Mimicking nature’s chirality with magnetic colloids
DOI: 10.1063/1.4796706
Symmetry abounds in nature, but the beauty of proteins and other biological polymers lies in their asymmetry. Chirality, or handedness, of DNA and other biopolymers plays a critical role in their biochemical pathways: The binding properties of a left-handed DNA double helix differ significantly from those of the right-handed counterpart. Mimicking nature has not proven easy for scientists attempting to model, study, and engineer asymmetric polymers. Colloids—nanometer- to micron-sized particles—have emerged as molecular building-block candidates (see Physics Today, June 2006, page 15 ). Left alone, however, they spontaneously clump together or form ordered crystals. A key to making helical structures is steric hindrance, in which the size of the building blocks—atoms, molecules, or colloids—constricts the resulting bond angles. A team of scientists from the Paris Institute of Technology in France and New York University have discovered that binary silica microspheres, joined into dumbbell shapes and with an iron-oxide ring around the joining bond, align and extend into long asymmetric polymer chains in the presence of a magnetic field. The researchers showed that steric repulsion causes either left- or right-handed helices to form when the particles have different diameters. The
