Magnetically Directed Two-Dimensional Crystallization of OmpF Membrane Proteins in Block Copolymers.

Two-dimensional (2D) alignment and crystallization of membrane proteins (MPs) is increasingly important in characterizing their three-dimensional (3D) structure, in designing pharmacological agents, and in leveraging MPs for biomimetic devices. Large, highly ordered MP 2D crystals in block copolymer (BCP) matrices are challenging to fabricate, but a facile and scalable technique for aligning and crystallizing MPs in thin-film geometries would rapidly translate into applications. This work introduces a novel method to grow larger and potentially better ordered 2D crystals by performing the crystallization process in the presence of a strong magnetic field. We demonstrate the efficacy of this approach using a ß-barrel MP, outer membrane protein F (OmpF), in short-chain polybutadiene-poly(ethylene oxide) (PB-PEO) membranes. Crystals grown in a magnetic field were up to 5 times larger than conventionally grown crystals, and a signal-to-noise (SNR) analysis of diffraction peaks in Fourier transforms of specimens imaged by negative-stain electron microscopy (EM) and cryo-EM showed twice as many high-SNR diffraction peaks, indicating that the magnetic field also improves crystal order.

Phase-selective chemical extraction of selenium and sulfur from nanoscale metal chalcogenides: a general strategy for synthesis, purification, and phase targeting.

Controlling the composition and phase formation of bulk and nanoscale solids underpins efforts to control physical properties. Here, we introduce a powerful new chemical pathway that facilitates composition-tunable synthesis, post-synthesis purification, and precise phase targeting in metal chalcogenide systems. When metal selenides and sulfides react with trioctylphosphine (TOP) at temperatures that range from 65 to 270 °C, selenium and sulfur are selectively extracted to produce the most metal-rich chalcogenide that is stable in a particular binary system. This general approach is demonstrated for SnSe(2), FeS(2), NiSe(2), and CoSe(2), which convert to SnSe, FeS, Ni(3)Se(2), and Co(9)Se(8), respectively. In-depth studies of the Fe-Se system highlight the precise phase targeting and purification that is achievable, with PbO-type FeSe (the most metal-rich stable Fe-Se phase) forming exclusively when other Fe-Se phases, including mixtures, react with TOP. This chemistry also represents a new template-based nanoparticle "conversion chemistry" reaction, transforming hollow NiSe(2) nanospheres into hollow NiSe nanospheres with morphological retention.

On-wire conversion chemistry: engineering solid-state complexity into striped metal nanowires using solution chemistry reactions.

Multisegment template-grown metal nanowires have become important one-dimensional materials for a variety of applications in chemistry, physics, engineering, biology, and medicine. Segmented nanowires are traditionally fabricated in anodic alumina membranes using electrodeposition, and this technique is applicable to a range of metals, alloys, and semiconductors. Here we report an alternative and simple solution chemistry strategy for incorporating multimetal components of controllable length and composition into template-grown metal nanowires. By reacting membrane-confined nanowires with metal salt solutions under reducing conditions, site-specific diffusion occurs to convert one or both nanowire tips or the entire nanowire into a variety of multimetal phases. Platinum-based intermetallic compounds were chosen as targets for demonstrating the feasibility of the on-wire conversion chemistry.