Synthesis of Pyridinium Amphiphiles Used for Transfection and Some Characteristics of Amphiphile/DNA Complex Formation

Pyridinium amphiphiles have found practical use for the delivery of DNA into cells. Starting from 4-methylpyridine, a general synthesis has been devised for the production of pyridinium amphiphiles which allows variation in both the hydrophobic part and in the headgroup area of the compounds. By means of differential scanning microcalorimetry, zeta potential, particle size measurements and cryo electron microscopy, some characteristics of the pyridinium amphiphile/ DNA complexes have been determined.

In Silico Studies of Carbon Nanotubes and Metal Clusters

Carbon nanotubes have been envisioned to become a very important material in various applications. This is due to the unique properties of carbon nanotubes which can be exploited in applications on length scales spanning from the nano world to our macroscopic world. For example, the electronic properties of carbon nanotubes makes them utterly suitable for nano electronics while the strength of them makes them suitable for reinforcements in plastics. Both of these applications do however require the ability for systematic production of carbon nanotubes with certain properties. This is called selective carbon nanotube growth and today this has not been achieved with total success. In the work presented in the thesis several different computational methods have been applied in our contribution to the systematic search for selective carbon nanotube growth. Put in a context of previous knowledge about carbon nanotube growth our results provide valuable clues to which parameters that control the carbon nanotube growth. In association with the latest results we even dare to, with all modesty, speculate about a plausible control mechanism. The studies presented in the thesis addressed different stages of carbon nanotube growth, spanning from the properties affecting the initiation of the growth to the parameters affecting the termination of the growth. In some more detail this included studies of the melting temperatures of nanoscaled metal clusters. The expected size dependence of the melting temperatures was confirmed and the melting temperatures of clusters on substrates were seen to depend both on the material and shape of the surface. As this constitute the premises prior to the carbon nanotube growth it was followed by studies of the interaction between carbon nanotubes and metal clusters of different size and constitution. This was done using different computational methods and at different temperatures. It soon became apparent that the clusters adapted to the carbon nanotube and not vice versa. This held true irrespectively of the constitution of the cluster, that is for both pure metal and metal carbide. It was also seen that there exist a minimum cluster size that prevent the carbon nanotube end from closing. Closure of the carbon nanotube end is likely to lead to the termination of the growth which lead to studies of other reasons for growth termination, e.g., Ostwald ripening of the catalyst particles. This was investigated with the result that the rate of the Ostwald ripening may depend on both the chirality and diameter of the carbon nanotubes. It is suggested that this may provide some answers to the controlled growth of carbon nanotubes

Sugar-Based Gemini Surfactant with a Vesicle-to-Micelle Transition at Acidic pH and a Reversible Vesicle Flocculation near Neutral pH

A sugar-based (reduced glucose) gemini surfactant forms vesicles in dilute aqueous solution near neutral pH. At lower pH, there is a vesicle-to-micelle transition within a narrow pH region (pH 6.0-5.6). The vesicles are transformed into large cylindrical micelles that in turn are transformed into small globular micelles at even lower pH. In the vesicular pH region, the vesicles are positively charged at pH < 7 and exhibit a good colloidal stability. However, close to pH 7, the vesicles become unstable and rapidly flocculate and eventually sediment out from the solution. We find that the flocculation correlates with low vesicle ζ-potentials and the behavior is thus well predicted by the classical DLVO theory of colloidal stability. Surprisingly, we find that the vesicles are easily redispersed by increasing the pH to above pH 7.5. We show that this is due to a vesicle surface charge reversal resulting in negatively charged vesicles at pH > 7.1. Adsorption, or binding, of hydroxide ions to the vesicular surface is likely the cause for the charge reversal, and a hydroxide ion binding constant is calculated using a Poisson-Boltzmann model.

Synthesis and Aggregation Behavior of Cyclic Single- and Double-Tailed Phosphate Amphiphiles: A Novel Class of Phosphate Surfactants - Comparison with the Aggregation Behavior of Sodium Di-n-alkyl Phosphates

Herein we describe the synthesis and aggregation of the sodium salts of a series of 5-alkyl-2-hydroxy-1,3,2-dioxaphosphorinan-2-ones and 5,5-dialkyl-2-hydroxy-1,3,2-dioxaphosphorinan-2-ones in aqueous solution. The results are compared with properties of previously studied sodium di-n-alkyl phosphates. The single-tailed surfactants (6a, b, g) form micelles whereas the double-tailed ones (6f, h-k) form vesicles, as revealed by transmission electron microscopy (TEM). Critical micelle concentrations (CMC) for 6a, b, g were determined using different techniques: UV spectroscopy, microcalorimetry, and conductometry. Phase transition temperatures of the bilayers were measured by differential scanning calorimetry (DSC) and by fluorescence depolarization. Fusion of the vesicles was studied employing the resonance energy transfer (RET) assay based on lipid mixing and TEM. Vesicles of 6h-k fuse upon addition of Ca2+ or Mg2+ ions, to almost the same extent in each case. Fusion only takes place above the phase transition temperature (Tc) of the different bilayers. The threshold concentrations of Ca2+ and Mg2+ ions for fusion of the different vesicles are below 0.1 mM. The initial rate of fusion is high and precludes the measurement of accurate rate constants. Upon addition of calcium chloride different processes occur. Vesicle fusion, crystallization, and formation of multilamellar sheets were observed, as was apparent from experiments with vesicles formed from 6h. Leakage through the vesicular bilayer of 6h was determined by measuring the carboxyfluorescein release from the aqueous compartment of the vesicles. All data are consistent with the notion that the alkyl chain packing in the bilayers of the vesicles formed from the cyclic phosphates is less efficient than that in the bilayers of vesicles composed of di-n-alkyl phosphates.

