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51.
Giorgio Adembri Angela Maria Celli Alessandro Sega 《Journal of heterocyclic chemistry》1997,34(2):541-547
Tetraacetylethylene ( 1 ), and cis-diacetylethylene ( 4 ) reacted under mild conditions with 3-amino-2-butenoic acid methyl ester ( 6 ), benzene-1,2-diamine and naphthalene-2,3-diamine to give polysubstituted pyrroles, 2,3-disubstituted quinoxalines and 2,3-disubstituted benzo[g]quinoxalines respectively. Some aspects of the reactions mechanisms are discussed. 相似文献
52.
Angela Agostiano D. Christopher Goetze Robert Carpentier † 《Photochemistry and photobiology》1992,55(3):449-455
Abstract— In this paper, the technique of cyclic voltammetry has been used in a photoelectrochemical cell in order to follow the redox species formed in solution by the photo-induced electron transfer between the thylakoids and various acceptors and donors. The photoelectrochemical behavior of artificial electron acceptors (such as 2,5-dichlorobenzoquinone and methylviologen) and donors (such as sym -diphenylcarbazide and durohydroquinone) specific for either Photosystem I or Photosystem II has been investigated. The influence of inhibiting agents (such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea and Tris) on the cell photoresponse has also been characterized, together with the capability of donors to restore the photocurrent. Evidence for H2 O2 formation by way of a Mehler-type reaction has been provided and an electrochemical model of its coupled photochemical and electrochemical reactions in solution is reported. 相似文献
53.
A collaborative study was conducted to compare a new enrichment procedure for the TECRA Salmonella Visual Immunoassay (TSVIA) with the reference method given in the U.S. Food and Drug Administration's Bacteriological Analytical Manual (7th Ed.). Three food types (milk powder, pepper, and soy flour) were analyzed in Australia and 3 food types (milk chocolate, dried egg, and raw turkey) were analyzed in the United States. Thirty-eight collaborators participated in the study. The TECRA method was evaluated using both Rappaport-Vassiliadis R10 (RV(R10)) and tetrathionate (TT) broths for selective enrichment. M broth cultures arising from each of the 2 selective enrichment broths were tested in the TSVIA using 2 individual wells, one for each selective broth, and a single well to test the pooled selective enrichment broths. The results for the pooled enrichment broths were reported elsewhere. This study presents the results for the use of single enrichment broths, i.e., RV(R10) only or TT only, with the TSVIA. No significant differences (p > 0.05) were observed for the pairwise comparison of the proportion of positive samples for either RV(R10) or TT used as a single enrichment broth for the TSVIA with that for the reference method. 相似文献
54.
Bihlmeier A Gonsior M Raabe I Trapp N Krossing I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(20):5041-5051
The unexpected but facile preparation of the silver salt of the least coordinating [(RO)3Al‐F‐Al(OR)3]? anion (R=C(CF3)3) by reaction of Ag[Al(OR)4] with one equivalent of PCl3 is described. The mechanism of the formation of Ag[(RO)3Al‐F‐Al(OR)3] is explained based on the available experimental data as well as on quantum chemical calculations with the inclusion of entropy and COSMO solvation enthalpies. The crystal structures of (RO)3Al←OC4H8, Cs+[(RO)2(Me)Al‐F‐Al(Me)(OR)2]?, Ag(CH2Cl2)3+[(RO)3Al‐F‐Al(OR)3]? and Ag(η2‐P4)2+[(RO)3Al‐F‐Al(OR)3]? are described. From the collected data it will be shown that the [(RO)3Al‐F‐Al(OR)3]? anion is the least coordinating anion currently known. With respect to the fluoride ion affinity of two parent Lewis acids Al(OR)3 of 685 kJ mol?1, the ligand affinity (441 kJ mol?1), the proton and copper decomposition reactions (?983 and ?297 kJ mol?1) as well as HOMO level and HOMO–LUMO gap and in comparison with [Sb4F21]?, [Sb(OTeF5)6]?, [Al(OR)4]? as well as [B(RF)4]? (RF=CF3 or C6F5) the [(RO)3Al‐F‐Al(OR)3]? anion is among the best weakly coordinating anions (WCAs) according to each value. In contrast to most of the other cited anions, the [(RO)3Al‐F‐Al(OR)3] anion is available by a simple preparation in conventional inorganic laboratories. The least coordinating character of this anion was employed to clarify the question of the ground state geometry of the Ag(η2‐P4)2+ cation (D2h, D2 or D2d?). In agreement with computational data and NMR spectra it could be shown that the rotation along the Ag‐(P‐P‐centroid) vector has no barrier and that the structure adopted in the solid state depends on packing effects which lead to an almost D2h symmetric Ag(η2‐P4)2+ cation (0 to 10.6° torsion) for the more symmetrical [Al(OR)4]? anion, but to a D2 symmetric Ag(η2‐P4)2+ cation with a 44° twist angle of the two AgP2 planes for the less symmetrical [(RO)3Al‐F‐Al(OR)3]? anion. This implies that silver back bonding, suggested by quantum chemical population analyses to be of importance, is only weak. 相似文献
55.
