Interaction forces, between membrane

It immediately follows from the existence of isoelectric points that if the two interacting membranes have different isoelectric points, then the interaction force alters its sign at these isoelectric points (note that the interaction force between membranes with the same isoelectric point does not change its sign). 

A possible mechanism that could decrease the interactional forces between membranes is a change in membrane composition. Altering the lipids and proteins present in one or both membranes could substantially change their electrostatic interactions. 

Berkowitz and Raghavan Interaction Forces between Membrane Surfaces 5... 

Berkowitz and Raghavan Interaction Forces between Membrane Surfaces 11 For k h >> 1, the repulsion follows the exponential law ... 

The dependence of the interaction force between two undulating phospholipid bilayers and of the root-mean-square fluctuation of their separation distances on the average separation can be determined once the distribution of the intermembrane separation is known as a function of the applied pressure. However, most of the present theories for interacting membranes start by assuming that the distance distribution is symmetric, a hypothesis invalidated by Monte Carlo simulations. Here we present an approach to calculate the distribution of the intermembrane separation for any arbitrary interaction potential and applied pressure. The procedure is applied to a realistic interaction potential between neutral lipid bilayers in water, involving the hydration repulsion and van der Waals attraction. A comparison with existing experiments is provided. 

An example is given in Fig. 16.2, which shows the interaction force between two membranes, each consisting of with two sublayers, in a monovalent symmetrical electrolyte solution as a function of the electrolyte concentration. Here membranes 1 and 2 have different isoelectric points. It is seen that the interaction force is positive (i.e., repulsive) at concentrations less than 0.07 M and higher than 0.18 M and negative (i.e., attractive) between 0.07 and 0.18M, corresponding to the isoelectric points at 0.07 M for membrane 1 and 0.18 M for membrane 2. Membranes consisting of more than two layers may exhibit more than one isoelectric point. The... 

The major physical forces, which help the membrane to maintain their structure, consist of hydrophobic and hydrophilic interactions, electrostatic forces, and van der Waals interactions. The main driving force for formation of the bilayer originates from the hydrophobic interactions and van der Waals interaction forces between hydrocarbon chains of the hpid molecules. The hydrophobic forces control the order and packing of hpids and electrostatic interactions between the polar head groups and their interaction with water molecules contribute to bUayer stabUization. The bUayer is continuous and it exhibits semirigid properties. The fluid nature of the membrane is governed by the hpid composition and the namre of the forces that exist between the constituent hpids and proteins. Due to fluid hpid bilayer, the diffusion constant for a phosphohpids is 1 m /s,... 

In the derivation of J. D. Ferry s formula. Equation (lb), it was assumed that the solute concentration within the accessible part of the membrane pore is uniform and equal to C2,f- Obviously this assumption cannot hold if we are to acknowledge the presence of Interactive forces between the solute and the pore wall (membrane). Here we will concentrate only on the effect of Van der Waals forces but analogous treatments could be developed for other interactive potentials (electrostatic, etc.). 

Thin, liquid films as such are not only systems of interest, they also occur frequently in nature and in laboratory practice, for example, in foams. In emulsions, to name another case, thin water films between oil (instead of air ) phases are present in a concentrated emulsion of small oil droplets dispersed in water. The properties of the thin water film determine the interaction forces between the oil droplets and will determine, for example, whether the emulsion in stable. Also the reverse case, oil films in water, occurs. Extremely thin ( 5 nm) oil-in-water films are prototypes of lipid bilayers occurring in biological membranes. Thin liquid films on a solid... 

The coefficients Ai and A2 reflect the relative size of and D2M respectively. Since the fitted value of Ai is much smaller than A2, this implies that the resistance of the membrane to hydronium diffusion is much larger than to water. Given that hydronium ions have a net charge while water does not, this is reasonable since we expect the interaction forces between the membrane (with charged sulfonate heads) and the hydronium ions to be stronger than the forces between membrane and water. Sensitivity analysis shows [23] that regardless of the order of magnitude of Z)i2 the ratio of the values of and... 

The silicon nitride tip is used mostly for C-AFM. Measurements can be done in ambient air, controlled atmospheres, or in non-aggressive liquids. AFM also allows surface forces, and even molecular forces, to be directly quantified [23]. For example, the interaction forces between a silicon tip and microfiltration and ultrafiltration membranes in an electrolyte solution can be measured [24]. The geometry of the cantilever is not simple, and in some cases not even known, so comparison with theory is difficult. However, attaching a sphere to the cantilever instead of a tip enables the measurement of interaction between surfaces of known geometry [25]. This technique has been used to measure interactions between different materials in air... 

Recently, Bowen et al. [27,28] and Hilal and Bowen [29] and Hilal et al. [30] applied the APM technique to study adhesion at the membrane sinface. The measurement of interaction forces between a colloid probe and a membrane smface allows quantification of the electrostatic double layer interactions when the colloid probe approaches the membrane surface, and of the adhesion force (van der Waals interaction force) when the colloid probe is withdrawn after it has been in contact with the membrane surface. Quantification of the interaction forces involved in fouling and chemical cleaning of fouled membranes is very important in order to imderstand the mechanism of fouling and to develop a favorable membrane for water treatment. 

