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Kinetic analysis of thermogravimetric data

XXVIII Thermal decomposition of some metal and ammonium salts of hexabromoplatinic acid

Journal of Thermal Analysis and Calorimetry
Authors:
G. Liptay
,
J. Zsakó
,
Cs. Várhelyi
, and
Cs. Novák
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The effect of sulfadiazine on dipalmitoylphosphatidylethanolamin-dipalmitoylphosphatidylglycerol-water (DPPE-DPPG/water, 20 mass/mass%, with 0.2 DPPG/DPPE+DPPG molar ratio) vesicles considered as a model system of the cytoplasmic bacterial membranes was studied using DSC and freeze-fracture methods. The sulfadiazine/lipid molar ratio was varied from 10-3 up to 1. It was found that the DPPE-DPPG/water system is drastically affected by the sulfadiazine, but there is no concentration effect in a wide range of sulfadiazine/lipid molar ratios from 10-2 up to 2·10-1. The DSC and freeze-fracture methods reveal that a homogeneous incorporation of the sulfadiazine molecules occurs in the liquid crystalline phase while in the gel phase separation appears. The different local structures can be classified into two different types: vesicle-like and block-type. Although the surface morphology of the domains of both types shows lamellar arrangement, the blocks are constituted from closely packed long units.

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Abstract  

Differential Scanning Calorimetry (DSC), thermogravimetry/derivative thermogravimetry (TG/DTG) and infrared spectroscopy (IR) techniques were used to investigate the compatibility between prednicarbate and several excipients commonly used in semi solid pharmaceutical form. The thermoanalytical studies of 1:1 (m/m) drug/excipient physical mixtures showed that the beginning of the first thermal decomposition stage of the prednicarbate (T onset value) was decreased in the presence of stearyl alcohol and glyceryl stearate compared to the drug alone. For the binary mixture of drug/sodium pirrolidone carboxilate the first thermal decomposition stage was not changed, however the DTG peak temperature (T peak DTG) decreased. The comparison of the IR spectra of the drug, the physical mixtures and of the thermally treated samples confirmed the thermal decomposition of prednicarbate. By the comparison of the thermal profiles of 1:1 prednicarbate:excipients mixtures (methylparaben, propylparaben, carbomer 940, acrylate crosspolymer, lactic acid, light liquid paraffin, isopropyl palmitate, myristyl lactate and cetyl alcohol) no interaction was observed.

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Solid inclusion complexes of TolperisoneHCl with five various cyclodextrins were prepared by kneading and spray drying. The complex formation between the drug and the cyclodextrins were proven using thermoanalytical methods, X-ray diffraction, IR spectroscopy. The results of the solid state investigations were supported by the liquid phase investigations, such solubility and parition constant measurements and stability constant determination. Among all cyclodextrins used the β- and γ-CD-s were found to be the best complexing agents.

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Kinetic analysis of thermogravimetric data

XXVII. Thermal decomposition of some metal and ammonium salts of hexachloroplatinic acid

Journal of Thermal Analysis and Calorimetry
Authors:
J. Zsakó
,
G. Liptay
,
Cs. Várhelyi
,
Cs. Novák
, and
I. Ganescu

Nineteen salts of hexachloroplatinic acid with monovalent metals, aromatic and heterocyclic amines and phosphine were obtained and characterized by chemical analysis. The thermal decomposition of these complexes was studied by means of derivatograph and differential scanning calorimetry. The nature of the pyrolysis processes is discussed. From the TG curves, kinetic parameters were derived for different stages of the thermal decompositions.

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Abstract  

Microencapsulation of Lippia sidoides essential oil was carried out by spray drying. Blends of maltodextrin and gum arabic were used as carrier. Spray dried microparticles were characterized using conventional (thermogravimetry, evolved gas analysis) and combined (thermogravimetry-mass spectrometry analysis) thermal analysis techniques in order to evaluate the abilities of carriers with different compositions in retaining and in releasing the core vs. dynamic heating. Thermal analysis was useful to evaluate the physico-chemical interactions between the core and carriers and to determine the protective effect of the carriers on the evaporation of essential oil.

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Abstract  

The purpose of the present work was to study the compatibility of metronidazole with different pharmaceutical excipients (hydroxypropyl methylcellulose, poly(ethylene oxide), microcrystalline cellulose, dicalcium phosphate dihydrate, and anhydrous dicalcium phosphate) using differential scanning calorimetry and diffuse reflectance spectroscopy. Dicalcium phosphate dihydrate was the only excipient that showed interaction with metronidazole even before storage. Changes referring to a possible transition to dihydrate form were observed in the thermal curves of anhydrous dicalcium phosphate after four weeks of storage. Although dicalcium phosphate dihydrate can be replaced by the anhydrous form in pharmaceutical formulations, the observed transition might negatively influence the stability of dosage forms.

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