Superlattice of rodlike virus particles formed in aqueous solution through like-charge attraction

Rodlike tobacco mosaic virus (TMV) has been found to assemble into a 2D superlattice in aqueous solution with hexagonally packed structures in the presence of Ba(2+) through like-charge attraction whereas lower-Z divalent ions such as Zn(2+), Cd(2+), Mg(2+), and Ca(2+) induce only liquidlike ordering. The molar ratio between Ba(2+) and TMV is a crucial parameter in the formation of the superlattice. There is a critical molar ratio of Ba(2+) to TMV at which TMV exhibits a transition from a nonordered colloidal state to an ordered crystalline state. It is also found that the superlattice is formed regardless of the pH and TMV concentration within the range studied.