Oleg Borodin

The best things come in threes: Triply linked porphyrin arrays, so called porphyrin tapes, are intriguing molecules in terms of their stability, far red‐shifted absorption band, multi‐charge storage ability, and conductivity. Recent advances in the chemistry of porphyrin tape are summarized in this Minireview, in particular, the development of porphyrin tape variants such as expanded porphyrin hybrid tape, porphyrin arch‐tape, corrole tape, and subporphyrin tape.

Abstract

Triply linked porphyrin arrays, so called porphyrin tapes, are intriguing molecules in terms of their planar structures, far red‐shifted absorption bands, multi‐charge storage abilities, and high conductivities. Recently, porphyrin tape variants such as porphyrin‐expanded porphyrin hybrid tapes, porphyrin arch‐tapes, corrole tapes, and a subporphyrin tape have been explored as novel π‐conjugated materials. These new molecules exhibit electronic and structural characteristics owing to direct triple linkages. This Minireview first discusses the fundamental properties of the parent porphyrin tapes and the peripherally functionalized porphyrin tapes. Then, a focus has been placed on the syntheses, structures, and unique properties of the recently explored porphyrin tape variants.

Water scarcity and inadequate membrane selectivity have spurred interest in biomimetic desalination membranes, in which biological or synthetic water channels are incorporated in an amphiphilic bilayer. As low channel densities (0.1 to 10%) are required for sufficient water permeability, the amphiphilic bilayer matrix will play a critical role in separation performance. We determine selectivity limits for biomimetic membranes by studying the transport behavior of water, neutral solutes, and ions through the bilayers of lipid and block-copolymer vesicles and projecting performance for varying water channel densities. We report that defect-free biomimetic membranes would have water/salt permselectivities ~10⁸-fold greater than current desalination membranes. In contrast, the solubility-based permeability of lipid and block-copolymer bilayers (extending Overton’s rule) will result in poor rejection of hydrophobic solutes. Defect-free biomimetic membranes thus offer great potential for seawater desalination and ultrapure water production, but would perform poorly in wastewater reuse. Potential strategies to limit neutral solute permeation are discussed.

Simple prebiotic synthesis of high diversity dynamic combinatorial polyester libraries

Simple prebiotic synthesis of high diversity dynamic combinatorial polyester libraries, Published online: 31 May 2018; doi:10.1038/s42004-018-0031-1

Common anionic nucleophiles such as those derived from inorganic salts have not been used for enantioselective catalysis because of their insolubility. Here, we report that merging hydrogen bonding and phase-transfer catalysis provides an effective mode of activation for nucleophiles that are insoluble in organic solvents. This catalytic manifold relies on hydrogen bonding complexation to render nucleophiles soluble and reactive, while simultaneously inducing asymmetry in the ensuing transformation. We demonstrate the concept using a chiral bis-urea catalyst to form a tridentate hydrogen bonding complex with fluoride from its cesium salt, thereby enabling highly efficient enantioselective ring opening of episulfonium ion. This fluorination method is synthetically valuable considering the scarcity of alternative protocols and points the way to wider application of the catalytic approach with diverse anionic nucleophiles.

Ring-through-ring molecular shuttling in a saturated [3]rotaxane

Ring-through-ring molecular shuttling in a saturated [3]rotaxane, Published online: 30 April 2018; doi:10.1038/s41557-018-0040-9

Machine learning methods are becoming integral to scientific inquiry in numerous disciplines. We demonstrated that machine learning can be used to predict the performance of a synthetic reaction in multidimensional chemical space using data obtained via high-throughput experimentation. We created scripts to compute and extract atomic, molecular, and vibrational descriptors for the components of a palladium-catalyzed Buchwald-Hartwig cross-coupling of aryl halides with 4-methylaniline in the presence of various potentially inhibitory additives. Using these descriptors as inputs and reaction yield as output, we showed that a random forest algorithm provides significantly improved predictive performance over linear regression analysis. The random forest model was also successfully applied to sparse training sets and out-of-sample prediction, suggesting its value in facilitating adoption of synthetic methodology.