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141.
Villar-Rodil S. Paredes J. I. Martínez-Alonso A. Tascón J.M.D. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):37-43
The pyrolysis behaviour of Nomex, poly(m-phenylene isophthalamide) fibres under argon has been investigated up to a temperature of 1173 K with different methods to
get direct information on the progressive changes taking place in the solid material and its carbon fibre residues. The main
stages of the pyrolytic degradation of the fibres were determined by thermal analysis (TG and DTA) and their chemical and
morphological evolution through the different steps was subsequently followed by Fourier transform infrared spectroscopy (FTIR)
and atomic force microscopy (AFM) measurements, respectively, on samples treated to various temperatures.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
142.
An analytical potential energy surface (PES) representation of the O(+)((4)S)+H(2)(X (1)Sigma(g) (+)) system was developed by fitting around 600 CCSD(T)/cc-pVQZ ab initio points. Rate constant calculations for this reaction and its isotopic variants (D(2) and HD) were performed using the quasiclassical trajectory (QCT) method, obtaining a good agreement with experimental data. Calculations conducted to determine the cross section of the title reaction, considering collision energies (E(T)) below 0.3 eV, also led to good accord with experiments. This PES appears to be suitable for kinetics and dynamics studies. Moreover, the QCT results show that, although the hypotheses of a widely used capture model are not satisfied, the resulting expression for the cross section can be applied within a suitable E(T) interval, due to errors cancellation. This could be a general situation regarding the application of this simple model to ion-molecule processes. 相似文献
143.
A dynamics study [cross section and microscopic mechanism versus collision energy (E(T))] of the reaction O+ + H2 --> OH+ + H, which plays an important role in Earth's ionosphere and interstellar chemistry, was conducted using the quasiclassical trajectory method, employing an analytical potential energy surface (PES) recently derived by our group [R. Martinez et al., J. Chem. Phys. 120, 4705 (2004)]. Experimental excitation functions for the title reaction, as well as its isotopic variants with D2 and HD, were near-quantitatively reproduced in the calculations in the very broad collision energy range explored (E(T) = 0.01-6.0 eV). Intramolecular and intermolecular isotopic effects were also examined, yielding data in good agreement with experimental results. The reaction occurs via two microscopic mechanisms (direct and nondirect abstraction). The results were satisfactorily interpreted based on the reaction probability and the maximum impact parameter dependences with E(T), and considering the influence of the collinear [OHH]+ absolute minimum of the PES on the evolution from reactants to products. The agreement between theory and experiment suggests that the reaction mainly occurs through the lowest energy PES and nonadiabatic processes are not very important in the wide collision energy range analyzed. Hence, the PES used to describe this reaction is suitable for both kinetics and dynamics studies. 相似文献
144.
Earlier work of potentiometric Ion-selective electrodes (ISEs) sensitive to nonionic surfactants of the polyethoxylate type is further extended. The ISEs constructed were all-solid-state sensors with plasticized PVC membranes. The sensing material was a tetraphenylborate salt of the barium complex with a polyethoxylate nonionic surfactant. As membrane component, the combinations of two polyethoxylates of the nonylphenoxy type, which differed in the number of oxyethylene units (5 or 12), and two different plasticizers, (o-nitrophenyloctyl ether and o-nitrophenylphenyl ether), were tested. The response of these electrodes to different nonionic surfactants and the interference effect of several species has been evaluated. For all the types of tested electrodes, the sensitivities shown were ca. 30.0 mV dec(-1) and the limit of detection, ca. 10(-5) M, when a nonylphenoxyde with 12 oxyethylene units was used as standard. The membrane with the best response characteristics was then applied in potentiometric titrations of this kind of surfactants in the presence of Ba(2+) ion and using tetraphenylborate as the titrant. 相似文献
145.
