A radical approach to radicals

Abstract

Nitroxide radicals are characterized by a long-lived spin-unpaired electronic ground state and are strongly sensitive to their chemical surroundings. Combined with electron paramagnetic resonance spectroscopy, these electronic features have led to the widespread application of nitroxide derivatives as spin labels for use in studying protein structure and dynamics. Site-directed spin labelling requires the incorporation of nitroxides into the protein structure, leading to a new protein–ligand molecular model. However, in protein crystallographic refinement nitroxides are highly unusual molecules with an atypical chemical composition. Because macromolecular crystallography is almost entirely agnostic to chemical radicals, their structural information is generally less accurate or even erroneous. In this work, proteins that contain an example of a radical compound (Chemical Component Dictionary ID MTN) from the nitroxide family were re-refined by defining its ideal structural parameters based on quantum-chemical calculations. The refinement results show that this procedure improves the MTN ligand geometries, while at the same time retaining higher agreement with experimental data.

Harnessing Smectic Ordering for Electric‐Field‐Driven Guided‐Growth of Surface Topography in a Liquid Crystal Polymer

“…LCP has long been investigated for the application of switchable topographic surfaces with many inspiring designs. [ 41–45 ] Consistent with our previous report, if the guided EHD growth is kept in Stage 1, the formed structures can be either maintained by quenching below T g or removed through thermal relaxation by maintaining the temperature above T g , after the applied electric field is turned off (Figure S7, Supporting Information). Nevertheless, if the EHD growth is extended into Stage 2, the formed structures cannot be completely removed anymore (Figure S8, Supporting Information), presumably due to the rotation and translation of smectic layers during the flow.…”

Precisely Controllable Artificial Muscle with Continuous Morphing based on “Breathing” of Supramolecular Columns

“…The extraordinary feature of P‐DCS12 is the precise photoprogrammability and temperature‐controllability, which are rare in conventional azobenzene‐based actuators that often have nonnegligible photothermal effect. [ 54–56 ] In P‐DCS12, the structural change of DCS moieties under blue light takes place much slower than that of azobenzenes, which might be ascribed to a lower extinction coefficient of DCS moiety at 450 nm (Figure S20, Supporting Information, ≈3.6 × 10 2 L mol −1 cm −1 vs ≈2 × 10 4 L mol −1 cm −1 for azobenzenes at 365 nm). [ 57,58 ] The relatively weak absorption allows the regulable penetration of blue light and thus the photoprogrammable bending.…”