ABSTRACT
The purpose of this study was to investigate the interaction between diosgenin analogues [DioA: diosgenin acetate (DAc) and (25R)-5α,6ß-dihydroxyspirostan-3ß-ol acetate (DSol)] and cholesterol (Ch) monolayers at the air/water interface. The surface tension of pure and mixed lipid monolayers at 22 °C was measured by using the Langmuir method with a Teflon trough and a Nima 9002 tensiometer. The surface tension values were used to calculate the π-A isotherms and to determine the molecular surface areas. The interactions between Ch and each DioA resulted in significant deviations from the additivity rule. The theory described in this work was used to determine the stability constants, the areas occupied by one molecule of Ch-DAc or Ch-DSol, and the complex formation energy (Gibbs free energy) values.
Subject(s)
Cholesterol/metabolism , Diosgenin/analogs & derivatives , Diosgenin/metabolism , Membranes, Artificial , Cholesterol/chemistry , Surface Tension , TemperatureABSTRACT
Diosgenin (Dio) has shown many treatment properties, but the most important property is cytotoxic activity in cancer cells. In this study, we investigated monolayers of Dio, cholesterol (Ch), and phosphatidylcholine (PC) at the air/water interface. The measurements were carried with a Langmuir Teflon trough and a Nima 9000 tensiometer program. The surface tension values of pure and mixed monolayers were used to calculate π-A isotherms and determine molecular surface areas. We were able to demonstrate the formation of complexes between Dio and PC and Dio and Ch molecules also. We considered the equilibrium between individual components and the formed complexes. In addition, we established that diosgenin and the lipids formed highly stable 1:1 complexes.
Subject(s)
Air , Cholesterol/chemistry , Diosgenin/chemistry , Phosphatidylcholines/chemistry , Water , Algorithms , Models, Chemical , Molecular Structure , TemperatureABSTRACT
The objective of this research was to evaluate postmortem changes concerning electric charge of human erythrocytes and thrombocytes in fatal accidental hypothermia. The surface charge density values were determined on the basis of the electrophoretic mobility measurements of the cells conducted at various pH values of electrolyte solution. The surface charge of erythrocyte membranes after fatal accidental hypothermia increased compared to the control group within whole range of experimental pH values. Moreover, a slight shift of the isoelectric point of erythrocyte membranes towards high pH values was observed. The surface charge of thrombocyte membranes in fatal accidental hypothermia decreased at low pH compared to the control group. However, at pH range 4-9, the values increased compared to the control group. The isoelectric point of thrombocyte membranes after fatal accidental hypothermia was slightly shifted towards low pH values compared to the control group. The observed changes are probably connected with the partial destruction and functional changes of the blood cell structure.
Subject(s)
Blood Cells/metabolism , Cell Membrane/metabolism , Hypothermia/metabolism , Static Electricity , Adult , Aged , Autopsy , Blood Cells/chemistry , Blood Platelets/metabolism , Cell Membrane/chemistry , Erythrocyte Membrane/chemistry , Erythrocyte Membrane/metabolism , Erythrocytes/metabolism , Female , Humans , Hydrogen-Ion Concentration , Hypothermia/blood , Isoelectric Point , Male , Middle Aged , Young AdultABSTRACT
Monolayers of phosphatidylcholine (PC), tetradecanol (TD), hexadecanol (HD), octadecanol (OD) and eicosanol (E) and their binary mixtures were investigated at the air/water interface. The surface tension values of pure and mixed monolayers were used to calculate π-A isotherms. The surface tension measurements were carried out at 22 °C using a Teflon trough and a Nima 9000 tensiometer. The interactions between phosphatidylcholine and fatty alcohols (tetradecanol, hexadecanol, octadecanol, eicosanol) result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air/water interface was developed in order to obtain the stability constants, Gibbs free energy values and areas occupied by one molecules of PC-TD, PC-HD, PC-OD and PC-E complexes. We considered the equilibrium between the individual components and the complex and established that phosphatidylcholine and fatty alcohols formed highly stable 1:1 complexes.
Subject(s)
Fatty Alcohols/chemistry , Phase Transition , Phosphatidylcholines/chemistry , Unilamellar Liposomes/chemistryABSTRACT
Bilayer lipid membranes composed of phosphatidylcholine and isoleucine or phosphatidylcholine and tyrosine were investigated using electrochemical impedance spectroscopy. Interaction between membrane components causes significant deviations from the additivity rule which can be explained by formation of the domain structures. The surface area of domains was calculated based on derived equations. We suggest that the stoichiometry of phosphatidylcholine-isoleucine domain is equal 3:1. In the case of tyrosine-modified phosphatidylcholine membranes, domain with stoichiometry 7:1 should be taken into consideration.
Subject(s)
Dielectric Spectroscopy/methods , Isoleucine/chemistry , Lipid Bilayers/chemistry , Phosphatidylcholines/chemistry , Tyrosine/chemistryABSTRACT
The dependence of the interfacial tension of a phosphatidylethanolamine (PE) monolayer on the pH of the aqueous solution has been studied. A theoretical equation is derived to describe this dependence. A simple model of the influence of pH on the phosphatidylethanolamine monolayer at the air/hydrophobic chains of PE is presented. The contributions of additive phosphatidylethanolamine forms (both interfacial tension values and molecular area values) depend on pH. The interfacial tension values and the molecular area values for PEH(+) and PEOH(-) forms of phosphatidylethanolamine were calculated. The assumed model was verified experimentally. The experimental results agreed with those derived from the theoretical equation in a whole range of pH values.
