Phospholipid electrostatic properties

These studies bear on the much debated question whether the AV effect of GaCl2 is caused by interaction of Ca++ ions with the phosphate group of the neutral phospholipid. We have maintained that such an interaction is absurd (1-6), whereas the opinion is divided among various laboratories, and strangely in the same laboratory after using two different techniques (7,8). This indicates that there is much to be clarified regarding architecture and molecular and electrostatic properties of the DPL-H20-electrolyte interface. 

Tab. 1.1 Phospholipid charged groups and their electrostatic properties. (Adapted from Table 2.2 of ref. 2 with permission from Macmillan)...

The transport properties of the acids did not respond significantly to the presence of the sink. This may be because at pH 7.4 the acids are negatively charged, as are the phospholipid membranes and also the surfactant micelles electrostatic repulsions balanced out the attractive forces due to increased membrane lipophilicity. Lowered surface pH may also play a balancing role [457]. 

For acids, the membrane retention actually increases in the case of egg lecithin, compared to soy lecithin. This may be due to decreased repulsions between the negatively charged sample and negatively charged phospholipid, allowing H-bond-ing and hydrophobic forces to more fully realize in the less negatively charged egg lecithin membranes. The neutral molecules display about the same transport properties in soy and egg lecithin, in line with the absence of direct electrostatic effects. These differences between egg and soy lecithins make soy lecithin the preferred basis for further model development. 

It is known that the method used to truncate the interatomic interactions can have an important effect. It has been demonstrated that the dielectric properties of simulated water are a sensitive function of the extent to which the long-range electrostatic interactions are included [40]. Simulations of phospholipid membrane-water systems showed that the behavior of the water near the membrane is incorrectly described if the electrostatic interactions are truncated at too short a distance, and hot water/cold-protein behavior is observed [10]. Given the importance of the potential/force truncation, we have investigated this issue for the copper system being simulated. This has been done in terms of the same properties as were used in examining convergence. 

Apart from the type of phospholipids the formation of phospholipid structures such as bilayers, micelles or inverted micelles are directly dependent on the degree of hydration, the hydrophobic forces on the tatty acyl chains, and the electrostatic forces that are present on the polar head group region of the bilayer. The properties of the aqueous medium (pH, ionic strength, dielectric properties) are factors that influence the type of phospholipid structures. 

Extensive research has established the relationship between the extent of distribution of compounds and their physicochemical properties. With this information, Vdss can be quite successfully predicted using in silico models [27-30], In silico prediction of distribution is based on physicochemical properties that relates to passive transmembrane diffusion and tissue binding, and it only predicts Vdss. The other factors that contribute to distribution, such as transporter-mediated distribution, were not taken into account. These algorithms are based on the assumption that all compounds will dissolve in intra- and extracellular tissue water, and the unionized portion will partition into the neutral lipids and neutral phospholipids located within tissue cells. For compounds categorized as a strong base (at least one basic group (p/fa >7), an additional mechanism of electrostatic interaction with tissue acidic phospholipids is incorporated. Acids and weak bases are assumed... 

The properties of liposomes (e.g., their permeability) depend on the phospholipids of which they are made. The basis is largely phosphatidylcholine. The often-used phospholipids from egg yolk or soy beans (asolectin) are mixtures of different phospholipids with unknown substances. The products from Avanti polar satisfy higher demands regarding purity. Cholesterol (e.g., phosphatidylcholineicholesterol 2 1) increases the stability and decreases the permeability of the liposomes, and negatively charged phospholipids such as phosphatidylserin prevent aggregation because of the electrostatic repulsion. 

In nature, endocytic pathways depend on the physical and chemical properties of molecules such as size, charge and shape. The net charge on nanoparticles can affect their cell entry capabilities. Several studies show that cationic nanoparticle uptake by different cell lines is easier than for anionic nanoparticles. The better uptake of cationic nanoparticles may be due to the electrostatic interaction with the cell membrane, because the plasma membrane has a negative surface charge due to the bilayer phospholipid chains (see Figure 11.2). 

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