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41.
Branka Kova
Edgar Heilbronner Horst Prinzbach Klaus Weidmann 《Helvetica chimica acta》1979,62(8):2841-2853
The photoelectron spectra of the hydrocarbons 1 to 4 have been recorded and interpreted by qualitative correlation with the spectra of their subsystems norbornadiene, quadricyclane, allene and cyclopropane. It has been shown that the interactions of the symmetry adapted orbitals of the subsystems are governed not only by their symmetry behaviour with respect to D2d in 1 and 2 , or C2ν in 3 and 4 , but also by the local symmetry at the points of attachment of the subsystems. 相似文献
42.
The influence of the primary structures of plant (Canavalia ensiformis) and bacterial (Bacillus pasteurii) ureases on the precipitation of calcium carbonate polymorphs in solutions of calcium salts and urea at room temperature was investigated. Despite a similar catalytic function in the decomposition of urea, these ureases exerted different influences on the crystal phase formation and on the development of unusual morphologies of calcium carbonate polymorphs. Spherical and uniform vaterite particles were precipitated rather than calcite in the presence of Bacillus urease, while the presence of Canavalia urease resulted in the precipitation of calcite only. Vaterite particles were shown to be built up of nanosized crystallites, proving the importance of nanoscale aggregation processes on the formation of colloidal carbonates. Reduction of the concentration of Bacillus urease in the reacting solution results in the formation of calcite crystals with a more complex surface morphology than the ones obtained by Canavalia urease. These differences may be explained by dissimilarities in the amino acid sequences of the two examined ureases and their different roles in nucleation and physicochemical interactions with the surface of the growing crystals, during the precipitation processes. This study exemplifies the diversity of proteins produced by different organisms for the same function, and the drastic effects of subtle differences in their primary structures on crystal phase formation and growth morphology of calcium carbonate precipitates, which occur as inorganic components in a large number of biogenic structures. 相似文献
43.
Branka Mihaljevic Branka Medved-Rogina Dusan Razem 《Radiation Physics and Chemistry》1999,55(5-6):593-597
The rate of the reaction of the tert-butoxyl radical (t-BuO√) with Fe2+ was measured using laser flash photolysis of methanolic solutions at room temperature. t-BuO√ were generated by homolytic photodecomposition of di-tert-butyl peroxide. The rate constant for oxidation of Fe2+ with t-BuO√ radicals was studied under pseudo-first order conditions. On the basis of competitive kinetics the quantum yield of oxidation, Φ(Fe3+), was determined as function of Fe2+ concentration by measuring the absorbance of Fe3+ as [FeCl]2+ complex. By using the literature values of the rate constants of relevant competing reactions, the desired rate constant was determined to be 3.0×108 M−1 s−1. 相似文献
44.
Elola MD Ladanyi BM Scodinu A Loughnane BJ Fourkas JT 《The journal of physical chemistry. B》2005,109(50):24085-24099
In this work we have studied the relaxation dynamics of the many-body polarizability anisotropy in liquid mixtures of benzene (Bz) and hexafluorobenzene (Hf) at room temperature by femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) experiments and molecular dynamics (MD) simulations. The computed polarizability response arising from intermolecular interactions was included using the first-order dipole-induced-dipole model with the molecular polarizability distributed over the carbon sites of each molecule. We found good qualitative agreement between experiments and simulations in the features exhibited by the nuclear response function R(t) for pure liquids and mixtures. The long-time diffusive decay of R(t) was observed to vary substantially with composition, slowing down noticeably with dilution of each of the species as compared with that in the corresponding pure liquids. MD simulation shows that the effect on R(t) is due to the formation of strong and localized intermolecular association between Bz and Hf species that hinder the rotational diffusive dynamics. The formation of these Bz-Hf complexes in the liquid mixtures also modifies the rotational diffusive dynamics of the component species in such a way that cannot be explained solely in terms of a viscosity effect. Even though the computed orientational diffusive relaxation times associated with Bz and Hf are larger by a factor of approximately 2 than those from experiments, we found similar trends in experiments and simulations for these characteristic times as a function of composition. Namely, the collective and single-molecule orientational correlation times associated with Bz are observed to grow monotonically with the dilution of Bz, while those corresponding to Hf species exhibit a maximum at the equimolar composition. We attribute the quantitative discrepancy between experiments and simulations to the use of the Williams potential, which seems to overestimate the intermolecular interactions and thus predicts not only a slower translational dynamics but also a slower rotational diffusion dynamics than in real fluids. 相似文献
45.
The photoelectron spectra (PE.) of ten cyclophanes ( 7 to 14, 16, 18 ) have been assigned on the basis of a simple molecular orbital model proposed recently for the cyclophanes 2 (1,4) to 6 . It is shown that the agreement between calculated and observed band positions provides strong evidence for the validity of the model. 相似文献
46.
The intensity of depolarized light scattering, I dep, is calculated as a function of concentration, X, of non-spherical scatterers in a solvent of spherical non-scatterers. The possibility of finding the second rank Kirkwood g-factor, g (2), from measurements of I dep versus X is discussed. 相似文献
47.
Samaržija-Jovanović Suzana Jovanović Vojislav Jovanović Tijana Petković Branka Marković Gordana Porobić Slavica Marinović-Cincović Milena 《Journal of Thermal Analysis and Calorimetry》2022,147(22):12467-12479
Journal of Thermal Analysis and Calorimetry - This work investigated the thermal characteristics of irradiated composite materials formulated on the urea–formaldehyde resin (UF) and... 相似文献
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Branka M. Ladanyi 《Journal of Molecular Liquids》1994,60(1-3):xxiii-xxvii