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151.
Yves Marchal 《Journal of Molecular Structure》1997,416(1-3):133-143
The procedure previously used to determine the interaction configurations of H2O molecules in various polysaccharides is applied to a protein: Stratum Corneum (SC). It consists of following by infrared (IR) spectrometry the evaporation, heating and addition of water to a SC membrane. Analyses of the spectra corresponding to these experiments show that even H2O molecules in equilibrium with the atmosphere are inserted in the protein itself and are held by one hydrogen bond which they accept from an N---H group of the protein and at least one hydrogen bond which they establish (donate) on a C=O group of the protein. At higher concentrations of water, H2O molecules aggregate and form microdroplets embedded in the protein. Addition of water followed by evaporation of the added H2O molecules results in an enhancement of the number of hydrogen bonds of type N---HO=C inside the protein. It makes water molecules appear as catalysts to rebuild hydrogen bonds in the protein. 相似文献
152.
Daniel M. Chipman 《Theoretical chemistry accounts》2004,111(2-6):61-65
The effect of bulk dielectric solvation on chemical shielding at nitrogen in CH3CN is studied with reaction field theory. A previous work has demonstrated the strong influence on this property from volume polarization, which describes that part of the reaction field arising from solute charge density penetrating outside its cavity. The essentially exact treatment of volume polarization used in that work is computationally demanding, and a more facile method for simulation of the volume polarization has recently been proposed. It is found in the present work that this simulation of the volume polarization yields results in excellent agreement with the essentially exact treatment of the strong volume polarization effects on nitrogen shielding in CH3CN.Contribution to the Jacopo Tomasi Honorary Issue 相似文献
153.
The present paper discusses the behaviour of transfer free energy of some amino acids from water to 4M, 6M and 8M aqueous urea. Dissection of transfer free energy into cavity term, interaction term and electrical term reveals that cavity forming free energy of transfer ΔG0t (cav) plays an important role in dictating actual interaction of amino acids in aqueous urea. Cavity forming free energy of transfer has been estimated by using Scaled Particle Theory (SPT). 相似文献
154.
Mickhail V. Ryzhkov Alexei Mirmelstein Sung‐Woo Yu Brandon W. Chung James G. Tobin 《International journal of quantum chemistry》2013,113(16):1957-1965
Calculations of the electronic structure of clusters of plutonium have been performed, within the framework of the relativistic discrete‐variational method. These theoretical results and those calculated earlier for related systems have been compared to spectroscopic data produced in the experimental investigations of bulk systems, including photoelectron spectroscopy. Observation of the changes in the Pu electronic structure as a function of size provides powerful insight for aspects of bulk Pu electronic structure. © 2013 Wiley Periodicals, Inc. 相似文献
155.
András Szenes 《Advances in Mathematics》2011,226(1):764
For a nontrivial measurable set on the real line, there are always exceptional points, where the lower and upper densities of the set are neither 0 nor 1. We quantify this statement, following work by V. Kolyada, and obtain the unexpected result that there is always a point where the upper and the lower densities are closer to 1/2 than to zero or one. The method of proof uses a discretized restatement of the problem, and a self-similar construction. 相似文献
156.
Montserrat Corbera Jaume Llibre Ernesto Pérez-Chavela 《Journal of Mathematical Analysis and Applications》2014
In this paper we prove the existence of two new families of spatial stacked central configurations, one consisting of eight equal masses on the vertices of a cube and six equal masses on the vertices of a regular octahedron, and the other one consisting of twenty masses at the vertices of a regular dodecahedron and twelve masses at the vertices of a regular icosahedron. The masses on the two different polyhedra are in general different. We note that the cube and the octahedron, the dodecahedron and the icosahedron are dual regular polyhedra. The tetrahedron is itself dual. There are also spatial stacked central configurations formed by two tetrahedra, one and its dual. 相似文献
157.
158.
Imperfect icosahedral quasicrystals are assumed to grow obeying a local rule which imposes the twin orientation of like building blocks. The vertex configurations and their representations are briefly discussed. The vertices are classified by their abundances and energies determined according to a simple model taking account of nearest-neighbour interactions and calculating the corresponding overlap volumes in dual space. 相似文献
159.
Robert Keiner Martina Herrmann Kirsten Küsel Jürgen Popp Torsten Frosch 《Analytica chimica acta》2015
The comprehensive investigation of changes in N cycling has been challenging so far due to difficulties with measuring gases such as N2 and N2O simultaneously. In this study we introduce cavity enhanced Raman gas spectroscopy as a new analytical methodology for tracing the stepwise reduction of 15N-labelled nitrate by the denitrifying bacteria Pseudomonas stutzeri. The unique capabilities of Raman multi-gas analysis enabled real-time, continuous, and non-consumptive quantification of the relevant gases (14N2, 14N2O, O2, and CO2) and to trace the fate of 15N-labeled nitrate substrate (15N2, 15N2O) added to a P. stutzeri culture with one single measurement. Using this new methodology, we could quantify the kinetics of the formation and degradation for all gaseous compounds (educts and products) and thus study the reaction orders. The gas quantification was complemented with the analysis of nitrate and nitrite concentrations for the online monitoring of the total nitrogen element budget. The simultaneous quantification of all gases also enabled the contactless and sterile online acquisition of the pH changes in the P. stutzeri culture by the stoichiometry of the redox reactions during denitrification and the CO2-bicarbonate equilibrium. Continuous pH monitoring – without the need to insert an electrode into solution – elucidated e.g. an increase in the slope of the pH value coinciding with an accumulation of nitrite, which in turn led to a temporary accumulation of N2O, due to an inhibition of nitrous oxide reductase. Cavity enhanced Raman gas spectroscopy has a high potential for the assessment of denitrification processes and can contribute substantially to our understanding of nitrogen cycling in both natural and agricultural systems. 相似文献
160.
Cavity Ring-Down Spectroscopy coupled with helium microwave-induced plasma for fluorine detection 总被引:1,自引:0,他引:1
Cavity Ring-Down Spectroscopy with a tunable diode laser has been used for the detection of fluorine at trace levels. A homemade experimental setup was constructed to accommodate the microwave-induced plasma glow discharge inside the optical cavity. The energy delivered by helium plasma discharge was successfully used not only for the dissociation of fluorine molecules but, more importantly, also for the excitation of fluorine atoms into their metastable level 3s4P5/2. The absorption observed at the 3s4P5/2–3p4Do7/2 transition (corresponding to a 685.603-nm atomic line) was used for fluorine atom detection. Good agreement between theoretical and measured absorption line shapes confirmed the selectivity of fluorine atomic absorption. We observed an absorption coefficient of 4 ? 10−6 cm−1, corresponding to a detection of F(3s4P5/2) atoms at about 1.5 ? 106 atoms cm−3. These data demonstrate that we achieved a detection limit of 100 ng g−1 under the conditions of our initial homemade experimental setup. However, the optimization of the system may lead to the improvement of the detection limit by approximately two orders of magnitude. 相似文献