Antunes MA Ferrence GM Domingos A McDonald R Burns CJ Takats J Marques N 《Inorganic chemistry》2004,43(21):6640-6643
Reaction of [(Tp(Me)2)(2)UI] with KNR(2) (R = C(6)H(5), SiMe(3)) in tetrahydrofuran (THF) afforded the monomeric trivalent actinide amide complexes [(Tp(Me)2)(2)U[N(C(6)H(5))(2)]], 1, and [(Tp(Me)2)(2)U[N(SiMe(3))(2)]], 2. The complexes have been fully characterized by spectroscopic methods and their structures were confirmed by X-ray crystallographic studies. In the solid state 1 and 2 exhibit distorted pentagonal bipyramidal geometries. The U-NR(2) bond lengths in both complexes are the same but in complex 2 the greater steric demands of the N(SiMe(3))(2) ligand led to elongated U-N(pz) bonds, especially those opposite the amido ligand. 相似文献
56.
The effects of addition of alkanols (ethanol, n-hexanol, and 3-ethyl-3-pentanol) on the micropolarity and microviscosity of the head group region in reverse micelles of AOT-heptane-water have been investigated by fluorescence probing methods (ANS fluorescence yield and TMADPH fluorescence anisotropy), complemented by the use of the solvatochromic probe E(T)(30) in absorption spectroscopy. For all the alkanols considered, ANS fluorescence in AOT reverse micelles (at W=3) is quenched by additive incorporation, being the effect elicited almost independent of the alkanol chain length and topology. As sensed by the E(T)(30) parameter, the micropolarity of the micelle surface increases, remains unmodified, and decreases upon addition of ethanol, 3-ethyl-3-pentanol, and hexanol, respectively. While ethanol barely modifies the fluorescence anisotropy of TMADPH, 3-ethyl-3-pentanol and n-hexanol addition strongly decrease it. The similarity of the tendencies of ANS data to TMADPH anisotropies and the differences between ANS data and E(T)(30) values would indicate that, at least for 3-ethyl-3-pentanol and n-hexanol, microviscosity, rather than micropolarity, must be considered to interpret the effect of the alkanols upon the fluorescent behavior of ANS. 相似文献
57.
D. Malferrari Maria Franca Brigatti Angela Laurora L. Medici S. Pini 《Journal of Thermal Analysis and Calorimetry》2006,86(2):365-370
The thermal behavior
of montmorillonite and organically modified montmorillonite, both treated
with heavy metal cations [Cu(II), Cd(II) and Hg(II)], was characterized via
thermal analyses (TG, DTG and DTA) combined with evolved species gas mass
spectrometry (MS-EGA), and X-ray diffraction at in situ controlled temperature
(HTXRD). The reactions involving Cu(II)- and Cd(II)-montmorillonite samples
are mostly related to H2O and OH loss, unlike Hg(II)-montmorillonite,
where effects associated to Hg(II) loss are also present. Finally reactions
related to dehydration, dehydroxylation and to organic matter decomposition
can be observed in montmorillonite samples treated with cysteine. 相似文献
58.
Jeremy M. Kaminski Angela Rodríguez-Serrano Fabian Dinkelbach Hector Miranda-Salinas Andrew P. Monkman Christel M. Marian 《Chemical science》2022,13(23):7057
Quantum chemical studies employing combined density functional and multireference configuration interaction methods suggest five excited electronic states to be involved in the prompt and delayed fluorescence emission of TpAT-tFFO. Three of them, a pair of singlet and triplet charge transfer (CT) states (S1 and T1) and a locally excited (LE) triplet state (T3), can be associated with the (Me → N) conformer, the other two CT-type states (S2 and T2) form the lowest excited singlet and triplet states of the (Me → Ph) conformer. The two conformers, which differ in essence by the shearing angle of the face-to-face aligned donor and acceptor moieties, are easily interconverted in the electronic ground state whereas the reorganization energy is substantial in the excited singlet state, thus explaining the two experimentally observed time constants of prompt fluorescence emission. Forward and reverse intersystem crossing between the singlet and triplet CT states is mediated by vibronic spin–orbit interactions involving the LE T3 state. Low-frequency vibrational modes altering the distance and alignment of the donor and acceptor π-systems tune the S1 and T3 states (likewise S2 and T3) into and out of resonance. The enhancement of intersystem crossing due to the interplay of vibronic and spin–orbit coupling is considered a general feature of organic through-space charge-transfer thermally activated delayed fluorescence emitters.DFT/MRCI quantum chemical studies suggest five excited electronic states to be involved in the prompt and delayed fluorescence emission of TpAT-tFFO. 相似文献
59.
60.
Richard Coupe Heather Welch Angela Pell E. Michael Thurman 《International journal of environmental analytical chemistry》2013,93(15):1127-1140
During 1996-1997, water samples were collected from five sites in the Yazoo River Basin and analysed for 14 herbicides and nine degradates. These included acetochlor, alachlor, atrazine, cyanazine, fluometuron, metolachlor, metribuzin, molinate, norflurazon, prometryn, propanil, propazine, simazine, trifluralin, three degradates of fluometuron, two degradates of atrazine, one degradate of cyanazine, norflurazon, prometryn, and propanil. Fluxes generally were higher in 1997 than in 1996 due to a greater rainfall in 1997 than 1996. Fluxes were much larger from streams in the alluvial plain (an area of very productive farmland) than from the Skuna River in the bluff hills (an area of small farms, pasture, and forest). Adding the flux of the atrazine degradates to the atrazine flux increased the total atrazine flux by an average of 14.5%. The fluometuron degradates added about 10% to the total fluometuron flux, and adding the norflurazon degradate flux to the norflurazon flux increased the flux by 82% in 1996 and by 171% in 1997. 相似文献