Bilipid Membranes

Nonpolar compounds, including the majority of xenobiotic chemicals and some metal complexes [249-252], generally diffuse passively through the lipid portions of the membrane by simple diffusion [21,246,253,254]. In this case, internalisation rates are reflected by compound permeability in the bilipid membrane [254,255] and can be predicted by Fick s law [254,256] ... 

A study of interaction between SQDs and biological structures has shown binding of peptide-functionalized colloidal SQDs to transmembrane proteins in the bilipid membranes of cells [3]. In this work SQDs are bound to CGGGRGDS peptide through the thiol link between the cysteine (C) and SQD. 

The electron involved in the donor-acceptor interaction need not originate from the actual surface layer but may well come from the interior of the bilipid membrane, for example, from intramembrane proteins. The electron escape depth in organic materials is comparable to intermolecular distances. 

The role of bacterio-rhodopsin in the proton pumping activity of halobacteria has been further investigated by Bagyinka /a/., while the light transduction via the pigmented bilipid membranes, of the purple membrane of H. halobium, has been studied by Ti Tien. ... 

Interface surface, line, point and overall barriers-symmetries (surface — bilipid membrane cells, free bubbles of surfactants, Langmuir Blodgett films line — genes, liquid crystals, microtubules point — fullerenes, micro-emulsions overall — dry foams, polymer... 

Fig. 4.8. (Below) A diagram of the bilipid layer membrane of a vesicle or a cell with (above) a typical lipid, phosphatidylcholine. Large molecules and ions cannot penetrate the membrane as illustrated by the ions surrounding and inside a cell, but the distribution is reversed in vesicles (see Chapter 7). The ions create chemical and electrical field gradients across the membrane.

This structure is called a cell, also known as a lysosome. Add a bunch of ions, DNA, organelles, plus many other biomolecules to the cell and you have a living cell. The bilipid barrier is called a plasma membrane, which you will learn all about in your biology classes. 

Free radicals may also be formed by (a) homolysis of covalent bonds, (b) addition of an electron to a neutral atom, or (c) loss of a single electron from a neutral atom. These radicals, especially if they are of low molecular weight, are usually extremely reactive hence, they are short-lived. Since they have an unpaired electron, they are highly electrophilic (i.e., electron loving ) and attack sites of increased electron density, as in compounds with nitrogen atoms (e.g., proteins, amino acids, DNA, RNA) and carbon-carbon double bonds (i.e., polyuunsaturated fatty acids and phospholipids which make up bilipid cell membranes). 

The lipid bilayer is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around the cell and thus acts as a good antibacterial agent. Derivatives of neomycin B are examples of bilipids [73, 74]. 

Free nano continua or discontinua can be defined, also, as surface, line, and point elements, and as their combinations. Free surface elements are ideally composed of two nanolayers placed symmetrically each other (Figure 1.6). Such structures are ideal membranes and can be composed of solid materials, liquids, and even gasses. Ideal membranes exist in nature, e.g., bilipide cell membranes and black surfactant bubbles (Figure 1.7a and b). It is visible that both membranes are composed of only two molecular layers of asymmetric surface-active molecules, with hydrophilic ends placed outward (cell membranes) or inward (surfactant bubbles). Ideal membranes, composed... 

FIGURE 1.7 Black bilipide cell membrane (a) and surfactant bubble (b). 

We have shown above that ferrocifens delivery to cells could be improved by CD complexation. However, it is clear that whether ferrocifens are delivered free or encapsulated, they must cross the bilipidic cellular membranes. The purpose of this section is to investigate their interactions with such bilayers. 

---