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31.
32.
The dissociation behaviour and valence-electronic structure of water adsorbed on clean and oxygen-covered Ru{0001}, Rh{111}, Pd{111}, Ir{111} and Pt{111} surfaces has been studied by high-resolution X-ray photoelectron spectroscopy with the aim of identifying similarities and trends within the Pt-group metals. On average, we find higher reactivity for the 4d metals (Ru, Rh, Pd) as compared to 5d (Ir, Pt), which is correlated with characteristic shifts in the 1b(1) and 3a(1) molecular orbitals of water. Small amounts of oxygen (< 0.2 ML) induce dissociation of water on all five surfaces, for higher coverages (> 0.25 ML) only intact water is observed. Under UHV conditions these higher coverages can only be reached on the 4d metals, the 5d metals are, therefore, not passivated. 相似文献
33.
Shlykov SA Giricheva NI Eyler GN Oberhammer H 《The journal of physical chemistry. A》2007,111(7):1368-1373
The geometric structure and conformational properties of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (diacetone diperoxide) have been studied by gas electron diffraction and quantum chemical calculations (MP2 and B3LYP methods with 6-31G(d,p) and 6-311+G(2df,p) basis sets). The molecule possesses a chair conformation with C2h symmetry and the following geometric parameters for the six-membered ring (rh1 values) have been determined: O-O = 1.463(5) A, C-O = 1.432 (4) A, O-C-O = 108.2(7) degrees, C-O-O = 107.7(4) degrees, phi(C-O-O-C) = 63.7(4) degrees, and phi(O-O-C-O) = -63.9(4) degrees. A small contribution of less than 3.5% of a twist conformer with C2 symmetry cannot be excluded. Quantum chemical calculations predict a contribution between 1 and 2%. Additional calculations for the parent compound 1,2,4,5-tetroxane (diformaldehyde diperoxide) demonstrate that methyl substitution at the carbon atoms has a minor effect on the ring geometry but a strong effect on the conformational properties. Methyl substitution reduces the energy difference between twist and chair conformers by more than 5 kcal/mol. 相似文献
34.
Leonie A. Menke Theo C.J. Sas Sophie H.L. van Koningsbrugge Maria A.J. de Ridder Gladys R.J. Zandwijken Bart Boersma Philippe H. Dejonckere Sabine M.P.F. de Muinck Keizer-Schrama Barto J. Otten Jan M. Wit 《Journal of voice》2011,25(5):602-610
Objectives/Hypothesis
Oxandrolone (Ox) increases height gain but may also cause voice deepening in growth hormone (GH)-treated girls with Turner syndrome (TS). We assessed the effect of Ox on objective and subjective speaking voice frequency in GH-treated girls with TS.Study Design
A multicenter, randomized, placebo (Pl)-controlled, double-blind study was conducted.Methods
One hundred thirty-three patients were included and treated with GH (1.33 mg/m2/d) from baseline, combined with Pl or Ox in a low (0.03 mg/kg/d) or conventional (0.06 mg/kg/d) dose from the age of 8 years and estrogens from the age of 12 years. Yearly from starting Ox/Pl until 6 months after discontinuing GH + Ox/Pl, voices were recorded and questionnaires were completed.Results
At start, mean (±standard deviation [SD]) voice frequency SD score (SDS) was high for age (1.0 ± 1.2, P < 0.001) but normal for height. Compared with GH + Pl, voices tended to lower on GH + Ox 0.03 (P = 0.09) and significantly lowered on GH + Ox 0.06 (P = 0.007). At the last measurement, voice frequency SDS was still relatively high in GH + Pl group (0.6 ± 0.7, P = 0.002) but similar to healthy girls in both GH + Ox groups. Voice frequency became lower than −2 SDS in one patient (3%) on GH + Ox 0.03 and three patients (11%) on GH + Ox 0.06. The percentage of patients reporting subjective voice deepening was similar between the dosage groups.Conclusions
Untreated girls with TS have relatively high-pitched voices. The addition of Ox to GH decreases voice frequency in a dose-dependent way. Although most voice frequencies remain within the normal range, they may occasionally become lower than −2 SDS, especially on GH + Ox 0.06 mg/kg/d. 相似文献35.
Ysa��as J. Alvarado Joanna Baricelli Jos�� Caldera-Luzardo N��stor Cubill��n Gladys Ferrer-Amado Yovani Marrero-Ponce Victoria Mancilla Miguel A. Rocafull Jos�� Ojeda-Andara Luz E. Thomas Joan Vera-Villalobos Miguel Morales-Toyo 《Journal of solution chemistry》2011,40(1):26-39
The solubilities in water (W) and in 3 mol?L?1 aqueous acetonitrile at 298.15 K of thiophene-2-, furan-2- and pyrrole-2-carboxaldehyde phenylhydrazone along with their nitro and 2,4-dinitro derivatives, referred to as PCT, PCF, PCP, NPCT, NPCF, NPCP, DPCT, DPCF and DPCP, respectively, are reported. The standard Gibbs energy of transfer from W to solvent mixtures ( $\Delta G^{\mathrm{transf}}_{\mathrm{W-mix}}$ ) was estimated for each solute. The results indicate that the transfer process for all systems is a spontaneous process. Calculations under the scaled-particle theory suggest that the work of cavity creation (????G c), which is associated with the transfer of the phenylhydrazone from W to mix, dominates the magnitude of $\mathrm {\Delta} G^{\mathrm{transf}}_{\mathrm{W-mix}}$ . UV spectroscopic measurements suggest that these compounds bind calf thymus(CT)-DNA via intercalation mode in a buffer?C3 mol?L?1 acetonitrile solution. The binding constant (K b) depends on the nitro-substitution on the phenyl moiety and the electronegativity of the heteroatom in the heterocyclic ring. The corresponding Gibbs energy of binding ( $\Delta G_{\mathrm{DNA-B}}^{0}$ ) of phenylhydrazone derivatives to CT-DNA shows a marked dependence with ????G c. The anticancer activity on human breast cancer cell lines MDA-231, MDA-435 and HT-29 human colon adenocarcinoma cell line was evaluated for the compounds NPCT, NPCF, DPCT and PCT. 相似文献
36.
