Chemistry Journal of Moldova

Physical chemistry and chemical physics

IMPLICATIONS OF GLOBAL AND LOCAL MOBILITY IN AMORPHOUS EXCIPIENTS AS DETERMINED BY DSC AND TM DSC

Author(s):

Ion Dranca, Tudor Lupascu


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2009 Volume 4, no.2
Pages: 105-115
Keywords: molecular mobility; excipients (sucrose & trehalose); α- and β-relaxations; activation energy; DSC & TM DSC.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2009.04(2).02

Graphical Abstract:
 The paper explores the use of differential scanning calorimetry (DSC) and temperature modulated differential scanning calorimetry (TM DSC) to study α- and β- processes in amorphous sucrose and trehalose. The real part of the complex heat capacity is evaluated at the frequencies, f, from 5 to 20mHz. β-relaxations were studied by annealing glassy samples at different temperatures and subsequently heating at different rates in a differential scanning calorimeter.

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ACTIVATION OF ACETYLENE BY COORDINATION TO BIS-TRIPHENYLPHOSPHINE COMPLEX OF Pt(0): DFT STUDY

Author(s):

N. N. Gorinchoy, B. Dobrova, M. Yu. Gorbachev, G. Munteanu, and I. Ya. Ogurtsov


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2009 Volume 4, no.1
Pages: 123-128
Keywords: chemical activation, quantum-chemical calculations, DFT method.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2009.04(1).01

Graphical Abstract:
 The present work is devoted to the theoretical study of the activation of the acetylene molecule coordinated in the [Pt(PPh3)2C2H2] complex. By means of DFT calculations it is shown that the geometrical and electronic characteristics of the C2H2 are essentially changed due to its coordination. The subsequent detailed analysis of the molecular orbitals (MO) of the active valence zone of this complex allows one to make important conclusion that this activation is being realized mainly due to the orbital back donation of 5d-electronic density from one of the occupied MOs of the complex [Pt(PPh3)2] to the unoccupied antibonding π*-MO of C2H2.

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CATALYTIC PROPERTY OF DOUBLE LAYERED PEROVSKITES A2MM’O6 FOR RADIOLYTICAL SPLIT OF WATER

Author(s):

Alexandru Cecal, Tudor Lupascu, Oana Roxana Hauta, Ioana Gorodea, Mircea Palamaru, Alexandra Raluca Iordan , Ada Macovei


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2009 Volume 4, no.1
Pages: 118-122
Keywords: catalytic effect, double perovskites, hydrogen production, water radiolysis.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2009.04(1).02

Graphical Abstract:
 This paper deals with a study of water splitting by gamma rays in the presence of some double perovskites A2MM’O6 and also Sr2Fe1-xTa1+xO6. The irradiation is performed using 60Co as a source with 3·104 Ci activity and 8.3 kGy/h dose rate, which simulated the radioactive wastes, resulted from reprocessing of spent nuclear fuel elements much more active: 108-109 Ci. The stable products of radiolysis, as well as the other chemical species are measured by mass spectrometry. The calculated radiation yield (GH2) generally decreases in the order: Sr2Fe1-xTa1+xO6 (x=0.5; 0.4; 0.3; 0.1) > Ca2AlTaO6 > Sr2AlTaO6 > Ba2AlTaO6, under the given experimental conditions; the yield was higher in the presence of these catalysts than in their absence.

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BITEMPLATE SYNTHESIS OF MESOPOROUS SILICAS WITH THIOUREA GROUPS

Author(s):

O. I. Gona, N. V. Stolyarchuk, Yu. L. Zub, and N. A. Yaroshenko


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2009 Volume 4, no.1
Pages: 111-117
Keywords: mesoporous silicas, bitemplate synthesis, thiourea functional group.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2009.04(1).03

Graphical Abstract:
 Mesoporous silicas with the thiourea functional group ≡Si(CH2)3NHC(S)NHC2H5 have been synthesized by monotemplate and bitemplate route (bitemplate is cetylpyridinium chloride as micelle-forming surfactant and monoethanolamide of saturated n-aliphatic acid as non-micelle-forming surfactant). The infl uence of a number of factors on mesoporous silicas structure has been studied: alkoxysilanes and surfactants concentration, and as well as the nature of medium in hydrothermal treatment of mesophases. The optimum conditions under which functionalized mesoporous silicas have possessing highly ordered hexagonal structure have been found. The surface area of mesoporous silicas synthesized using optimum bitemplate solubilization composition reaches 1055-1350 m2/g and sorption volume and pore diameter are 0.75-0.95 cm3/g and 2.5-2.9 nm respectively.

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INELASTIC NEUTRON SCATTERING, EPR AND SPIN CHIRALITY IN SPIN-FRUSTRATED V3 and Cu3 NANOMAGNETS WITH DZIALOSHINSKY-MORIYA EXCHANGE

Author(s):

Moisey I. Belinsky


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2009 Volume 4, no.1
Pages: 103-110
Keywords: inelastic neutron scattering, EPR transitions, V3 and Cu3 nanomagnets.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2009.04(1).04

Graphical Abstract:
 The inelastic neutron scattering (INS) and EPR transitions are considered for the spin-frustrated V3 and Cu3 nanomagnets. It is shown that the DM exchange and distortions determine the Q-dependence and redistribution of the intensities of the intra- and inter-doublet INS transitions in the 2(S=1/2) states as well as the intensities of the EPR transitions. The peculiarities of the INS and EPR spectra of the V3 ring of V15 quantum molecular magnet and EPR spectra of the V3 and Cu3 nanomagnets are described by the isosceles Heisenberg model with the DM exchange. Spin chirality and spin structure of the Cu3 and V3 nanomagnets with the Dzialoshinsky-Moriya (DM) exchange interaction are analysed in the vector and scalar spin chirality models. The vector chirality model describes the field, orientation and deformation dependence of the spin chirality κn. The spin chirality is formed by the DM interaction and depends on the sign of the DM parameter Gz. The DM exchange and distortions determine the degree of chirality κn<1 in the isosceles clusters.

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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.

Downloads: 19

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.

Downloads: 20