Biomedical subjects

S Zalac

Publications and source records attributed to S Zalac.

3 recordsLinked to original sources

PubMed2000

Charged Surfaces and Interfacial Ions.

Interfacial charge in a solid/liquid system is due to interactions of ions with surface sites affected by the electrostatic potential that is a consequence of their accumulation. The present theoretical approach is based on the so-called Surface Complexation Model that has several modifications known as either the 1-pK, the 2-pK, or the "MUSIC" model. These models assume different surface reactions and their equilibrium constants, taking into account electrostatic interactions. For that purpose the relationships between potentials affecting the state of interfacial ions and their surface densities need to be known, so that a certain model of the electrical interfacial layer should be introduced. The complexity of the problem results in the use of a variety of different theoretical approaches that cannot be distinguished experimentally. This article discusses several aspects of the problem, such as counterion association, structure of the electrical interfacial layer, potential-charge relationships, surface potentials, the zero charge condition, enthalpy of surface reactions, and the influence of the interfacial ionic equilibrium on the colloid stability. Copyright 2000 Academic Press.

Journal Article↗

PubMed1999

Electrostatic Contribution to the Enthalpy of Charging at Hematite/Electrolyte Interface.

A calorimetry study of hematite surface reactions is reported, with special emphasis on the estimation of the electrostatic contribution to the enthalpy of charging. The calorimetry titrations were performed outside the point of zero charge region where the electrostatic contribution is significant. The results were interpreted by the surface complexation model. The interpretation enabled the evaluation of standard protonation and deprotonation enthalpies as well as the electrostatic contribution to these quantities. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Paracetamol-propyphenazone interaction and formulation difficulties associated with eutectic formation in combination solid dosage forms.

Polymorphic behaviours of paracetamol and propyphenazone and interaction between these two compounds were investigated using differential scanning calorimetry (DSC), X-ray powder diffraction and Fourier transform-infrared (FT-IR)-spectroscopy. Binary mixtures containing various ratios of the compounds were prepared as physical and fused mixtures and analysed by DSC to study their thermal behaviours. Phase diagrams obtained from the melting endotherms of the binary mixtures demonstrated formation of an eutectic mixture at a paracetamol-propyphenazone combination of about 35:65 (w/w) with an eutectic temperature of 56 degrees C. The FT-IR spectroscopy revealed no chemical interaction due to eutectic formation, and a lower degree of crystallinity of the eutectic mixture than individual substances was observed by X-ray powder diffraction analysis. The DSC and X-ray powder diffraction data demonstrated a polymorphic change in propyphenazone as a result of melting of the compound. Tablets, containing both paracetamol and propyphenazone in a combination formulation and prepared using standard wet granulation technology, were found to have physical instability when packed in either polyvinylchloride// aluminium or polyvinylchloride/polyvinyldienechloride// aluminium blisters and stored for one month at 40 degrees C with either 75% relative humidity or without any humidity control. The instability of the tablets was more apparent under the high humidity condition.

Acetaminophen↗