Time-domain dielectric relaxation of poly(methyl methacrylate) and nitrile rubber

The time-domain dielectric response (after-effect) of poly(methyl methacrylate) (PMMA) and nitrile butadiene rubber (NBR) to a voltage step (100 V) was measured at varying temperatures. From the variation of the sample capacitanceC with time, we determined the ratioF _d/C, withF _d=(dC/dlnt)_max and C denoting the difference between the initial and the extrapolated equilibrium capacitance values. For PMMA around room temperature (RT) this ratio assumed values similar to those reported for mechanical stress relaxation. With NBR, such values were observed only at temperatures significantly below RT. A modified Kohlrausch-Williams-Watts (stretched exponential) function provided a good fit to the measuredC(t) data.     

Regeneration of carbonyl compounds by cleavage of CN bonds under mild and completely heterogeneous conditions

Oximes, hydrazones, semicarbazones and azines are converted to the corresponding carbonyl compounds using a combination of Zr(HSO₄)₄ and wet SiO₂ in good to high yields under completely heterogeneous conditions.     

Modeling of biliverdin reduction process: regio-specificity and H-bonding

Octa ethyl biliverdin (OEBV) has been employed as a model for natural biliverdin and its geometry has been optimized by using semiempirical (AM1, PM3), DFT, and hybrid ONIOM methods. Geometries and energetics of formation of octa ethyl bilirubin (OEBR) formed by reduction from OEBV via three carbon sites β, γ, and δ have been obtained. It has been shown that γ-OEBR has two configurational isomers (named γ₁ and γ₂), which can convert to each other by internal 1,5-hydrogen shift. The results show that, within the accuracy level of semiempirical methods, all three isomers namely, β, γ₁, and δ-OEBR are of similar stability whereas, at higher level of theory, γ₁-OEBR is less stable than others. Moreover, γ₂-isomer with one more of its pyrrole rings being aromatic can achieve a higher symmetry, and is the most stable among others by at least 5–6 kcal mol⁻¹ based on various methods employed. It is interesting to note that the ridge-tile conformation, which has been confirmed for natural bilirubin was not observed for calculated geometries of γ₁- and γ₂-isomers. A conformational analysis show that an energy barrier of 25 kcal mol⁻¹ must be surmounted for γ₂ to obtain the ridge-tile geometry.

OEBV was synthesized and purified from octa ethyl porphyrin iron (III) chloride, and was reduced to OEBR by sodium borohydride (NaBH₄). Chemical reduction of OEBV with NaBH₄ was followed in CDCl₃ and CD₃OD solutions and the product was characterized by ¹H NMR and UV–Vis spectroscopy. The results show that γ₂-isomer as the major product, forms along with γ₁ via an equilibrium tautomerization reaction.     

Reaktion von primären Alkylhydroperoxiden mit Amidoschwefelsäurechlorid: Alkyl(amidosulfonyl)peroxide

The novel peroxides H₂NSO₂OOCH₂ R (1 a:R=CH₂CH₃;1 b:R=CH₂CH₂CH₃) are obtained by reaction of sulphamoyl chloride with the appropriate hydroperoxides in the presence of pyridine (temperature below –30 °C, solvent diethyl ether). The solvent-free liquids1 deflagrate at ca. 0 °C. Hydrolysis or ammonolysis of1 generates the hydroperoxide and sulphamic acid or sulphamide, respectively. Controlled thermolysis of1 affords sulphamic acid and carbonyl compounds, i.e. propanal andn-propyl propanoate from1 a, butanal, 2-methylpropanal andn-butyln-butyrate from1 b. These products suggest a nonradical cyclic decomposition path-way.

