Electrostatic complexation

FIG. 15 Cellular entry and intracellular kinetics of the cationic lipid-DNA complexes. Cationic lipid-DOPE liposomes form electrostatic complexes with DNA, and, in this case, also transferrin (Tf) is incorporated. Cellular uptake by endoc5dosis and endosomal acidification can be blocked with cytochaiasin B and bafilomycin Aj, respectively. DNA is proposed to be released at the level of endosomal wall after fusion of the carrier lipids with endosomal bilayer. This process is facilitated by the formation of inverted hexagonal DOPE phase as illustrated in the lower corner on the right. After its release to the C5doplasm DNA may enter the nucleus. (From Ref. 253. By permission of Nature Publishing Group.)... 

Similar IPEC-based aqueous micelles can be obtained from the mixing of a double-hydrophilic copolymer AB with a homopolymer C or a diblock copolymer AC or a diblock copolymer DC, provided that IPECs can form between the B and C blocks. This kind of electrostatic complex has also been referred to as block ionomer complexes, or BIC. 

Braun M, Atalick S, Guldi Dirk M, Lanig H, Brettreich M, Burghardt S, Hatzimarinaki M, Ravanelli E, Prato M, Van Eldik R, Hirsch A (2003) Electrostatic Complexation and Photoinduced Electron Transfer between Zn-Cytochrome c and Polyanionic Fullerene Dendrimers. Chem. Eur. J. 9 3867-3875. 

Schmitt, C., Kolodziejczyk, E., Leser, M.E. (2005). Interfacial and foam stabilization properties of p-lactoglobulin + acacia gum electrostatic complexes. In Dickinson, E. (Ed.). Food Colloids Interactions, Microstructure and Processing, Cambridge, UK Royal Society of Chemistry, pp. 284-300. 

The anticoagulant heparin is a polysaccharide sulfate which can form an electrostatic complex with blood-clotting factors (see ASIDE on blood clotting) and prevent the cascade from progressing. 

Another group37 has explored the potential surface of C2H701 using the G2 procedure, which led to the identification of four stable structures protonated species (C2H50H2)+ and (Me20H)+, and the electrostatic complexes (C2H4 H 0+H2)... 

The possibility exists to condense DNA through proton donor and proton acceptor non-electrostatic interactions with DNA-grooves. This type of non-electrostatic complex has been developed for sequence-specific binding to DNA. Several prominent works were recently accomplished in this field (Dervan, 1997 Kiclkopf et al., 1998 Minchan et al, 2000). 

The necessity of more efficient gene delivery methods prompted the search for novel, less charged or non-cationic gene delivery systems. These non-electrostatic complexes can be advantageous for in vitro and in vivo applications, since unlike cationic lipid/DNA complexes, the novel molecules could not lead to a compacted state of DNA, and could therefore potentially lead to different kinetics of DNA release from complexes. Several compounds are able to bind to double stranded DNA along the grooves by the formation... 

Soto, J., Bessodes, M., Pitard, B., Mailhe, P., Scherman, D. and Byk, G. (2000) Non-electrostatic complexes with DNA Towards novel synthetic gene delivery systems. Bioorg. Med. Chem. Lett., 10, 911-914. 

The different conformational behavior of the azobenzoyl- and the azobenzenesul-fonyl-L-lysine polymers was explained on the basis that the monomeric units VI may interact with HFP differently than units V do (Scheme 4). The strongly proto-nating solvent HFP (pKa = 9.30) 36 is known to form electrostatic complexes with various organic compounds, including amines and dimethylsulfoxide 1371 on the other hand, sulfonamides are significantly protonated in acid media 38 so it may be presumed that protonation and formation of electrostatic complexes can occur for azobenzenesulfonyl-L-lysine residues, as well. In HFP therefore, polypeptides of structure V can adopt the ordered a-helix structure, while polypeptides of structure VI should be forced by the electrostatic interactions arising from complexation with HFP to adopt a disordered conformation. 

Of course, stability and formation of HFP-azosulfonyl-Lys complexes is less favored on going from pure HFP to HFP/MeOH or HFP/DCE solvent mixtures. At appropriate and critical solvent compositions, the formation of the electrostatic complexes described above might be favored or inhibited by the electronic situation of the azo moieties, which differs depending on whether they are in the apolar, conjugated trans form, or in the more polar, unconjugated cis form. In other words, the trans-cis photoisomerization of the azo units, which is the primary photochemical event, does not seem to be sufficient to induce appreciable variations of the back-... 

A few doubly substituted nitrobenzenes, such as 3,5-bis (trifluoromethyl)nitrobenzene, were also included in the same investigation296. The structural assignment in these cases is more difficult since the tendency toward (7-bonded complexes 137 and axial electrostatic complexes 136 is expected to increase upon multiple substitution with CN, CF3, N02. Probably, the energies of these Br complexes (136 and 137) come quite close to that of the C—H -Br complex (134) for these triply substituted benzenes and all three forms of bonding become competitive296. 

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