Chemistry Journal of Moldova

Physical chemistry and chemical physics

AB INITIO STUDY OF THE POSSIBLE SINGLE-CENTER UNITS FOR BINUCLEAR IRON COMPLEX [Fe2(bpym)3Cl4]

Author(s):

Tihonovschi Andrei


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2008 Volume 3, no.2
Pages: 114-118
Keywords: iron complexes, bipyrimidine complexes, magnetic properties, ab initio study.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2008.03(2).02

Graphical Abstract:
 In present work we study two possible single-center units for binuclear iron complex Fe2(bpym)3Cl4 –[Fe(bpym)3]2+ and Fe(bpym)2Cl2. The obtained ground states for both studied systems are singlet states. In the case of Fe(bpym)2Cl2 the lowest excited states were calculated to be 240cm-1 (triplet) and 660cm-1 (quintet) above the ground state and so are placed according to Lande rule. These states could be populated at room temperatures. For [Fe(bpym)3]2+ first excited state was found to be about 6000cm-1 above the ground state and so cannot be populated at normal temperatures.

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THE THEORETICAL STUDY OF SOME REACTIONS WITH THE PARTICIPATION OF OH AND HO2 RADICALS

Author(s):

Ion Arsene


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2008 Volume 3, no.2
Pages: 109-113
Keywords: the radicals reactions, decomposition of hydrogen peroxide, the thermodynamic stability.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2008.03(2).18

Graphical Abstract:
 The geometry of the H2O2, OH, HO2, O2 particles and the energy profiles of the initial reactions between them, that are supposed to take place during the process of decomposition of hydrogen peroxide, were studied by ab initio calculations. It was shown that the differences between the energies of reactants and the products of all analysed reaction are positive values and correlate with the experimental data.

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DIHYDROXYFUMARIC ACID TRANSFORMATION

Author(s):

Natalia Secara


Field: Physical chemistry and chemical physics
Type: Short communication
Issue: 2008 Volume 3, no.1
Pages: 127-128
Keywords: dihydroxyfumaric acid, decarboxylation, activation energy.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2008.03(1).06

Graphical Abstract:
This short communication presents several preliminary results obtained during kinetic investigation of dihydroxyfumaric acid decarboxylation. The reaction order towards the hydrogen ions concentration has been established, the correlation between the decarboxylation velocity and temperature has been found, the Arrhenius equation for the decarboxylation constant has been drawn.

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AB INITIO ANALYSIS OF EXCHANGE INTERACTIONS IN [V2O(BIPY)4CL2]2+ COMPLEX

Author(s):

Ivan Ogurtsov, Andrei Tihonovschi


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2008 Volume 3, no.1
Pages: 112-117
Keywords: binuclear vanadium complex, binuclear μ-oxo-bridged complex, exchange interactions, magnetic properties, theoretical ab initio study.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2008.03(1).08

Graphical Abstract:
The ground state was calculated to be a quintet, which means a ferromagnetic interaction between centers. The
orbitals participating in exchange interaction according to ROHF+CI calculations are two molecular orbitals consisting of vanadium d-orbitals and two molecular orbitals with main contributions from p-orbitals of bipyridine ligands perpendicular to V-V axis, vanadium d- and p-orbitals and μ-oxygen p-orbital. Calculated energy values of the multielectronic states are placed in accordance with Lande rule. The value of magnetic moment at 293K calculated for the complex in vacuum taking into consideration the Boltzmann distribution and the energies of the excited states is 3.95BM which is in accordance with experimental value of 3.99BM (for complex in acetone).

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Author(s):

N. N. Gorinchoy, I. Ya. Ogurtsov and Ion Arsene


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2008 Volume 3, no.1
Pages: 105-111
Keywords: hydrogen peroxide, electronic structure, pseudo Jahn-Teller effect.
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DOI:
dx.doi.org/10.19261/cjm.2008.03(1).12

Graphical Abstract:
 The vibronic origin of instability of the symmetrical forms (D¥ h, C2h and C2v) of the hydrogen peroxide molecule H2O2 was revealed using ab initio calculations of the electronic structure and the adiabatic potential energy curves. The vibronic constants in this approach were estimated by fitting of the ab initio calculated adiabatic potential in the vicinity of the high-symmetry nuclear configurations to its analytical expression. It was shown that the equilibrium “skewed” anticline shape of the C2 symmetry can be realized in two ways: D¥h ® C2v® C2 or D¥h ® C2h® C2 with the decreasing of the adiabatic potential energy at every step.

