Hazards of errors in the palladium storage in determination by GFAAS

Losses of palladium in weakly acidic solutions during storage process, which occur by its hydrolysis and/or adsorption onto the surface of storage vessels, are studied and ways of overcoming them are proposed. A fast and effective procedure for cleaning of laboratory ware with 0.2 mol L(-1) thiourea in 0.1 mol L(-1) HCl is described. Preparing palladium solutions in quartz vessels as well as using autosampler cups made from quartz glass, enabled to diminish the detection limit of palladium in synthetic solutions by GFAAS from 0.94 ng/mL to 0.27 ng/mL.     

Neutron activation analysis of water and waste

The neutron activation method has been applied to the determination of Ag, Cd, Co, Cr, Cu, Fe, Hg, Mo, Se and Zn in waters and wastes. The method involves decomposition of organic substances by ozonation, preconcentration of elements to be determined by coprecipitation with thionalide at pH 9 or sorption on Dowes 1×2 loaded with 8-hydroxyquinoline-5-sulfonic acid at pH 7, irradiation of the concentrate, radiochemical separation of the respective radioisotopes and gamma spectrometric measurement of the activity. Accuracy and precision of the determination have been evaluated.     

Some aspects of the phase changes of the CuCl2−KCl system

The mixtures of CuCl₂ and KC1 with Cu to K molar ratios from 0.2 to 2.0 were analysed by thermogravimetry in air and argon atmosphere under different conditions. The samples differed in the temperature of their preparation. Conclusions were drawn concerning the phase changes and the constitution of the CuCl₂?KC1 system.     

Activation analysis of mercury in environmental samples

Neutron-activation analysis has been applied to the determination of mercury in a variety of environmental samples (Table 11) and so far has played an important role in the environmental research concerned with mercury pollution. The virtues of this method as its high sensitivity, applicability to various samples make the method attractive. On the other hand the high cost, limited availability of irradiation facilities, the time consumming analysis (due to irradiation and cooling) are important drawbacks and limit the use of the method, particularly in routine work. With the development of flameless atomic absorption mercury determination is more and more carried out with the aid of the latter technique. It seems, however, that activation analysis will remain a reference method and an anchorage in the cases when other methods fail.     

Near infrared study of aqueous rare-earth ethylsulfates

The near infrared spectra of aqueous solutions of the ethylsulfates of La, Nd, Gd, Tb, Er, Yb, Lu, Y, and Na have been determined from about 0.2 mol-dm^–3 to nearly saturation. The extinction coefficients of water have been calculated taking into account the absorption of ethylslfate anions determined in separate experiments. Their values appeared to be nearly the same as that of pure water. The relative contents of free OH groups in 0.5 and 0.7M solutions have been estimated from the absorbances at 1160 nm. They were lower in solutions of the heavy rare-earth ethylsulfates (Tb, Er, Yb, Lu) than in equimolar solutions of the lighter ones (La, Nd), confirming our previous view that secondary hydration of the heavy trivalent rare-earth cations is distinctly stronger than that of the lighter ones. A comparison of the spectra of these aqueous ethylsulfates with those of perchlorates shows that the structure-breaking ability of the C₂H₅SO ₄ ^– ion is much smaller than that of perchlorate anion.     

Excitation Energy Transport in a Concentrated System of Flavomononucleotide in Polyvinyl Alcohol Films

Excitation energy transport mechanism of flavomononucleotide polyvinyl alcohol films is studied. Excitation wavelength and temperature dependences of fluorescence spectra and quantum yields for different concentrations of the dye are investigated. These measurements together with those of absorption reveal that dimers are imperfect traps for excitation energy and that the energy transfer can occur both in the forward and in the reverse direction. It was found that, contrary to liquid solutions, the dimerization constant of flavomononucleotide in polyvinyl alcohol films does not depend on temperature and that the irregularities observed can be explained by the temperature-dependent changes in the quantum yield of the monomer–dimer system and the effect of inhomogeneous orientation broadening of energy levels.     