Subject(s)
Air , Lipid Bilayers/chemistry , Phosphatidylethanolamines/chemistry , Solutions/chemistry , Algorithms , Hydrogen-Ion Concentration , Hydrophobic and Hydrophilic Interactions , Models, Chemical , Surface Tension , Water/chemistryABSTRACT
Monolayers of sphingomyelin (SM), ceramide (Cer) and cholesterol (Ch) and binary mixtures SM-Ch, SM-Cer and Cer-Ch were investigated at the air-water interface. SM, Cer and Ch were used in the experiment. The surface tension values of pure and mixed monolayers were used to calculate π-A isotherms. Surface tension measurements were carried out at 22 °C using a Teflon trough and a Nima 9000 tensiometer. Interactions between sphingolipid and Ch as well as sphingolipid and another sphingolipid result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air-water interface was developed in order to obtain the stability constants and Gibbs free energy values of SM-Ch, SM-Cer and Cer-Ch complexes. We considered the equilibrium between the individual components and the complex and established that sphingolipid and Ch as well as sphingolipid and another sphingolipid formed highly stable 1:1 complexes.
Subject(s)
Air , Cholesterol/chemistry , Sphingolipids/chemistry , Water , Ceramides/chemistry , Membranes, Artificial , Sphingomyelins/chemistry , Surface Properties , Surface TensionABSTRACT
The pH dependence of the interfacial tension is an important factor in the behavior of sphingomyelin (SM) monolayers. We developed a theoretical model to describe this dependence in which the interfacial tension and molecular area contributions of each sphingomyelin form were additive and dependent on pH. The interfacial tension values and the molecular areas values for the SMH(+) and SMOH(-) forms of sphingomyelin were calculated and the proposed model was experimentally verified. The theoretical predictions agreed with the experimental results for pH values ranging from 2 to 12.
Subject(s)
Sphingomyelins/chemistry , Air , Hydrogen-Ion Concentration , Solutions , Surface Properties , Water/chemistryABSTRACT
We have monitored the effect of ergosterol on electrical capacitance and electrical resistance of the phosphatidylcholine bilayer membranes using chronopotentiometry method. The chronopotentiometric characteristic of the bilayers depends on constant-current flow through the membranes. For low current values, no electroporation takes place and the membrane voltage rises exponentially to a constant value described by the Ohm's law. Based on these kinds of chronopotentiometric curves, a method of the membrane capacitance and the membrane resistance calculations is presented.
Subject(s)
Ergosterol/chemistry , Lipid Bilayers/chemistry , Phosphatidylcholines/chemistry , Potentiometry/methods , Models, TheoreticalABSTRACT
Bilayer lipid membranes composed of phosphatidylcholine and decanoic acid or phosphatidylcholine and decylamine were investigated using electrochemical impedance spectroscopy. Interaction between membrane components causes significant deviations from the additivity rule. Area, capacitance, and stability constant values for the complexes were calculated based on the model assuming 1:1 stoichiometry, and the model was validated by comparison of these values to experimental results. We established that phosphatidylcholine and decylamine form highly stable 1:1 complexes. In the case of decanoic acid-modified phosphatidylcholine membranes, complexes with stoichiometries other than 1:1 should be taken into consideration.
Subject(s)
Amines/chemistry , Decanoic Acids/chemistry , Dielectric Spectroscopy/methods , Lipid Bilayers/chemistry , Phosphatidylcholines/chemistry , Algorithms , Models, MolecularABSTRACT
The effect of pH on the interfacial tension of a sphingomyelin membrane in aqueous solution has been studied. Three models describing H(+) and OH(-) ion adsorption on the bilayer lipid surface are presented. In models I and II, the membrane surface is continuous, with uniformly distributed functional groups as centers of H(+) and OH(-) ion adsorption. In model III, the membrane surface is composed of lipid molecules, with and without adsorbed H(+) and OH(-) ions. The contribution of each individual lipid molecule to the overall interfacial tension of the bilayer was assumed to be additive in models I and II. In model III, the Gibbs isotherm was used to describe adsorption of H(+) and OH(-) ions at the bilayer surface. Theoretical equations are derived to describe the interfacial tension as a function of pH for all three models. Maximum interfacial tension was observed experimentally at the isoelectric point.
Subject(s)
Lipid Bilayers/chemistry , Sphingomyelins/chemistry , Hydrogen-Ion Concentration , Isoelectric Point , Membrane Fluidity , Models, Chemical , Surface TensionABSTRACT
Electrochemical impedance spectroscopy was used for the study of two-component lipid membranes. Phosphatidylcholine and ceramide were to be investigated, since they play an important biochemical role in cell membranes. The research on biolipid interaction was focused on quantitative description of processes that take part in a bilayer. Assumed models of interaction between amphiphilic molecules and the equilibria that take place there were described by mathematical equations for the studied system. The possibility of complex formation for two-component system forming bilayers was assumed that could explain the deviation from additivity rule. Equilibria were described by mathematical equations that were further verified experimentally. The determined values of parameters (stability constant, molecular area of complex, capacitance and conductance of the lipid membranes formed from molecules and complexes) were used for calculation of model curves. The comparison of model curves and experimental points verified the assumed model.
