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991.
Balbeur D Widart J Leyh B Cravello L De Pauw E 《Journal of the American Society for Mass Spectrometry》2008,19(7):938-946
Gas-phase hydrogen/deuterium exchange of small oligonucleotides (dTG, dC(6) and C(6)) with CD(3)OD was performed in the second hexapole of a Fourier transform ion-cyclotron resonance (FTICR) mass spectrometer. Ion activation experiments were conducted by accelerating the ions at the entrance of the H/D exchange cell under conditions promoting exclusively collisional isomerization. These experiments allowed us to assess the presence of several conformers, and to probe the height of the isomerization barrier separating these conformers. Ion mobility experiments were also performed. Their results were consistent with the H/D exchange data. A model accounting for the competing isomerization and H/D exchange reactions is proposed. Comparing the ion acceleration experiments for H/D exchange and for ion mobility reveals that the most compact conformer displays the fastest H/D exchange. This observation shows that H/D exchange and ion mobility provide us with complementary information because hydrogen accessibility and macromolecule compactness are not univocally associated. 相似文献
992.
The low-lying XSigma+, a3Delta, A1Delta, b3Sigma+, B1Pi, c3Pi, C1Phi, D1Sigma+, E1Pi, d3Phi, and e3Pi electronic states of RhB have been investigated at the ab initio level, using the multistate multiconfigurational second-order perturbation (MS-CASPT2) theory, with extended atomic basis sets and inclusion of scalar relativistic effects. Among the eleven electronic states included in this work, only three (the X1Sigma+, D1Sigma+, and E1Pi states) have been investigated experimentally. Potential energy curves, spectroscopic constants, dipole moments, binding energies, and chemical bonding aspects are presented for all electronic states. 相似文献
993.
We developed an analytical solution to describe how the chain length distribution (CLD) of polymers made with coordination polymerization catalysts vary as a function of time for very short polymerizations considering non‐instantaneous site activation. This solution is an extension of our previous analytical expression for instantaneous site activation. We validated the analytical solution with dynamic Monte Carlo simulation and obtained excellent agreement. Simulation results indicate that, unless the catalyst activation rate is much lower than the propagation rate, it will have only a minor effect on the initial shape of the CLD of polymers made in stopped‐flow reactors (SFR). We also show how incorrect polymerization kinetic parameters may be estimated when assuming instantaneous site activation when this hypothesis is not applicable to the polymerization data under investigation.
994.
Joana Dias M. Eugénia Captivo João Clímaco 《Central European Journal of Operations Research》2008,16(3):251-280
In this paper a capacitated dynamic location problem with opening, closure and reopening of facilities is formulated and a
primal-dual heuristic that can solve this problem is described. The problem formulated considers the situation where a facility
is open (or reopens) with a certain maximum capacity that decreases as clients are assigned to that facility during its operating
periods. This problem is NP-hard. Computational results are presented and discussed.
This research was partially supported by research project POCTI/ISFL-1/152 and POCTI/MAT/139/2001. 相似文献
995.
Djairo G. de Figueiredo João Marcos do Ó Bernhard Ruf 《Journal of Fixed Point Theory and Applications》2008,4(1):77-96
We establish a priori bounds for positive solutions of semilinear elliptic systems of the form
where Ω is a bounded and smooth domain in . We obtain results concerning such bounds when f and g depend exponentially on u and v. Based on these bounds, existence of positive solutions is proved.
Dedicated to Felix Browder on the occasion of his 80th birthday 相似文献
996.
997.
Silva EM Domingues P Tomé JP Faustino MA Neves MG Tomé AC Dauzonne D Silva AM Cavaleiro JA Ferrer-Correia AJ Domingues MR 《European journal of mass spectrometry (Chichester, England)》2008,14(1):49-59
Beta-nitroalkenyl meso-tetraphenylporphyrins [beta-TPPCHC(NO(2))R)], as free-bases and Zn(II) complexes, were studied by electrospray mass spectrometry (ESI-MS). Under this ionisation condition the [M + H](+) ions are formed. The fragmentation pattern of the resulting [M + H](+) ions were studied by electrospray tandem mass spectrometry (ESI-MS/MS). The ESI-MS/MS of beta- nitroalkenylporphyrins, either as free-bases or as Zn(II) complexes, show several interesting features, distinct from the typical behaviour of nitro compounds. For the studied compounds, common main fragmentation patterns are observed, namely characteristic losses of NO(2), HNO(2), 2OH, RNO(2), RCNO, RCNO(2), RCH(2)NO(2), C(6)H(5) plus NO(2) and the formation of the protonated macrocycle, [TPP + H](+) or [ZnTPP + H](+). However, depending on the presence or absence of the metal and the nature of the R substituent, important differences are observed on the relative abundances of the ions formed by the same fragmentation pathway. The presence of bromine in the alkenyl group leads to a peculiar behaviour, since the main fragmentation pattern corresponds to the combined elimination of the bromine atom with the typical nitro group fragments. When R = Br, the loss of the nitro group occurs in low relative abundance (11-16%). However, when R = CH(3), the relative abundance of the ion due to the loss of HNO(2) changes drastically from 100%, observed for the free-base porphyrin, to 29% in the case of the Zn(II) complex. These variations of the relative abundance of the fragment corresponding to the loss of the nitro moiety (typically considered as a diagnostic fragment) can induce to an erroneous interpretation of their MS/MS spectra. Some fragmentations are observed only for the free-base porphyrins, namely the loss of CH(NO(2)R and HNO(2) plus C(2)H(2), while the loss of OH, H(2)O, OH plus H(2)O and RCCH plus H(2)O is observed only for the complexes. Unusual and unexpected fragmentations are also observed, namely the losses of RCNO, RCNO(2) and HNO(2) plus C(2)H(2). This work demonstrates that valuable structural information about the beta-nitroalkenyl substituents linked to meso- tetraarylporphyrins can be achieved using MS/MS. These results can also be useful for the interpretation of the mass spectra of other nitroalkenyl substituted compounds. 相似文献
998.
Cailliez F Trzpit M Soulard M Demachy I Boutin A Patarin J Fuchs AH 《Physical chemistry chemical physics : PCCP》2008,10(32):4817-4826
We report a joint experimental and molecular simulation study of water intrusion in silicalite-1 and ferrerite zeolites. The main conclusion of this study is that water condensation takes place through a genuine first-order phase transition, provided that the interconnected pores structure is 3-dimensional. In the extreme confinement situation (ferrierite zeolite), condensation takes place through a continuous transition, which is explained by a shift of both the first-order transition line and the critical point with increasing confinement. The present findings are at odds with the common belief that conventional phase transitions cannot take place in microporous solids such as zeolites. The most important features of the intrusion/extrusion process can be understood in terms of equilibrium thermodynamics considerations. We believe that these findings are very general for hydrophobic solids, i.e. for both nonwetting as well as wetting water-solid interface systems. 相似文献
999.
Fenstad J 《Physical chemistry chemical physics : PCCP》2008,10(2):311-319
A new concept is presented for analysing the excess properties of mixing for asymmetric homogeneous mixtures. In its current form the concept is limited to binary mixtures, but applies to numerous classes of materials, and a wide selection of mixing properties. This paper demonstrates that this Log-symmetry concept is general enough to include (as special cases) several existing mixture models; specifically the Regular Solution Theory, van Laar equation, and the Rogalski-Malanowski expression. The above finding suggests log-symmetry is inherently fundamental, in a way that is (yet) not fully explored. In its most basic implementation (the Mirror Data Method) log-symmetric modelling requires merely one independent parameter. This paper employs high-precision experimental data to validate the concept. 相似文献
1000.