2,6‐Dimethoxy‐7,9‐dimethylpurinium iodide hemihydrate

In the title compound, C₉H₁₃N₄O₂⁺·I⁻·0.5H₂O, the non‐H atoms of the ionic components lie on a mirror plane in Cmca, with the O atom of the partial water molecule lying on a twofold rotation axis. Whereas one of the methoxy methyl groups is directed away from the adjacent N‐methyl group, the other methoxy methyl group is directed towards its adjacent N‐methyl group. The conformation of the methoxy methyl groups provides an explanation for the outcomes of intramolecular thermal rearrangements of 2,6‐dialkoxy‐7,9‐dimethylpurinium salts.     

Physicochemical Characterization of the Loganic Acid–IR,Raman, UV-Vis and Luminescence Spectra Analyzed in Terms of Quantum Chemical DFT Approach

The molecular structure and vibrational spectra of loganic acid (LA) were calculated using B3LYP density functional theory, the 6–311G(2d,2p) basis set, and the GAUSSIAN 03W program. The solid-phase FTIR and FT-Raman spectra of LA were recorded in the 100–4000 cm⁻¹ range. The assignment of the observed bands to the respective normal modes was proposed on the basis of the PED approach. The stability of the LA molecule was considered using NBO analysis. The electron absorption and luminescence spectra were measured and discussed in terms of the calculated singlet, triplet, HOMO, and LUMO electron energies. The Stokes shift derived from the optical spectra was 20,915 cm⁻¹.     

Structural Modeling of TRPA1 Ion Channel—Determination of the Binding Site for Antagonists

TRPA1 is a transmembrane cation channel, one of the most promising targets in the context of respiratory diseases. Its general structure has already been experimentally resolved, but the binding site of TRPA1 antagonists such as HC-030031, a model methylxanthine derivative, remains unknown. The present study aimed to determine the potential binding site of xanthine antagonists and to describe their binding mode, using a molecular modeling approach. This study represents the first attempt to bring together site-directed mutagenesis reports and the latest cryo-EM structure of an antagonist bound to TRPA1. Our research suggests that the core moiety of HC-030031 binds to a pocket formed by the TRP-like domain and the pre-S1, S4, S5 helices of one subunit. The structure, determined by cryo-EM, shows interactions of a core hypoxanthine moiety in the same area of the binding site, sharing the interaction of xanthine/hypoxanthine with Trp-711. Moreover, the predicted binding mode of HC-030031 assumes interaction with Asn-855, a residue demonstrated to be important for HC-030031 recognition in site-directed mutagenesis studies. Our model proved to be advantageous in a retrospective virtual screening benchmark; therefore, it will be useful in research on new TRPA1 antagonists among xanthine derivatives and their bioisosteres.     

Mechanochemistry and Eco-Bases for Sustainable Michael Addition Reactions

The Michael addition reaction was revisited with a full focus on sustainability combined with efficiency, using mechanochemistry in mild conditions. First, the synthesis of cyclopentenone derivatives was chosen as a model reaction to find optimal conditions in mechanochemistry while using classical but weak bases. The reaction was efficient (84–95% yields), fast (2–6 h), solvent free, and required 0.1 equivalent of base. Aiming to reach greener conditions, classical bases were then replaced using new bio-sourced bases, called Eco-bases, that were easily prepared from plants and led to heterogeneous catalysts. The composition and structure of Eco-bases were characterized by MP-AES, XRPD, EBSD/EDS, HRTEM/EDX and ion chromatography. Interestingly, a high ratio of potassium was observed with the presence of K₂Ca(CO₃)₂ for the most effective Eco-base. The new Eco-bases were used for the mechanical-assisted construction of functionalized alkenone derivatives. The versatility of the method has been successfully applied with good to excellent yields to different Michael donors and acceptors. Eco-bases were recycled and reused four times with the same performances. Combining Eco-bases and mechanochemistry in Michael addition reactions allowed reaching a maximum degree of sustainability (efficient, rapid, low catalyst loading, solvent-free reactions with bio-sourced catalysts) and participating in the development of mechanochemistry in sustainable chemistry.