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Author(s):

N. N. Gorinchoy, I. Ya. Ogurtsov, A. Tihonovschi, I. Balan, I. B. Bersuker, A. Marenich and J.Boggs


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2008 Volume 3, no.1
Pages: 94-104
Keywords: aquatic toxicity, electron-conformational method, QSAR.
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DOI:
dx.doi.org/10.19261/cjm.2008.03(1).13

Graphical Abstract: 
The electron-conformational (EC) method is employed to reveal the toxicophore and to predict aquatic toxicity quantitatively using as a training set a series of 51 compounds that have aquatic toxicity to fish. By performing conformational analysis (optimization of geometries of the low-energy conformers by the PM3 method) and electronic structure calculations (by ab initio method corrected within the SM54/PM3 solvatation model), the Electron-Conformational Matrix of Congruity (ECMC) was constructed for each conformation of these compounds. The toxicophore defined as the EC sub-matrix of activity (ECSA), a sub-matrix with matrix elements common to all the active compounds under consideration within minimal tolerances, is determined by an iterative procedure of comparison of their ECMC’s, gradually minimizing the tolerances. Starting with only the four most toxic compounds, their ECSA (toxicophore) was found to consists of a 4x4 matrix (four sites with certain electronic and topologic characteristics) which was shown to be present in 17 most active compounds. A structure-toxicity correlation between three toxicophore parameters and the activities of these 17 compounds with R2=0.94 was found. It is shown that the same toxicophore with larger tolerances satisfies the compounds with les activity, thus explicitly demonstrating how the activity is controlled by the tolerances quantitatively and which atoms (sites) are most flexible in this respect. This allows for getting slightly different toxicophores for different levels of activity. For some active compounds that have no toxicophore a bimolecular mechanism of activity is suggested. Distinguished from other QSAR methods, no arbitrary descriptors and no statistics are involved in this EC structure-activity investigation.

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Author(s):

Gheorghe Duca, Natalia Secara, Daniela Duca


Field: Physical chemistry and chemical physics
Type: Review
Issue: 2008 Volume 3, no.1
Pages: 22-30
Keywords: fast reactions kinetics, spectroscopy, relaxation, flow methods.
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DOI:
dx.doi.org/10.19261/cjm.2008.03(1).15

Graphical Abstract:
 This review presents the basic concepts of the methods used for investigation of fast reactions kinetics, such as: flow methods, with particular emphasis on the stopped-flow approach, NMR, ESR, electrochemical methods, with particular emphasis on the time resolved Fourier Transform electrochemical impedance spectroscopy, flash photolysis, and several others. It offers a brief description of fast reactions commonly encountered in chemical systems, providing an insight into the possibilities of performing kinetic investigations of such reaction systems.

Downloads: 19

Author(s):

Ion Dranca


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2008 Volume 3, no.1
Pages: 31-43
Keywords: activation energy; differential scanning calorimetry (DSC); α- and β-relaxation; advanced isoconversional method; kinetics (polym. and pharm.)
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DOI:
dx.doi.org/10.19261/cjm.2008.03(1).17

Graphical Abstract: 
Differential scanning calorimetry has been used to study the α-relaxation (glass transition) in virgin polystyrene (PS), PS-clay nanocomposite, amorphous indomethacin (IM), maltitol (Mt) and glucose (Gl). Variation of the effective activation energy (E) throughout the glass transition has been determined by applying an advanced isoconversional method to DSC data on the glass transition. The relaxations have been characterized by determining the effective activation energies (E) and evaluating the sizes of cooperatively rearranging regions at the glass transition (Vg). The values of Vg have been determined from the heat capacity data. The α-relaxation demonstrates markedly larger values of E (~340 vs ~270 kJ mol-1) for the PS-clay system than for virgin PS. For IM in the glass transition region, the effective activation energy of relaxation decreases with increasing temperature from 320 to 160 kJ mol-1. In the Tg region E decreases (from~250 to ~150 kJ mol-1 in maltitol and from~220 to ~170 kJ mol-1 in glucose) with increasing T as typically found for the α-relaxation. It has been found that in the sub-Tg region E decreases with decreasing T reaching the values ~60 (glucose) and ~70 (maltitol) kJ -1 that are comparable to the literature values of the activation energies for the β-relaxation. Heat capacity measurements have allowed for the evaluation of the cooperatively rearranging region in terms of the linear size The PS-clay system has also been found to have a significantly larger value of Vg, 36.7 nm3 as compared to 20.9 nm3 for PS. Heat capacity measurements of IM have allowed for the evaluation of the cooperatively rearranging region (CRR) in term of linear size (3.4 nm) and the number of molecules (90). The size of CRR have been determined as 3.1 (maltitol) and 3.3 (glucose) nm.

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