Acid-base equilibria of polyvalent electrolytes and theoretical description of polyelectrolyte behavior in electrokinetic separations.

The problem of the theoretical description of the dissociation of polyvalent electrolytes is considered. It is shown that the traditional model which assumes some constant microstate mobility values may have limited applications, since for each microstate the rate of conversion into other states is strongly dependent on pH and thus it may often become comparable with the characteristic times of other important processes (ionic atmosphere relaxation, biopolymer acceleration by electric field). The question of correct modelling of the electrophoretic flux, electrophoretic mobility and conductivity is discussed.

Membrane photopotential generation by interfacial differences in the turnover of a photodynamic reaction.

The adsorption of a membrane-impermeable photosensitizer to only one membrane leaflet is found to trigger a localized photodynamic reaction; i.e., the amount of carbonyl cyanide m-chlorophenylhydrazone (CCCP) molecules damaged in the leaflet facing the photosensitizer is roughly identical to the total amount of CCCP inactivated. Whereas the latter quantity is assessed from the drop in membrane conductivity G, the former is evaluated from the photopotential phi that is proportional to the interfacial concentration difference of the uncoupler. Localized photodestruction is encountered by CCCP diffusion to the site of photodamage. A simple model that accounts for both photoinhibition and diffusion predicts the dependence of the photopotential on light intensity, buffer capacity, and pH of the medium. It is concluded that only a limited amount of the reactive oxygen species responsible for CCCP photodamage diffuses across the membrane. If the concentration of reactive oxygen species is decreased by addition of NaN(3) or by substituting aqueous oxygen for argon, phi is inhibited. If, in contrast, their life time is increased by substitution of H(2)O for D(2)O, phi increases.

Adsorption of haematoporphyrins on the planar bilayer membrane.

Adsorption of haematoporphyrin derivatives with different hydrophobicities of peripheral groups on a planar bilayer lipid membrane (BLM) was studied in the dark and upon illumination by the visible light. Haematoporphyrin molecules were shown to adsorb on the BLM as anions. The adsorption changed the boundary potential at the membrane/water interface, in particular, it altered the potential in the diffuse part of the double layer outside the membrane and increased an additional unscreenable potential drop inside it. Illumination decreased the value of the negative potential drop due probably to the appearance of a positive charge in the haematoporphyrin macrocycle. The adsorption of haematoporphyrins affected the BLM conductivity induced by different ionophores, which can be explained by changes in membrane structure. Haematoporphyrin derivatives with higher hydrophobicities adsorbed deeper inside the membrane, caused greater changes in its structure and displayed a stronger photodynamic effect.

Photosensitized damage of bilayer lipid membrane in the presence of haematoporphyrin dimethylether.

The variations in electrical conductivity and surface tension of planar bilayer lipid membranes (BLMs) sensitized by a haematoporphyrin dimethylether (HpDME) on visible light irradiation are reported. The irradiation of BLMs immediately leads to a decrease in membrane surface tension. On irradiation the conductivity of BLMs remains constant for a certain period of time (induction time), followed by an increase, terminated by membrane breakage. The induction time is not dependent on stirring of the solution, the addition of azide or ferricyanide to the solution, the addition of antioxidant to the lipid or substitution of air for argon in the cell. The induction time decreases for repeated irradiations or for any new BLM formed in the same cell immediately after the previous membrane has been broken. The conductivity shift consists of reversible and irreversible components. These results suggest that the irradiation of BLMs sensitized by HpDME leads to an accumulation of photoproducts in the membrane which induce pore formation and to a decrease in BLM stability when the concentration of the photoproducts exceeds a critical level.

[Modeling of damage to cell membranes during photodynamic therapy: photosensitization of planar lipid bilayers by hematoporphyrin dimethyl ether]. / Modelirovanie povrezhdeniia kletochnykh membran pri fotodinamicheskoi terapii: fotosensibilizatsiia ploskogo lipidnogo bisloia dimetilovym efirom gematoporfirina.

The variations of electrical conductance of planar bilayer lipid membranes (BLM) sensitized by hematoporphyrin dimethyl ether under visible light illumination were studied. The conductance of BLM does not change for some period after switching on the light, then an increase in the conductance starts and the membrane breaks. This "induction" time does not depend on addition of azide or ferricyanide to the solution, on addition of BHT to the lipid and on substitution of air for argon in the cell. The induction time for any new BLM, formed in the same cell immediately after the previous membrane was broken, is shorter. The variation of BLM boundary potentials during induction time was not observed. The results obtained suggest that the photodamage of BLM sensitized by HPD leads to accumulation of uncharged reaction products and oxygen does not take part in this process.