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61.
Brazilian poly(hydroxybutyrate), PHB, as well as its copolymer, poly(hydroxybutyrate-co-valerate), P(HB-co-HV), containing 6.3 mol% of valerate, were irradiated with γ radiation (60Co) at ambient temperature and in the presence of oxygen. The viscosity-average molar mass (Mv) was analyzed by the viscosity technique using an Ostwald-type capillary viscometer. The polymers showed a decrease in molar mass with the increase in dose, reflecting the scissions that occurred at random in the main chain. The value G (scissions/100 eV of energy transferred to the system) and the parameter α (scissions per original molecule) were also obtained by the viscosity technique. The melting temperature (Tm) was determined by differential scanning calorimetry (DSC) and showed a decrease with increasing irradiation dose. Analyses of DSC also revealed double endothermic peaks, associated with the polymorphic transitions, which became a single peak with increased dose. Thermogravimetry analysis (TGA) revealed small differences between the decomposition temperatures of the irradiated and non-irradiated samples. The degree of crystallinity of PHB samples, on the other hand, which were obtained by the DSC and X-ray diffraction techniques, increased with the irradiation dose. Changes in the lattice parameter of the irradiated samples and in the size of the crystallites were also observed by X-ray diffraction. The samples used in this work did not pass through any purification process and were analyzed in powder form, exactly as they arrived from the factory. 相似文献
62.
Marius Bruvoll Selma Dizdarevic Nina Fimland Jasmina Hafizovic Carl Henrik Grbitz Helen Therese Kalfjs Kristian Vestli Alexander Krivokapic 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(1):o22-o25
The structures of the title dipeptides, C9H18N2O4·0.33H2O, C12H16N2O4 and C8H16N2O4S·0.34H2O, complete a series of investigations focused on l ‐Xaa‐l ‐serine peptides, where Xaa is a hydrophobic residue. All three structures are divided into hydrophilic and hydrophobic layers. The hydrophilic layers are thin for l ‐phenylalanyl‐l ‐serine, rendered possible by an unusual peptide conformation, and thick for l ‐isoleucyl‐l ‐serine and l ‐methionyl‐l ‐serine, which include cocrystallized water molecules on the twofold axes. 相似文献
63.
Exposure of acetonitrile/methanol solutions of [PPN][Ru(DPPBT)3] [PPN = bis(triphenylphosphoranylidene); DPPBT = 2-diphenylphosphinobenzene thiolate] to oxygen initiates metal-centered oxidation, yielding the ruthenium(III) thiolate Ru(DPPBT)3. Ru(DPPBT)3 further reacts with oxygen, at sulfur, to give the ruthenium(III) sulfinate complex [Ru(DPPBT-O2)2(DPPBT)], which is reduced under ambient conditions to [PPN][Ru(DPPBT-O2)2(DPPBT)]. Ruthenium(II) sulfinate is the only product isolated from acetonitrile/methanol. Yellow crystals of [PPN][Ru(DPPBT-O2)2(DPPBT)] were obtained. Ruthenium(III) sulfinate was isolated as green prism-shaped crystals upon oxygenation of [PPN][Ru(DPPBT)3] in chlorobenzene/hexane. Electrochemical oxidation of ruthenium(II) sulfinate yields the ruthenium(III) derivative, which is rapidly reduced back to ruthenium(II) upon the addition of hydroxide. 相似文献
64.
