Biomedical subjects

Marieta Nichifor

Publications and source records attributed to Marieta Nichifor.

4 recordsLinked to original sources

PubMed2006

Transport properties of some cationic polysaccharides 2. Charge density effect.

The charge density effect on the behavior of some cationic polysaccharides in aqueous and nonaqueous (methanol) solutions was studied by viscometric and conductometric measurements. The polyelectrolytes investigated contain quaternary ammonium salt groups, N-alkyl-N,N-dimethyl-2-hydroxypropylene ammonium chloride, attached to a dextran backbone. This new class of polyelectrolytes has various linear charge density parameters, xi, located below and above the critical threshold value of counterions condensation, xi(c)=1(xi=0.25-3.18). The viscometric data revealed that all copolymers exhibit a polyelectrolyte behavior and were plotted in the terms of Rao equation. The conductometric measurements of solutions of these copolymers were presented as a function of polymer concentration and charge density. The results were analyzed within the Manning's theory and lower experimental values of the equivalent conductivity than the theoretical ones were found. Possible reasons of this discrepancy have been discussed. The interaction parameters were evaluated and these were found to depend on both the polymer concentration and the charge density. The conductometric behavior of these cationic polysaccharides has shown that counterion condensation is not a threshold phenomenon, their association to the charged groups of the polyions taking place for xi>1 as well as xi<1.

Journal Article↗

PubMed2005

Thermodynamics of self-assembling of hydrophobically modified cationic polysaccharides and their mixtures with oppositely charged surfactants in aqueous solution.

Microcalorimetric techniques, combined with turbidity measurements, were used to study the thermodynamics of self-assembling of hydrophobically modified cationic polysaccharides and their mixtures with oppositely charged surfactants in aqueous solution. The studied polyelectrolytes were a series of polymers based on dextran having pendant N-(2-hydroxypropyl)-N,N-dimethyl-N-alkylammonium chloride groups randomly distributed along the polymer backbone. The parameters for their micellization process are evaluated from the results of the observed dilution enthalpy curves and compared with those of the related cationic surfactants (DTAC and CTAC). The microcalorimetric results for the mixed systems (polyelectrolytes with oppositely charged surfactants) are used along with turbidity measurements to characterize systematically the thermodynamics of their interaction. The phase behavior is described and the interaction enthalpies are derived from the differences between the observed enthalpy curves with and without polyelectrolyte. Therefore, we discuss in detail the effect of changing the alkyl chain length of polyelectrolyte pendant groups, the molecular weight of the dextran backbone, and the temperature of the measurements on the interactions between polyelectrolyte and surfactant.

Cations↗

PubMed2005

Thermodynamic characterization of the interaction behavior of a hydrophobically modified polyelectrolyte and oppositely charged surfactants in aqueous solution: effect of surfactant alkyl chain length.

We have used a precision isothermal titration microcalorimeter (ITC) to measure the enthalpy curves for the interaction of a hydrophobically modified polyelectrolyte (D40OCT30) with oppositely charged surfactants (SC(n)S) in aqueous solution. D40OCT30 is a newly synthesized polymer based on dextran having pendant N-(2-hydroxypropyl)-N,N-dimethyl-N-octylammonium chloride groups randomly distributed along the polymer backbone with degree of substitution of 28.1%. The employed anionic surfactants are sodium octyl sulfate (SC(8)S) and sodium tetradecyl sulfate (SC(14)S). Microcalorimetric results along with turbidity and kinematic viscosity measurements demonstrate systematically the thermodynamic characterization of the interaction of D40OCT30/SC(n)S. A three-dimensional diagram with the derived phase boundaries is drawn to describe the effect of the alkyl chain length of surfactant and of the ratio between surfactant and pendant groups on the interaction. A more complete picture of the interaction mechanism for D40OCT30/SC(n)S systems is proposed here.

Journal Article↗

PubMed2002

Polymeric materials containing bile acids.

Bile acids are biological compounds in the body that have interesting properties and have been used to make special chemical structures in molecular recognition. Various polymers have been synthesized from bile acids. The materials should preserve some of the properties of bile acids, such as biocompatibility, high stability of the steroid nucleus, reactivity of the side groups, optical activity and self-assembling capacity. The synthesis and applications proposed for such polymers are discussed.

Bile Acids and Salts↗