scholarly journals Изотопные эффекты в спектрах комплексов с водородными связями. Ангармонические расчеты изотопологов комплекса [F(HF)-=SUB=-2-=/SUB=-]-=SUP=---=/SUP=-

2020 ◽  
Vol 128 (8) ◽  
pp. 1077
Author(s):  
В.П. Булычев ◽  
М.В. Бутурлимова ◽  
К.Г. Тохадзе
Keyword(s):  
Basis Set ◽  
Ir Absorption ◽  
Absorption Bands ◽  
Spectral Parameters ◽  
Basis Set Superposition Error ◽  
Band Frequency ◽  
Normal Vibrations ◽  
K Meson ◽  
Anharmonic Interactions ◽  
Good Agreement

The frequencies and intensities of IR absorption bands of symmetric and asymmetric H-bonded complexes [FL1FL2F]- (L1, L2 = K-meson Ka, proton H, deuton D, and triton T) are calculated. The equilibrium configuration and potential energy and dipole moment surfaces of isotopologues [FL1FL2F]- were calculated by the MP2/6-311++G(3df,3pd) method with the basis set superposition error taken into account. The calculations of spectral parameters with allowance for anharmonic interactions of all vibrations were carried out using the second-order vibrational perturbation theory. Variation of Li and L2 masses in wide regions allowed significant changes in the forms of normal vibrations and values of anharmonic interaction constants upon isotopic substitution to be obtained. The trends in the changes of spectral parameters were determined upon transition from one symmetric isotopologue to another and upon transition from symmetric to asymmetric isotopologues. The D-F stretching band frequency predicted for [FHFDF]- is in good agreement with the experimental value. The assignment of this band was improved.

A DENSITY FUNCTIONAL THEORY INVESTIGATION ON THE TAUTOMERS AND CRYSTAL OF 2-DIAZO-4,6-DINITROPHENOL

2004 ◽  
Vol 03 (04) ◽  
pp. 599-607 ◽  
Author(s):  
XUE-HAI JU ◽  
HE-MING XIAO
Keyword(s):  
Density Functional ◽  
Density Functional Method ◽  
Lattice Energy ◽  
Functional Method ◽  
Basis Set ◽  
Functional Theory ◽  
Basis Set Superposition Error ◽  
Conduction Bands ◽  
Valence Bands ◽  
Good Agreement

Density functional method was applied to the study of the highly efficient primary explosive 2-diazo-4,6-dinitrophenol (DDNP) in both gaseous tautomers and its bulk state. Two stable tautomers were located. It was found that the structure (I) with open diazo, i.e. with linear CNN, is more stable than that with diazo ring tautomer (II) of DDNP. The structure I is in good agreement with the structure in the bulk. The lattice energy is -89.01 kJ/mol, and this value drops to -83.29 kJ/mol when a 50% correction of the basis set superposition error was adopted. The frontier bands are quite flat. The carbon atoms in DDNP make up the upper valence bands. While the lower conduction bands mainly consist of carbon and diazo N atoms. The bond populations of C–N bonds (both C–Nitro and C–Diazo) are much less than those of the other bonds and the detonation may be initiated through the breakdown of C–N bonds.

THE IR STUDY OF AMORPHOUS THIN FILMS OF MIXED OXIDES In2O3–SnO2 SYSTEM

2007 ◽  
Vol 14 (01) ◽  
pp. 5-16 ◽  
Author(s):  
M. ANWAR ◽  
S. A. SIDDIQI ◽  
I. M. GHAURI
Keyword(s):  
Film Thickness ◽  
Substrate Temperature ◽  
Mixed Oxides ◽  
Ir Absorption ◽  
Absorption Bands ◽  
Band Frequency ◽  
Annealing Temperatures ◽  
Ir Study ◽  
Indium Interstitials ◽  
Cation Sites

The IR spectra of thin amorphous films of mixed oxides In 2 O 3– SnO 2 system have been studied in the spectral range 4000–400 cm-1 by Fourier transform infrared technique. The effects of changes in composition, film thickness, substrate temperature and annealing on the IR absorption bands are observed. A shift in frequency and intensity of the bands with varying preparation parameters and an increase in ordering at higher annealing temperatures are observed in the infrared curves. Some new peaks appear, which reveal the presence of lower valency states both in In 2 O 3 and SnO 2. The disappearance of bands at higher annealing temperatures is assigned to the removal of point defects in which oxygen plays an important role. The shift in band frequency with an increase in (i) the Sn content is attributed to the incorporation of Sn 4+ ions in the In 2 O 3 lattice, (ii) the film thickness is attributed to the large concentration of donor centers, (iii) the substrate temperature is attributed to the increase in diffusion of Sn atoms from interstitial locations into the In cation sites, and (iv) the annealing temperature is attributed to the oxygen vacancies and indium interstitials.