Some five-coordinated dimethyltin(IV) complexes of the type Me2SnL (where L is the anion of a bifunctional tridentate Schiff base) were synthesized. These Schiff bases are N-(3-hydroxypyridine-2-yl)-3-methoxysalicylideneimine, HOC6H3OCH3CH=NC5H3NOH (1), N-(3-hydroxypyridine-2-yl)-3-ethoxysalicylideneimine, HOC6H3OC2H5CH=NC5H3NOH (2), N-(3-hydroxypyridine-2-yl)-5-chlorosalicylideneimine, HOC6H3ClCH=NC5H3NOH (3), and N-(3-hydroxypyridine-2-yl)-3-methoxy-5-bromosalicylideneimine, HOC6H2OCH3BrCH=NC5H3NOH (4). Dimethyltin(IV) complex of 3 (3a) was characterized by single crystal X-ray diffraction method and a coordination geometry that is nearly halfway between
trigonal–bipyramidal and square pyramidal arrangement was found. Dimethyltin complexes of (1), (2), and (4) were also prepared and characterized by the comparison of their elemental analysis and 1H-NMR-, IR-, UV- and mass spectral data with those of (3a). For example, in the 1H-NMR spectra, the 2J(119Sn-1H) in the Sn-CH3 moiety have values between 80 Hz and 90 Hz, typical of five-coordinated tin species. By using these values in Lockart’s Equations,
H3C–Sn–CH3 angles in the complexes were estimated to lie between 130° and 145°. X-ray diffraction value for 3a, confirms this estimate within 3.4% relative deviation (129.7° exp. Vs. 134.9° estimate). 相似文献
65.
Sara Atailia Dr. Abdoullatif Baraket Selma Rabai Messaoud Benounis Nicole Jaffrezic Hala Araar Abdelyamine Naït-Bouda Abdecharif Boumaza Abdelhamid Errachid Moussa Houhamdi 《Electroanalysis》2023,35(9):e202200502
In this study, a novel, sensitive electrochemical enzyme-based biosensor for urea detection was presented. This biosensor combines a three-electrode system consisting of a classic Glassy Carbon Electrode (GCE) as the working electrode, a platinum counter electrode, and Ag/AgCl as the reference electrode. To construct this urea platform, a GCE was modified with a polyaniline (PANi) film. Then, bacterial urease from Proteus mirabilis was immobilized on the modified GCE (Pm-Urease-PANi-GCE). For the characterization of surface modification, Cyclic Voltammetry (CV) and Scanning Electron Microscope (SEM) were applied, while the Square Wave Voltammetry (SWV) technique was performed for urea detection. The main analytical characteristics of the Pm-Urease-PANi-GCE biosensor showed a good linear range from 0.1 to 10 mM of urea, a limit of detection (LOD) of 0.1 mM, a Michaelis-Menten Km of 0.23 mM, and a sensitivity value 46 μA/mM/cm2. This biosensor allows the detection of urea in solutions, and it could be improved for further medical, environmental, or engineering applications. 相似文献
66.
Vougo-Zanda M Anokhina EV Duhovic S Liu L Wang X Oloba OA Albright TA Jacobson AJ 《Inorganic chemistry》2008,47(11):4746-4751
Three metal-oxide organic frameworks have been synthesized and characterized: vanadium 1,4-benzenedicarboxylate, V2O2F0.6(OH)1.4(BDC).0.4H 2O (1); indium 1,4-benzenedicarboxylate, In 2F2.2(OH)1.8(BDC).1.6H2O (2); and aluminum 1,4-benzenedicarboxylate Al2F3(OH)(BDC) (3). The three-dimensional structures of 1, 2, and 3 have the same framework topology as the previously reported vanadium (III) 1,4-benzenedicarboxylate, VIII2(OH)2F2(BDC). The frameworks consist of inorganic layers constructed from corner sharing ML 6 octahedra (M=V, In, Al and L=OH, F) linked by BDC ligands. The structures are related to a general class of perovskite-related layer structures with composition MM'X4. The layers show characteristic distortions that can be related to tilting of the ML 6 octahedra. In particular the structure of 1 consists of O-V distances that strongly alternate along the b axis. The electronic consequences of this distortion then create a tilting of the 1,4-benzenedicarboxylate ligand about the a axis. Crystal data: 1, orthorhombic, space group Pmna, a=7.101(2) A, b=3.8416(11) A, c=20.570(6) A; 2, orthorhombic, space group Cmcm, a=7.490(4) A, b=21.803(1) A, c=8.154(4) A; 3, monoclinic, space group P2(1)/m, a=10.7569(8) A, b=6.7615(3) A, c=7.1291(3) A, beta=76.02(1) degrees. 相似文献
67.
68.
