Preparation and Characterization of Vesicles from Mono-n-alkyl Phosphates and Phosphonates

Abstract

The aggregation properties of different linear, single-chain alkyl phosphates and phosphonates in water were investigated at concentrations of up to 50 mM as a function of pH, focusing in particular on spontaneous vesicle formation. Under conditions where about half the molecules are monoionic and half the molecules are completely protonated (pH ≈ 2), n-dodecylphosphoric acid, n-decylphosphonic acid, and n-dodecylphosphonic acid spontaneously form vesicles at room temperature. For n-hexadecylphosphoric acid, stable vesicles only form above ∼40 °C. The presence of vesicles was evidenced by light and electron microscopy and in the case of n-dodecylphosphoric acid by entrapment experiments using as water soluble probes glucose, dextran, and pepsin. The phase-transition temperature of vesicles of n-dodecylphosphoric acid was 2.3 °C, as determined by differential scanning calorimetry. For n-hexadecylphosphoryladenosine evidence for micelle formation has been obtained with a cmc of 20−50 μM at 25 °C. In an experimental extension of the vesicle self-reproduction principles to phosphoamphiphiles, results are also presented on the alkaline hydrolysis of the water-insoluble di-n-decyl-4-nitrophenyl phosphate, which led to the formation of 4-nitrophenol and di-n-decyl phosphate, the latter being a known vesicle-forming amphiphile.

Biomimetic Synthesis and Properties of Polyprenoid

“…Moreover, the intermolecular hydrogen bonding network between the head group area of polyprenyl phosphate and the polyprenyl www.intechopen.com alcohol contributes also to the stabilization of the vesicles at basic pH ( Fig. 6) (Apel et al, 2002;Walde et al, 1997). Consistently, we observed that the addition of the free polyprenol decreases the water permeability of polyprenyl phosphate vesicles.…”

Microscopic Imaging of Fluorescence Anisotropy of Rhodamine B at the Free and Surfactant-Modified Toluene/Water Interfaces Excited under Total Internal Reflection Conditions

“…The octadecyl-group of C 18 RB may interact with two hexadecyl-groups These low reproducibility and large in r values suggest partial two-dimensional crystallization or the assembling of Hdhp and/or dhp -at the toluene/water interface. The high viscosity of the micelle surface of Hdhp or monoalkyl dihydrogen phosphate was also reported at about pH 5 [27,28], in which a hydrogen-bonding structure was suggested between the non-dissociated and dissociated forms [28].…”

Self-Assembly of Phosphate Amphiphiles in Mixtures of Prebiotically Plausible Surfactants

“…Interestingly, phosphate amphiphiles have not yet attracted much attention from researchers who investigate protocell or precellular compartments. This lack of interest is likely due to the very narrow pH range in which stable vesicles can be formed by pure phosphate amphiphiles (Walde et al, 1997).…”

“…Whereas the fatty acid molecules were only partially carrying a single negative charge, which could be easily stabilized by an H bond, all phosphate headgroups were anionic, with approximately 50% of them being in principle dianionic, a state that certainly induces an increase in the electrostatic repulsion between the amphiphiles. As a result, half the molecules should be considered to have a wedge shape, which is known to promote the formation of micelles instead of bilayers (Walde et al, 1997;Schuler et al, 2001). Indeed, the higher curvature of micellar structures allows the reduction of the repulsive interactions between the charged headgroups.…”

“…Indeed, whereas investigations of fatty acid structure formation have been carried out in mixtures, the few studies dealing with single-chain phosphate amphiphiles, which established their ability to form bilayers in a narrow acidic pH range (around pH 2) (Walde et al, 1997;Sakai et al, 2012), have only pertained to pure phosphate amphiphile membranes.…”