Jos Ruiz M. Teresa Martínez Consuelo Vicente Venancio Rodríguez Gregorio Lpez Jos Prez Penny A. Chaloner Peter B. Hitchcock 《无机化学与普通化学杂志》2005,631(11):2227-2231
Mononuclear palladium‐hydroxo complexes of the type [Pd(N–N)(C6F5)(OH)][(N–N) = 2,2′‐bipyridine (bipy), 4,4′‐dimethyl‐2,2′‐bipyridine (Me2bipy), 1,10‐phenantroline (phen) or N,N,N′,N′‐tetramethylethylenediamine (tmeda) react with phenols ArOH in tetrahydrofuran giving the corresponding aryloxo complexes [Pd(N–N)(C6F5)(OAr)]. Elemental analyses and spectroscopic (IR, 1H and 19F) methods have been used to characterize the new complexes. The X‐ray crystal structure of [Pd(tmeda)(C6F5)(OC6H4NO2‐p)] has been determined. In the crystal packing the planes defined by two C6H4 rings show a parallel orientation. There are also intermolecular C–H···F and C‐H···O hydrogen bonds. 相似文献
146.
R. Alan Jones Pilar Martinez Fresneda Teresa Aznar Saliente José Sepúlveda Arques 《Tetrahedron》1984,40(23):4837-4842
The overall rates of reaction of 1-substltuted-1- (1-methyl-2-indolyl)ethenes with dimethyl acetylenedicarboxylate are considerably lower than those of the corresponding 2-vinyl- pyrroles. Steric interaction between the N-methyl group on the indole ring and the 1-substituent on the ethenyl group prevents the diene system adopting a coplanar configuration and, thereby, inhibits the π4 + π2 cycloaddition reaction of the system with dimethyl acetylenedicarboxylate. Under such conditions, the indolylethene preferentially undergoes a Michael addition reaction at the 3-position. The π4 + π2 cycloaddition reaction is promoted at elevated temperatures. No evidence was found for a Cope rearrangement of the Michael adducts to give the dihydrocarbazole. 相似文献
147.
Summary The influence of Cr2O7
2–, MnO4
–, Ce4+, H2O2 and S2O8
2– as oxidising agents in lead determination as volatile covalent hydride using NaBH4 is reported in this paper.The reaction conditions for every oxidising agents (pH, quantity and concentration of the oxidising agent, quantity and concentration of the NaBH4 and reaction time) are optimized, determining sensitivity and detection limit by measuring the peak height.The recovery of lead from solution has been measured by flameless atomic absorption spectroscopy.A linear relationship the logarithm of absorbance values and the redox potential of the system is obtained with a correlation coefficient of 0.999. The results and their interpretation are given in this paper.
Paper presented to Euroanalysis V. Cracow, August 1984. 相似文献
Der Einflu oxidierender Reagentien auf die Bleibestimmung mittels Flammenatomabsorptionsspektrometrie nach Hydridbildung
Zusammenfassung Es wird über den Einfluß der Oxidantien Cr2O7, MnO4 –, Ce4+, H2O2 und S2O8 2 – auf die Bleibestimmung als kovalentes Hydrid berichtet. Für jede oxidierende Substanz werden die Reaktionsbedingungen optimiert (pH, Menge und Konzentration des Oxidans, Menge und Konzentration von NaBH4 und Reaktionszeit), um Empfindlichkeit und Nachweisgrenze durch Peakhöhenauswertung zu bestimmen.Die Wiederfindungsrate wurde durch elektrothermale Atomabsorptionsspektrometrie von Blei in der Lösung bestimmt.Der Zusammenhang zwischen dem Logarithmus der Extinktion und dem Redoxpotential des Oxidans ergibt eine lineare Beziehung mit einem Korrelationskoeffizienten von 0.999. Die Ergebnisse und deren Interpretation werden in dieser Arbeit beschrieben.
Paper presented to Euroanalysis V. Cracow, August 1984. 相似文献
148.
Martínez-Galera M López-López T Gil-García MD Martínez-Vidal JL Picón-Zamora D Cuadros-Rodríguez L 《Analytical and bioanalytical chemistry》2003,375(5):653-660
A comparative study of two mathematical approaches was performed in order to correct systematic errors due to the presence of the unexpected interferences which appear when the quantitation of the analyte in real samples is carried out with calibration curves built using standards in pure solvent. These methods consisted in the establishment of different mathematical expressions which transform the concentration (Cs) obtained using calibration graphs built using pure solvent into the corrected concentration (C(M)) that should be obtained if the quantitation is carried out with calibration curves built using standards dissolved in blank matrix extracts. In the two approaches the correction is performed from the results of an intermediate precision study which was carried out using both calibration graphs (prepared using pure solvent and blank matrix extract). By using ANCOVA to compare the slope of both solvent-based and matrix-matched calibration graphs, matrix effect was found in the determination of deltamethrin in tomato and acrinathrin in tomato and pepper. In these cases, both approaches led to good results. 相似文献
149.