ELECTRON TOPOLOGICAL AND ENERGETIC STUDY OF THE INTERMOLECULAR HALOGEN BONDING INTERACTIONS IN COMPLEXES H2O ⋯ M (M = F2, ClF, ANDCF4)

2009 ◽  
Vol 08 (04) ◽  
pp. 615-629 ◽  
Author(s):  
HAI-BEI LI ◽  
YU BIN BAI ◽  
SHAN XI TIAN ◽  
JINLONG YANG
Keyword(s):  
Hydrogen Bonding ◽  
Interaction Strength ◽  
Halogen Bonding ◽  
Basis Set ◽  
Basis Set Superposition Error ◽  
Error Corrections ◽  
Bond Stretching ◽  
High Level ◽  
Induction Energy ◽  
Good Agreement

The halogen bonding complexes H 2 O ⋯ M ( M = F 2, ClF , and CF 4) in comparison with the hydrogen bonding H 2 O ⋯ HF complex are studied by high-level ab initio calculations and electron topological atoms-in-molecules (AIM) analyses. The basis set superposition error corrections are important to predict if the structures are in good agreement with the experimental results. Both the CCSD(T)/aug-cc-pVTZ calculations and the AIM analyses indicate a interaction strength order: H 2 O ⋯ HF > H 2 O ⋯ ClF ⋯ H 2 O ⋯ F 2 ⋯ H 2 O ⋯ CF 4, with the interaction energies –7.91, –4.16, –1.11, and –1.05 kcal/mol, respectively. The symmetry-adapted perturbation theory analyses have been carried out towards understanding of the nature of the halogen bonding interactions in the complexes H 2 O ⋯ M ( M = F 2, ClF , and CF 4), where the exchange energies are the predominant repulsive components. For the complexes involving polar monomers, the hydrogen bonding H 2 O ⋯ HF and the halogen bonding H 2 O ⋯ ClF , the largest attractive contributions are the electrostatic energies. However, in H 2 O ⋯ F 2 and H 2 O ⋯ CF 4, the attractive dispersion energies become more important, and the induction energy in the former complex is a little higher than that in the latter. In contrary to the red-shifts of H – F , Cl – F , and F – F bond stretching vibrational frequencies in the complexes H 2 O ⋯ M ( M = HF , ClF , and F 2), the blue-shifts are predicted for C – F bonds neighboring water in H 2 O ⋯ CF 4.

Nevirapine Pharmaceutical Cocrystal: Design, Development and Formulation

2019 ◽  
Vol 9 (3) ◽  
pp. 240-247
Author(s):  
Prabhakar Panzade ◽  
Priyanka Somani ◽  
Pavan Rathi
Keyword(s):  
Dosage Form ◽  
In Vitro Dissolution ◽  
Soluble Form ◽  
Ir Absorption ◽  
Stoichiometric Ratio ◽  
Design Development ◽  
Formulation Development ◽  
Scanning Calorimetry ◽  
Absorption Bands ◽  
Pharmaceutical Cocrystal

Background and Objective: The top approach to deliver poorly soluble drugs is the use of a highly soluble form. The present study was conducted to enhance the solubility and dissolution of a poorly aqueous soluble drug nevirapine via a pharmaceutical cocrystal. Another objective of the study was to check the potential of the nevirapine cocrystal in the dosage form. Methods: A neat and liquid assisted grinding method was employed to prepare nevirapine cocrystals in a 1:1 and 1:2 stoichiometric ratio of drug:coformer by screening various coformers. The prepared cocrystals were preliminary investigated for melting point and saturation solubility. The selected cocrystal was further confirmed by Infrared Spectroscopy (IR), Differential Scanning Calorimetry (DSC), and Xray Powder Diffraction (XRPD). Further, the cocrystal was subjected to in vitro dissolution study and formulation development. Results: The cocrystal of Nevirapine (NVP) with Para-Amino Benzoic Acid (PABA) coformer prepared by neat grinding in 1:2 ratio exhibited greater solubility. The shifts in IR absorption bands, alterations in DSC thermogram, and distinct XRPD pattern showed the formation of the NVP-PABA cocrystal. Dissolution of NVP-PABA cocrystal enhanced by 38% in 0.1N HCl. Immediate release tablets of NVP-PABA cocrystal exhibited better drug release and less disintegration time. Conclusion: A remarkable increase in the solubility and dissolution of NVP was obtained through the cocrystal with PABA. The cocrystal also showed great potential in the dosage form which may provide future direction for other drugs.

On basis set superposition error corrected stabilization energies for large n-body clusters

2011 ◽  
Vol 135 (13) ◽  
pp. 134118 ◽  
Author(s):  
Katarzyna Walczak ◽  
Joachim Friedrich ◽  
Michael Dolg
Keyword(s):  
Basis Set ◽  
Basis Set Superposition Error ◽  
Large N ◽  
Stabilization Energies

ELECTRONIC STRUCTURE AND OPTICAL PROPERTIES OF CRYSTALLINE C60

1992 ◽  
Vol 06 (06) ◽  
pp. 309-321 ◽  
Author(s):  
W.Y. CHING ◽  
MING-ZHU HUANG ◽  
YONG-NIAN XU ◽  
FANQI GAN
Keyword(s):  
Optical Properties ◽  
Electronic Structure ◽  
First Principles ◽  
Optical Spectrum ◽  
Local Density ◽  
Low Dielectric Constant ◽  
Experimental Measurements ◽  
Absorption Bands ◽  
Low Dielectric ◽  
Good Agreement

The electronic structure and optical properties of crystalline C 60 and their pressure dependence have been studied by first-principles local density calculations. It is shown that fcc C 60 has a low dielectric constant and an optical spectrum rich in structures. The spectrum shows five disconnected absorption bands in the 1.4 to 7.0 eV region with sharp structures in each band that can be attributed to critical point transitions. This is a manifestation of the localized molecular structure coupled with long range crystalline order unique to the C 60 crystal. At a sufficient high pressure, the structures in the optical spectrum start to merge due to the merging of the bands. These results are in good agreement with some recent experimental measurements.

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