Covalent, sequence-specific attachment of long DNA molecules to a surface using DNA-templated click chemistry.

We present a novel method that covalently and sequence-specifically attaches long DNA molecules to a surface that is compatible with high-resolution atomic force microscopy (AFM) imaging. Surfaces prepared with this approach are ideally suited for performing biophysical experiments on single DNA molecules.

Predicting the relative solubilities of racemic and enantiopure crystals by density-functional theory.

Isolation of chiral molecules as pure enantiomers remains a fundamental challenge in chemical research. Enantioselective enrichment through preferential crystallization is an efficient method to achieve enantiopure compounds, but its applicability depends on the relative stability of the enantiopure and racemic crystal forms. Using a simple thermodynamic model and first-principles density-functional calculations, it is possible to predict the difference in solubility between the enantiopure and racemic solid phases. This approach uses dispersion-corrected density functionals and is capable of accurately predicting the solution-phase entantiomeric excess to within about 10 % of experimental measurements on average. The accuracy of the exchange-hole dipole moment (XDM) model of dispersion enables the viability of the proposed method.

Pasteur's tweezers revisited: on the mechanism of attrition-enhanced deracemization and resolution of chiral conglomerate solids.

Insights into the mechanism of attrition-enhanced deracemization and resolution of solid enantiomorphic chiral compounds are obtained by crystal size and solubility measurements and by isotopic labeling experiments. Together these results help to deconvolute the various chemical and physical rate processes contributing to the phenomenon. Crystal size measurements highlight a distinct correlation between the stochastic, transient growth of crystals and the emergence of a single solid enantiomorph under attrition conditions. The rapid mass transfer of molecules between the solution and solid phases under attrition is demonstrated, and the concept of a crystal-size-induced solubility driving force is exploited to overcome the stochastic nature of the crystal growth and dissolution processes. Extension to non-racemizing conditions provides a novel methodology for chiral resolution. Implications both for practical chiral separations and for the origin of biological homochirality are discussed.