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41.
A method for the analysis of avermectines (abamectine, doramectine and ivermectine) in soils has been developed. The analytes are extracted with acetonitrile/water (90:10) by using microwave assisted extraction. The extract is cleaned-up through solid phase extraction with Oasis HLB cartridges and analyzed by ultra high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Separation is obtained in 3 min. Extraction of analytes from the soil, that is the most critical point, has been studied in detail, and the effect of soil composition and aging time on the analytes recovery has been investigated. 相似文献
42.
Bruijnincx PC Buurmans IL Huang Y Juhász G Viciano-Chumillas M Quesada M Reedijk J Lutz M Spek AL Münck E Bominaar EL Klein Gebbink RJ 《Inorganic chemistry》2011,50(19):9243-9255
The newly synthesized dinuclear complex [Fe(III)(2)(μ-OH)(2)(bik)(4)](NO(3))(4) (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe···Fe (3.0723(6) ?) and Fe-O distances (1.941(2)/1.949(2) ?) compared to other unsupported Fe(III)(2)(μ-OH)(2) complexes. The bridging hydroxide groups of 1 are strongly hydrogen-bonded to a nitrate anion. The (57)Fe isomer shift (δ = 0.45 mm s(-1)) and quadrupole splitting (ΔE(Q) = 0.26 mm s(-1)) obtained from Mo?ssbauer spectroscopy are consistent with the presence of two identical high-spin iron(III) sites. Variable-temperature magnetic susceptibility studies revealed antiferromagnetic exchange (J = 35.9 cm(-1) and H = JS(1)·S(2)) of the metal ions. The optimized DFT geometry of the cation of 1 in the gas phase agrees well with the crystal structure, but both the Fe···Fe and Fe-OH distances are overestimated (3.281 and 2.034 ?, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 ?) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J by 35%. Spontaneous reduction of 1 was observed in methanol, yielding a blue [Fe(II)(bik)(3)](2+) species. Variable-temperature magnetic susceptibility measurements of [Fe(II)(bik)(3)](OTf)(2) (2) revealed spin-crossover behavior. Thermal hysteresis was observed with 2, due to a loss of cocrystallized solvent molecules, as monitored by thermogravimetric analysis. The hysteresis disappears once the solvent is fully depleted by thermal cycling. [Fe(II)(bik)(3)](OTf)(2) (2) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C-H bond oxidation was observed with adamantane (3°/2° value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of O(2), and a low retention of configuration in cis-1,2-dimethylcyclohexane oxidation were observed. Stereoselective oxidation of olefins with dihydrogen peroxide yielding epoxides was observed under both limiting oxidant and substrate conditions. 相似文献
43.
Tsunashima R Long DL Endo T Noro S Akutagawa T Nakamura T Cabrera RQ McMillan PF Kögerler P Cronin L 《Physical chemistry chemical physics : PCCP》2011,13(16):7295-7297
The Dawson-type polyanion [α-Mo(18)O(54)(SO(3))(2)](4-), with two SO(3)(2-) templates embedded inside a polyoxomolybdate(vi) cage, exhibits thermochromism over an exceptionally wide temperature range (~500 K). The temperature dependence of the cluster structure, established from X-ray crystallography, IR and Raman spectroscopy and DFT calculations, is related to a decreasing HOMO-LUMO gap in the near UV with increasing temperature. We postulate this is due to geometrical changes that affect both the occupied and unoccupied frontier molecular orbitals of this cluster anion. 相似文献
44.
W. Ouerghui J. Martinez-Pastor J. Gomis M. A. Maaref D. Granados J. M. García 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):217-223
Exciton recombination dynamics in vertical stacks of InGaAs quantum rings have been studied by means of continuous wave and
time resolved
photoluminescence under low excitation density conditions. We have paid
special attention to the effect of the carrier coupling on the exciton
radiative lifetime: weak (14 nm spacer sample), intermediate (4.5 nm spacer
sample), where the size filtering effects (towards small rings) compensate
partially that arising from carrier coupling (towards lower energies), and
strong electron and hole coupling (1.5 nm spacer sample) between layers.
Experimental decay times in the latter two cases have been compared to the
times simulated with a multi-quantum well based model, which accounts for
the observed change of carrier coupling regime. The most important effect is
observed when the hole wave function overlap along the growth direction
becomes important (1.5 nm spacer sample). This situation makes important the
lateral tunneling of excitons between rings, given their large lateral size,
which is characterized by times around 5 ns at the emission peak energy
(rings with the most probable size of the distribution). 相似文献
45.
The properties of the negative parity states of55Fe and57Fe are investigated in the framework of the intermediate coupling model. In the model, a neutron or a quasineutron is coupled to anharmonic vibrations of the core. Anharmonicities of the vibrations are estimated through the observed properties of the core. Energy levels, spectroscopic factors and electromagnetic properties have been calculated. The results of the present calculations are also compared with available experimental results and other theoretical results. The model reasonably accounts for many of the properties of the low-lying states. 相似文献
46.
Arvela RK Leadbeater NE Sangi MS Williams VA Granados P Singer RD 《The Journal of organic chemistry》2005,70(1):161-168
We present here a reassessment of our transition-metal free Suzuki-type coupling protocol. We believe that, although the reaction can be run without the need for addition of a metal catalyst, palladium contaminants down to a level of 50 ppb found in commercially available sodium carbonate are responsible for the generation of the biaryl rather than, as previously suggested, an alternative non-palladium-mediated pathway. We present a revised methodology for Suzuki couplings using ultralow palladium concentrations for use with aryl and vinyl boronic acids and discuss the effects of the purity of the boronic acid on the reaction. 相似文献
47.
A pyrrolylamidothiourea deprotonates in the presence of one equivalent of not only fluoride, but also acetate, benzoate or dihydrogen phosphate in DMSO solution with structural studies using synchrotron radiation confirming thiourea deprotonation in the solid state. 相似文献
48.
M. Salazar-Ramírez D. Martínez V. D. Granados R. D. Mota 《International Journal of Theoretical Physics》2010,49(5):967-973
We apply the Schrödinger factorization to construct the generators of the dynamical algebra su(1,1) for the radial equation of the generalized MICZ-Kepler problem. 相似文献
49.
50.
Alicia Cantón Ana Granados Domingo Pestana José M. Rodríguez 《Central European Journal of Mathematics》2013,11(10):1817-1830
We prove that under appropriate assumptions adding or removing an infinite amount of edges to a given planar graph preserves its non-hyperbolicity, a result which is shown to be false in general. In particular, we make a conjecture that every tessellation graph of ?2 with convex tiles is non-hyperbolic; it is shown that in order to prove this conjecture it suffices to consider tessellation graphs of ?2 such that every tile is a triangle and a partial answer to this question is given. A weaker version of this conjecture stating that every tessellation graph of ?2 with rectangular tiles is non-hyperbolic is given and partially answered. If this conjecture were true, many tessellation graphs of ?2 with tiles which are parallelograms would be non-hyperbolic. 相似文献