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961.
Barluenga J Diéguez A Rodríguez F Flórez J Fañanás FJ 《Journal of the American Chemical Society》2002,124(31):9056-9057
Eight-membered carbocycles with up to five new stereogenic centers are enantioselectively obtained following a one-pot procedure that involves the coupling of three components: an alkenyl Fischer carbene complex, a ketone enolate, and allyl lithium. 相似文献
962.
I. Labádi E. Pál R. Tudose O. Costisor 《Journal of Thermal Analysis and Calorimetry》2006,83(3):681-686
The
thermal behaviour of the mixed-ligand complexes of cobalt(II) and copper(I)
ions with antipyrine derivatives of 1,2-ethanediamine or piperazine (BAMP
and TAMEN), with water and with 2-mercapto-benzothiazole (Hmbt) was investigated.
The complexes contain 2-mercaptobenzothiazole (Hmbt, in the case of cobalt(II)
ion) or dimercaptobenzothiazine (mbt–mbt, in the case of copper(I) ion)
molecules as ligands and perchlorate (ClO4–) or
thiocyanate (SCN – ) ion as counterion. By heating, water and ligands
release the solid phase at lower temperature. At higher temperatures process
of different organic reactions of ligands (e.g. polymerization, polycondensation)
could be suggested to interpret the relative high final mass values. 相似文献
963.
Jaime González Velasco 《Central European Journal of Chemistry》2005,3(3):470-481
The analytical treatment of a model considering the electrooxidation of p-porous silicon layers under galvanostatic conditions
is able to give account of experimental facts such as the shape and location of the electroluminescence peak as well as of
the spectral shift of the electroluminescence peak produced by oxidation. The proposed model considers electroluminescence
to be the result of electron injection into the conduction band by an adsorbed intermediate produced by electrooxidation of
the surface coverage with hydrogen or siloxene of the silicon nanocrystallites. The access of holes to the surface is made
possible by low accumulation layer conditions and is the rate determining step in the electroluminescence mechanism. In this
way it is possible to give a satisfactory explanation to the shift towards the blue experimented by the electroluminiscence
emission maximum as a consequence of electrooxidation. 相似文献
964.
Based on the method of SAMSAHL a programmed, semi-automated processing system has been developed and tested for the neutron
activation analysis of the following elements: As, Se, Sb, Br, Sn and Te. The main characteristics of the procedure are the
following: wet ashing of the sample (by means of digestion in a mixture of concentrated sulphuric acid and hydrogen peroxide),
bromination, and chlorination. The procedure is controlled via the appropriate dosage of the reagents and a carefully managed
thermal balance. The chemical yield and its reproducibility were determined by tracer techniques using exactly the same parameters
as for the active runs. According to the results the method can be used for the routine determination of the given elements
except antimony.
Presented at the 4th Symposium on the Recent Developments in Neutron Activation Analysis, 1975, Cambridge. 相似文献
965.
Katarína Györyová Ján Skoršepa Jozef Chomič 《Monatshefte für Chemie / Chemical Monthly》1983,114(10):1137-1139
Two cyano complexes of the type [R 3S]2 [Pd(CN)4] (R 3S+=Me 3S+,Ph 3S+ cations) were prepared. The identity of the obtained samples was verified by chemical analysis and investigated by IR-spectroscopy. Thev CN stretching frequencies of the complexes were compared with similar frequencies of the corresponding alkaline cyano complex. The thermal decomposition of the compounds was examined. 相似文献
966.
The model of two interacting ethylene molecules having D
2h symmetry was studied using generalized Hückel method. The validity of - separation was tested on this model. The general character of the ground state and lower lying excited states of the model was discussed and the implications drawn concerning transannular interaction and excimer formation. The values obtained for the dissociation energy of the first excited state of our model and corresponding equilibrium intermolecular distance are of right order of magnitude.
Zusammenfassung Mittels der verallgemeinerten Hückel-Methode wurde das Modell von zwei Äthylenmolekülen mit der Symmetrie D 2h studiert. An diesem Modell wurde die Gültigkeit der - -Separation geprüft. Der allgemeine Charakter des Grundzustandes und der niedriger liegenden angeregten Zustände des Modells wird erörtert und die Folgerungen in Bezug auf transannulare Wechselwirkung und Excimer-Entstehung diskutiert. Die erhaltenen Werte für die Dissoziationsenergie des ersten angeregten Zustandes von unserem Modell und den entsprechenden intermolekularen Gleichgewichtsabstand haben die richtige Größenordnung.
Résumé Le modèle à symétrie D 2h de deux molécules d'éthylène en interaction a été étudié en utilisant la méthode généralisée de Hückel. On a examiné la validité de la séparation - sur ce modèle. Le caractère général de l'état fondamental et celui des états excités inférieurs du modèle furent discutés et on a fait des déductions sur l'interaction transannulaire et sur la formation d'«excimères». Les valeurs obtenues pour l'énergie de dissociation du premier état excité de notre modèle et la distance intermoléculaire d'équilibre corréspondante ont l'ordre de magnitude correct.相似文献
967.
