Biomedical subjects

M Tomoaia-Cotişel

Publications and source records attributed to M Tomoaia-Cotişel.

4 recordsLinked to original sources

PubMed1990

Influence of stearic acid monolayers upon the procaine adsorption from underlying alkaline aqueous solutions.

Adsorption of procaine at the air/water interface and its penetration into stearic acid monolayers from aqueous subphase of pH 8 are studied by measuring surface tension of aqueous procaine solutions and by recording surface pressure vs. mean molecular area curves for stearic acid monolayers spread onto procaine solutions of different concentrations. The amount of procaine in the interface is derived by means of Gibbs' equation. Results are compared to those obtained earlier at pH 2 and on unbuffered subphases. With increasing pH an increasing procaine adsorption and procaine penetration is observed. This phenomenon is interpreted in terms of protolytic equilibria in which participate both surfactants procaine and stearic acid.

Adsorption↗

PubMed1989

Surface characteristics of phosphatidylglycerol phosphate from the extreme halophile Halobacterium cutirubrum compared with those of its deoxy analogue, at the air/water interface.

The relationship between area per molecule and surface pressure of monolayers of phosphatidylglycerol phosphate from extreme halophile Halobacterium cutrirubrum and its deoxy analogue, deoxyphosphatidylglycerol phosphate, spread at an air/water interface was examined. The effect of ionization of the primary and secondary acidic functions of the phosphate groups of the two lipids on surface characteristics of compression isotherms was determined by spreading monolayers on subphases with pH values ranging from below the apparent pKa of the primary ionization (pH 0) to greater than that of secondary ionization (pH 10.9). The limiting molecular area increases with decreasing pH below 2. Ionization of the primary phosphate functions of both phospholipids (with bulk pK1 values close to 4) is associated with a marked expansion of the films, as judged by values of limiting molecular area. Ionization of the secondary phosphate functions causes further expansion of the films, with the apparent pK2 of deoxyphosphatidylglycerol phosphate slightly less than that indicated for phosphatidylglycerol phosphate. Values of surface-compressibility modulus calculated from the surface characteristics of the phosphatidylglcerol phosphate monolayers showed that films spread on subphases with a pH of about the apparent pK1 of the primary phosphate functions were the least compressible. Increasing or decreasing subphase pH caused an increase in compressibility; this effect on compressibility was much less with monolayers of deoxyphosphatidylglycerol phosphate at high pH. The effect of inorganic counter-ions on monolayer characteristics of phosphatidylglycerol phosphate was examined by using subphases of NaCl concentrations varying from 0.01 to 1 M. The limiting molecular area was found to increase exponentially with respect to the subphase NaCl concentration.

Halobacterium↗

PubMed1987

Intermolecular interactions in lipid/carotenoid monolayers.

The collapse pressure at the air-water interface of monomolecular films of 1,2-distearoyl derivatives of phosphatidylcholine and digalactosyldiacylglycerol containing various proportions of the carotenoid astaxanthin was related to the composition of the monolayer. The results were analysed by using a regular-association approximation by which it is assumed that there is a stepwise formation of ABi-type associations where A and B represent the diacyl lipid and astaxanthin respectively and 1 less than or equal to i less than or equal to 6. This treatment provides an adequate description of the experimental data and permits calculation of equilibrium constants for the steps in complex-formation; each step is said to have the same equilibrium constant. The value for the collapse-surface-pressure increment associated with formation of ABi complexes was also derived. Calculated values of equilibrium constants and collapse-surface-pressure increments are greater for phosphatidylcholine/astaxanthin mixed monolayers than for digalactosyldiacylglycerol/astaxanthin mixed monolayers. These differences are discussed in terms of intermolecular interactions between components in the two systems.

Carotenoids↗

PubMedDate not supplied

Surface complexes of xanthophyll films with transition metal ions.

Compression isotherms of astaxanthin (AX; 3,3'-dihydroxy-4,4'-dioxo-beta-carotene) monolayers, recorded at the air/water interface show, on the one hand, the collapse pressure to depend on the subphase pH, indicating the ionisation of AX at high pH values, and on the other hand, the subphase Co2+ ions to have a condensing effect upon the monolayer and to entail the increase of its collapse pressure. The latter effects are assigned to surface complex formation. The interfacial tension at the benzene/water interface (the benzene phase containing AX, the water phase Co2+ ions) exhibit a maximum at a molar ratio AX: Co of about 3.6, pleading for the formation of relatively stable Co(AX)4 type interfacial complex. Geometric model and ligand field considerations show besides the dative type sigma-bond formation, the possibility of both dative and retrodative type pi-bond formation between Co2+ and the AX ligands. Under the working conditions used, the formation of a neutral non-electrolyte type complex of the composition [Co(LH)2L2] is postulated, where LH stands for the neutral AX molecule, L- for its anion.

Air↗