Physicochemical Properties of Biological Membranes

Log Kow is the most widely used descriptor for baseline QSARs but has many disadvantages in the context of our model. First, because octanol does not perfectly mimic the physicochemical properties of biological membranes, there are two different QSAR equations for nonpolar and polar compounds. This complication can be overcome by using the liposome-water partition coefficient log Kupw as the descriptor instead [32]. We therefore recalculated the Kow-based QSARs from the EU Technical Guidance Documents [31] using relationships between log Kow and logKupw for nonpolar (Eq. 9) and polar compounds (Eq. 10), which had been experimentally determined by Vaes et al. [33,34]. 

Qeveral recent investigations using various physicochemical methods have provided convincing evidence to support the contention that the basic structure of most biological membranes consists of a phospholipid bilayer (1,2,3, 4). Studies on phospholipid model membranes can therefore be expected to yield relevant information on the role played by phospholipids in determining the characteristic properties of biological membranes (5). One important aspect of this problem concerns the mechanisms of interaction between the phospholipids and other membrane constituents such as cholesterol, proteins, and different inorganic... 

During recent decades, the use of artificial phospholipid membranes as a model for biological membranes has become the subject of intensive research. As discussed above, biological membranes are composed of complex mixtures of lipids, sterols, and proteins. Defined artificial membranes may therefore serve as simple models of membranes that have many striking similarities with biological membranes. A comparison of some important physicochemical properties of biological and artificial membranes is given in Table 1.8 [2]. 

A close relationship exists between physicochemical properties of pigment molecules and their ability to be absorbed and thus to exhibit biological functions. Carotenoids are hydrophobic molecules that require a lipophilic environment. In vivo, they are found in precise locations and orientations within biological membranes. For example, the dihydroxycarotenoids such as lutein and zeaxanthin orient themselves perpendicularly to the membrane surface as molecular rivets in order to expose their hydroxyl groups to a more polar environment. 

Leermakers, F. A. M. and Kleijn, J. M. (2004). Molecular modelling of biological membranes. Structure and permeation properties. In Physicochemical Kinetics and Transport at Biointerfaces, eds. van Leeuwen, H. P. and Koster, W., Vol. 9, IUPAC Series on Analytical and Physical Chemistry of Environmental Systems, Series eds. Buffle, J. and van Leeuwen, H. P., John Wiley Sons, Ltd, Chichester, pp. 15-111. 

The induction of unconsciousness may be the result of exposure to excessive concentrations of toxic solvents such as carbon tetrachloride or vinyl chloride, as occasionally occurs in industrial situations (solvent narcosis). Also, volatile and nonvolatile anesthetic drugs such as halothane and thiopental, respectively, cause the same physiological effect. The mechanism(s) underlying anesthesia is not fully understood, although various theories have been proposed. Many of these have centered on the correlation between certain physicochemical properties and anesthetic potency. Thus, the oil/water partition coefficient, the ability to reduce surface tension, and the ability to induce the formation of clathrate compounds with water are all correlated with anesthetic potency. It seems that each of these characteristics are all connected to hydrophobicity, and so the site of action may be a hydrophobic region in a membrane or protein. Thus, again, physicochemical properties determine biological activity. 

It is interesting that work on the internal motions of the molecules that produce lyotropic mesophases is more advanced. This is mainly because of the importance of the microscopic properties of these systems in solubilization and interfacial problems, problems which are encountered in industry as well as in cell membrane biology. The structural and functional roles of lipid molecules in biomembranes are much discussed investigations of the physicochemical properties of lipid media thus might provide orientations for biological studies. Moreover, the findings on the flexibility of the paraffinic chains in lyotropic mesophases might also be relevant to similar problems in thermotropic mesophases. 

The first synthetic amphiphiles found to self-organize into bilayers, were quaternary ammonium salts bearing two long alkyl chains 1.13.47.48.49 it is interesting to note that these molecules did not contain a connector moiety between the polar and the apolar part, as in the case of the biolipids. While the physicochemical properties of these bilayers were found to be comparable to those of the biological membranes, the synthetic lipids were found to... 

PURPOSE AND RATIONALE Lipophilicity expressed as logPow correlates with membrane affinity and other biological properties as summarised in Kern s (2001) review on physicochemical profiling. However, the interfacial (anisotropic) character of bilayer membranes and the ionisable phospholipid head groups of biological membranes influence the partition properties of drugs. These... 

Liposomes are considered as substantial models for the study of biological membranes. They have many physicochemical properties, such as membranes permeability, osmotic activity, interaction with various solutes, surface characteristics and chemical composition similar to cell membranes. The fluidity of their membranes and their self-closed structure are essential parameters for the study of the biological membrane function. 

It is widely believed that the unique properties of water are responsible for various physicochemical phenomena such as the aggregation of surfactants, the stability of biological membranes, the folding of nucleic acids and proteins, the binding of enzymes to substrates and more generally complex molecular associations in molecular recognition [6]. 

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