Interfacial tension of the lipid membrane formed from lipid-fatty acid and lipid-amine systems

Understanding the Unique Role of Phospholipids in the Lubrication of Natural Joints: An Interfacial Tension Study

Some solid lubricants are characterized by a layered structure with weak (van der Waals) inter-interlayer forces which allow for easy, low-strength shearing. Solid lubricants in natural lubrication are characterized by phospholipid bilayers in the articular joints and phospholipid lamellar phases in synovial fluid. The influence of the acid–base properties of the phospholipid bilayer on the wettability and properties of the surface have been explained by studying the interfacial tension of spherical lipid bilayers based on a model membrane. In this paper, we show that the phospholipid multi-bilayer can act as an effective solid lubricant in every aspect, ranging from a ‘corrosion inhibitor’ in the stomach to a load-bearing lubricant in bovine joints. We present evidence of the outstanding performance of phospholipids and argue that this is due to their chemical inertness and hydrophilic–hydrophobic structure, which makes them amphoteric and provides them with the ability to form lamellar structures that can facilitate functional sliding. Moreover, the friction coefficient can significantly change for a given phospholipid bilayer so it leads to a lamellar-repulsive mechanism under highly charged conditions. After this, it is quickly transformed to result in stable low-friction conditions.

Influence of pH on sphingomyelin monolayer at air/aqueous solution interface

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.

The interfacial tension of the lipid membrane formed from lipid-amino acid systems

The interfacial tension of lipid membranes composed of phosphatidylcholine (lecithin, PC)-valine (Val), phosphatidylcholine-isoleucine (Ile), phosphatidylcholine-tyrosine (Tyr), and phosphatidylcholine-phenylalanine (Phe) has been studied. The membrane components formed 1:1 complexes. The interfacial tension measurements were used to determine the membrane surface concentration A (3)(-1), the membrane interfacial tension γ(3), and the stability constant K.

Interfacial tension of bilayer lipid membranes

Interfacial tension is an important characteristic of a biological membrane because it determines its rigidity, thus affecting its stability. It is affected by factors such as medium pH and by the presence of certain substances, for example cholesterol, other lipids, fatty acids, amines, amino acids, or proteins, incorporated in the lipid bilayer. Here, the effects of various parameters to on interfacial tension values of bilayer lipid membranes are discussed.

The mathematically derived and experimentally confirmed results presented in this paper are of importance to the interpretation of phenomena occurring in lipid bilayers. These results can lead to a better understanding of the physical properties of biological membranes. The simple interfacial tension method proposed herein may be successfully used to determine the interfacial tension values of 1:1 lipid-lipid, lipid-cholesterol, lipid-fatty acid, lipid-amine, and lipid-amino acid systems.

The equilibria of phosphatidylcholine-fatty acid and phosphatidylcholine-amine in monolayers at the air/water interface

Monolayers of phosphatidylcholine, fatty acid and amine and binary mixtures phosphatidylcholine-fatty acid or phosphatidylcholine-amine were investigated at the air/water interface. Phosphatidylcholine (lecithin, PC), stearic acid (SA), palmitic acid (PA), decanoic acid (DA) and decylamine (DE) were used to the experiment. 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 an improved Teflon trough and a Nima 9000 tensiometer. The Teflon trough was filled with a subphase of triple-distilled water. Known amounts of lipid dissolved in 1-chloropropane were placed at the surface using a syringe. The interactions between lecithin and fatty acid as well as phosphatidylcholine and amine result in significant deviations from the additivity rule. An equilibrium theory to describe the behaviour of monolayer components at the air/water interface was developed in order to obtain the stability constants of PC-SA, PC-PA, PC-DA and PC-DE complexes. We considered the equilibrium between the individual components and the complex and established that lecithin and fatty acid as well as phosphatidylcholine and amine formed highly stable 1:1 complexes.

Adsorption equilibria at interface separating electrolyte solution and phosphatidylcholine-stearylamine liposome membrane

The effect of the pH of an electrolyte solution on the electric surface charge of the liposome membrane was studied. The membrane of vesicles contained egg phosphatidylcholine (PC) with different proportions of stearylamine (ST). The surface charge density of the membrane was determined as a function of pH from electrophoretic mobility measurements. A six equilibria model describing the solution ions adsorption on the PC-ST liposome membrane surface was presented in this paper. The knowledge of the association constants of the -PO(-) and -N(+)CH(3)(3) groups of PC with H(+), OH(-), Na(+), Cl(-) ions: K(A(1)H), K(B(1)OH), K(A(1)Na), K(B(1)Cl), that had been presented earlier, allowed to determine the association constants of the -N(+)H(3) group of ST with OH(-) and Cl(-) ions: K(B(2)OH), K(B(2)Cl). The proposed model has been proved to be correct by comparing the resulting theoretic charge variation curves of the PC-ST liposomal membrane with the experimental data.