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.

Model lipid layers are very promising in investigating the complex network of recognition, transport and signaling processes at membranes. We have developed a novel and generic approach to create supported lipid membranes tethered by metal-affinity binding. By self-assembly we have generated various interfaces that display histidine sequences (6xHis) via polymer spacers. These histidine-functionalized interfaces are designed to allow specific docking and fusion of vesicles containing metal-chelating lipids. By means of surface plasmon resonance and atomic force microscopy we analyzed the formation and subsequently the structure of these solid-supported membranes. Although the affinity constant of single ligand-receptor pairs is only in the micromolar range, very stable immobilization of these membranes was observed. This behavior can be explained by multivalent interactions resembling many features of cell adhesion. The process is highly specific, because vesicle docking and bilayer formation are strictly dependent on the presence of metal-affinity ligand-receptor pairs. The surface accessibility and geometry of these tethered membranes were probed by binding of histidine-tagged polypeptides. The supported membranes show adsorption kinetics and values similar to planar supported monolayers. Using various combinations of metal-chelating and histidine-tagged lipids or thiols these metal-affinity-tethered membranes should make a great impact on probing and eventually understanding the dynamic dialog of reconstituted membrane proteins.

Protein structure and function rely on a still not fully understood interplay of energetic and entropic constraints defined by the permutation of the twenty genetically encoded amino acids. Many attempts have been undertaken to design peptide-peptide interaction pairs and synthetic receptors de novo by using this limited number of building blocks. We describe a rational approach to creating a building block based on a tailored metal-chelating amino acid. Nepsilon,Nepsilon-bis(carboxymethyl)-L-lysine can be flexibly introduced into peptides by 9-fluorenylmethoxycarbonyl solid-phase chemistry. The corresponding metal-chelating peptides act as metal sensors and synthetic receptors for histidine-tagged proteins. These biochemical tweezers will open new ways to control protein-protein interactions, to design peptide-based interaction pairs, or to generate switchable protein function.

In an attempt to get a better insight in specific base pairing by self-organization of DNA or RNA, the synthesis of a complete set of monoalkyl ribonucleotides is described. The thermodynamic phase and mixing properties of these self-organizing RNA amphiphiles were analyzed within two dimensions using film balance technique. The pure compounds form stable monolayers at the air−water interface on a physiological buffer. In analogy to base-paired RNA or DNA in solution, the monolayers were mostly stabilized by complexing the phosphate groups by calcium or magnesium ions. By use of mixtures of RNA amphiphiles, specific recognition and base-pair formation of monoalkyl phospho adenosine/uridine were demonstrated.

We describe the properties of aqueous micelles obtained from n-alkyl phosphoryl nucleosides, in particular n-hexadecylphosphoryladenosine (C16-AMP), uridine (C16-UMP), and -cytidine (C16-CMP). These compounds were obtained enzymatically. It is shown that each of these compounds form micelles spontaneously in water with a critical micelle concentration in the range of 20−35 μM and an aggregation number of 69, which indicates that the chemical structure of the bases has no significant influence on the aggregation behavior. UV-absorption and circular dichroic measurements suggest that the nucleoside is in an aqueous environment, as expected from the amphiphilic character of the compounds. UV absorption suggests a moderate self-stacking among the bases for each type of micelle. When we mixed micelles bearing complementary bases with each other (e.g., C16-AMP with C16-CMP), a weak hypochromic effect was observed, which can be taken as an indication of complementary base interaction. However, such electronic perturbation was observed also in noncomplementary bases, e.g., when C16-CMP micelles were mixed with C16-UMP micelles. These micelle data are compared with the corresponding data obtained with liposomes obtained from phosphatidyl nucleosides. All together, these data illustrate a novel type of polymeric nucleoside interaction with which no covalent bonds form among the monomers, and in which the nucleobases are distributed as a supramolecular spherical aggregate.

In an attempt to adjust the lateral density of monolayer and multilayer films of a ferroelectric liquid crystalline copolymer, blends of the copolymer were made with the corresponding mesogenic monomer unit. The monomer was chosen as the second component since it forms monolayer films which are more condensed than the copolymer and because of its miscibility with the structurally similar copolymer. Analysis of the interaction between the molecules of the mixed monolayers included II-area isothermal data, calculation of the excess AGmh, thermal dependence of isotherms, and Brewster angle microscopy. On the basis of these results, the films appear to be completely miscible over all conditions presented and the blend monolayer films are more condensed than the pure copolymer films.

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