Dynamic Diastereomerism on Chiral Surfaces.

Adsorption of chiral molecules on chiral surfaces implies diastereomerism, evident in the adoption of distinct adsorption geometries. We show here that this diastereomerism produces a signature in the motion of chiral molecules desorbing from a chiral surface. The rotations of S- and R-alanine molecules are analyzed upon desorption from R-Cu{531} using first-principles molecular dynamics simulations. S-Ala molecules exhibit a larger angular momentum, with a clear preference for one rotational sense, whereas no such preference is observed for R-Ala molecules upon desorption from this surface. These trends would be reversed for desorption from the S-Cu{531} surface. Possible applications include chiral separation techniques and enantiospecific sensors.

Self-Assembly Dynamics of Reconfigurable Colloidal Molecules.

Colloidal molecules are designed to mimic their molecular analogues through their anisotropic shape and interactions. However, current experimental realizations are missing the structural flexibility present in real molecules thereby restricting their use as model systems. We overcome this limitation by assembling reconfigurable colloidal molecules from silica particles functionalized with mobile DNA linkers in high yields. We achieve this by steering the self-assembly pathway toward the formation of finite-sized clusters by employing high number ratios of particles functionalized with complementary DNA strands. The size ratio of the two species of particles provides control over the overall cluster size, i.e., the number of bound particles N, as well as the degree of reconfigurability. The bond flexibility provided by the mobile linkers allows the successful assembly of colloidal clusters with the geometrically expected maximum number of bound particles and shape. We quantitatively examine the self-assembly dynamics of these flexible colloidal molecules by a combination of experiments, agent-based simulations, and an analytical model. Our "flexible colloidal molecules" are exciting building blocks for investigating and exploiting the self-assembly of complex hierarchical structures, photonic crystals, and colloidal metamaterials.

Surface Chirality Influences Molecular Rotation upon Desorption.

Chiral surfaces offer great potential as a medium for enantioselective synthesis or separation, yet their dynamic enantiospecific interactions with adsorbates are not well understood. Here, the influence of chiral surfaces on the molecular rotations of desorbing molecules is investigated. Formic acid desorption from Cu{531} and Cu{110} serve as model systems for desorption processes of an achiral adsorbate from a chiral and an achiral surface. Our first-principles molecular dynamics study reveals a much larger and more directed angular momentum for molecules desorbing from the chiral surface and a clear preference for one sense of rotation. This result provides new insight into desorption and adsorption processes and propensities on chiral surfaces.