Patrycja Dynarowicz-Ła̧tka

Grazing Incidence Diffraction and X-ray Reflectivity Studies of the Interactions of Inorganic Mercury Salts with Membrane Lipids in Langmuir Monolayers at the Air/Water Interface

The interactions of mercury ions with the membrane phospholipids are considered to be of great importance regarding the toxicity of this metal in living organisms. To obtain deeper insight into this problem, we performed systematic studies applying the Langmuir technique complemented with synchrotron X-ray scattering methods (grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XR)). We focused our attention on the interactions of inorganic mercury salts dissolved in the aqueous subphase with lipid monolayers, formed by selected membrane phospholipids, namely, dipalmitoylphosphatidylglicerol (DPPG), dipalmitoylphosphatidylcholine (DPPC), 1-octadecyl 2-sn-phosphatidylcholine (lyso-PC), and sphingomyelin (SM). Two different inorganic mercury salts, one of a hydracid, HgCl(2), and the other of an oxacid, Hg(NO(3))(2), have been investigated. Our results proved that the elastic properties of phospholipid monolayers are a key factor regarding the interactions with mercury ions. Significant differences in mercury ions complexation are observed with double-chain phospholipids (such as DPPG and DPPC) forming fluid layers of low compressibility and phospholipids forming more compressible films (like SM and lyso-PC). Namely, important changes in the monolayer characteristic were observed only for the latter kind of lipids. This is an important finding taking into account the accumulation of mercury in the central nervous system and its neurotoxic effects. SM is one of the most abundant lipids in neurons shells and therefore can be considered as a target lipid complexing mercury ions.

Quantitative treatment of surface potentials in Langmuir films from aromatic amphiphiles

It is shown that the surface potentials of Langmuir monolayers from aromatic compounds can be interpreted using the three-layer capacitor model of Demchak and Fort, with the same local dielectric constants employed for aliphatic compounds. Based on new data for monolayers from an acid, amine and ester compounds with an aromatic hydrophobic part, we show that the dielectric constant for the monolayer/water interface region is 6±1. Good agreement between experiment and theory was obtained by taking the dielectric constant of the monolayer/interface as 3.0±0.6, which are essentially the same as those obtained for long tail aliphatic compounds.

Langmuir monolayer study toward combined antileishmanian therapy involving amphotericin B and edelfosine.

In this work, the results of comparative studies on the effect of lysophospholipid analogue, edelfosine (ED), and its mixtures with the polyene antibiotic, amphotericin B (AmB), on model erythrocyte and parasite membranes are presented. Both compounds are known for their antileishmanian activity; however, the application of AmB is limited by its toxicity, while the treatment with alkyl-lysophospholipids (edelfosine) is expensive in addition to its lower therapeutic activity as compared to the polyene. An additional problem is the emergence of resistance to both groups of drugs. The foregoing facts inspired the investigations toward combined amphotericin B/alkyl-lysophospholipid therapy. In this aspect, the effect of edelfosine on model erythrocyte versus parasite membrane has been verified by the incorporation of the drug into binary sterol/phospholipid monolayer of the proportion corresponding to the respective cellular membrane. Afterward, amphotericin B/edelfosine mixtures of various proportions (1:9; 1:1, and 9:1) have been added into sterol/phospholipid model membranes in the concentration of 1, 5, and 10%. The interactions between amphotericin B and edelfosine in mixed monolayers have also been investigated. The obtained results indicate that differences in the organization of erythrocyte versus parasite membranes are of great importance for selectivity of edelfosine toward the parasite membrane. The mixtures of drugs practically do not modify the properties of model erythrocyte membrane; however, their incorporation in the parasite membrane is thermodynamically unfavorable and causes membrane destabilization. The strongest differences in the influence of drug mixtures on erythrocyte versus parasite model membrane occur for 1% content of 1:9 and 1:1 AmB/edelfosine mixture. Moreover, when edelfosine is combined with amphotericin B, a decrease in edelfosine concentration needed to induce a similar effect on parasite membranes as edelfosine alone does is observed. As a consequence of strong interactions between edelfosine and amphotericin B, the decrease of the activity of their mixtures on model membranes was found.

Langmuir monolayers of polyphenylene carboxylic acids

Abstract A series of polyphenyl carboxylic acids with 3–6 uncondensed benzene rings and some of their analogues with a nitro and/or cyano group were synthesized and investigated at the air-water interface. They all can be treated as substituted m-terphenyls. It is determined that a system with at least four phenyl groups with the carboxyl group at a peripheral position are a prerequisite for the ability of monolayer formation. Their isotherms exhibit a large plateau attributed to the formation of bilayers.