The degradation behaviour of methylmercury (MeHg) under microwave irradiation is investigated, as is the (different) degradation
behaviour of ethylmercury (EtHg) under similar irradiation. A simple and highly sensitive SPME-GC-pyrolysis-AFS system was
used to analyse the aqueous MeHg and EtHg standard solutions after derivatization with sodium tetraphenylborate (NaBPh4). Samples were irradiated in a microwave digester at microwave powers ranging from 20 to 160 W for durations of 2 to 10 min.
The different tolerances towards microwave treatment of the two organomercury species were evident. Practically no degradation
was experienced for MeHg for up to 8 minutes of irradiation at 120 W or for up to 4 minutes at 160 W. Significant analyte
loss was observed for EtHg after 2 minutes at 40 W of microwave power.
Awarded a Poster Prize on the occasion of the European Winter Conference on Plasma Spectrochemistry, February 2005, Budapest,
Hungary 相似文献
968.
The stability and characteristics of the ornithine (Orn), lysine (Lys), putrescine (Put), cadaverine (Cad), 1,7-diaminoheptane (Diah), spermidine (Spd) and spermine (Spm) derivatives obtained with the o-phthalaldehyde (OPA)-ethanethiol (ET)-fluorenylmethyl chloroformate (FMOC) reagent has been investigated. The stoichiometry of the introduced, two-step derivatization process has been followed by photodiode array (DAD) and fluorescence (FL) detections, simultaneously, while the composition of derivatives was confirmed by on-line HPLC-electrospray ionization (ESI) MS measurements. Depending on the composition of the OPA reagents, in addition to the secondary amino group-containing Spd and Spm, under common aqueous conditions also Orn and Lys do react with FMOC resulting in derivatives of various compositions. Applying the OPA-ET reagent of increasing methanol (Met) content (38-80%, v/v) the formation of the FMOC group containing Orn and Lys derivatives could be considerably decreased. Optimum elution condition (18 min, including equilibration) was developed for the simultaneous quantitation of Orn, Lys, Put, Cad, Diah, Spd and Spm, in the presence of the rest of protein amino acids. The practical utility of the method was demonstrated by the analysis of mouse tissues. Average reproducibility of quantitations, characterized with the relative standard deviation percentages of fluorescence intensities and UV responses, in order of listing, proved to be 2.1% and 2.1%, respectively. 相似文献
969.
Close DM Crespo-Hernández CE Gorb L Leszczynski J 《The journal of physical chemistry. A》2005,109(41):9279-9283
In the present study the ionization energy thresholds (IET's) of uracil and thymine have been calculated (with the B3LYP, PMP2, and P3 levels of theory using the standard 6-31++G(d,p) basis set) with one to three water molecules placed in the first hydration shell. Then (B3LYP) polarizable continuum model (PCM) calculations were performed with one to three waters of the hydration shell included. Calculations show there is a distinct effect of microhydration on uracil and thymine. For uracil, one added water results in a decrease in the IET of about 0.15 eV. The second and third water molecules cause a further decrease by about 0.07 eV each. For thymine, the first water molecule is seen to decrease the IET by about 0.1 eV, while the second and third water molecules cause a further decrease of less than 0.1 eV each. The changes in IET calculated here for thymine with one to three waters of hydration are smaller than the experimental values determined by Kim et al. (Kim, S. K.; Lee, W.; Herschbach, D. R. J. Phys. Chem. 1996, 100, 7933). Preliminary results presented here indicate that the experimental results may involve keto-enol tautomers of thymine. The results of placing the microhydrated structures of uracil and thymine in a PCM cavity was seen to make very little difference in the IET when compared to the IET of ordinary uracil or thymine in a PCM cavity. The implications are that accurate calculations of the IET's of uracil and thymine can be obtained by simply considering long-range solvation effects. 相似文献
970.
Bajor G Veszprémi T Riague el H Guillemin JC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(15):3649-3656
Vinyl, allyl, and homoallyl selenols were easily prepared by a chemoselective reduction of the corresponding selenocyanates with aluminum hydrides. Two stable vinyl and five stable allyl conformers of both series were predicted on the potential-energy surface. The interaction of SeH or SeCN groups with the vinyl group has been investigated with UV photoelectron spectroscopy and quantum chemical calculations, using the MP2/cc-pVTZ and B3LYP/cc-pVTZ levels. In the vinyl derivatives, a surprisingly strong direct conjugation of the selenium lone electron pair and the C=C double bond was observed. On the other hand, in allyl position the selenium lone pair is independent on the C=C double bond, and the hyperconjugation between the Se-C bond and the double bond is the ruling effect. Thus is clarified the type and extent of the interaction between the SeH or SeCN group and the unsaturated moiety. 相似文献