Selective methane oxidation to formaldehyde using polymorphic T-, M-, and H-forms of niobium(V) oxide as catalysts

The investigations of selective methane oxidation to formaldehyde over T-Nb₂O₅, the mixture of M-Nb₂O₅ and H-Nb₂O₅ as well as H-Nb₂O₅ were carried out. The tests were conducted under atmospheric pressure, in the temperature range 420–750°C, using oxygen as the oxidizing agent. T-Nb₂O₅ samples were examined at the contact time 0.7–1.8 s (GHSV 2000–5143 h⁻¹). Other polymorphic forms of niobium(V) oxide were examined at the contact time 0.9 s. Various polymorphic forms of Nb₂O₅ displayed various formaldehyde and carbon dioxide yield. Using H-Nb₂O₅ and M-Nb₂O₅ phases with a block type structure, made it possible to obtain higher formaldehyde selectivity (78 % at 0.9 s) as compared to T-Nb₂O₅ (47 % at 0.9 s), a polymorphic form which does not have a block type structure. However, the highest space time yield of formaldehyde (46 g per kg of catalyst per h) was obtained over T-Nb₂O₅ supported on SiO₂. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

DNA binding and antitumor activities of zinc(II) complexes with some S-alkenyl derivatives of thiosalicylic acid

Transition Metal Chemistry - Two zinc(II) complexes with S-alkenyl derivatives of thiosalicylic acid as ligands have been synthesized and characterized by microanalysis, IR, 1H and 13C NMR...     

Influence of ultrasonic processing on the macromolecular properties of poly (d,l-lactide-co-glycolide) alone and in its biocomposite with hydroxyapatite

In this work poly(d,l-lactide-co-glycolide) (PLGA) and a poly(d,l-lactide-co-glycolide)/hydroxyapatite (PLGA/HAp) composite processed in an ultrasonic field at higher (25 °C) and lower (8 °C) temperatures were studied with respect to the molecular properties of the obtained materials. The processing of the PLGA and the PLGA/HAp composite in an ultrasonic field resulted in a change of molar mass averages of the polymer/polymeric part of these materials, while an amorphous structure and a 50:50 lactide-to-glycolide co-monomer ratio were preserved without the formation of crystalline oligomers. However, mobility of polymeric chains obtained after ultrasonic processing was lower indicating ordering the structure of polymeric chains as a result of processing. Additionally, it was observed that the mobility of the PLGA macromolecules was lower within the composite in comparison with the mobility of the chains within the PLGA alone in the case when both were obtained after ultrasonic processing. This was a consequence of the structure formation through the interactions between the PLGA and the HAp. Based on these results different degradation rate of PLGA in composite can be expected, which is important in the application of this material for the controlled drug delivery of medicaments.     

DNA binding,antibacterial and antifungal activities of copper(II) complexes with some S-alkenyl derivatives of thiosalicylic acid

The biological activities of two binuclear copper(II) complexes containing S-alkenyl derivatives of thiosalicylic acid are reported [alkenyl = propenyl (L1), isobutenyl (L2)]. The structure of the complex with the S-isobutenyl derivative (C2) was confirmed by single-crystal X-ray structure analysis, which revealed that the structure consists of centrosymmetric, dinuclear complex molecules [Cu₂(S-i-butenyl-thiosal)₄(DMSO)₂] containing two Cu(II) centers bridged by four S-isobutyl-thiosalicylate ligands in a paddle-wheel type structure. The Cu(II) atom is situated in a distorted square-pyramidal environment formed by carboxylate oxygen atoms in the basal plane and a DMSO ligand in the axial position. The reactivities of the complexes toward guanosine-5′-monophosphate (5′-GMP) were investigated. Complex C2 ([Cu₂(S-i-butenyl-thiosal)₄(H₂O)₂]) reacted more rapidly with 5′-GMP than complex C1. The interactions of complexes C1 and C2 with calf thymus DNA (CT-DNA) were examined by absorption (UV–Vis) and emission spectral studies (ethidium bromide displacement studies), revealing good DNA interaction abilities. The antimicrobial activities of the free ligands and their complexes were tested by microdilution method, and both minimal inhibitory and microbicidal concentrations were determined. All the tested substances demonstrated selective and moderate antibacterial activity on gram-positive bacteria, but low antibacterial activity on gram-negative bacteria. Also, the tested substances demonstrated low antifungal activity.     

Anodic Sampling of Titanium by Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - Titanium as the pure metal or as commercial titanium alloys has been widely used in dentistry. To determine the composition of...     

Laser damage in ferrites of MnZn spinels and other possible interactions

Pulsed laser damage of ferrites of MnZn spinels was studied. Some of the samples were treated by nuclear gamma radiation and α particles and then exposed to laser beams in different working conditions. The sample and damage quality was evaluated on the basis of X-ray, optical and SEM microscopy and micro-hardness experiments. The characteristic brittleness after nuclear gamma irradiation of ferrites and other materials was confirmed in the cases of interactions with laser beams. Characteristic cases of material cracks with CO₂ laser were found.     

The self-consistent determination of HF electroconductivity of strongly coupled plasmas

Here is presented the calculation of the dynamic electrical conductivity of fully ionized, strongly coupled plasmas as a function of the external electric field frequency ω. The calculations are based on the formula for the energy-dependent collision frequency which is determined by means of the Green function theory methods, as a sum over the Matsubara frequencies. The domain of extremely high electron density: ¹⁰²¹?ne?¹⁰²⁴ cm−3, and for the temperature varying from 10 kK to 1000 kK was examined. The real and imaginary parts of the conductivity for every electron density are presented in the generalized Drude-like form as a two-parameter function of the frequency ω in the region 0<ω<0.5ωp, where ωp is the plasma frequency. A good agreement between the obtained results and the existing theoretical and computing simulation data is shown.     

Stark-broadening regularities of lithium-like and sodium-like isoelectronic sequences

The Stark width (w) of spectral lines of multiply ionized atoms as a function of the upper-level ionization potential (I), the net core charge (z) and the electron temperature (T), was found to be of the form: w=az ² T ^?1/2 I ^?b normalized to 1×10²³ m^?3 electron density for a given transition array. Coefficientsa andb are independent of the upper-level ionization potential, the net core charge, the electron temperature and density. This paper proves the validity of this equation for Stark widths in domains of electron densities of (0.5–1.5)×10²³ m^?3 and temperatures of 20 000–80 000 K. The reduced Stark width (wT ^1/2/z ²) dependence on the inverse value of upper-level ionization potential is represented by a linear trend (in log-log scale) of the experimental and relevant theoretical results within maximal scatter of less than ±30%. For a givenns-np transition array, this trend is equally applicable to spectral lines of (i) successive ionization stages of the same atom and (ii) ions of isoelectronic sequences of the second and third periods of the periodic system. It is also shown that coefficientsa andb depend on the energy state of the electron emitter core. Using the obtained trends, one can quite successfully predict the Stark width of spectral lines of corresponding transitions that have not yet been measured.     

Stark widths and shifts of SnI,HgII, HgIII and PbII spectral lines

Stark widths and shifts of neutral and ionized heavy atom spectral lines have been measured and calculated. The Stark parameters of three SnI (284.0, 286.3 and 303.4 nm), five HgII (226.2, 398.4, 222.5, 615.0 and 326.4 nm), two PbII (220.4 and 438.6 nm) and one HgIII (235.4 nm) spectral lines were measured for the first time except the Stark widths of one HgII (398.4 nm) and one PbII (438.6 nm) line. Stark width values for a number of corresponding transitions were calculated on the bases of semiclassical and semiempirical formulae.