This section is from the book "Research In Physiopathology As Basis Of Guided Chemotherapy With Special Application To Cancer", by Emanuel Revici. Also available from amazon: Research In Physiopathology
According to Bloor: "Lipids may be defined as a group of naturally occurring substances consisting of the higher fatty acids, their naturally occurring compounds and substances found naturally in chemical association with them. The group is characterized in general by insolubility in water and solubility in "fat solvents," e.g., ether, chloroform, benzene, etc." (226)
From a physico mathematical analysis of our definition of lipoids, J. Mariani arrives to the following conclusions:
Any substance will behave like a lipoid with respect to a polar solvent when in:
If will be positive. The electrical attractions given by: will not be able to balance the attractive forces:
due to van der Waals forces (and to the polar groups of A). But we can simplify this definition. Let us consider a solvent the molecules of which are dipolar and form polar groups similar to those contained in the solute. We can call those substances lipoids for which the dipole interaction energy in the cavity occupied by the molecule is less than the energy arising from van der Waals forces. We get:
where now a represents van der Waals forces in a cavity occupied by the molecule and Σ the dipolar forces at the surface of the cavity.
The possibility of having a membrane with polar groups at both surfaces, as shown in mitochondria, represents one of the most important means used in biology to separate two aqueous solutions. (228) One of the characteristics of such a membrane is that often it represents an isolating boundary rather than a membrane with functional activity. This is seen in the fact that very often such a membrane breaks when the two separated aqueous media have to mix.