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31.
Ahmady A. Yassin Nadia A. Rizk 《Journal of polymer science. Part A, Polymer chemistry》1978,16(7):1475-1485
Charge-transfer complexes of N,N-dimethylaniline (DMA) and triethylamine (TEA) with chloranil have been investigated as inhibitors for the sensitized polymerization of methyl methacrylate (MMA) in bulk and in solution. Complete inhibition is achieved by the complexes of both amines followed by retardation only in case of DMA. The higher inhibiting efficiency of the TEA complexes is attributed to their greater stability. The polymers formed in the presence of chloranil alone or its complexes with both amines are quinonoid and contain no combined nitrogen. The results support the idea that inhibition reaction involve electron transfer from the growing chains to the quinone, with formation of molecular complexes of polymeric cations and semiquinone anions. The latter are the actual inhibiting species, so that the efficiency of inhibiting depends on their concentration, which is determined by the stability of the molecular complexes formed. The inhibition reactions should accordingly be considered as oxidation–reduction processes in which the growing chains are the electron donors. The suggested mechanism affords an explanation for the great differences in the inhibiting power of a particular quinone for the polymerization of different monomers. 相似文献
32.
A. Z. Abyshev I. P. Sidorova D. Z. Abyshev V. N. Florya V. P. Zmeikov Yu. B. Kerimov 《Chemistry of Natural Compounds》1982,18(4):400-407
The results are given of the identification of (?)-trans-khellactone and its 4′-methyl ether and (?)-3′(S), 4′(S)-trans-3′-senecioyloxy-4′-angeloyloxy-3′,4′-dihydroseselin and of the establishment of the structure of three new khellactone derivatives — campestrol (VII), C19H22O6, [α] D 20 + 32° (c 7.8; chloroform), campestrinol (X), C24H26O7, mp 116–118°C, and campestrinoside (I), C20H24O10, mp 172–173°C, [α]D ?272.5° (c 4.7; ethanol). It has been shown on the basis of chemical and spectral characteristics that campesol, earlier described as a new substance, is a mixture of two isomeric compounds — 4′-hydroxy-3′-senecioyloxy-3′,4′-dihydroseselin and 3′-angeloyloxy-4′-hydroxy-3′,4′-dihydroseselin. 相似文献
33.
Benturquia N Couderc F Sauvinet V Orset C Parrot S Bayle C Renaud B Denoroy L 《Electrophoresis》2005,26(6):1071-1079
Serotonin or 5-hydroxytryptamine (5-HT) is a major neurotransmitter in the central nervous system. In this work, a method for analyzing 5-HT in brain microdialysis samples using a commercially available capillary electrophoresis (CE) system has been developed. A pH-mediated in-capillary preconcentration of samples was performed, and after separation by capillary zone electrophoresis, native fluorescence of 5-HT was detected by a 266 nm solid-state laser. The separation conditions for the analysis of 5-HT in standard solutions and microdialysates have been optimized, and this method has been validated on both pharmacological and analytical bases. Separation of 5-HT was performed using a 80 mmol/L citrate buffer, pH 2.5, containing 20 mmol/L hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and +30 kV voltage. The detection limit was 2.5 x 10(-10) mol/L. This method allows the in vivo brain monitoring of 5-HT using a simple, accurate CE measurement in underivatized microdialysis samples. 相似文献
34.
Tetraphenylmethanes with multiple hydrogen-bonding sites are known to associate to form robust porous supramolecular networks. Analogous anionic networks can be built from the corresponding tetraphenylborates. Crystallization of the tetraphenylphosphonium salt of tetraphenylborate 2 produces an anionic network in which 74% of the volume is available for including cations and neutral guests. Other salts of anion 2 with diverse cations crystallize consistently to form the same network, whereas a neutral analogue of anion 2, tetraphenylmethane 1, produces an uncharged network that is far less open. Cations can be exchanged in single crystals of salts of tetraphenylborate 2 with retention of crystallinity and with selectivities similar to those observed in typical zeolites. Together, these observations provide new strategies for making ordered molecular materials by design, and they reveal that constructing such materials from charged subunits offers special advantages. 相似文献
35.
