial counts and surface ATP levels; however, zones of cleanliness values are of great help in determining the high points of contamination, aka ‘hotspots’, which should be given special attention during sampling and investigation using other methods. In addition, various aspects of the possible implementation of the ATP bioluminescence method in an integrated system of wall painting conservation are discussed.     

Experimental Investigation of the Biofunctional Properties of Nickel–Titanium Alloys Depending on the Type of Production

Nickel–titanium alloys used in dentistry have a variety of mechanical, chemical, and biofunctional properties that are dependent on the manufacturing process. The aim of this study was to compare the mechanical and biofunctional performances of a nickel–titanium alloy produced by the continuous casting method (NiTi-2) with commercial nitinol (NiTi-1) manufactured by the classical process, i.e., from remelting in a vacuum furnace with electro-resistive heating and final casting into ingots. The chemical composition of the tested samples was analyzed using an energy dispersive X-ray analysis (EDX) and X-ray fluorescence (XRF). Electron backscatter diffraction (EBSD) quantitative microstructural analysis was performed to determine phase distribution in the samples. As part of the mechanical properties, the hardness on the surface of samples was measured with the static Vickers method. The release of metal ions (Ni, Ti) in artificial saliva (pH 6.5) and lactic acid (pH 2.3) was measured using a static immersion test. Finally, the resulting corrosion layer was revealed by means of a scanning electron microscope (SEM), which allows the detection and direct measurement of the formatted oxide layer thickness. To assess the biocompatibility of the tested nickel–titanium alloy samples, an MTT test of fibroblast cellular proliferation on direct contact with the samples was performed. The obtained data were analyzed with the IBM SPSS Statistics v22 software. EDX and XRF analyses showed a higher presence of Ni in the NiTi-2 sample. The EBSD analysis detected an additional NiTi₂-cubic phase in the NiTi-2 microstructure. Additionally, in the NiTi-2 higher hardness was measured. An immersion test performed in artificial saliva after 7 days did not induce significant ion release in either group of samples (NiTi-1 and NiTi-2). The acidic environment significantly increased the release of toxic ions in both types of samples. However, Ni ion release was two times lower, and Ti ion release was three times lower from NiTi-2 than from NiTi-1. Comparison of the cells’ mitochondrial activity between the NiTi-1 and NiTi-2 groups did not show a statistically significant difference. In conclusion, we obtained an alloy of small diameter with an appropriate microstructure and better response compared to classic NiTi material. Thus, it appears from the present study that the continuous cast technology offers new possibilities for the production of NiTi material for usage in dentistry.     

Studies on the stability of MF resin solutions: investigations on network formation

The phenomenon of thixotropy of melamine-formaldehyde (MF) resins has been investigated. A series of MF-resins with varying F/M ratios, different condensation times and pH during the condensation has been prepared. The storage stability at room temperature was measured using viscosimetry, polarization microscopy, NMR-spectroscopy and XRD. The visible changes observed in polarization microscopy (i. e. the formation of micron sized structures) correlate with the increase of viscosity related to the formation of thixotropy. The formation of a transient network can be concluded on basis of nmr-relaxation measurements and viscosimetry.