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951.
Poterya V Fedor J Pysanenko A Tkáč O Lengyel J Ončák M Slavíček P Fárník M 《Physical chemistry chemical physics : PCCP》2011,13(6):2250-2258
Photochemistry of HI molecules on large Ar(n) and (H(2)O)(n), n ~ 100-500, clusters was investigated after excitation with 243 nm and 193 nm laser radiation. The measured H-fragment kinetic energy distributions pointed to a completely different photodissociation mechanism of HI on water than on argon clusters. Distinct features corresponding to the fragment caging (slow fragments) and direct exit (fast fragments) were observed in the spectra from HI photodissociation on Ar(n) clusters. On the other hand, the fast fragments were entirely missing in the spectrum from HI·(H(2)O)(n) and the slow-fragment part of the spectrum had a different shape from HI·Ar(n). The HI·(H(2)O)(n) spectrum was interpreted in terms of the acidic dissociation of HI on (H(2)O)(n) in the ground state, and hydronium radical H(3)O formation following the UV excitation of the ionically dissociated species into states of a charge-transfer-to-solvent character. The H(3)O generation was proved by experiments with deuterated species DI and D(2)O. The experiment was complemented by ab initio calculations of structures and absorption spectra for small HI·(H(2)O)(n) clusters, n = 0-5, supporting the proposed model. 相似文献
952.
Ferus M Kubelík P Kawaguchi K Dryahina K Španěl P Civiš S 《The journal of physical chemistry. A》2011,115(10):1885-1899
Time-resolved Fourier transform (FT) spectrometry was used to study the dynamics of radical reactions forming the HCN and HNC isomers in pulsed glow discharges through vapors of BrCN, acetonitrile (CH(3)CN), and formamide (HCONH(2)). Stable gaseous products of discharge chemistry were analyzed by selected ion flow tube mass spectrometry (SIFT-MS). Ratios of concentrations of the HNC/HCN isomers obtained using known transition dipole moments of rovibrational cold bands v(1) were found to be in the range 2.2-3%. A kinetic model was used to assess the roles the radical chemistry and ion chemistry play in the formation of these two isomers. Exclusion of the radical reactions from the model resulted in a value of the HNC/HCN ratio 2 orders of magnitude lower than the experimental results, thus confirming their dominant role. The major process responsible for the formation of the HNC isomer is the reaction of the HCN isomer with the H atoms. The rate constant determined using the kinetic model from the present data for this reaction is 1.13 (±0.2) × 10(-13) cm(3) s(-1). 相似文献
953.
954.
Filip J Yngard RA Siskova K Marusak Z Ettler V Sajdl P Sharma VK Zboril R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(36):10097-10105
The reaction of potassium ferrate(VI), K2FeO4, with weak‐acid dissociable cyanides—namely, K2[Zn(CN)4], K2[Cd(CN)4], K2[Ni(CN)4], and K3[Cu(CN)4]—results in the formation of iron(III) oxyhydroxide nanoparticles that differ in size, crystal structure, and surface area. During cyanide oxidation and the simultaneous reduction of iron(VI), zinc(II), copper(II), and cadmium(II), metallic ions are almost completely removed from solution due to their coprecipitation with the iron(III) oxyhydroxides including 2‐line ferrihydrite, 7‐line ferrihydrite, and/or goethite. Based on the results of XRD, Mössbauer and IR spectroscopies, as well as TEM, X‐ray photoelectron emission spectroscopy, and Brunauer–Emmett–Teller measurements, we suggest three scavenging mechanisms for the removal of metals including their incorporation into the ferrihydrite crystal structure, the formation of a separate phase, and their adsorption onto the precipitate surface. Zn and Cu are preferentially and almost completely incorporated into the crystal structure of the iron(III) oxyhydroxides; the formation of the Cd‐bearing, X‐ray amorphous phase, together with Cd carbonate is the principal mechanism of Cd removal. Interestingly, Ni remains predominantly in solution due to the key role of nickel(II) carbonate, which exhibits a solubility product constant several orders of magnitude higher than the carbonates of the other metals. Traces of Ni, identified in the iron(III) precipitate, are exclusively adsorbed onto the large surface area of nanoparticles. We discuss the relationship between the crystal structure of iron(III) oxyhydroxides and the mechanism of metal removal, as well as the linear relationship observed between the rate constant and the surface area of precipitates. 相似文献
955.
956.
Zins EL Milko P Schröder D Aysina J Ascenzi D Zabka J Alcaraz C Price SD Roithová J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(14):4012-4020
The bimolecular reactivity of xenon with C7Hn2+ dications (n=6–8), generated by double ionization of toluene using both electrons and synchrotron radiation, is studied by means of a triple‐quadrupole mass spectrometer. Under these experimental conditions, the formation of the organoxenon dications C7H6Xe2+ and C7H7Xe2+ is observed to occur by termolecular collisional stabilization. Detailed experimental and theoretical studies show that the formation of C7H6Xe2++H2 from doubly ionized toluene (C7H82+) and xenon occurs as a slightly endothermic, direct substitution of dihydrogen by the rare gas with an expansion to a seven‐membered ring structure as the crucial step. For the most stable isomer of C7H6Xe2+, an adduct between the cycloheptatrienyldiene dication and xenon, the computed binding energy of 1.36 eV reaches the strength of (weak) covalent bonds. Accordingly, electrophiles derived from carbenes might be particularly promising candidates in the search for new rare‐gas compounds. 相似文献
957.
