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121.
B A Finnin M A A O'Neill S Gaisford A E Beezer J Hadgraft P Sears 《Journal of Thermal Analysis and Calorimetry》2006,83(2):331-334
Isothermal
calorimetry is becoming indispensable as a tool for the study of a wide variety
of systems. As with all scientific instruments it is essential that robust
calibration routines be developed in order to validate the data obtained.
Chemical test reactions offer many advantages over (the traditionally used)
joule effect heating methods, not least because they have the potential to
validate instrument performance (i.e. they can be used to assess all aspects
of calorimeter operation). In this work the results of a validation exercise,
conducted by Thermal Hazard Technology as part of an installation routine,
using the base catalysed hydrolysis of methyl paraben are discussed. In the
case described, a systematic misreporting of the reported temperature of a
calorimeter was identified, caused by an upgrade to the calorimeter's
firmware, a discrepancy which may not have been noted using traditional electrical
calibration methods and one which highlights the importance of both manufacturers
and end-users adopting chemical test reactions into their test and validation
routines. 相似文献
122.
The absorption spectrum of neodymium (III) (Nd3+ doped in poly(methyl methacrylate) was measured. The Nephlauxetic effect was found in the spectrum compared to other spectra of Nd3+ doped in various matrices. The experimental data used, Slater-Condon parameters (F2,F4,F6) and Lander parameter (ζ4f) were calculated by the Taylor series expansion based on the assumption that the energy separation between J-levels of the 4fn-configuration is a function of F2,F4,F6 and ζ4f. The Judd-Ofled intensity parameters (Ω2,Ω4,Ω6) were also calculated. Analysis of the Nephlauxetic effect and the parameters variation on the host matrices was carried out. 相似文献
123.
124.
G. Clouet P. Chaumont P. Corpart 《Journal of polymer science. Part A, Polymer chemistry》1993,31(11):2815-2824
The thermal bulk polymerization of methyl methacrylate (MMA) in a wide range of temperatures has been studied using a dilatometric reactor. It is shown that, irrespective of the care taken to purify the MMA, the evolution of the time-conversion curve can be explained only if we account for the presence of an impurity associated with the monomer acting as a free radical initiator. The activation energy for the decomposition of this impurity has been estimated as 98 kJ/mol. Having accounted for this impurity, the activation energy for the real thermal polymerization of the MMA has been estimated to be 75 kJ/mol. © 1993 John Wiley & Sons, Inc. 相似文献
125.
Olga?V.?DorofeevaEmail author Igor?F.?Shishkov Lev?V.?Vilkov István?Hargittai 《Structural chemistry》2005,16(6):617-628
The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by
electron diffraction at 130∘C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface
has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified.
Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations
resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ
energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data
to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter
values (ra in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers
are r(C–C) = 1.507(5), r(C–C)ring, av = 1.397(3), r(C–S)av = 1.814(4), r(C–N) = 1.495(4), r(N–O)av = 1.223(3), ∠(C–C–C)ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the
rotation about C–N bond, φC−N, were found to be 30.5–36.5∘ for different conformers. As to internal rotation about C–C and C–S bonds, values of φC−C = 68–118∘ and φC−S = 66–71∘ were obtained for the three most stable conformers with gauche orientation with respect to these bonds.
Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701. 相似文献
126.
Lamia T. Abou El-Kassem Usama W. Hawas Mohamed S. Abdelfattah Ayat A. Mostafa 《Natural product research》2020,34(5):613-620
AbstractA new rotenoid named 12-O-methylrotenolol along with five known rotenoid and isoflavone metabolites were isolated from the seeds of Dalbergia lanceolaria subsp. paniculata, collected from Egypt. The structures of these compounds were identified by physical and spectroscopic data measurements ([α]D, UV, 1D- and 2D-NMR and MS). The methanol extract of the seeds exhibited strong antioxidant activity with IC50 value 0.7?µg/µl against DPPH radical, in respect to quercetin as antioxidant reference (IC50 1.5?μM), while the tested compounds from this extract showed weak activities with IC50 values ranged from 19.6 to 33.0?µM. 相似文献
127.
A sensitive and convenient high-performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS) assay is described for the (5-HT(lB/lD)) receptor agonist sumatriptan in human plasma. Sumatriptan was recovered from plasma (81.8 +/- 6.8%) by liquid-liquid extraction. The mobile phase flow rate was 0.3 mL/min and consisted of methanol:water:formic acid (90:10:0.1, v/v/v). The analytical column (4.6 x 100 mm) was packed with Partisil C(8) (5 micro m). The standard curve was linear from 0.7 to 70.4 ng/mL (r(2) > 0.99). The lower limit of quantitation was 0.7 ng/mL. The assay was specific, accurate (percentage deviation from nominal concentrations were <15%), precise and reproducible (within- and between-day coefficients of variation <10.3%). Sumatriptan in plasma was stable over three freeze/thaw cycles and at room temperature for one day. The utility of the assay was demonstrated by following sumatriptan plasma concentrations in two healthy subjects for 8-12 h following a single 20 mg intranasal dose. 相似文献
128.
After mixing a methylbenzene 4 with “magic blue” solution in F113 (CClF2CCl2F) containing bis{perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl}nitroxide 2 and perfluoro-1-nitroso-1-[1-(2-fluorosulfonyl)ethoxy]ethane 3 at room temperature, benzylic H-atom of 4 could be selectively abstracted by 2, and benzyl radical 5 thus generated was immediately trapped by 3. Based on hyper-fine splitting constants (hfsc), the structure of the spin adducts perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl benzyl nitroxides 6 derived from seven methylbenzenes have been identified. The mechanism of the H-abstraction/spin trapping process is also discussed. 相似文献
129.
Freezing temperatures of dilute aqueous solutions of ethyl acetate and mixtures with myo-inositol, D-mannitol, formamide, 1,3,5-trioxane, 1,4-dioxane, acetamide, hexamethylenetetramine, and methyl formate have been measured. In addition, freezing temperatures of dilute aqueous solutions of methyl formate and mixtures with the above solutes have been measured. From these data, the pairwise molecular Gibbs energies of interaction between the molecules were calculated. Using the additivity principle, the pairwise functional group Gibbs energies of interaction were calculated for ester group interactions with a variety of other functional groups. 相似文献
130.