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Partial thermal reduction of ammonium paratungstate tetrahydrate

Evolved gas analysis (TG/DTA-MS) and solid state studies (XRD, FTIR)

Journal of Thermal Analysis and Calorimetry
Authors:
I. Szilágyi
,
J. Madarász
,
F. Hange
, and
G. Pokol

Abstract  

Thermal decomposition of ammonium paratungstate tetrahydrate, (NH4)10[H2W12O42]4H2O has been followed by simultaneous TG/DTA and online evolved gas analysis (TG/DTA-MS) in flowing 10% H2/Ar directly up to 900C. Solid intermediate products have been structurally evaluated by FTIR spectroscopy and powder X-ray diffraction (XRD). A previously unexplained exothermic heat effect has been detected at 700–750C. On the basis of TG/DTA as well as H2O and NH3 evolution curves and XRD patterns, it has been assigned to the formation and crystallization heat of γ-tungsten-oxide (WO2.72/W18O49) from β-tungsten-oxide (WO2.9/W20O58) and residual ammonium tungsten bronze.

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Kinetic analysis of thermogravimetric data. X

Thermal decomposition of some tris-ethylenediamine-cobalt(III) and chromium(III) complexes

Journal of Thermal Analysis and Calorimetry
Authors:
J. Zsakó
,
Cs. Várhelyi
,
G. Liptay
, and
K. Szilágyi

A study was made of the thermal decompositions of 22 derivatives of[M(en) 3]X 3 type complexes. Partial de-amination leading to the formation of[M(en) 2 X 2]X type complexes occurs in the case ofM=Cr(III) ifX=Cl, Br, I orNCS, but in the case ofM=Co(III) it is possible only ifX=Cl. In other cases redox reactions hinder the formation of stable intermediates. Kinetic parameters were derived for the dehydration of 19 compounds.

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Abstract  

Inclusion complexes of Lippia sidoides essential oil and β-cyclodextrin were obtained by slurry method and its solid powdered form was prepared using spray drying. The influence of the spray drying, as well as the different essential oil:β-cyclodextrin ratio on the characteristics of the final product was investigated. With regard to the total oil retention 1:10 mass/mass ratio as optimal was found between the essential oil and β-cyclodextrin. Thermoanalytical techniques (TG, EGD, TG-MS) were used to support the formation of inclusion complex and to examine their physicochemical properties after accelerated storage conditions. It may be assumed that the thermal properties of the complexes were influenced not only by the different essential oil/ β-cyclodextrin ratio but also by the storage conditions. In the aspect of their thermal stabilities, complex prepared with 1:10 m/m ratio (essential oil:β-cyclodextrin) was the most stable one.

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Abstract  

A number of 7 complexes of the [Co(DH)2(amine)2)]I type (DH2 stands for dimethyloxime) have been studied by means of thermogravimetry and differential scanning calorimetry in nitrogen atmosphere, by using heating rates of 2.5, 5 and 10 K min–1. In all cases an endothermal deamination reaction occurs leading to the relatively stable [Co(DH)2I(amine)] intermediate. For this reaction apparent kinetic parameters have been derived. The influence of heating rate is discussed. The validity of a linear and a non-linear kinetic compensation law was verified.

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Acta Alimentaria
Authors:
K. Szentmihályi
,
M. Szilágyi
,
J. Balla
,
L. Ujhelyi
, and
A. Blázovics

