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Journal of Thermal Analysis and Calorimetry
Authors: Suzana Samaržija-Jovanović, Vojislav Jovanović, Sandra Konstantinović, Gordana Marković, and Milena Marinović-Cincović

Introduction Urea–formaldehyde resins are the most important type of the so-called amino plastic resins. Amino resins are often used to modify properties of other materials. These resins are added during the processing of

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Andersson, G., Andersson, L. and Carlström, G. (1986): Determination of milk urea by flow injection analysis. J. Vet. Med. A 33 , 53-58. Determination of milk urea by flow injection

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halloysite can be intercalated almost completely with dimethyl sulphoxide or hydrazine, in the light of potential industrial applications these hazardous compounds should be avoided. Expansion of the layers with urea—a more friendly reagent—can be made either

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of solution of amino acid in water [ 6 ] and the value of parameter of pair interaction of amino acid with urea in aqueous solution [ 7 ] which can serve as a criteria of hydrophobicity, proline is located between glycine and alanine. The

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Abstract  

The reaction of urea with ZnO was investigated by FTIR and TPD. It was found that urea was thermally decomposed into isocyanic acid on ZnO, and the adsorbed isocyanic acid reacted with ZnO to form zinc isocyanate. Catalytic evaluation showed that ZnO had high activity towards urea methanolysis in a batch reactor, and zinc element and isocyanate were all detected in the product solution. Furthermore, the soluble zinc content was proportional to the DMC yield. Sample analyses suggested that the soluble zinc existed in the form of Zn(NCO)2(NH3)2, which originated from the reaction of ZnO with urea. It was the complex (not ZnO) that catalyzed the urea methanolysis. Based on these observations, a possible mechanism was suggested.

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Abstract  

Joint results of the differential scanning calorimetry (DSC) and thermogravimetry (TG) experiments were the basis for the fusion enthalpy and temperature determination of the biuret (NH2CO)2NH (synthesis by-product of the urea fertilizer (NH2)2CO). Recommended values are Δm H = (26.1 ± 0.5) kJ mol−1, T m = (473.8 ± 0.4) K. The DSC method allowed for the phase diagrams of “water–biuret,” “water–urea,” “urea–biuret” binary systems to be studied; as a result, liquidus and solidus curves were precisely defined. Stoichiometry and decomposition temperature of the biuret hydrate identified, composition of the compound in “urea–biuret” system was suggested.

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Abstract  

Bismuth ferrite (BiFeO3) was obtained by a combustion reaction staring from two precursors systems, namely Fe(NO3)3 · 9H2O–Bi5O(OH)9(NO3)4 · 9H2O–glycine/urea with different metal nitrate/fuel molar ratios. The precursors’ thermal behavior is dependent on the fuel nature but practically independent to the fuel content. In glycine containing systems not all Bi2O3 is included into mixed oxides during the decomposition. Its presence was identified through the existence of two endothermic phase transitions (TDTA max at 745 and 818 °C) assigned to Bi2O3 α→δ transition, and its melting. The thermal investigations performed on oxides samples reveal for all oxides, independent on the precursor system, a similar behavior. For all the oxides was identified both the Curie temperature (which decreases with the annealing cycles) and the incongruent melting point (which is with ~10 °C higher for glycine generated oxides comparative with urea ones). The structural analysis shows in the case of the oxides prepared using urea as fuel, a faster evolution toward a single phase composition with the temperature, the formation of the BiFeO3 perovskite phase being completed in the temperature range of 500–550 °C. Only some traces of Bi36Fe2O57 were identified at the detection limit. TEM analysis performed on the BiFeO3 thermally treated at 500 °C for 3 h revealed the presence of small particles with an average size of ~33 nm and polycrystalline agglomerates with an average size of ~100 nm for glycine/urea derived oxides.

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Abstract  

The kinetics of bovine serum albumin (BSA) denaturation in the absence and the presence of urea was studied by the iso-conversional method and the master plots method using differential scanning calorimetry (DSC). The observed denaturation process was irreversible and approximately conformed to the simple order reaction, and the denaturation did not follow rigorously first-order kinetic model or other integral order reaction models. The denaturation temperature (T m), apparent activation energy (E a), approximate order of reaction (n), and pre-exponential factor (A) all distinctly decreased as the 2 mol L−1 urea was added, which indicated that the urea accelerated the denaturation process of BSA and greatly reduced thermal and kinetic stability of BSA. This study also demonstrated that the iso-conversional method, in combination with the master plots method, provides a valuable and useful approach to the study of the kinetic process of protein denaturation.

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Abstract  

New zinc(II) salicylate complex compounds of general formula (X-C6H3-2-(OH)COO)2Zn · Ln · xH2O (where X = H, 5-Cl; L = theophylline, urea; n = 2, 4; x = 1, 2, 4) were prepared and their thermal, spectral and biological properties were studied. It was found that the thermal decomposition of hydrated compounds starts with the release of water. During the thermal decomposition of anhydrous compounds, the release of salicylic acid, theophylline, urea, CO2, H2O and C6H5Cl takes place. Zinc oxide was found as the final product of the thermal decomposition heated up to 900 °C. The complexes were tested against bacteria, yeasts and filamentous fungi. The highest biological activity show 5-chlorosalicylate compounds.

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Abstract  

The standard molar enthalpies of solution at infinite dilution
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of glycylglycine, dl-alanyl-dl-alanine and glycylglycylglycine in aqueous solutions of potassium chloride and ethanol as well as of glycylglycine and glycylglycylglycine in the solutions containing urea and water have been determined by calorimetry at the temperature 298.15 K. Changes of solution enthalpy, expressed in a form so-called heterotactic interaction coefficients,
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were used for analysis of interactions occurring between the investigated solutes in water. The group contributions illustrating the interactions of KCl, urea and ethanol with selected functional groups in the peptide molecules, namely CH2, “pep,” and “ion” groups, were calculated and discussed.
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