Double-chained surfactants form semipermanent coatings that prevent protein adsorption in capillary electrophoresis (CE). To make such coatings more permanent, vesicles of the unsaturated phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine were prepared and subjected to free-radical-initiated polymerization, both inside the capillary and in free solution. The latter generated oligomers of 2-5 units based on ESI-TOF MS, and formed the more stable coating in CE. Rinsing the capillary with a solution of the ex situ oligomerized DOPC suppressed EOF (0.8 x 10(-)(8) m(2)/V.s) for more than 20 h, whereas in situ oligomerized electroosmotic flow (EOF) suppressed the EOF for only 10 h. Mixtures of anionic and cationic proteins were separated under neutral pH and low ionic strength buffer with efficiencies of 480,000-930,000 plates/m and recoveries of 75-99%.

Mixtures of the cationic surfactant cetyltrimethylammonium bromide (CTAB) with the anionic surfactant sodium dodecyl sulfate (SDS) form more stable coatings in fused-silica capillaries than CTAB alone. The reversed electroosmotic flow (EOF) generated by CTAB/SDS mixtures remains stable for over 80 min after removal of the surfactants from the buffer. Enhanced stability (relative to CTAB alone) was found even when the ratio of SDS to CTAB was as low as 1%. This greater coating stability is attributed to the structural transition from adsorbed micelle to bilayer, which is induced by addition of SDS. Separation of a mixture of basic proteins yielded efficiencies of 364 000-562 000 plates/m and recoveries ranging from 85% to 98%. Migration time reproducibility was less than 0.9% relative standard deviation (RSD) from run to run and less than 2.6% RSD from day to day.

Cationic gemini surfactants, N,N-bis(dimethylalkyl)-alpha,omega-alkanediammonium dibromide [C(m)H(2m+1)(CH(3))(2)N(+)(CH(2))(s)N(+)(CH(3))(2)C(m)H(2m+1) x 2 Br(-), or m-s-m], have proven to be effective synthetic vectors for gene delivery (transfection). Complexes (lipoplexes) of gemini compounds, where m = 12, s = 3, 12 and m = 18 : 1(oleyl), s = 2, 3, 6, with DNA have been investigated using isothermal titration calorimetry (ITC), dynamic light scattering (DLS), zeta potential, atomic force microscopy (AFM) and circular dichroism (CD) techniques. The results show that lipoplex properties depend on the structural properties of the gemini surfactants, the presence of the helper lipid dioleoylphosphatidylethanolamine (DOPE), and the titration sequence. ITC data show that the interaction between DNA and gemini surfactants is endothermic and the observed enthalpy vs. charge ratio profile depends upon the titration sequence. Isoelectric points (IP) of lipoplex formation were estimated from the zeta potential measurements and show good agreement with the reaction endpoints (RP) obtained from ITC. DLS data indicate that DNA is condensed in the lipoplex. AFM images suggest that the lipoplex morphology changes from isolated globular-like aggregated particles to larger-size aggregates with great diversity in morphology. This change is further accentuated by the presence of DOPE in the lipoplexes. The results are interpreted in terms of some current models of lipoplex formation.

Gemini surfactants are potential candidates as synthetic vectors for the delivery of genes into cells to induce protein expression. With the ultimate objective of obtaining a better understanding of the mechanism of DNA transfection, two new asymmetric gemini surfactants (py-3-12 and py-6-12) have been synthesized as fluorescence probes. The physicochemical properties and morphologies of the self-assembled aggregates formed in aqueous solution have been studied using surface tension, specific conductance, dynamic light scattering (DLS), isothermal titration calorimetry (ITC), and fluorescence techniques. The interaction between pyrene-based gemini surfactants and DNA was investigated by using UV-vis and fluorescence spectroscopy. Binding constants for the DNA (salmon sperm)-gemini lipoplexes were measured. Fluorescence studies show that excimer emission occurs upon complexation with DNA.