Selma Mededovic Thagard Gunnar R. Stratton Mikhail Vasilev Patrick Conlon Douglas Bohl 《Plasma Chemistry and Plasma Processing》2018,38(4):719-741
In this work, particle image velocimetry has been used to visualize and quantify plasma-induced flow fields in liquid water. Experiments were performed in a rod-plane plasma reactor with a thin wire electrode suspended above the surface of the liquid in argon gas and a grounded plate immersed in the liquid. The velocity field has been quantified for two types of solutions: (1) aqueous NaCl solutions of varying solution conductivities and discharge frequencies and (2) aqueous NaCl solutions containing varying concentrations of the following four organic compounds: rhodamine B dye, caffeine, fluoxetine, and perfluorooctanoic acid. Results show that in neat water and aqueous caffeine solutions, the liquid is “pulled” along by the interaction of the gas molecules with the liquid molecules at the free surface and thus the direction of the liquid flow is in the direction of the gas phase flow (i.e., away from the discharge location). However, the flow was reversed (i.e., towards the discharge) for those solutions with strong surfactants such as perfluorooctanoic acid. The magnitude of the reversal depended on the initial concentration of the compound and for some compounds as time progressed the reversed flow pattern weakened and then reverted to a normal flow pattern. To determine the most likely cause of these flow reversals, a simple numerical model of the velocity field was developed to estimate relative contributions of various flow inducing mechanisms. The model indicates that in the presence of surfactants, Marangoni stresses are responsible for inducing the flow in the liquid. 相似文献
69.
Microwave‐assisted solvent‐free synthesis of novel benzoxazines: A faster and environmentally friendly route to the development of bio‐based thermosetting resins 下载免费PDF全文
Jéssica R. Oliveira Lloyd R. V. Kotzebue Francisco W. M. Ribeiro Beatriz C. Mota Dávila Zampieri Selma E. Mazzetto Hatsuo Ishida Diego Lomonaco 《Journal of polymer science. Part A, Polymer chemistry》2017,55(21):3534-3544
Microwave‐assisted organic synthesis (MAOS) is a well‐established technique that has been used in the enhancement of chemical reactions. Here, the versatility of MAOS is explored describing an environmentally friendly one‐pot route to novel bio‐based benzoxazines under solvent‐free conditions. The lignin derivative, guaiacol, along with paraformaldehyde and different conjugated and nonconjugated amines are successfully fused into guaiacol‐derived 3,4‐dihydro‐2H‐1,3‐benzoxazines. The reactions conducted under microwave irradiation are completed much faster than those under traditional heating, reducing the reaction time from hours to only 6 min, with good yields. The chemical structures of novel benzoxazines are confirmed by 1H and 13C NMR spectroscopy, FTIR, and HR‐MS. The thermal behavior of the resins are evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), showing that these polymers have good thermal stability and wide processing‐window, with onset temperature of polymerization above 230 °C. These results indicate dramatic improvement over the traditional methodologies for the production of this class of resins, which are usually obtained by time‐consuming procedures and in the presence of toxic solvents. Therefore, MAOS can be considered a green and efficient strategy for the synthesis of eco‐friendly benzoxazines. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3534–3544 相似文献
70.
Horacio J. Salavagione Diego Cazorla-Amors Selma Tidjane Mohammed Belbachir Abdelghani Benyoucef Emilia Moralln 《European Polymer Journal》2008,44(5):1275-1284
A detailed study about the synthesis, characterization and properties of poly(o-methylaniline)(PoMea)/maghnite nanocomposites has been performed. Changes in the characteristics of the nanocomposites, depending on the intercalated cation between the clay layers before the synthesis, have been observed. Intercalated morphology has been detected by TEM in nanocomposites containing copper-treated maghnite (Magh-Cu), while when maghnite treated with strong acids was used (Magh-H); an exfoliated material has been obtained. Also, remarkable differences in the properties of the polymers have been observed by TG-MS and FTIR, suggesting that the polymer produced with Magh-H has a higher degree of branching. The electrochemical behavior of the polymers extracted from the nanocomposites has been studied by cyclic voltammetry. Good electrochemical response has been observed for PoMea grown into Magh-Cu but not for the one polymerized into Magh-H. 相似文献