Intercalating membranes

Improved Carrier Extraction by Intercalating Membranes. With light trapping, the condition for good extraction of electrons and holes requiring Le,h l, is also relaxed, since a smaller thickness of the solar cell is possible. For low mobility organic materials, this condition is still a problem. It ensures that electrons and holes generated in the absorber reach the membrane within their recombination lifetime. They can then pass into the external circuit. The distance of the membranes, however, is not limited by the thickness l of the absorber, as can be seen in Fig. 4.11, and can be made arbitrarily short. 

Fig. 4.11. Intercalating membranes in the absorber reduces the distance that electrons and holes have to travel from the place where they are generated in the absorber to the membranes...

There are other ways in which the lateral organization (and asymmetry) of lipids in biological membranes can be altered. Eor example, cholesterol can intercalate between the phospholipid fatty acid chains, its polar hydroxyl group associated with the polar head groups. In this manner, patches of cholesterol and phospholipids can form in an otherwise homogeneous sea of pure phospholipid. This lateral asymmetry can in turn affect the function of membrane proteins and enzymes. The lateral distribution of lipids in a membrane can also be affected by proteins in the membrane. Certain integral membrane proteins prefer associations with specific lipids. Proteins may select unsaturated lipid chains over saturated chains or may prefer a specific head group over others. 

CTC, used extensively to monitor calcium release in both whole cells and isolated organelles (28-33), is an amphipathic molecule that easily passes through cell membranes (see Figure 1). The fluorescence of this probe is enhanced more than fiftyfold by binding of calcium when the dye is intercalated into biological membranes. 

The most common sterol in membranes is cholesterol (Chapter 14), which resides mainly in the plasma membranes of mammalian cells but can also be found in lesser quantities in mitochondria, Golgi complexes, and nuclear membranes. Cholesterol intercalates among the phospholipids of the membrane, with its hydroxyl group at the aqueous interface and the remainder of the molecule within the leaflet. Its effect on the fluidity of membranes is discussed subsequently. 

Subczynski, W. K., J. S.Hyde, and A. Kusumi. 1991. Effect of alkyl chain unsaturation and cholesterol intercalation on oxygen transport in membranes A pulse ESR spin labeling study. Biochemistry 30 8578-8590. 

Fig. 8.19 SEM images of mesolamellar thin films produced by intercalation of nanosheets of (A) aminopropyl-functionalized silica or (B) AMP between stacked purple membrane fragments containing bacteriorhodopsin (scale bars= 10pm).

Bromley, KM., Patil, A.J., Seddon, A. M., Booth, P. and Mann, S. (2007) Bio-functional mesolamellar nanocomposite based on inorganic/ polymer intercalation in purple membrane (Bacteriorhodopsin) films. Advanced Materials, 19, 2433—2438. 

In the latter work it was suggested that the intercalation of SB 211475 into the glycerol phosphate hydrocarbon interface makes the membrane more resistant to lipid peroxidation.)... 

There is not a unique binding site for all sorts of xenobiotics, but the compounds are intercalated in such a way into the membrane that they interact most favourably with the membrane components and with least perturbation. Some compounds, such as hydrophobic and neutral molecules, are actually dissolved in the membrane interior, whereas others exhibit more specific interactions in the polar region of the membrane. In general, interaction of the xenobiotics with the head groups leads to a stronger perturbation of the bilayer than intercalation in the membrane core [170]. 

Alkanes and short alcohols actually partition into the interior of the membrane [171]. The well-shielded tetraphenylphosphonium (TPP+) and tetraphe-nylborate (TPB-) ions are also deeply intercalated into the lipid bilayer [6,169]. The binding site of TPB- is located somewhere below the head-group region in the vicinity of the ester groups, while the cation TPP+ binds a few tenths of a nanometre further outwards [6],... 

The neutral species of a HIOC is usually deeper intercalated into the membrane than its corresponding charged species, which is also reflected in a higher Kmw value [174]... 

Fullerene showed antibacterial activity, which can be attributed to different interactions of C60 with biomolecules (Da Ros et al., 1996). In fact, there is a possibility to induce cell membrane disruption. The fullerene sphere seems not really adaptable to planar cellular surface, but for sure the hydrophobic surface can easily interact with membrane lipids and intercalate into them. However, it has been demonstrated that fullerene derivatives can inhibit bacterial growth by unpairing the respiratory chain. There is, first, a decrease of oxygen uptake at low fullerene derivative concentration, and then an increase of oxygen uptake, which is followed by an enhancement of hydrogen peroxide production. The higher concentration of C60 seems to produce an electron leak from the bacterial respiratory chain (Mashino et al., 2003). 

Radler JO, Koltover I, Salditt T, Safinya CR. Structure of DNA-cationic liposome complexes DNA intercalation in multilamellar membranes in distinct interhelical packing regimes. Science 1997 275(5301) 810-814. 

Depending upon its properties, the paramagnetic material can be encapsulated into the aqueous core of the liposome (if hydrophilic), incorporated or intercalated in the membrane (if lipophilic or amphiphatic), or directly attached by chemical bond to the surface membrane (107-109). 

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