No abstract

The superior surfactant properties of cationic gemini surfactants are applied to the complex problem of introducing genes into cells. Of almost 250 new compounds tested, of some 20 different structural types, a majority showed very good transfection activity in vitro. The surfactant is shown to bind and compact DNA efficiently, and structural studies and calculations provide a working picture of the "lipoplex" formed. The lipoplex can penetrate the outer membranes of many cell types, to appear in the cytoplasm encapsulated within endosomes. Escape from the endosome--a key step for transfection--may be controlled by changes in the aggregation behavior of the lipoplex as the pH falls. The evidence suggests that DNA may be released from the lipoplex before entry into the nucleus, where the new gene can be expressed with high efficiency.

The n-octyl β-d-glucoside/water binary phase diagram (temperature vs concentration) and the aggregation parameters of the individual phases have been determined. n-Octyl β-d-glucoside forms four different phases together with water. At temperatures below 22 °C, there is an isotropic solution region from neat water extending up to almost 60 wt % n-octyl β-d-glucoside. As the concentration is further increased, three liquid crystalline phases form in the following order:  hexagonal, cubic, and lamellar. At high surfactant concentrations (>93 wt %) the lamellar phase is in equilibrium with hydrated crystals. The hexagonal phase disappears at temperatures slightly higher than 20 °C. The solution region has been investigated with 1H-NMR to deduce the self-diffusion coefficients of both n-octyl β-d-glucoside and water. From these results it has been possible to draw conclusions about the surfactant aggregation behavior at dilute concentrations and when the n-octyl β-d-glucoside concentration is increased. The water diffusion in the n-octyl β-d-glucoside/water system has been compared with the diffusion process of water in a glucose solution, and it has been possible to interpret the data in terms of water diffusion in a glucose solution with some additional obstruction effects from the micellar hydrocarbon cores. The liquid crystalline phases have been examined by means of small-angle X-ray scattering and analyzed in terms of repetition distances and area/head group in the hexagonal, cubic, and lamellar phases. An important result of this study is the fact that the area per glucose unit in the surfactant is an almost invariant quantity across the phase diagram.

The binding of SDS to cellulose polymers in the semidilute concentration regime has been studied by means of NMR, ion-selective electrode, and a time-resolved fluorescence technique. Two polymers have been used, differing only in a low degree of hydrophobic modification of one of them. NMR self-diffusion and activity measurements show that the binding of SDS to the nonmodified polymer has a fairly pronounced critical aggregation concentration (cac), while binding to the hydrophobically modified polymer is less cooperative up to a concentration of about the cac in the nonmodified polymer/SDS system. NMR T 2 relaxation and fluorescence studies indicate that surfactants bound to the hydrophobically modified polymers in the non-cooperative regime have slow dynamics compared to micellized surfactants, to surfactants bound to the unmodified polymer, and to surfactants bound to the hydrophobically modified polymer in the cooperative regime. Furthermore, in the non-cooperative regime the fluorescence studies imply that the SDS aggregation number of the mixed micelles is low and that the number of hydrophobic zones is invariant with respect to the surfactant concentration.

The formation of triblock copolymer/surfactant complexes upon mixing a nonionic Pluronic polymer (PEO-PPO-PEO) with a cationic surfactant, hexadecyltrimethylammonium chloride (CTAC), has been studied in dilute aqueous solutions using small-angle X-ray scattering, static and dynamic light scattering, and self-diffusion NMR. The studied copolymer (denoted P123, EO(20)PO(68)EO(20)) forms micelles with a radius of 10 nm and a molecular weight of 7.5 x 10(5), composed of a hydrophobic PPO-rich core of radius 4 nm and a water swollen PEO corona. The P123/CTAC system has been investigated between 1 and 5 wt % P123 and with varying surfactant concentration up to approximately 170 mM CTAC (or a molar ratio n(CTAC)/n(P123) = 19.3). When CTAC is mixed with micellar P123 solutions, two different types of complexes are observed at various CTAC concentrations. At low molar ratios (>/=0.5) a "P123 micelle-CTAC" complex is obtained as the CTAC monomers associate noncooperatively with the P123 micelle, forming a spherical complex. Here, an increased interaction between the complexes with increasing CTAC concentration is observed. The interaction has been investigated by determining the structure factor obtained by using the generalized indirect Fourier transformation (GIFT) method. The interaction between the P123 micelle-CTAC complexes was modeled using the Percus-Yevick closure. For the low molar ratios a small decrease in the apparent molecular weight of the complex was obtained, whereas the major effect was the increase in electrostatic repulsion between the complexes. Between molar ratios 1.9 and 9 two coexisting complexes were found, one P123 micelle-CTAC complex and one "CTAC-P123" complex. The latter one consists of one or a few P123 unimers and a few CTAC monomers. As the CTAC concentration increases above a molar ratio of 9, the P123 micelles are broken up and only the CTAC-P123 complex that is slightly smaller than a CTAC micelle exists. The interaction between the P123/CTAC complexes was modeled with the hypernetted-chain closure using a Yukawa type potential in the GIFT analysis, due to the stronger electrostatic repulsion.