Suleiman IA Radny MW Gladys MJ Smith PV Mackie JC Kennedy EM Dlugogorski BZ 《Physical chemistry chemical physics : PCCP》2011,13(21):10306-10311
The effect of chlorine (Cl) chemisorption on the energetics and atomic structure of the Cu(001) surface over a wide range of chlorine pressures and temperatures has been studied using equilibrium ab initio atomistic thermodynamics to elucidate the formation of cuprous chloride (CuCl) as part of the Deacon reaction on copper metal. The calculated surface free energies show that the 1/2 monolayer (ML) c(2 × 2)-Cl phase with chlorine atoms adsorbed at the hollow sites is the most stable structure for a wide range of Cl chemical potential, in agreement with experimental observations. It is also found that at very low pressure and exposure, but elevated temperature, the 1/9 ML and 1/4 ML phases become the most stable. By contrast, a high coverage of Cl does not lead to thermodynamically stable geometries. The subsurface adsorption of Cl atoms, however, dramatically increases the stability of the 1 ML and 2 ML adsorption configurations providing a possible pathway for the formation of the bulk-chloride surface phases in the kinetic regime. 相似文献
37.
Maria C. Blanco Diego G. Franco Yamile Jalit Elisa V. Pannunzio Miner Graciele Berndt Andrea Paesano Jr. Gladys Nieva Raúl E. Carbonio 《Physica B: Condensed Matter》2012,407(16):3078-3080
The samples Bi2BB′O7, with B=Cr and Fe and B′=Nb, Ta and Sb were prepared by solid state method. The crystallographic structure was investigated on the basis of X-ray powder diffraction data. Rietveld refinements show that the crystal structure is cubic, space group Fd-3m. The Bi3+ cation on the eight-coordinate pyrochlore A-site shows displacive disorder, as a consequence of its lone pair electron con?guration. There is also a considerable A-site disorder shown by Rietveld Analysis and confirmed in the case of the iron containing samples with Mössbauer spectroscopy. The magnetic measurements show paramagnetic behavior at all temperatures for the Cr oxides. The Fe pyrochlores show antiferromagnetic order around 10 K. 相似文献
38.
Clayane Carvalho dos Santos Marcelo de Assis Thales Rafael Machado Paula Fabiana dos Santos Pereira Gladys Minguez‐Vega Eloisa Cordoncillo Hector Beltran‐Mir Carlos Doate‐Buendía Juan Andrs Elson Longo 《Particle & Particle Systems Characterization》2019,36(6)
In this work, for the first time, the instantaneous nucleation and growth processes of Ag nanoparticles on Ag3PO4 mediated by femtosecond laser pulses are reported and analyzed. The investigated samples are pure Ag3PO4 sample, electron‐irradiated Ag3PO4 sample, and laser‐irradiated sample. Complete characterization of the samples is performed using X‐ray diffraction (XRD), Rietveld refinements, field emission scanning electron microscopy, and energy dispersive spectroscopy (EDS). XRD confirms that the irradiated surface layer remains crystalline, and according to EDS analysis, the surface particles are composed primarily of Ag nanoparticles. This method not only offers a one‐step route to synthesize Ag nanoparticles using laser‐assisted irradiation with particle size control, but also reports a complex process involving the formation and subsequent growth of Ag nanoparticles through an unexpected additive‐free in situ fabrication process. 相似文献
39.
40.
Ysaías J. Alvarado José Caldera-Luzardo Gladys Ferrer-Amado Victoria Mancilla-Labarca Elba Michelena 《Journal of solution chemistry》2007,36(1):1-11
High-precision densitometry and high-accuracy refractometry measurements of extremely dilute solutions of the thiophene-2-
(TCPH), pyrrole-2- (PCPH) and furan-2-carboxaldehyde-phenylhydrazone (FCPH) compounds in acetonitrile have been obtained at
293.15 K. The partial molar volumes V
2^∞ of each compound at infinite dilution were determined. The apparent molar refraction of these solutes at infinite dilution
at 293.15 K has been experimentally determined within the Kohner-Geffcken-Grunwald-Haley approximation. The volumetric and
refractometric results were interpreted in terms of the Pauling electronegativity and intrinsic molar volume of the heteroatom,
and the aromaticity of the heterocyclic rings. The experimental results indicate that solute-solute interactions are negligible
within the concentration range studied. Theoretical calculations at the DFT-B3LYP/6−311++G(3d,3p) level of molecular volumes
support the interpretation that the volumetric contribution from the solute-solvent interactions to the limiting partial molar
volumes of solutes are very small and thus solute molecules are isolated in this medium. 相似文献