ABSTRACT
Self-assembly takes place through both a reversible non-covalent interaction and a unique recognition involving a variety of building blocks. The components involved in the formation of two-dimensional (2-D) and three-dimensional (3-D) nano-or µm scaled periodicities such a cubic, cylindrical, or mesophases are van der Waals and electrostatic forces, hydrogen bonding as well as p-p stacking forces (Gazit, 2010). The various observed phases have been investigated extensively for example surfactant water (Seddon, 1996), block copolymers (Matsen and Bates, 1996), and thermotropic materials (Tschierske, 2001). Lyotropic materials can provide templates for porous inorganic materials (Attard et al., 1997) and lyotropics such as double chained N-cationic lipids (Clancy and Paradies, 1997; Clancy et al., 1995). These materialsare also capable of forming complexes with DNA and neutral lipids as well as being useful as carriers in gene therapy and other pharmaceutical formulations (Koltover et al., 1998; Paradies, 1992; Thies et al., 1996). Other important materials in self-assembly are dendrons (Rosen et al., 2009) and nanostructural soft matter which show a tapered shape and account for the formation of bulk phases such as lyotropic materials (Bates and Fredrickson, 1999) or block copolymers (Anderson et al., 1988). Recently, Ungar et al. (2003)showed that a self-organized supramolecular dendrimer nanostructure possessed a noncubic phase and established a relationship between the chemical structure and the self-assembly composed of tapered dendrons. These materials reveal s and BCC phases with an increase in temperature. Subsequently, dodecahedral quasicrystals were formed, displaying wedge-shaped dendrimer molecules that self-assembled into virtually spherical particles. It was established that each spherical particles from the branched compounds contained on average 11.6 molecules, on a tetragonal lattice with 30 particles per unit cell. Similar hierarchical structures, though not identical, have been found for colloidal crystals of lipid A-phosphates from the bacterial E. coli source (Faunce and Paradies, 2010). Understanding the characteristics of jammed lipid A-phosphate packings provides basic insights into the structural arrangements of lipid A-phosphate liquid crystals and bulk properties of these supramolecular liquid crystals, glasses, and selected aspects of their biological actions. This contribution also covers recent advances in understanding jammed packings of polydisperse sphere mixtures, non-spherical particles for example ellipsoids within the assembly and polyhedra for example by “E.coli Autovaccines” (Zimmermann et al., 2003)
The most conserved component in lipopolysaccharides (LPS) from gram-negative bacteria is lipid A. Lipid A is linked to a core of oligopolysaccharides (Raetz and Whitefield, 2002), and in its di-phosphorylated form consists of a b-1,6-linked Dglucosamine disaccharide carrying six saturated fatty-acid residues and two negatively charged phosphates at the reducing and non-reducing end of the glucosamine (Figure 1). Approximately 1,00,000 patients die in the United States every year from infections acquired while in the hospital or nursing homes due to the presence of LPS from gram-negative bacteria. The lipophilic part of LPS, lipid A-diphosphate is associated with lethal endotoxicity, pyrogenicity, specific immune response. It is also responsible for triggering a cascade of cellular mediators, for example tumor necrosis factor (TNF) α, interleukins, leukotrienes, thromboxane A2 from monocytesand macrophages. A detailed insight into the spatial-structure and the packing of toxic and non-toxic lipid A phosphates will aid in the understanding of the following: self-assembly, physical interactions with gram-negative bacteria, biofilm associations, LPS components, antibiotic resistance, membrane components, cationic antimicrobial (CAM) peptides, membrane fusion, and divalent cations, particularly Mg2+ and Ca2+ ions (Ernst et al., 1999; Faunce et al., 2005). From specular neutron scattering studies it is observed that these divalent counterions modulate the mechanical properties of interacting LPS membranes (Schneck et al., 2009).
