Polypeptide-based aerosol nanoparticles: self-assembly and control of conformation by solvent and thermal annealing.

Nanoconfined self-assemblies within aerosol nanoparticles and control of the secondary structures are shown here upon ionically complexing poly(L-lysine) (PLL) with dodecylbenzenesulfonic acid (DBSA) surfactant and using solvents chloroform, 1-propanol, or dimethylformamide. Different solvent volatilities and drying temperatures allowed tuning the kinetics of morphology formation. The supramolecular self-assembly and morphology were studied using cryo-TEM and SEM, and the secondary structures, using FT-IR. Highly volatile chloroform led to the major fraction of α-helical conformation of PLL(DBSA), whereas less volatile solvents or higher drying temperatures led to the increasing fraction of ß-sheets. Added drugs budesonide and ketoprofen prevented ß-sheet formation and studied PLL(DBSA)-drug nanoparticles were in the α-helical conformation. Preliminary studies showed that ketoprofen released with a slower rate than budesonide which was hypothesized to result from different localization of drugs within the PLL(DBSA) nanoparticles. These results instruct to prepare polypeptide aerosol nanoparticles with internal self-assembled structures and to control the secondary structures by aerosol solvent annealing, which we foresee to be useful, e.g., toward controlling the release of poorly soluble drug molecules.

Oblique self-assemblies and order-order transitions in polypeptide complexes with PEGylated triple-tail lipids.

We report on highly ordered oblique self-assemblies in ionic complexes of PEGylated triple-tail lipids and cationic polypeptides, as directed by side-chain crystallization, demonstrating also reversible oblique-to-hexagonal order-order transitions upon melting of the side chains. This is achieved in bulk by complexing cationic homopolypeptides, poly-l-lysine (PLys), poly-l-arginine (PArg), and poly-l-histidine (PHis), in stoichiometric amounts with anionic lipids incorporating two hydrophobic alkyl tails and one hydrophilic polyethylene glycol (PEG) tail in a star-shaped A(2)B geometry. Based on Fourier transform infrared spectroscopy (FTIR), the PLys and PArg complexes fold into α-helical conformation. Aiming to periodicities at different length scales, that is, hierarchies, the PEG tails were selected to control the separation of the polypeptide helices in one direction while the alkyl tails determine the distance between the hydrophilic polypeptide/PEG layers, resulting in an oblique arrangement of the helices. We expect that the high overall order, where the self-assembled domains are in 2D registry, is an outcome of a favorable interplay of plasticization due to the hydrophobic and hydrophilic lipid tails combined with the shape persistency of the peptide helices and the crystallization of the lipid alkyl chains. Upon heating the complexes over the melting temperature of the alkyl tails, an order-order transition from oblique to hexagonal columnar morphology was observed. This transition is reversible, that is, the oblique structure with 2D correlation of the helices is fully returned upon cooling, implying that the alkyl tail crystallization guides the structure formation. Also PHis complex forms an oblique self-assembly. However, instead of α-helices, FTIR suggests formation of helical structures lacking intramolecular hydrogen bonds, stabilized by steric crowding of the lipid. The current study exploits competition between the soft and harder domains, which teaches on concepts toward well-defined polypeptide-based materials.

Effect of double-tailed surfactant architecture on the conformation, self-assembly, and processing in polypeptide-surfactant complexes.

This work describes the solid-state conformational and structural properties of self-assembled polypeptide-surfactant complexes with double-tailed surfactants. Poly(L-lysine) was complexed with three dialkyl esters of phosphoric acid (i.e., phosphodiester surfactants), where the surfactant tail branching and length was varied to tune the supramolecular architecture in a facile way. After complexation with the branched surfactant bis(2-ethylhexyl) phosphate in an aqueous solution, the polypeptide chains adopted an alpha-helical conformation. These rod-like helices self-assembled into cylindrical phases with the amorphous alkyl tails pointing outward. In complexes with dioctyl phosphate and didodecyl phosphate, which have two linear n-octyl or n-dodecyl tails, respectively, the polypeptide formed antiparallel beta-sheets separated by alkyl layers, resulting in well-ordered lamellar self-assemblies. By heating, it was possible to trigger a partial opening of the beta-sheets and disruption of the lamellar phase. After repeated heating/cooling, all of these complexes also showed a glass transition between 37 and 50 degrees C. Organic solvent treatment and plasticization by overstoichiometric amount of surfactant led to structure modification in poly(L-lysine)-dioctyl phosphate complexes, PLL(diC8)(x) (x = 1.0-3.0). Here, the alpha-helical PLL is surrounded by the surfactants and these bottle-brush-like chains self-assemble in a hexagonal cylindrical morphology. As x is increased, the materials are clearly plasticized and the degree of ordering is improved: The stiff alpha-helical backbones in a softened surfactant matrix give rise to thermotropic liquid-crystalline phases. The complexes were examined by Fourier transform infrared spectroscopy, small- and wide-angle X-ray scattering, transmission electron microscopy, differential scanning calorimetry, polarized optical microscopy, and circular dichroism.