Methylthiouracil‐modified Carbon Paste Electrode as a New Voltammetric Sensor Based on a 1,4‐Michael Addition Reaction for Detection of Dopamine

A sensitive dopamine sensor was constructed based on the modified carbon paste electrode with methylthiouracil as a nucleophile in the 1,4‐Michael addition reaction. An ECE mechanism was suggested for dopamine oxidation at the modified electrode. Design of experiments was used in the optimization of variables. Under the optimum conditions, calibration graph was linear in the range of 0.20–15.0 µM with a detection limit of 73 nM. The relative standard deviations (n=5) for 0.50 µM of dopamine was 3.83 %. The selectivity of the sensor was also studied. The developed sensor was applied for analysis of pharmaceutical and biological samples.     

Time resolved alteration process of oxide glasses

Dissolution of oxide glasses by water has been studied by small angles X-ray scattering. It is shown that the altered residual surface layer due to dissolution and recondensation of Si atoms is a porous material with nanometer size pores. Based on five elements oxide glass (18NaO2-17B2O3-4CaO-yZrO2-(61-y)SiO2 with y=0, 1, 2, 4 and 8) the experiment highlights a strong influence of insoluble element on both the kinetic of alteration and the structure of the altered layer. It is shown that above 2% Zr content, the fraction of porous volume and the surface of exchange in the altered layer pass through a maximum value in the first hours of alteration corresponding to an overshoot of Si lixiviation without recondensation as the saturation limit is not reached. When the saturation limit is reached the porous volume fraction is just below the fraction of volume occupied primarily by the sodium and the boron.     

Comparison of sample preparation methods for determination of free carbon in boron carbide by X-ray powder diffraction

Several sample preparation methods were evaluated for determination of free carbon in boron carbide powders by quantitative X-ray diffraction method, including ultrasonication, wet ball milling and dry ball milling–wet mixing. Quantitation was based on measuring the integral peak area ratio of the diffraction lines of graphite (002) to boron carbide (012) in samples spiked with pure graphite. The dry milling–wet mixing method provided the best precision and accuracy in all the measurements as well as in determination of free carbon in a boron carbide reference material. There was a linear relationship between the integral peak area ratios and graphite added to boron carbide samples which were purified from their free carbon content. The method provided a low detection limit of 0.05 wt% free carbon.     

Characterization of single wall carbon nanotubes by means of rare gas adsorption

Based on the formalisms of Langmuir and Fowler, theoretical adsorption isotherms are calculated for different bundle geometries of single wall carbon nanotubes in a triangular lattice. The authors show the dependence of the adsorption properties on the nanotube diameter and on the specific morphology of the bundles they constitute. The authors demonstrate how isotherm curve analysis can help to experimentally determine what kinds of tubes form a given bundle and the ratio of open to closed tubes in a sample having undergone a complete or incomplete opening protocol. In spite of the model's simplicity, quite satisfactory agreement is observed between experiments and the authors' calculations.     

Stability analysis of internally damped rotating composite shafts using a finite element formulation

This paper deals with the stability analysis of internally damped rotating composite shafts. An Euler–Bernoulli shaft finite element formulation based on Equivalent Single Layer Theory (ESLT), including the hysteretic internal damping of composite material and transverse shear effects, is introduced and then used to evaluate the influence of various parameters: stacking sequences, fiber orientations and bearing properties on natural frequencies, critical speeds, and instability thresholds. The obtained results are compared with those available in the literature using different theories. The agreement in the obtained results show that the developed Euler–Bernoulli finite element based on ESLT including hysteretic internal damping and shear transverse effects can be effectively used for the stability analysis of internally damped rotating composite shafts. Furthermore, the results revealed that rotor stability is sensitive to the laminate parameters and to the properties of the bearings.     

New 7-piperazinylquinolones containing (benzo[<Emphasis Type="BoldItalic">d</Emphasis>]imidazol-2-yl)methyl moiety as potent antibacterial agents

A series of 7-piperazinylquinolones containing a (benzo[d]imidazol-2-yl)methyl moiety were designed and synthesized as new antibacterial agents. The antibacterial activity of title compounds was evaluated against Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis and Bacillus subtilis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumonia) microorganisms. Among the tested compounds, the N1-cyclopropyl derivative 4a showed the highest activity against S. aureus, S. epidermidis, B. subtilis and E. coli (\(\text {MIC} = 0.097\) \(\upmu \)g/mL), being 2–4 times more potent than reference drug norfloxacin. A structure-activity relationship study demonstrated that the effect of the nitro group on the benzimidazole ring depends on the pattern of substitutions on the piperazinylquinolone.     

Solid State Structure of 6,7-Dihydro-1,4-Di(2′-Pyridyl)-5<Emphasis Type="Italic">H</Emphasis>-Cyclopenta[d]Pyridazine

Abstract  The X-ray structure of 6,7-dihydro-1,4-di(2′-pyridyl)-5H-cyclopenta[d]pyridazine ligand (5-dppn) shows the existence of a trans/trans conformation. The 5-dppn crystallizes in a triclinic space group P-1 with a = 7.1048(15) ?; b = 9.008(2) ?; c = 10.986(3) ?; α = 88.279(16)°; β = 85.454(15)°; γ = 69.104(12)°; V = 654.7(3) ?³ and Z = 2. The analysis of 5-dppn crystal structure demonstrates the presence of edge-edge Ar–H···N and face-face Aliph-H···N centrosymmetric dimer interactions. The unit cell packing arrangement confirmed the presence of two molecules opposite to each other. Index Abstract  The X-ray structure of 6,7-dihydro-1,4-di(2′-pyridyl)-5H-cyclopenta[d]pyridazine ligand (5-dppn) shows the existence of a trans/trans conformation.      

Comparison of Some Classical Topologies on Hyperspaces within the Framework of Point Spaces

S. Dolecki, G. Greco and A. Lechicki call a space X consonant if the co-compact topology and the upper Kuratowski topology on the set of closed subsets of X coincide. We call a space X hyperconsonant if Fell's topology and the (Kuratowski) convergence topology coincide. Recently, we proved that a first countable, locally paracompact, T ₃-space is hyperconsonant if and only if the space possesses at most one point without a compact neighbourhood, extending the same result of D. Fremlin obtained for metrizable spaces. In this paper, we pursue the study of hyperconsonance within the framework of point spaces (countable T ₁-spaces with exactly one accumulation point) and we compare consonance and hyperconsonance in such spaces. In particular, we answer a question of T. Nogura and D. Shakhmatov: does there exist a nonconsonant point space? We provide a Fréchet, -point space which is not consonant. Moreover, this example proves that the consonance is not preserved by continuous closed compact-covering maps of separable complete metrizable spaces onto Hausdorff spaces.