     

Use and Evaluation of Newly Synthesized Fluorescence Probes to Detect Generated OH• Radicals in Fibroblast Cells

Reactive oxygen species (ROS) are pro-oxidant molecules synthesized in body with various functions and are essential for life. Increasing in reactive oxygen species or decreasing in antioxidants level cause oxidative stress which is very harmful. OH? radical is one of ROS’s, with tendency to bind to lipids, DNA and proteins which cause irreversible damage in cells. The most devastating consequences related to excess OH? radicals occur via direct binding to nucleic acids and proteins. Quantification of this high reactive radical with short life time is difficult. Electron Spin Resonance, Fluorescence, and Luminescence Spectroscopy are commonly used to determine the level of ROS. Fluorescence Probes have higher specificity and sensitivity with their excellent sensors to detect ROS’s compare to the other methods. Also, there are different probes specifically designed for each radical. The purpose of this study was to identify the probe better suiting for detection of OH? radical levels. The two most recommended fluorescence probes, 2-[6-(4 V-Hydroxy) phenoxy-3H-xanthen-3-on-9-yl]benzoic acid (HPF) and coumarin-3-carboxylic acid (3-CCA) to determine OH? radical levels were compared. Following the formation of OH? radical with Fenton reaction, HPF and 3-CCA probes were added to cells and spectrofluorometric measurements were performed in their respective wavelengths. The mean amplitude of fluorescence for HPF was 32.72?±?2.37 F.I (n?=?40) and for 3-CCA was 52.11?±?0.5 F.I (n?=?40). This difference was statistically significant. 3-CCA also demonstrated more stable measurements at different days compered to HPF.     

Base-free green synthesis of copper(II) oxide nanoparticles using highly cross-linked poly(curcumin) nanospheres: synergistically improved antimicrobial activity

Research on Chemical Intermediates - Antimicrobial activity of metal containing formulas has drawn attention and been widely investigated. In this research, CuO/hc-pCUR nanocomposite composed of...     

Mesoporous nanocrystalline MgAl2O4: A new heterogeneous catalyst for the synthesis of 2,4,6-triarylpyridines under solvent-free conditions

In this paper, one-pot synthesis of 2,4,6-triarylpyridine by condensation of subsisted acetophenone (II), aromatic aldehydes (I), and ammonium acetate (III) in the presence of nanocrystalline MgAl₂O₄ as a new heterogeneous catalyst under solvent-free conditions is reported. Advantages of this method are the use of spatially-hindered aldehydes such as 2-methoxy-, 2-fluoro-, and 2-chlorobenzaldehydes, a new nanocatalyst with high surface area, shorter reaction time, easier workup, higher yield, and its environmental friendliness. The performance of this reaction under solvent free conditions using heterogeneous catalysts like MgAl₂O₄ could enhance its efficiency from an economic as well as green chemistry point of view.     

Increasing the octane number of gasoline using functionalized carbon nanotubes

The octane number is one of the characteristics of spark-ignition fuels such as gasoline. Octane number of fuels can be improved by addition of oxygenates such as ethanol, MTBE (methyl tert-butyl ether), TBF (tertiary butyl formate) and TBA (tertiary butyl alcohol) as well as their blends with gasoline that reduce the cost impact of fuels. Carbon nanotubes (CNTs) are as useful additives for increasing the octane number. Functionalized carbon nanotubes containing amide groups have a high reactivity and can react with many chemicals. These compounds can be solubilized in gasoline to increase the octane number. In this study, using octadecylamine and dodecylamine, CNTs were amidated and the amino-functionalized carbon nanotubes were added to gasoline. Research octane number analysis showed that these additives increase octane number of the desired samples. X-ray diffraction (XRD), Fourier transforms infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and thermal gravimetry analyses (TGA) were used for characterization of the prepared functionalized carbon nanotubes.     

Synthesis, characterization, and crystal structural study of the iron(II) 4,4′-bithiazole complex [Fe(C6H4N2S2)3]2+(NO3?)2

Abstract  

The complex [Fe(C₆H₄N₂S₂)₃]²⁺(NO₃⁻)₂ was prepared from the reaction of 4,4′-bithiazole with Fe(NO₃)₃·9H₂O in methanol. It was characterized by IR, UV-Vis, luminescence, ¹H NMR and ¹³C NMR spectroscopy, and X ray crystallography. The structure was solved in the orthorhombic space group P2₁2₁2₁ with a = 12.1500(5), b = 12.8434(6), c = 16.2222(7) ?, V = 2531.43(19) ?³, Z = 4, and with wR ₂  = 0.0897.