Stability constants of the Li+, Na+, H3O+, NH4+, Ag+, and K+ complexes of the cone conformer of tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate in nitrobenzene saturated with water

Abstract  

From extraction experiments in the two-phase water–nitrobenzene system and γ-activity measurements, the stability constants of the tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate (cone)·M⁺ complexes (M⁺ = Li⁺, H₃O⁺, NH₄ ⁺, Ag⁺, or K⁺) were determined in water-saturated nitrobenzene. It was found that these constants increase in the cation order NH₄ ⁺ < K⁺ < H₃O⁺ < Ag⁺ < Li⁺ < Na⁺.     

Solvent extraction of silver trifluoromethanesulfonate from water into nitrobenzene in the presence of silver ionophore?IV

Abstract  

From extraction experiments in the two-phase water/nitrobenzene system, the stability constant of the silver ionophore IV (i.e., 5,11,17,23-tetra-tert-butyl-25,27-bis[2-(methylthio)ethoxy]calix[4]arene)–Ag⁺ complex in nitrobenzene saturated with water was determined. Furthermore, the most probable structure of the resulting complex was derived by means of density functional level of theory calculations.     

Supramolecular dimer formation through hydrogen bond extensions of carboxylate ligands – Path for magnetic exchange

A new complex of unusual composition [Cu(3-O₂Nbz)₂(nia)(H₂O)₂] (1) (nia = nicotinamide, 3-O₂Nbz = 3-nitrobenzoate) has been prepared and studied together with two other complexes of composition [Cu(4-O₂Nbz)₂(nia)₂(H₂O)₂] (2) and [Cu(4-O₂Nbz)₂(nia)₂]?(4-O₂NbzH)₂ (3) (4-O₂Nbz = 4-nitrobenzoate). The composition of all complexes has been determined by elemental analysis, the complexes have been studied by electronic, infrared and EPR spectroscopy, as well as by magnetization measurements over the temperature range 1.8–300 K, and their structures have been solved. The structure of complex (1) consists of molecules, where Cu(II) atom is monodentately coordinated by the pair of 3-nitrobenzoato anions in trans  -positions together with water and nicotinamide molecules, forming nearly tetragonal basal plane, and by another water molecule in axial position of tetragonal-pyramidal coordination polyhedron. The neighboring molecule coordination polyhedron basal planes are coplanar and allow formation of supramolecular dimers with strong H-bonds between hydrogen atoms from equatorially coordinated water molecules and uncoordinated carboxylate oxygen atoms thus giving the nearest Cu?$?$Cu distance of 4.886(2) Å. Magnetization measurements showed that complex (1) exhibits maximum of magnetic susceptibility at 6.5 K and a fit to Bleaney-Bowers equation gave singlet–triplet energy gap 2J = −6.25 cm⁻¹, and zJ′ = −0.03 cm⁻¹. This might be an experimental proof that the carboxylate bridges extended with hydrogen bonds are the pathway of the spin–spin interactions. The temperature dependence of changes in EPR spectra of (1) and the spectrum at 4.2 K have confirmed its hydrogen bonded dimeric structure. The calculated Cu?$?$Cu distance 4.8 Å is in very good agreement with the value obtained from crystal structure. The complexes (2) and (3) at 300 K exhibit magnetic moment μ_eff = 1.98 B.M. and μ_eff = 1.84 B.M., respectively. These values practically do not change with lowering the temperature up to 5 K and only small drops to μ_eff = 1.87 B.M. (for (2)) and μ_eff = 1.79 B.M. (for (3)) at 1.8 K have been observed. The EPR spectra of complex (2) at room temperature as well as at 77 K are of axial type with g_⊥ = 2.062 and g_|| = 2.285 and exhibit resolved parallel hyperfine splitting with A_|| = 160 Gauss. The EPR spectra of complex (3) at room temperature as well as at 77 K are of axial type with g_⊥ = 2.065 and g_|| = 2.235 and exhibit unresolved parallel hyperfine splitting. EPR spectra of (2) and (3) are consistent with the X-ray structure.     

Realization of an active inductance for a low power high bandwidth DC power line communication network transceiver

An active inductor based on an improved gyrator circuit is proposed. The active inductor is developed to be implemented in a high impedance transceiver for a wearable DC power line communication network where requirements such as low power consumption, high bandwidth and numerous nodes support are prioritized. A load isolation step is introduced to ensure the stability of the active inductance's size on different load currents. The proposed gyrator circuit is analyzed and optimized by means of theoretical calculations. The theoretical results are then verified by simulations and experiments in the frequency range up to 10 MHz.     

Quorum sensing regulates electric current generation of Pseudomonas aeruginosa PA14 in bioelectrochemical systems

Here, we show that quorum sensing (QS) modulates the current generation of the anode-respiring bacterium Pseudomonas aeruginosa because it controls the production of phenazines, which mediate the electron transfer to the anode. The current generation by a wildtype (WT) strain P. aeruginosa PA14 and the GacS/GacA protein-regulatory mutant retS was investigated under different environmental conditions. The retS mutant generated significantly higher current (45-fold) than the WT under anaerobic conditions. Anaerobic current generation by the WT was 28-fold higher with extraneously supplied lactones (a QS-signaling molecule). Compared to anaerobic conditions, the WT with some oxygen (microaerobic conditions) exhibited enhanced phenazine production (39-fold) and current levels (48-fold). Iron-rich medium and microaerobic conditions had a negative impact on current generation by retS. All these results were directly linked to QS activity in P. aeruginosa, thus, demonstrating the importance of this bacterial communication system for current generation in BESs. We also show that BESs represent a new tool for real-time investigation of phenazine-related QS activity.     

Synthesis of 6-amino-5-cyano-1,4-disubstituted-2(1H)-pyrimidinones via copper-(I)-catalyzed alkyne-azide 'click chemistry' and their reactivity

In this paper we present the room temperature synthesis of a novel serie of 1,4-disubstituted-1,2,3-triazoles 4a-l by employing the (3+2) cycloaddition reaction of pyrimidinones containing alkyne functions with different model azides in the presence of copper sulphate and sodium ascorbate. To obtain the final triazoles, we also synthesized the major precursors 6-amino-5-cyano-1,4-disubstituted-2(1H)-pyrimidinones 3a-r from ethyl 2,2-dicyanovinylcarbamate derivatives 2a-c and various primary aromatic amines containing an alkyne group. The triazoles were prepared in good to very good yields.     

Preparation of Fe2O3-exfoliated graphite composite and its electrochemical properties investigated in alkaline solution

In the present work, a simple method of preparation of FeCl₄⁻- graphite intercalation compounds from HCl/FeCl₃ solution with the aid of chemical oxidant is presented. Based on X-ray diffraction measurements it was concluded, that stages 8, 6, and 5 FeCl₄⁻-graphite intercalation compounds were obtained. The compounds thus obtained were thermally treated to obtain Fe₂O₃-exfoliated graphite composites. The dispersion of Fe₂O₃ in the exfoliated graphite flakes was examined with the aid of the energy dispersive X-ray analysis combined with a scanning electron microscopy. Electrochemical behavior of electrodes was investigated in 6 M KOH solution. Electrochemical investigations proved the formation of FeOOH on the surface of exfoliated graphite during the anodic process. Besides, electrochemical investigations showed that the lower limit potential strongly affects the redox behavior of the Fe₂O₃-EG electrode.