Magnesium participates in numerous enzymatic reactions in the human body and it has essential role in the maintenance of the antioxidant system. Since several magnesium compounds have been applied in the food and pharmaceutical industry, our purpose was to investigate the antioxidant/free radical scavenging activity of some magnesium compounds in vitro. The antioxidant/prooxidant effect of inorganic salts (e.g. MgCl2) and organic complexes (e.g. Mg-gluconate) was determined with chemiluminometric method (H2O2/•OH-microperoxidase-luminol) and heme mediated LDL oxidation (LDL-heme-H2O2 ) in vitro. It has been stated that the chemiluminescence method and LDL (low density lipoprotein) oxidation measurement is applicable in the presence of magnesium salts and complexes. Most of the compounds do not generate free radicals and the antioxidant/prooxidant effect depends on the quality of the ligand and the concentration. In the concentration range used, some representatives of the magnesium compounds (MgO, Mg-gluconate, Mg-polygalacturonate) investigated showed radical generating activity measured with chemiluminescence method, whereas the LDL oxidation has not been affected. Magnesium citrate and malate proved to be antioxidants measured with the chemiluminescence method and they slightly accelerate the LDL oxidation in the system and in the concentration applied. In vitro some of the ligands of magnesium compounds showed antioxidant activities.

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Acta Veterinaria Hungarica
Authors:
Beáta Kovács
,
Mathilda Toussaint
,
E. Gruys
,
Ibolya Fábián
,
L. Szilágyi
,
J. Janan
, and
P. Rudas

Serum amyloid A (SAA) is of interest as the circulating precursor of amyloid A protein, the fibrillar component of AA (secondary) amyloid deposits, and also as an extremely sensitive and rapid major acute phase protein. Serum concentrations of acute phase proteins (APPs) provide valuable information about the diagnosis and prognosis of various diseases, and thus the relevance of APPs for monitoring the health status of domestic animals is widely accepted. More importantly, the measurement of SAA concentration assists in assessing the prognosis in secondary amyloidosis, which is a common disease of geese, affecting an increasing number of animals. In the present study we introduce a highly sensitive goose-specific ELISA method for measuring SAA concentration in goose serum or plasma samples. Samples were taken from geese of the Landes Grey and Hungarian White breeds, which were stimulated for an acute phase reaction by administration of a commercially available fowl cholera vaccine containing inactivated Pasteurella multocida . Strong and characteristically rapid acute phase responses were measured in both breeds, peaking at approximately 24 h after inoculation. The maximum SAA concentration was 1200 μg/ml. At 72 h post-inoculation, the concentrations returned to pre-inoculation values. There was significantly (p = 0.004) less intense response in the control groups; however, a very mild increase of SAA levels was detected due to the stress inevitably caused by the sampling procedure.

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Abstract  

This paper discusses the changes in the structure and thermal reduction of nanosize hexagonal ammonium tungsten bronze (HATB), (NH4)0.33−xWO3−y, which were caused by K+ ion exchange (doping) and studied by XRD, XPS, 1H-MAS NMR, FTIR, SEM and TG/DTA-MS. Comparison of the cell parameters of undoped and doped HATB revealed that both a and c cell parameters decreased after the ion exchange reaction, which showed that smaller K+ ions partly replaced the larger NH4 + ions in the hexagonal channels of HATB. After the reaction, from the hexagonal channels less NH3 evolved, which also supported the incorporation of K+ ions into the hexagonal channels.

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Journal of Thermal Analysis and Calorimetry
Authors:
I. Szilágyi
,
Judit Pfeifer
,
C. Balázsi
,
A. Tóth
,
Katalin Varga-Josepovits
,
J. Madarász
, and
G. Pokol

Abstract  

We studied the thermal stability of different hexagonal tungsten trioxide, h-WO3 samples, which were prepared either by annealing hexagonal ammonium tungsten bronze, (NH4)0.33−xWO3−y, or by soft chemical synthesis from Na2WO4. The structure and composition of the samples were studied by powder XRD, SEM-EDX, XPS and 1H-MAS NMR. The thermal properties were investigated by simultaneous TG/DTA, on-line evolved gas analysis (TG/DAT-MS), SEM and in situ powder XRD. The preparative routes influenced the thermal properties of h-WO3 samples, i.e. the course of water release, the exothermic collapse of the hexagonal framework and the phase transformations were all affected.

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