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101.
Conformational flexibility of pyrimidine rings of nucleic acid bases in polar environment: PCM study
The results of calculations of molecular structures of nucleic acid bases in polar environment using Polarized Continuum Model
of solvent combined with the MP2/cc-pvdz level of ab initio theory demonstrate considerable polarization of thymine, cytosine,
and guanine. This phenomenon can be related to considerable contribution of zwitter-ionic resonant forms into total structure
of the studied species. It leads to significant increase (about 30%) of frequencies of the out-of-plane pyrimidine ring vibrations
and is related to considerable decrease of conformational flexibility of heterocycle due to smaller out-of-plane deformability
of pyrimidine ring in zwitter-ionic resonant forms. In the case of adenine, the presence of a polar environment results in
an increase of conformational flexibility of pyrimidine ring. 相似文献
102.
Oleg V. Shishkin Irina S. Konovalova Leonid Gorb Jerzy Leszczynski 《Structural chemistry》2009,20(1):37-41
Investigation of characteristics of hydrogen bonding between pyridine and water by MP2/aug-cc-pvdz method reveals that these
two molecules may form three types of hydrogen bonds depending on nature of proton withdrawal site of pyridine. Change of
orientation of water with respect to plane of aromatic ring leads to transformation of the O–H···N bond to O–H···π bond via
wide region of the potential energy surface where both lone pair of the nitrogen atom and π-system make significant contribution
into hydrogen bonding. Hydrogen bond in this intermediate region may be considered as mixed O–H···N/O–H···π bond representing
new type of H bonds. 相似文献
103.
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105.
We introduce and demonstrate a new microscopy concept: imaging interferometric microscopy (IIM), which is related to holography, synthetic-aperture imaging, and off-axis-dark-field illumination techniques. IIM is a wavelength-division multiplex approach to image formation that combines multiple images covering different spatial-frequency regions to form a composite image with a resolution much greater than that permitted by the same optical system using conventional techniques. This new type of microscopy involves both off-axis coherent illumination and reinjection of appropriate zero-order reference beams. Images demonstrate high resolution, comparable with that of a high-numerical-aperture (NA) objective, while they retain the long working distance, the large depth of field, and the large field of view of a low-NA objective. A Fourier-optics model of IIM is in good agreement with the experiment. 相似文献
106.
Rudzevich Y Rudzevich V Moon C Schnell I Fischer K Böhmer V 《Journal of the American Chemical Society》2005,127(41):14168-14169
Selective and independent dimerization of tri- and tetraurea derivatives was used to build up dendritic assemblies which are uniform in size and structure. Dendrimers with the total molecular masses of about 25 000 g/mol were obtained. The existence of uniform assemblies was proved by 1H and 1H DOSY NMR experiments and also by dynamic light scattering. 相似文献
107.
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109.
Are the reduction and oxidation properties of nitrocompounds dissolved in water different from those produced when adsorbed on a silica surface? A DFT M05‐2X computational study 下载免费PDF全文
Liudmyla K. Sviatenko Olexandr Isayev Leonid Gorb Frances C. Hill Danuta Leszczynska Jerzy Leszczynski 《Journal of computational chemistry》2015,36(14):1029-1035
The reduction and oxidation properties of four nitrocompounds (trinitrotoluene [TNT], 2,4‐dinitrotoluene, 2,4‐dinitroanisole, and 5‐nitro‐2,4‐dihydro‐3H‐1,2,4‐triazol‐3‐one [NTO]) dissolved in water as compared with the same properties for compounds adsorbed on a silica surface were studied. To consider the influence of adsorption, cluster models were developed at the M05/tzvp level. A hydroxylated silica (001) surface was chosen to represent a key component of soil. The PCM(Pauling) and SMD solvation models were used to model water bulk influence. The following properties were analyzed: electron affinity, ionization potential, reduction Gibbs free energy, oxidation Gibbs free energy, and reduction and oxidation potentials. It was found that adsorption and solvation decrease gas phase electron affinity, ionization potential, and Gibbs free energy of reduction and oxidation, and thus, promote redox transformation of nitrocompounds. However, in case of solvation, the changes are more significant than for adsorption. This means that nitrocompounds dissolved in water are easier to transform by reduction or oxidation than adsorbed ones. Among the considered compounds, TNT was found to be the most reactive in an electron attachment process and the least reactive for an electron detachment transformation. During ionization, a deprotonation of adsorbed NTO was found to occur. © 2015 Wiley Periodicals, Inc. 相似文献
110.
Close DM Crespo-Hernandez CE Gorb L Leszczynski J 《The journal of physical chemistry. A》2006,110(23):7485-7490
In the present study the ionization energy thresholds (IETs) of thymine, and thymine keto-enol tautomers, have been calculated (with the B3LYP, and P3 levels of theory using the standard 6-31++G(d,p) basis set) with 1-3 water molecules placed in the first hydration shell. Calculations show there is a distinct effect of microhydration on the IET of thymine. The first water molecule is seen to decrease the IET by about 0.1 eV, whereas the second and third water molecules cause a further decrease of less than 0.1 eV each. The changes in IET calculated here for thymine with 1-3 waters of hydration are smaller than the experimental values determined by Kim et al. (J. Phys. Chem. 1996, 100, 7933). Therefore calculations have been performed on the microhydrated keto-enol tautomers of thymine. The calculated results on the keto-enol tautomers are seen to be in better agreement with the experimental results. However, the keto-enol thymine tautomers are considerably higher in energy than the canonical form of thymine, and there is presently no good evidence that these thymine tautomers are actually present in a supersonic jet-cooled experiment. 相似文献