Molecular-level insights into a tripolyphosphate and pyrophosphate templated membrane assembly.

Templated assembly of small molecules into nano-structural architectures has been used extensively by nature throughout its evolution. These systems have also been studied in artificial systems to design a phosphate templated assembly. However, it is yet to be investigated how the molecules interact among themselves at the molecular level and whether the phosphate templated assembly has any role in the formation of prebiotic protocellular membranes. Here, we report the prebiotic synthesis of choline-based cationic amphiphiles (-N+Me3) and the templated assembly of these amphiphiles with tripolyphosphate (TPP) and pyrophosphate (PPi). SEM, TEM, FLIM, DLS, fluorescence, and encapsulation studies suggest that the number of phosphate units in the phosphate backbone controls the formation and size of the protocell vesicles. Isothermal titration calorimetry, turbidimetric studies, and NMR experiments suggest that the cationic amphiphile forms a 3 : 1 catanionic complex with TPP and a 2 : 1 catanionic complex with PPi. The templated catanionic complex further self-assembles into vesicles, and the structure of the complex guides the size of the assembly. The size-controlling ability of the phosphate backbone might have been utilized in the prebiotic era to support the dynamics and tunability of protocellular membrane compartments.

Lipidated Lysine and Fatty Acids Assemble into Protocellular Membranes to Assist Regioselective Peptide Formation: Correlation to the Natural Selection of Lysine over Nonproteinogenic Lower Analogues.

The self-assembly of prebiotically plausible amphiphiles (fatty acids) to form a bilayer membrane for compartmentalization is an important factor during protocellular evolution. Such fatty acid-based membranes assemble at relatively high concentrations, and they lack robust stability. We have demonstrated that a mixture of lipidated lysine (cationic) and prebiotic fatty acids (decanoic acid, anionic) can form protocellular membranes (amino acid-based membranes) at low concentrations via electrostatic, hydrogen bonding, and hydrophobic interactions. The formation of vesicular membranes was characterized by dynamic light scattering (DLS), pyrene and Nile Red partitioning, cryo-transmission electron microscopy (TEM) images, and glucose encapsulation studies. The lipidated nonproteinogenic analogues of lysine (Lys), such as ornithine (Orn) and 2,4-diaminobutyric acid (Dab), also form membranes with decanoate (DA). Time-dependent turbidimetric and 1H NMR studies suggested that the Lys-based membrane is more stable than the membranes prepared from nonproteinogenic lower analogues. The Lys-based membrane embeds a model acylating agent (aminoacyl-tRNA mimic) and facilitates the colocalization of substrates to support regioselective peptide formation via the α-amine of Lys. These membranes thereby assist peptide formation and control the positioning of the reactants (model acylating agent and -NH2 of amino acids) to initiate biologically relevant reactions during early evolution.