Cell membrane complex reactivity

Spin trapping methods were also used to show that when carotenoid-P-cyclodextrin 1 1 inclusion complex is formed (Polyakov et al. 2004), cyclodextrin does not prevent the reaction of carotenoids with Fe3+ ions but does reduce their scavenging rate toward OOH radicals. This implies that different sites of the carotenoid interact with free radicals and the Fe3+ ions. Presumably, the OOH radical attacks only the cyclohexene ring of the carotenoid. This indicates that the torus-shaped cyclodextrins, Scheme 9.6, protects the incorporated carotenoids from reactive oxygen species. Since cyclodextrins are widely used as carriers and stabilizers of dietary carotenoids, this demonstrates a mechanism for their safe delivery to the cell membrane before reaction with oxygen species occurs. 

The tetraazatriphenylene chromophore attached to the cyclene ring acted as an efficient sensitiser for Eu3+ and Tb2+ emission but also intercalated between the base pairs of DNA. The complexes were tested as cellular imaging and reactive probes using the mouse fibroblast cell line. The complexes were quickly taken up by the fibroblast cells and localised in nucleus and around the cell membrane. The process was visualised by fluorescence microscopy. Photolysis at 340 nm and 350 nm damaged plasmid supercoiled DNA producing nicked (form II) and linear (form III) DNA. DNA damage is known to induce apoptotic cell death and these complexes may be therefore considered for the development as therapeutic probes, for example in the treatment of accessible tumours, such as skin melanoma. 

Enzyme-lectin histochemistry has many features in common with EIH. Lectins are of non-immune origin but recognize fine differences in complex saccharide structures. Usually lectin specificity is expressed as reactivity to a given monosaccharide, but it has been demonstrated repeatedly (e.g.. Debray et al., 1981) that this is an oversimplification (Section 3.4). It is becoming increasingly clear that cellular differentiation, maturation and neoplastic transformation are associated with changes of carbohydrate composition of the cell membrane (Ponder, 1983). 

At Stanford, Harden M. McConnell developed a new technique, called spin labelling, based upon EPR spectroscopy. While carbon-centered free radicals are extremely reactive and short-lived, radical oxides of nitrogen, such as NO and NO2, are moderately stable. McConnell noted that nitroxyl radicals (RR N-O) are extremely stable if R and R are tertiary and can be chemically attached to biological molecules of interest. In 1965, he published the concept of spin labeling and, in 1966, demonstrated that a spin-labelled substrate added to a-chymotrypsin forms a covalent enzyme-substrate complex. The EPR signal was quite broad suggesting restricted motion consistent with Koshland s induced-fit model. In 1971, McConnell published a smdy in which spin labelling indicated flip-flop motions of lipids in cell membranes. This was the start of dynamic smdies of cell membranes. 

To compare different polymers with respect to their chemical stability, the Fenton test is widely applied in fuel cell membrane research. In these tests, membrane samples are immersed in hydrogen peroxide solution containing a small amount of Fe " ", e.g., iron(lI)sulfate. In the presence of the metal ion, the decomposition of hydrogen peroxide is accelerated. The ongoing reactions are very complex, and several reactive intermediates are formed. Just as an example and demonstrating the catalytic nature, the following partial reactions of the so-called Haber-Weiss mechanism are highlighted, as shown in (6.28)-(6.31) [49, 50]. 

---