A synthetic strategy for novel nonsymmetrical bola amphiphiles based on carbohydrates

A number of novel nonionic bolaform amphiphiles with nonidentical aldityl head groups, 1-(1-deoxy-D-galactitol-1-ylamino)-6-(1-deoxy-D-glucitol-1-ylamino)hexane, 1-(1-deoxy-D-mannitol-1-ylamino)-6-(1-deoxy-D-glucitol-1-ylamino)hexane, and 1-(1-deoxy-D-galactitol-1-ylamino)-6-(1-deoxy-D-mannitol-1-ylamino)hexane were synthesized by two successive reductive aminations involving 1,6-diaminohexane and the appropriate D-aldohexoses (D-glucose, D-mannose, and D-galactose) using 5% Pd on carbon as the catalyst. Typical reaction conditions were 40°C, 4MPa hydrogen and a reaction time of 4.5 h. The compounds were isolated as white solids in yields ranging from 39% to 72%. The intermediate aminoalditols, 1-(1-deoxy-D-glucitol-1-ylamino)-6-aminohexane and 1-(1-deoxy-D-galactitol-1-ylamino)-6-aminohexane were obtained as off-white solids in 80–85% yield. The bolaform amphiphiles containing 1-deoxy-D-glucitol head group(s) showed markedly lower melting points than the compounds with the 1-deoxy-D-mannitol and 1-deoxy-D-galactitol head groups, due to the presence of 1,3-syn interactions within the carbohydrate moiety. The novel bolaform compounds are potential starting materials for the synthesis of a broad range of gemini surfactants with nonidentical, carbohydrate-based head groups.

Sugar-Based Gemini Surfactants with pH-Dependent Aggregation Behavior: Vesicle-to-Micelle Transition, Critical Micelle Concentration, and Vesicle Surface Charge Reversal

In a recent report, we presented data on the rich and unusual pH-dependent aggregation behavior of a sugar-based (reduced glucose) gemini surfactant (Johnsson et al. J. Am. Chem. Soc. 2003, 125, 757). In the present study, we extend the previous investigation by introducing a different sugar headgroup (reduced mannose), by varying the spacer between the two main surfactant parts, and by introducing, in one of the surfactants, an amide linkage (instead of an amine linkage) between the headgroup and the unsaturated (C18:1) hydrocarbon tails. The aggregation behavior of these four gemini surfactants has been studied and compared by means of light scattering, cryo-transmission electron microscopy, electrophoretic mobility, and fluorescence measurements. We find that all four surfactants form vesicles near neutral or high pH. However, the vesicles made from the amine-containing geminis are transformed into cylindrical or wormlike micelles at lower pH values (pH < ~5.5). The micellization is driven mainly by an increased electrostatic repulsion, caused by the protonation of the tertiary amino groups, and we find that the nature of the sugar or spacer has little influence on this process. At low pH (pH 2), solely small globular micelles are found, and the critical micelle concentration at this pH is about 0.005-0.010 mM for the different amine-containing surfactants. As was expected, the gemini surfactant with the amide instead of the amine functional groups in the headgroup does not undergo the vesicle-to-micelle transition but displays only vesicle formation within the investigated pH range. The electrophoretic mobility measurements on the vesicular samples formed from the amine-containing geminis show that the vesicles are cationic below pH ~7-7.5; however, the vesicles acquire a substantial negative charge at a higher pH. The most probable explanation for this charge reversal is a strong adsorption (or binding) of hydroxide ions onto the vesicle surface. In accordance with this hypothesis, we find that the vesicles made from the amide-containing gemini are anionic (no protonation) even at a low pH (pH <5). Using a simple Poisson-Boltzmann model, we are able to describe the obtained ζ-potential profiles reasonably well and derive a hydroxide-ion binding constant (KOH) for the respective systems. We find that the nature of the sugar does have a small influence on KOH. The colloidal stability of all four types of the gemini vesicles seems to be well-described by the classical Derjaguin-Landau-Verwey-Overbeek theory, and the vesicles aggregate/flocculate rapidly in the limit of low surface potential. However, the flocculated vesicles can be easily redispersed by, for example, raising the pH of the solution, and this flocculation/redispersal process is completely reversible.

Synthesis and aggregation behavior of 2-(4-butyloctyl) malonic acid in aqueous solution. The formation of physically and colloidally stable vesicles by a branched-chain malonate

A new surfactant with a branched monoalkyl chain and a malonate headgroup has been synthesized: 2-(4-butyloctyl)malonic acid (BOMA). From the geometry of the surfactant, reflected in a packing parameter (P), it was anticipated that the surfactant would preferably aggregate in bilayers. This expectation was borne out in practice by the aggregation behavior, as studied by transmission electron microscopy (TEM) with negatively stained samples and freeze-fracture samples of aqueous vesicle dispersions. The structure of the surfactant headgroup has been varied by changes in pH of the vesicle dispersions. Over a wide pH range (pH 2.8-12.8) small unilamellar vesicles with a size of 20-50 nm were observed. Multilamellar vesicles were observed as well in the pH range 2.8-5.1. Phase-penetration experiments using an optical polarization microscope showed the birth and growth of myelins and multilamellar vesicles over a pH range 1.5-13.1. At pH < 2.8, a phase separation occured into a surfactant-rich, optically isotropic phase and a surfactant-lean phase. The physical and colloidal stability of the vesicular aggregates is high: up to one year as confirmed by TEM. The fusogenic properties of BOMA vesicles were examined. Upon the addition of Ca2+ ions, aggregates tended to become larger, but the formation of Ca2+ surfactant crystals was also observed