Nadia Marino Giuseppe Bruno Archimede Rotondo Giovanna Brancatelli Francesco Nicol 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(10):o587-o589
The title compound, C8H8NO4+·Cl−·H2O, is the chlorohydrated form of 2‐aminobenzene‐1,4‐dicarboxylic acid, the basic crystal structure of which is still not known. Molecules are linked by classical N—H⋯O, O—H⋯O, N—H⋯Cl and O—H⋯Cl hydrogen bonds, mainly along the molecular plane, into sheets built by unusual R64(26), R64(22) and R43(22) rings. The stacking between layers is stabilized by another N—H⋯Cl hydrogen bond and by π–π interactions between aromatic rings facing each other. 相似文献
36.
Ti(III)-induced free-radical decomposition of a phenyldiazonium salt, followed by phenyl radical iodine-atom abstraction from alkyl iodides, leads to a one-pot selective alkyl radical addition to the C-atom of imines generated in situ under aqueous acidic conditions. [reaction: see text] 相似文献
37.
38.
I. I. Popov N. S. Vashurin S. E. Putilin S. A. Stepanov V. T. Sidorova N. I. Sushentsov 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(2):152-155
A femtosecond stimulated photon echo is detected for the first time in thin semiconductor films with thicknesses of 100, 800, and 2400 nm. It is established that relaxation time T 1 varies with ZnO film thickness, taking values of 0.96, 2.96, and 4.312 ps at thicknesses of 2400, 800, and 100 nm, respectively. For ZnO/Si+/Si? trilayer films, the relaxation time is T 1 = 12.73 ps. 相似文献
39.
Pencil beam algorithms used in computerized electron beam dose planning are usually described using the small angle multiple scattering theory. Alternatively, the pencil beams can be generated by Monte Carlo simulation of electron transport. In a previous work, the 4th version of the Electron Gamma Shower (EGS) Monte Carlo code was used to obtain dose distributions from monoenergetic electron pencil beam, with incident energy between 1 MeV and 50 MeV, interacting at the surface of a large cylindrical homogeneous water phantom. In 2000, a new version of this Monte Carlo code has been made available by the National Research Council of Canada (NRC), which includes various improvements in its electron-transport algorithms. In the present work, we were interested to see if the new physics in this version produces pencil beam dose distributions very different from those calculated with oldest one. The purpose of this study is to quantify as well as to understand these differences. We have compared a series of pencil beam dose distributions scored in cylindrical geometry, for electron energies between 1 MeV and 50 MeV calculated with two versions of the Electron Gamma Shower Monte Carlo Code. Data calculated and compared include isodose distributions, radial dose distributions and fractions of energy deposition. Our results for radial dose distributions show agreement within 10% between doses calculated by the two codes for voxels closer to the pencil beam central axis, while the differences are up to 30% for longer distances. For fractions of energy deposition, the results of the EGS4 are in good agreement (within 2%) with those calculated by EGSnrc at shallow depths for all energies, whereas a slightly worse agreement (15%) is observed at deeper distances. These differences may be mainly attributed to the different multiple scattering for electron transport adopted in these two codes and the inclusion of spin effect, which produces an increase of the effective range of electrons. 相似文献
40.
M. Rasul Jan Jasmin Shah Nadia Bashir 《International journal of environmental analytical chemistry》2013,93(1):27-35
Abstract A method for the dechlorination of PCB mixtures (Aroclor formulations) to biphenyl was extended to soils. The contaminated sample was mixed with magnesium flakes, potassium hexachloropalladiate (K2PdCl6), propan-2-ol and water then permitted to react for up to six hours. Biphenyl, recovered by extraction into hexane, was quantified by gas chromatography with flame ionization detection. The reaction was very efficient in propan-2-ol / water (~95%), surfactant emulsion or sand mixture and virtually complete in soil provided that excess magnesium (2 g) and the K2PdCl6 were added to the sample prior to the addition of water. Higher PCB loadings were readily determined in field contaminated soils either by direct determination within the matrix or by standard additions. However, analyte concentrations were appreciably over-estimated in Soxhlet or sonication extracts of a certified reference material that contained sub-ppm levels of analyte. The over-estimation is considered to result from the conversion in part of natural organic matter to biphenyl. 相似文献