Vidal JL Vega AB Arrebola FJ González-Rodríguez MJ Sánchez MC Frenich AG 《Rapid communications in mass spectrometry : RCM》2003,17(18):2099-2106
A fast method for the determination of eight organotin compounds (OTs), monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), tetrabutyltin (TeBT), monophenyltin (MPhT), diphenyltin (DPhT), triphenyltin (TPhT) and tetraphenyltin (TePhT), in water, sediments and mussels, was developed using low-pressure gas chromatography/tandem mass spectrometry (LPGC/MS/MS). The method is based on sodium diethyldithiocarbamate (DDTC) complexation of the ionic organotins, followed by extraction of the target matrices and derivatization by a Grignard reagent, as described in a previously published method for water samples. Solid-phase extraction was selected as extraction method from water samples after comparison with liquid-liquid extraction, but extraction of the OTs from sediment and mussel samples was performed using toluene. Matrix-matched calibration standards were used to minimize matrix effects. The analytical process was validated by the analysis of spiked blank samples. Performance characteristics such as linearity, detection limit (LOD), quantitation limit (LOQ), precision, and recovery were determined. Recoveries of OTs in spiked matrices ranged from 86-108% in water and from 78-110% in sediments and mussels, with precision values lower than 18%. Detection limits ranged from 0.1-9.6 ng L(-1) in water, and 0.03-6.10 microg kg(-1) in the other matrices. The present implementation of LPGC rather than conventional capillary GC permitted use of large-volume injection and reduced analysis time by a factor of two. The proposed methodology was applied to the determination of OTs in real samples of water, marine sediments and mussels from the west coast of the Mediterranean Sea (Spain). 相似文献
150.
Abarca A Galakhov MV Gracia J Martín A Mena M Poblet JM Sarasa JP Yélamos C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(10):2337-2346
Treatment of [[Ti(eta(5)-C(5)Me(5))(micro-NH)](3)(micro(3)-N)] (1) with the imido complexes [Ti(NAr)Cl(2)(py)(3)] (Ar=2,4,6-C(6)H(2)Me(3)) and [Ti(NtBu)Cl(2)(py)(3)] in toluene affords the single azatitanocubanes [[Cl(2)(ArN)Ti]( micro(3)-NH)(3)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]].(C(7)H(8)) (2.C(7)H(8)) and [[Cl(2)Ti](micro(3)-N)(2)(micro(3)-NH)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]] (3), respectively. Similar reactions of complex 1 with the niobium and tantalum imido derivatives [[M(NtBu)(NHtBu)Cl(2)(NH(2)tBu)](2)] (M=Nb, Ta) in toluene give the single azaheterometallocubanes [[Cl(2)(tBuN)M](micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]] (M=Nb (4), Ta (5)), both complexes react with 2,4,6-trimethylaniline to yield the analogous species [[Cl(2)(ArN)M](micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]].(C(7)H(8)) (Ar=2,4,6-C(6)H(2)Me(3), M=Nb (6.C(7)H(8)), Ta (7.C(7)H(8))). Also the azaheterodicubanes [M[micro(3)-N)(2)(micro(3)-NH)](2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)](2)].2C(7)H(8) [M=Ti (8.2C(7)H(8)), Zr (9.2C(7)H(8))], and [M[(micro(3)-N)(5)(micro(3)-NH)][Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)](2)].2 C(7)H(8) (Nb (10.2C(7)H(8)), Ta (11.2C(7)H(8))) were prepared from 1 and the homoleptic dimethylamido complex [M(NMe(2))(x)] (x=4, M=Ti, Zr; x=5, M=Nb, Ta) in toluene at 150 degrees C. X-ray crystal structure determinations were performed for 6 and 10, which revealed a cube- and double-cube-type core, respectively. For complexes 2 and 4-7 we observed and studied by DNMR a rotation or trigonal-twist of the organometallic ligands [[Ti(eta(5)-C(5)Me(5))(micro-NH)](3)(micro(3)-N)] (1) and [(micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]](1-). Density functional theory calculations were carried out on model complexes of 2, 3, and 8 to establish and understand their structures. 相似文献