15N NMR study of substituted 2-(phenylamino)-5-phenyl-1,3,4-oxadiazoles

Substituted 2-(phenylamino)-5-phenyl-1,3,4-oxadiazoles were studied by 15N NMR spectroscopy. All signals were assigned on the basis of HMQC and HMBC experiments. Chemical shifts values were correlated with empirical Hammett parameters as well as with calculated electron densities and chemical shieldings.     

Gadolinium(III) complexes of mono- and diethyl esters of monophosphonic acid analogue of DOTA as potential MRI contrast agents: solution structures and relaxometric studies

Two new macrocyclic DOTA-like chelates containing one phosphonate pendant arm were synthesised as potential contrast agents for MRI (magnetic resonance imaging). The chelates bind to the lanthanide(III) in an octadentate manner, via four nitrogen atoms, three carboxylate and one phosphonate oxygen atoms. Solution structures of [Ln(do3ap(OEt2))(H(2)O)] and [Ln(do3ap(OEt))(H(2)O)](-) were studied using (31)P and (1)H NMR spectroscopy and SAP (square-antiprismatic)/TSAP (twisted square-antiprismatic) isomerism was observed. Depending on the nature of the lanthanide(III) ion, the lanthanide(III) complexes of H(4)do3ap(OEt) are present in solution as up to four different diastereoisomers observable with NMR. The TSAP isomer is the most abundant at the beginning of the lanthanide series and, with a decrease of the ionic radius of lanthanide(III) ions, both TSAP and SAP forms were observed. A second interconversion (SAP<-->TSAP') becomes important at the end of the series (TSAP' means the TSAP species without a coordinated water molecule). The remaining axial coordination site is occupied by one water molecule for the Gd(3+)-complex. The calculated fraction of the TSAP isomer in the gadolinium(III) complexes increases in the order [Gd(DOTA)(H(2)O)](-) < [Gd(do3ap(OEt2))(H(2)O)] < [Gd(do3ap(OEt))(H(2)O)](-) < [Gd(do3ap)(H(2)O)](2-). Gadolinium(III) complexes of phosphorus-containing chelates, generally, have the advantage of a relatively fast water exchange rate due to a greater sterical demand of the phosphorus acid moiety and of the presence of the second-sphere water shell, which also contributes to the overall relaxivity. The [Gd(do3ap(OEt2))(H(2)O)] and [Gd(do3ap(OEt))(H(2)O)](-) complexes were studied by variable-temperature (17)O NMR and (1)H NMRD. The experimental data were evaluated simultaneously with commonly used equations based on Solomon-Bloembergen-Morgan approximation, extended by a contribution of the second coordination sphere. The water exchange rates were found to be strongly dependent on the TSAP/SAP isomeric ratio and the overall charge of the complex: the monoanionic [Gd(do3ap(OEt))(H(2)O)](-) complex with TSAP molar fraction equal to 0.36 has the water exchange rate of 20 x 10(6) s(-1) (tau(M) = 50 ns) while neutral [Gd(do3ap(OEt2))(H(2)O)] complex with TSAP molar fraction 0.28 has an exchange rate equal to 4.4 x 10(6) s(-1) (tau(M) = 227 ns).     

On idempotent modifications of <Emphasis Type="Italic">MV</Emphasis>-algebras

The notion of idempotent modification of an algebra was introduced by Ježek. He proved that the idempotent modification of a group is subdirectly irreducible. For an MV-algebra we denote by , A and the idempotent modification, the underlying set or the underlying lattice of , respectively. In the present paper we prove that if is semisimple and is a chain, then is subdirectly irreducible. We deal also with a question of Ježek concerning varieties of algebras.     

Switching on the electrocatalytic ethene epoxidation on nanocrystalline RuO2

Ruthenium-based oxides with rutile structure were examined regarding their properties in electrocatalytic ethene oxidation in acid media. A possible promoting effect of chloride ions toward oxirane formation was explored. Online differential electrochemical mass spectrometry combined with electrochemical polarization techniques were used to monitor the potential dependence of organic products resulting from ethene oxidation as well as the reaction solution decomposition products. Quantum chemical modeling by means of density functional theory was employed to study key reaction steps. The ethene oxidation in acid media led to CO(2), whereas oxirane was formed in the presence of 0.3 M Cl(-). In the Cl(-) promoted oxidation on RuO(2), oxirane and a small amount of CO(2) were the only detected electro-oxidation products at potentials below the onset of Cl(2) and O(2) evolution, resulting from Cl(-) and water oxidation. It is demonstrated here that the epoxidation is a surface-related electrocatalytic process that depends on the surface properties. Cl acts as the epoxidation promoter that switches off the combustion pathway toward CO(2) and enables the epoxidation reaction channel by surface reactive sites blocking. The proposed epoxidation mechanism implies binuclear (recombination) mechanism for O(2) evolution reaction on considered surfaces.     

