Chemistry Journal of Moldova

Physical chemistry and chemical physics

COMPARATIVE KINETICS STUDY OF THE THERMAL AND THERMO-OXIDATIVE DEGRADATION OF A POLYSTYRENE-CLAY NANOCOMPOZITE BY TGA AND DSC

Author(s):

Ion Dranca, Nicon Ungur,Tudor Lupascu, Oleg Petuhov


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2010 Volume 5, no.2
Pages: 68-72
Keywords: degradation; fire resistance; nanocomposites; thermogravimetric analysis (TGA); differential scanning calorimetry (DSC).
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2010.05(2).09

Graphical Abstract:
The methods of thermogravimetry (TGA) and differential scanning calorimetry (DSC) have been used to study the thermal and thermo-oxidative degradation of polystyrene (PS) and a PS-clay nanocomposite. An advanced isoconversional method has been applied for kinertic analysis. Introduction of the clay phase increasers the activation energy and affects the total heat of degradation, which suggests a change in the reaction mechanism. The obtained kinetic data permit a comparative assessment of the fire resistance of the studied materials.

Downloads: 17

METALLIC COMPOUNDS IN THE PHASE OF THE RETICULATED IONIC POLYMERS

Author(s):

Vasilii Gutsanu, Constantin Turta, George Filoti


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2010 Volume 5, no.2
Pages: 73-82
Keywords: ion exchangers, Mossbauer spectra, iron, superparamagnetic, complexes, polymer phase.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2010.05(2).10

Graphical Abstract:
Using the Mossbauer spectroscopy and other physical methods it was demonstrated the presence of different iron compounds like β-FeOOH, α-Fe2O3, and jarosite mineral type compounds: (R4N,H3O)[Fe3(OH)6(SO4)2] or coordination modes: {RCOO-Fe(L4)-OOCR}1+, {R-CO2=Fe(X2)=O2C-R}n, {R-COO-Fe(X4)-OOC-R}n, and {(-NCH2CH2N-)= Fe(X2) =(-NCH2CH2N-)}, where X= H2O, OH-, SO42-., n= from 3- to 1+ in the ion-exchange resins (KU-2, AN-31, AV-17, Varian – AD, EDE-10P) after the contact with sulphate of iron(III) solutions at different conditions: type of solvent, temperature, air atmosphere. In special conditions the ultrafine superparamagnetic particles of Fe2O3 have been obtained.

Downloads: 16

STOPPED-FLOW SPECTROPHOTOMETRIC STUDIES OF THE KINETICS OF INTERACTION OF DIHYDROXYFUMARIC ACID WITH THE DPPH FREE RADICAL

Author(s):

Secara Natalia


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2010 Volume 5, no.2
Pages: 83-87
Keywords: DPPH; antioxidant activity; stoichiometry; stopped-flow; kinetics; dihydroxyfumaric acid.
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DOI:
dx.doi.org/10.19261/cjm.2010.05(2).11

Graphical Abstract:
 The reaction of dihydroxyfumaric acid with the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) was studied using the stopped-flow method, in order to describe the reaction kinetics. Dihydroxyfumaric acid reacts very rapidly with DPPH, the reaction being completed in several minutes. This 2-stoichiometric reaction proceeds in two stages, with reaction orders of 1 and 0.76 with respect to DPPH, and 0.5 and 0.3 with respect to DHF, respectively. The rate constant of the two stages of the reaction were found to be 39.1 (L/mol•s) and 0.0012 (s-1) at 20º C and pH 4.0.

Downloads: 19

AB INITIO STUDY OF CHEMICAL ACTIVATION AND HYDROGENATION OF WHITE PHOSPHORUS IN REACTION WITH RHODIUM TRIHYDRIDE COMPLEX

Author(s):

Iolanta I. Balan, Natalia N. Gorinchoy


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2011 Volume 6, no.2
Pages: 84-90
Keywords: white phosphorus, triphos, rhodium trihydride complex, ab initio calculations.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2011.06(2).18

Graphical Abstract:
 The four-stage mechanism of reaction of the rhodium trihydride complex [(triphos)RhH3] (triphos=1,1,1-tris(diphenylphosphanylmethyl)ethane) with the white phosphorus molecule resulting in the phosphane and the cyclo-P3 complex [(triphos)M(η3-P3] is analyzed on the basis of ab initio calculations of reactants, products, and intermediate complexes of reaction. It is shown that generation of the transient complex  [(triphos)RhH(η1:η1-P4)] followed by intramolecular hydrogen atom migration from the metal to one of the phosphorus atoms is the energetically favourable process. Calculations also show that P4 molecule is activated by coordination to the above complex: the metal-bonded P-P edge is broken, and the tetrahedron P4 is opened to form the butterfly geometry. This activation is realized mainly due to the one-orbital back donation of 4d-electron density from the atom of Rh to the unoccupied antibonding triple degenerate t1*-MO of P4.

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PHARMACEUTICAL AMORPHOUS ORGANIC MATERIALS CHARACTERIZATION BY USING THE DIFFERENTIAL SCANNING CALORIMETRY AND DYNAMIC MECHANICAL ANALYSIS

Author(s):

Ion Dranca, Igor Povar and Tudor Lupascu


Field: Physical chemistry and chemical physics
Type: Research paper
Issue: 2011 Volume 6, no.2
Pages: 91-95
Keywords: DSC –differential scanning calorimetry; DMA –dynamic mechanical analysis; drugs; excipients; glass transition; α- and β –relaxations; crystallization; kinetics.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2011.06(2).19

Graphical Abstract:
 This research has been carried out in order to demonstrate the use of differential scanning calorimetry (DSC) in detecting and measuring α- and β-relaxation processes in amorphous pharmaceutical systems. DSC has been employed to study amorphous samples of poly (vinylpyrrolidone) (PVP), indomethacin (InM), and ursodeoxycholic acid (UDA) that are annealed at temperature (Ta) around 0.8 of their glass transition temperature (Tg). Dynamic mechanical analysis (DMA) is used to measure β- relaxation in PVP. Yet, the DSC has been used to study the glassy indomethacin aged at 0 and -10 oC for periods of time up to 109 and 210 days respectively. The results demonstrate the emergence of a small melting peak of the α-polymorph after aging for 69 days at 0°C and for 147 days at -10°C (i.e., ~55°C below the glass transition temperature) that provides evidence of nucleation occurring in the temperature region of the β-relaxation.

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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.

Downloads: 24

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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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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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.

Downloads: 6