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The molecular conformations of shortened molecular models of vitamin E (tocopherol and tocotrienol) and their sulfur and selenium congeners were studied computationally at the DFT level of theory [B3LYP/6-31G(d)]. The sequence of ...
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The molecular conformations of shortened molecular models of vitamin E (tocopherol and tocotrienol) and their sulfur and selenium congeners were studied computationally at the DFT level of theory [B3LYP/6-31G(d)]. The sequence of stabilization by the various heteroatoms was found to be the following: O ～ Se > S. On the basis of the present structural results it seems that the seleno-congener of vitamin E is a distinct possibility.
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Molecular dynamics of three derivatives of 1,2,4-benzothiadiazine-1,1-dioxide, hydrochlorothiazide (HCTZ), althiazide (ATZ) and chlorothiazide (CTZ), was studied by Cl-35 nuclear quadrupole resonance (NQR) spectroscopy. The temper...
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Molecular dynamics of three derivatives of 1,2,4-benzothiadiazine-1,1-dioxide, hydrochlorothiazide (HCTZ), althiazide (ATZ) and chlorothiazide (CTZ), was studied by Cl-35 nuclear quadrupole resonance (NQR) spectroscopy. The temperature dependence of the resonance frequency was analyzed within the 6 known standard models. The activation energies estimated from the temperature dependence of the Cl-35 NQR frequency assuming the Bayer model were 1.07, 2.35 and 2.76 kJ/mol for HCTZ, ATZ and CTZ respectively, which confirms that HCTZ is less rigid than CTZ and ATZ is much more rigid than HCTZ, and.suggests that the mechanism of relaxation is based on small amplitude librations. The characteristic temperatures estimated from the Bayer model, with that for CTZ (332.5 K) being much higher than for HCTZ (132.1 K), mean that the intermolecular interactions in CTZ are much stronger than in HCTZ, as suggested by the melting point of CTZ being higher than that for HCTZ. For ATZ the characteristic temperature (288 K) takes an intermediate value, which suggests that the intermolecular interactions in this compound are stronger than in HCTZ and weaker than in CTZ. A significant narrowing of the resonance Cl-35 NQR line observed for all these compounds at room temperature, relative to that at the liquid nitrogen temperature, suggests an averaging of dipolar interactions as a result of fast rotation of nonquadrupole nuclei in the vicinity of the quadrupole nuclei, when 2piv(Q)tau(c) much greater than 1 (a rotation of the -NH2 group in the direct neighborhood of the chlorine nuclei) or a change in the gradient orientation with its value preserved (which is equivalent to rotation of the quadrupole nucleus Q. The influence of the rotations of the -NH2 and -CH2SCH2CH=CH2 groups (ATZ) or -CHCl2 group (TCTZ) on the Cl-35 NQR frequency was modelled by the B3LYP/6-31G* method. The frequencies of the libration vibrations calculated from the temperature dependence of the NQR resonance frequency were compared with experimental ones and those implied by the density functional theory, infrared and Raman spectra. For HCTZ the anomalies in the temperature dependence of the Cl-35 NQR frequency, the lack of hysteresis and small but notable changes in the slope and the jump in the frequency observed at 253 K which does not exceed 0.05 MHz suggest a second-order phase transition at 253 K. [References: 29]
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The geometry of each of the four isomers (1-,2-,4- and 5-) of (2-furyl) imidazole in the two different stable conformations obtained by rotation of the mutual orientation of the rings was studied by ab inito calculations at the HF...
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The geometry of each of the four isomers (1-,2-,4- and 5-) of (2-furyl) imidazole in the two different stable conformations obtained by rotation of the mutual orientation of the rings was studied by ab inito calculations at the HF/3-21G, HF/6-31G** and MP2/6-31G** levels. Both conformers of 1-(2-fury) imidazole and one each of 2-and 4-(2-furylimidazole were found to have their rings in a twisted orientation while the rings in the other molcules were coplanar. While misleading results were obtained with the smaller hartree-Fock-3-21G* basis, calculations at the MP2/6-31G** level were decisive in indicating the degree of nonplanarity. The potential energy curves for the internal rotation computed at the MP2/6-31G** level pointed out different bechavior for every isomer.