Room-temperature electrochemical reduction of epitaxial magnetite films to epitaxial iron films

The electrochemical reduction of oxides to metals has been studied for decades. Earlier work produced polycrystalline bulk metals. Here, we report that pre-electrodeposited epitaxial face-centered cubic magnetite thin films can be electrochemically reduced to epitaxial body-centered cubic iron thin films in aqueous solution on single-crystalline gold substrates at room temperature. This technique opens new possibilities to produce special epitaxial metal/metal oxide heterojunctions and a wide range of epitaxial metallic alloy films from the corresponding mixed metal oxides.     

Complemented quasiorder lattices of monounary algebras

We characterize monounary algebras whose lattices of quasiorders are complemented. As a consequence, monounary algebras with Boolean quasiorder lattices are described.     

White light excitation of the near infrared Er3+ emission in exchanged zeolite sensitised by oxygen vacancies

A new material based on Er(3+)-exchanged zeolite L crystals, in which oxygen vacancies have been generated, is proposed as an efficient emitter in the near infrared third telecommunication window. The rare earth ions photoluminescence is efficiently generated by energy transfer from the excited oxygen vacancies, which act as wide range light harvesters. The proposed material can be excited in the whole Near UV-VIS-NIR spectral range from 355 to 700 nm, thus representing the first step toward versatile, zeolite based NIR sources that can be excited with white light.     

Charge carrier mobility in poly[methyl(phenyl)silylene] studied by time-resolved terahertz spectroscopy and molecular modelling

Time-resolved terahertz spectroscopy and combination of quantum chemistry modeling and molecular dynamics simulations were used for the determination of charge carrier mobility in poly[methyl(phenyl)silylene]. Using time-resolved THz spectroscopy we established the on-chain charge carrier drift mobility in PMPSi as 0.02 cm(2) V(-1) s(-1). This value is low due to the formation of polarons: the hole is self-trapped in a potential formed by local chain distortion and the transient THz conductivity spectra show signatures of its oscillations within this potential well. This view is supported by the agreement between experimental and calculated values of the on-chain charge carrier mobility.     

Theoretical modeling of peptide α-helical circular dichroism in aqueous solution

Reliable modeling of protein and peptide circular dichroism (CD) spectra in the far UV presents a challenge for current theoretical approaches. In this study, the time-dependent density functional theory (TDDFT), configuration interaction with single excitation (CIS), and transition dipole coupling (TDC) were used to assess the most important factors contributing to the CD spectra of the α-helical secondary structure. The dependence on the peptide chain length and also the role of the flexibility and solvent environment were investigated with a model oligopeptide Ac-(Ala)(N)-NH-Me, (N = 1, ..., 18). Both the TDDFT and TDC-like methods suggest that the CD curve typical for the α-helix arises gradually, but its basic characteristic is discernible already for peptides with 4-5 amino acid residues. The calculated dependence was in a qualitative agreement with experimental spectra of short α-helices stabilized by the histidine-metal binding. The TDDFT computations of the CD were found to be unusually sensitive to the basis set and solvent model. Explicit hydration and temperature fluctuations of the peptide geometry, simulated with the aid of molecular dynamics (MD), significantly influenced the CD and absorption spectral shapes. An extensive averaging over MD configurations is thus required to obtain a converged spectral profile in cluster simulations. On the other hand, both the TDDFT and TDC models indicate only a minor influence of the alanine side chains. The CIS and TDC calculations also point toward a relatively small effect of the helix-helix interaction on the CD spectral profiles. For a model system of two helices, the CIS method predicted larger changes in the spectra than TDC. This suggests other than interactions between peptide chains, such as mutual polarization, can have a minor, but measurable, effect on the CD spectrum.     

Decolourization of vat dyes on cotton fabric with infrared laser light

A method for the decolourization of coloured cotton fabric dyed with vat dyes, based on exposure to infrared laser light, has been tested. Pulsed CO₂ laser has been used for all experiments. To detect changes in colour shade, reflection data of original and dyed cotton irradiated at various fluency of infrared laser light were measured on a UV–VIS spectrophotometer, and then colour intensity was calculated for each vat dye. To observe changes in chemical composition and morphology of fiber surfaces, an analysis was performed by X-ray photoelectron spectroscopy and scanning electron microscopy due to thermal effects. Thermal stability of vat dyes and cotton fabric was determined with differential scanning calorimetry method to simulate the heating process during exposure of samples to the infrared laser irradiation.