The solubility parameter is a parameter to express the nature and magnitude of the interaction force working between molecules. When applied to the membrane, the solubility parameter can give a measure to the interaction force working between the molecules that constitute the membrane material, and also the interaction force between the latter molecule and the permeant molecule. They are intrinsic to the chemical structure. In other words, the interaction force measured by the solubility parameter is uniquely determined when the molecular formula of the molecules involved in the interaction are given. 

The research indicates a good compatibihty in the ethylcellulose/cellulose acetate system, whereas the thermal stabihty of mixtiu-es is improved compared to that of pure ethyl cellulose [142], Thus, this blend met the best equilibrium conditions at the membrane-solution interface of membrane separation in liquid chromatography experiments. In this context, knowledge on the interaction force between solute and interface of the membrane is necessary. It is observed that the interfacial adsorption properties and hydrophilidty of ethylcellulose are improved when blending the solution with cellulose acetate, and also that the alloys are superior to ethylcellulose in the separation efficiency for non-dissociable polar organic solutes. The obtained results are useful especially for orientational membrane fabrication. 

Ionomer membrane types have been developed that show the different types of interaction forces between the blend components. In Table 8.2, an overview is given of the different ionomer membrane types developed. In the following, the developed (blend) membrane types are described in more detail. 

The interaction forces between the acidic and basic blend component include electrostatic and hydrogen bridge interaction. The sulfonated poly(ethersulfones) and poly(etherketones) were combined both with commercially available basic polymers (e.g., polybenzimidazole Celazole (Celanese), poly(4-vinylpyridine), polyCethylene imine)), and with self-developed basic polymers derived from poly(ethersulfones) [47] and poly(etherketones), including polymers that carry both sulfonic and basic groups onto the same backbone [48]. A wide variety of acid-base blend membranes with a broad property range were obtained. The most important characterization results of the ionically cross-linked ionomer membranes are... 

Perhaps the least-understood set of interactions involving membranes is that between bilayers or other amphiphilic surfaces. Yet, no discussion of membrane functions would be complete without considering these forces because of their essential role in cell-cell interactions and membrane fusion. The forces acting between membranes are often called hydration forces . This name originates in the tendency at one time to ascribe many unexplained or ubiquitous effects seen in various colloidal systems to the effects of aqueous solvation. However, it is still unclear, despite recent experimental and theoretical advances, whether or not these forces are mainly due to hydration , as understood in the conventional sense. In this section, we describe some of the major issues involving hydration forces between membranes, and provide a summary of selected theoretical and experimental works. More complete reviews, with different emphases, can be found in articles by Israelachvili, et al. [136,137] and Leikin, et al. [138]. 

In the earliest theory of cell adhesion or aggregation, Tyler (1947) and P. Weiss (1947) proposed an antigen-antibody interaction as the cause of attraction. The requirement of destruction of the antigen or antibody site for detachment (Roseman, 1974) and the probable absence of antibodies at the surface of cells (Roth, 1973) makes this concept unlikely. Curtis (1960 1962) based his theory of cell adhesion or aggregation on the Verwey and Overbeck (1948) theory applied to the adhesion of two parallel membranes at about 150 A of distance. This theory is based on the existence of van der Waals forces between membranes if the constitutions of these membranes are similar. It is evident that the sialic acid residues, which have a flexible chain of alcohol groups (C7 to C9), could play an important role in this type of interaction. 

With an AFM adhesion force measurement technique, Bowen et al. [42] characterized an interaction force between a colloidal silica probe and a rough membrane surface. It was found that membrane surface roughness significantly reduced electrostatic repulsion between the colloid and the surface, and the valley regions experienced a greater adhesion force. 

All the long-range forces discussed in this chapter play a role in biological processes. Interactions between membranes, proteins, ligands, antibodies... 

The interest in vesicles as models for cell biomembranes has led to much work on the interactions within and between lipid layers. The primary contributions to vesicle stability and curvature include those familiar to us already, the electrostatic interactions between charged head groups (Chapter V) and the van der Waals interaction between layers (Chapter VI). An additional force due to thermal fluctuations in membranes produces a steric repulsion between membranes known as the Helfrich or undulation interaction. This force has been quantified by Sackmann and co-workers using reflection interference contrast microscopy to monitor vesicles weakly adhering to a solid substrate [78]. Membrane fluctuation forces may influence the interactions between proteins embedded in them [79]. Finally, in balance with these forces, bending elasticity helps determine shape transitions [80], interactions between inclusions [81], aggregation of membrane junctions [82], and unbinding of pinched membranes [83]. Specific interactions between membrane embedded receptors add an additional complication to biomembrane behavior. These have been stud-... 

---