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This paper presents the results of ab initio quantum-chemical calculations of supramolecular complexes C_(60)CdHal, [C_(60)]_4CdHal, and [C_(60)]_6CdHal (Hal = S, Te), which simulate the defects forming in fullerite during the abs...
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This paper presents the results of ab initio quantum-chemical calculations of supramolecular complexes C_(60)CdHal, [C_(60)]_4CdHal, and [C_(60)]_6CdHal (Hal = S, Te), which simulate the defects forming in fullerite during the absorption or adsorption of cadmium telluride (sulfide). Calculations of the electronic structure of complexes with inclusion of their relaxation to the equilibrium state have been performed in terms of the density functional theory with the B3LYP hybrid functional. The obtained enthalpies of formation of complexes show that their formation leads to the energy gain of the order of 0.5–1.5 eV depending on the complex type. It has been shown that the formation of tetrahedral complexes [C_(60)]_4CdTe with the intercalated CdTe molecule is possible only with a considerable distortion of the tetrahedral void. The energy spectrum of low-lying excited electron states for the linear and octahedral complexes has been calculated. It has been found that a decrease in symmetry with the formation of complexes leads to the appearance of excited states of allowed singlet transitions in the electron spectrum, which are forbidden in optical spectra of initial components.
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We have performed a computational study to investigate the cyclosulfurization of the pentagon-pentagon (p-p) junctions in the non-IPR fullerenes C-60(D-3) and C-70(C-2v), and also Stone-Wales defective C-60 fullerene. Our results ...
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We have performed a computational study to investigate the cyclosulfurization of the pentagon-pentagon (p-p) junctions in the non-IPR fullerenes C-60(D-3) and C-70(C-2v), and also Stone-Wales defective C-60 fullerene. Our results indicate the exothermic character of cyclosulfurization processes which can be related to the increase of pyramidalization angle (spherical excesses) and p characters of natural hybrid orbitals of C atoms at the p-p junctions. In fact these lead to the structural strain relief and stability of the cyclosulfurization derivatives of the non-IPR fullerenes. Moreover, the cyclosulfurization reaction of p-p bonds on the C-70(C-2v) is more energetically favorable than that of C-60(D-3), due to the higher curvature of carbon sites and the larger values of the p characters of natural hybrid orbitals in the C-70(C-2v). On the other hand, localization of the excess electrons on the C atoms at the p-p junctions leads to the low tendency of the charged non-IPR fullerenes to cyclosulfurization process. The desulfurization pathway of the exohedral derivatives of C-70(C-2v) indicates that it is energetically unfavorable for the functionalized fullerenes to break into individual fullerene and sulfur molecules. HOMO-LUMO gaps almost are independent of the number of pentathiepin rings while sensitive to the type of parent fullerene. (C) 2016 Elsevier Ltd. All rights reserved.
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Silicon (Si) is currently the basis of most of nanodevice technology, therefore ultrathin materials based on Si have the great advantage of easy integration into existing circuitry. First flat silicon nanoparticles have been obtai...
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Silicon (Si) is currently the basis of most of nanodevice technology, therefore ultrathin materials based on Si have the great advantage of easy integration into existing circuitry. First flat silicon nanoparticles have been obtained with perfluorophenyl (PFPh) ligand coating. The size of these particles varied from 15 to 50 nm. Their thickness evaluated with the atomic force microscopy was about 3.3 nm. Based on ab initio DFT calculations we investigate the geometries and electronic structures of free-standing PFPh-stabilized 2D silicon in order to see if such systems have promising electronic and optical properties. We also examined the effect of doping PFPh-stabilized 2D silicon by the Mn atoms.
