Coassembled molecular structures are known to exhibit a large variety of geometries and morphologies. A grand challenge of self-assembly design is to find techniques to control the crystal symmetries and overall morphologies of multicomponent systems. By mixing +3 and -1 ionic amphiphiles, we assemble crystalline ionic bilayers in a large variety of geometries that resemble polyhedral cellular crystalline shells and archaea wall envelopes. We combine TEM with SAXS and WAXS to characterize the coassembled structures from the mesoscopic to nanometer scale. The degree of ionization of the amphiphiles and their intermolecular electrostatic interactions are controlled by varying pH. At low and high pH values, we observe closed, faceted vesicles with two-dimensional hexagonal molecular arrangements, and at intermediate pH, we observe ribbons with rectangular-C packing. Furthermore, as pH increases, we observe interdigitation of the bilayer leaflets. Accurate atomistic molecular dynamics simulations explain the pH-dependent bilayer thickness changes and also reveal bilayers of hexagonally packed tails at low pH, where only a small fraction of anionic headgroups is charged. Coarse-grained simulations show that the mesoscale geometries at low pH are faceted vesicles where liquid-like edges separate flat crystalline domains. Our simulations indicate that the curved-to-polyhedral shape transition can be controlled by tuning the tail density in regions where sharp bends can form the polyhedral edges. In particular, the pH acts to control the overall morphology of the ionic bilayers by changing the local crystalline order of the amphiphile tails.

The delivery of nucleic acids has the potential to revolutionize medicine by allowing previously untreatable diseases to be clinically addressed. Viral delivery systems have shown immunogenicity and toxicity dangers, but synthetic vectors have lagged in transfection efficiency. Previously, we have developed a modular, linear-dendritic block copolymer architecture with high gene transfection efficiency compared to commercial standards. This rationally designed system makes use of a cationic dendritic block to condense the anionic DNA and forms complexes with favorable endosomal escape properties. The linear block provides biocompatibility, protection from serum proteins, and can be functionalized with a targeting ligand. In this work, we quantitate performance of this system with respect to intracellular barriers to gene delivery using both high-throughput and traditional approaches. An image-based, high throughput assay for endosomal escape is described and applied to the block copolymer system. Nuclear entry is demonstrated to be the most significant barrier to more efficient delivery and will be addressed in future versions of the system.

The crystallization of molecules with polar and hydrophobic groups, such as ionic amphiphiles and proteins, is of paramount importance in biology and biotechnology. By coassembling dilysine (+2) and carboxylate (-1) amphiphiles of various tail lengths into bilayer membranes at different pH values, we show that the 2D crystallization process in amphiphile membranes can be controlled by modifying the competition of long-range and shortrange interactions among the polar and the hydrophobic groups. The pH and the hydrophobic tail length modify the intermolecular packing and the symmetry of their crystalline phase. For hydrophobic tail lengths of 14 carbons (C 14 ), we observe the coassembly into crystalline bilayers with hexagonal molecular ordering via in situ small-and wide-angle X-ray scattering. As the tail length increases, the hexagonal lattice spacing decreases due to an increase in van der Waals interactions, as demonstrated by atomistic molecular dynamics simulations. For C 16 and C 18 we observe a reentrant crystalline phase transition sequence, hexagonalrectangular-C-rectangular-P-rectangular-C-hexagonal, as the solution pH is increased from 3 to 10.5. The stability of the rectangular phases, which maximize tail packing, increases with increasing tail length. As a result, for very long tails (C 22 ), the possibility of observing packing symmetries other than rectangular-C phases diminishes. Our work demonstrates that it is possible to systematically exchange chemical and mechanical energy by changing the solution pH value within a range of physiological conditions at room temperature in bilayers of molecules with ionizable groups.amphiphilic membranes | self-assembly | hydrophobic interaction N ature uses electrostatic interactions among positively and negatively charged groups to induce the organization of biomolecules into highly complex structures that respond to ionic changes (1, 2). The structure of the aggregates at specific ionic conditions is intimately related to its function. Therefore, understanding the mechanisms that control the structure of molecules with hydrophobic and polar groups at physiological conditions is of great importance in molecular biology and biotechnology. In particular, amphiphilic molecules that have polar ionizable groups, such as proteins and lipids, can change their structures and functions in response to the pH and the concentration of ions in the solution (3), thereby affecting their physical properties and functions. For example, the structure of lipid membranes affects the structure and activity of membrane-bound proteins (4-6). Furthermore, the intermolecular packing density and structure are known to affect the molecular diffusion rates of water and ions across membranes (7,8). Changing the packing density of molecules within membranes could also be useful for controlling encapsulation and release efficiency of molecules inside a vesicle (9). Additionally the spacing between amphiphilic molecules within a membrane may control the capacity to encapsulate or release...

The radial distribution of monovalent cations surrounding spherical nucleic acid-Au nanoparticle conjugates (SNA-AuNPs) is determined by in situ small-angle x-ray scattering (SAXS) and classical density functional theory (DFT) calculations. Small differences in SAXS intensity profiles from SNA-AuNPs dispersed in a series of solutions containing different monovalent ions (Na(+), K(+), Rb(+), or Cs(+)) are measured. Using the "heavy ion replacement" SAXS (HIRSAXS) approach, we extract the cation-distribution-dependent contribution to the SAXS intensity and show that it agrees with DFT predictions. The experiment-theory comparisons reveal the radial distribution of cations as well as the conformation of the DNA in the SNA shell. The analysis shows an enhancement to the average cation concentration in the SNA shell that can be up to 15-fold, depending on the bulk solution ionic concentration. The study demonstrates the feasibility of HIRSAXS in probing the distribution of monovalent cations surrounding nanoparticles with an electron dense core (e.g., metals).

Charged nanoscale filaments are well-known in natural systems such as filamentous viruses and the cellular cytoskeleton. The unique properties of these structures have inspired the design of self-assembled nanofibers for applications in regenerative medicine, drug delivery, and catalysis, among others. We report here on an amphiphile of completely different chemistry based on azobenzene and a quaternary ammonium bromide headgroup that self-assembles into highly charged nanofibers in water and orders into two-dimensional crystals. Interestingly small-angle X-ray scattering (SAXS) shows that these fibers of 5.6 nm cross-sectional diameter order into crystalline arrays with remarkably large interfiber spacings of up to 130 nm. Solution concentration and temperature can be adjusted to control the interfiber spacings, and addition of salt destroyed the crystal packing indicating the electrostatic repulsions are necessary for the observed ordering. Our findings here demonstrate the universal nature of this phenomenon in systems of highly charged nanoscale filaments.