Linda Zaoralkova Ales Hrdlicka Vitezslav Otruba Petr Sulovsky Nicole Gilon Detlef Günther Viktor Kanicky 《Chemical Papers》2011,65(6):769-781
The applicability of laser ablation (LA) inductively coupled plasma (ICP) spectrometry for assessing elemental distributions
in layered ceramics was investigated and compared with electron probe microanalysis (EPMA). Ordinary glazed wall tiles were
employed as model specimens due to their defined structure and composition. They were used for calibration in the analysis
of ancient pottery. A qualitative depth profile was acquired by single-spot laser drilling perpendicular to coatings with
a Nd:YAG (1064 nm) laser coupled with an ICP optical emission spectrometer (OES). The lower lateral resolution associated
with the laser spot diameter of 1.0 mm led to smoothing of the depth profile due to the averaging of local irregularities.
In addition, transverse line scans by ablation across the tile section using an ArF* (193 nm) laser coupled with an ICP mass
spectrometer (MS) were performed. LA-ICP-OES depth profiles and LA-ICP-MS transverse scans were validated by EPMA section
scans and 2D back-scattered electrons images. The LA-ICP-OES acquisition was less dependent on sample surface and layer irregularities,
whereas the transverse line scan over the tile section with the small-spot beam offered insight into the micromorphology of
the individual layer. The combined approach revealed the occurrence of individual mineral grains, micro-heterogeneities and
the character of interfaces between layers. 相似文献
958.
Interaction of octyl-phenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO, the 'classical' rare metal extraction agent) with fully ionized hydrated protons (HP) was studied in acetonitrile-d(3) using (1)H, (13)C, (31)P NMR, PFG NMR and magnetic relaxation. The experimental results were confronted with high-precision ab initio DFT calculations. Relative chemical shifts of NMR signals of CMPO (0.01 mol/L) under the presence of HP in the molar ratio β = 0-2.0 mol/mol show binding between CMPO and HP. Self-diffusion measurements using (1)H PFG NMR demonstrate that larger complexes with higher content of CMPO are generally formed at β < 0.75. Analyzing the collective dependence of (13)C and (31)P NMR chemical shifts on β by the use of program LETAGROP, we obtained very good fitting for the assumed coexistence of two complexes (CMPO)(2)·HP (C(2)) and CMPO.HP (C(1)). The logarithms of the respective stabilization constants log K(i) were found to be 7.518 (C(2)) and 4.581 (C(1)). The system dynamics was studied by measuring the transverse (1)H NMR relaxation using CPMG sequence with varying delays t(p) between the π pulses in the mixtures with β = 0.4-0.8. The following exchange correlation times were obtained: τ(10) = 2.35 × 10(-5), τ(20) = 0.82 × 10(-4), τ(21) = 0.45 × 10(-3) s. The DFT calculations support the conclusion that the complexes C(1) and C(2) are the main species in the mixtures of CMPO with HP. They also agree with the NMR and FTIR observation that the main site to which H(3) O(+) is bound is the P=O group, whereas the amide group does not form a strong bond with the ion when excess water molecules are present. 相似文献
959.
Dobeš P Fanfrlík J Rezáč J Otyepka M Hobza P 《Journal of computer-aided molecular design》2011,25(3):223-235
A semiempirical quantum mechanical PM6-DH2 method accurately covering the dispersion interaction and H-bonding was used to
score fifteen structurally diverse CDK2 inhibitors. The geometries of all the complexes were taken from the X-ray structures
and were reoptimised by the PM6-DH2 method in continuum water. The total scoring function was constructed as an estimate of
the binding free energy, i.e., as a sum of the interaction enthalpy, interaction entropy and the corrections for the inhibitor
desolvation and deformation energies. The applied scoring function contains a clear thermodynamical terms and does not involve
any adjustable empirical parameter. The best correlations with the experimental inhibition constants (ln K
i) were found for bare interaction enthalpy (r
2 = 0.87) and interaction enthalpy corrected for ligand desolvation and deformation energies (r
2 = 0.77); when the entropic term was considered, however, the correlation becomes worse but still acceptable (r
2 = 0.52). The resulting correlation based on the PM6-DH2 scoring function is better than previously published function based
on various docking/scoring, SAR studies or advanced QM/MM approach, however, the robustness is limited by number of available
experimental data used in the correlation. Since a very similar correlation between the experimental and theoretical results
was found also for a different system of the HIV-1 protease, the suggested scoring function based on the PM6-DH2 method seems
to be applicable in drug design, even if diverse protein–ligand complexes have to be ranked. 相似文献
960.
J coupling in NMR spectroscopy is conventionally associated with covalent bonds. A noncovalent contribution often called through-space coupling (TSC) has been observed for heavy atoms. In this study, the TSC was detected and analyzed for the more common (1)H-(1)H coupling as well. In synthesized model molecules the hydrogen positions could be well controlled. For several coupling constants the through-space mechanism was even found to be the predominant factor. The nature and magnitude of the phenomenon were also analyzed by density functional computations. Calculated carbon- and hydrogen-coupling maps and perturbed electronic densities suggest that the aromatic system strongly participates in the noncovalent contribution. Unlike covalent coupling, which is usually governed by the Fermi contact, TSC is dominated by the diamagnetic term comprising interactions of nuclei with the electron orbital angular momentum. The computations further revealed a strong distance and conformational dependence of TSC. This suggests that the through-space coupling can be explored in molecular structural studies in the same way as the covalent one. 相似文献