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Substitutional defects C, Si, Al and Ti included in c-BN are examined using ab initio calculations employing various sizes of supercell to simulate the dependence of the electronic properties on defect concentration. We suggest so...
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Substitutional defects C, Si, Al and Ti included in c-BN are examined using ab initio calculations employing various sizes of supercell to simulate the dependence of the electronic properties on defect concentration. We suggest some of these defects may be readily absorbed into c-BN occupying either of the B and N lattice sites. However, apart from C, the rate of defect solubility markedly changes with defect concentration. The change in compressibility as measured by a substantial lowering of the Bulk Modulus strongly suggests that there would be a related softening of c-BN critically depending on the nominal defect concentration and the chemical character of the defect.
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The equilibrium magnetic and structural reference states of Co- and Cr-doped NiMnIn Heusler alloy are investigated by means of the first-principles method using a supercell approach. Three different ferrimagnetic and one ferromagn...
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The equilibrium magnetic and structural reference states of Co- and Cr-doped NiMnIn Heusler alloy are investigated by means of the first-principles method using a supercell approach. Three different ferrimagnetic and one ferromagnetic (FM) spin configurations, as well as two supercells with different distributions of excess Mn and In atoms, were considered. It is found that for supercell #1, the FM spin state in austenite is stable, where the martensite with different spin configurations is unstable, while in the case of supercell #2, a ferrimagnetic configuration for both austenite and martensite is favorable. The different trends for martensitic transformation were studied by calculations for the tetragonal and orthorombic distortions of supercells along the -axis and the -axis, showing martensitic variants for supercell #2 at a ratio and .
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Microwave spectra have been recorded for 1-phenyl-2-propanol, methamphetamine, and 1-phenyl-2-propanone from 11 to 24 GHz using a Fourier-transform microwave spectrometer. Only one spectrum from a single conformational isomer was ...
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Microwave spectra have been recorded for 1-phenyl-2-propanol, methamphetamine, and 1-phenyl-2-propanone from 11 to 24 GHz using a Fourier-transform microwave spectrometer. Only one spectrum from a single conformational isomer was observed for each species. The rotational transitions in the spectrum of 1-phenyl-2-propanone were split into separate transitions arising from the A- and E-torsional levels of the methyl rotor. The fit of the E-state transitions to a "high-barrier" internal rotation Hamiltonian determines V-3 = 238(1) cm(-1) and rotor- axis angles of theta(a) = 87.7(5)degrees, theta(b) = 50.0(5)degrees, and theta(c) = 40.0(5)degrees. Ab initio optimizations (MP2/6-31G*) and single-point calculations (MP2/6-311++G**) were used to model the structures of 1-phenyl-2-propanol, methamphetamine, and 1-phenyl-2-propanone. The lowest energy conformations of these species were found to be stabilized by weak OH-pi, NH-pi, and CH-pi hydrogen-bonding interactions. Moments of inertia, derived from the model structures, were used to assign the spectra to the lowest energy conformation of each species. A series of MP2/6-31G* partial optimizations along the internal rotation pathway were used to estimate the barrier to methyl rotation to be 355 cm(-1) for 1-phenyl-2-propanone.
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A first-principles study of the anisotropic thermal expansion of hcp metals Be and Y is reported. According to quasiharmonic approximation, the phonon spectra were computed at a set of lattice parameters using the pseudopotential ...
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A first-principles study of the anisotropic thermal expansion of hcp metals Be and Y is reported. According to quasiharmonic approximation, the phonon spectra were computed at a set of lattice parameters using the pseudopotential plane wave method with the local density approximation in the framework of the density functional perturbation theory. The free energies were obtained according to the calculated phonon spectra and thermal properties such as specific heat at constant volume (pressure) were calculated. The electronic contribution to specific heat was found important to metal Y not only at very low temperature but also over room temperature. The calculated results are in good agreement with available experimental data in a wide range of temperature. (C) 2007 Elsevier Ltd. All rights reserved.
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