Structural States of Self-Assembled Lamellar DNA-Membrane Templates During Artificial Biomineralization of CdS Nanorods

INTRODUCTION Self-assembled complexes comprised of anionic polyelectrolytes and cationic lipids have recently received intense experimental and theoretical attention. In this preprint, we examine CdS growth within self-assembled lamellar DNA-membrane templates, a simple prototypical biomineralization system in which the structures, charge distributions, and phase behavior of the components can be controlled precisely. DNA-membrane complexes were originally conceived as non-viral gene delivery systems. The addition of DNA to cationic liposomes induces a topological transition from liposomes to condensed, birefringent liquid crystalline globules with a novel multilamellar structure, in which a periodic one-dimensional (1D) lattice of parallel DNA chains is confined between stacked two-dimensional (2D) lipid sheets. The interhelical distance between DNA chains in the 1D lattice intercalated between the lamellar membrane sheets can be tuned between 2.5-6.0 nm by changing the relative proportion of cationic and neutral lipids. DNA within these lamellar complexes can condense in the presence of divalent counterions into close-packed rafts. In this work, we use Cd, the cationic component of CdS, to drive this 2-D DNA condensation within the membrane lipid galleries. Since the Cd ions are confined and organized by the inter-DNA nanopores, we can use the DNA-membrane complex as a nanoreactor to template the growth of CdS nanorods via reaction with H2S. We also examine how the structure of the templated CdS nanorods are affected when the charge of the membrane is tuned relative to the charge of the DNA, as well as when the degree of overcharging is varied for both positively and negatively charged templates. We show that crystallographic control of inorganic nanostructures is possible using these simple DNA-membrane complexes as templates.