Halogen bonding with carbon:directional assembly of non-derivatised aromatic carbon systems into robust supramolecular ladder architectures †

Carbon, although the central element in organic chemistry, has been traditionally neglected as a target for directional supramolecular interactions. The design of supramolecular structures involving carbon-rich molecules, such as arene hydrocarbons, has been limited almost exclusively to non-directional π-stacking, or derivatisation with heteroatoms to introduce molecular assembly recognition sites. As a result, the predictable assembly of non-derivatised, carbon-only π-systems using directional non-covalent interactions remains an unsolved fundamental challenge of solid-state supramolecular chemistry. Here, we propose and validate a different paradigm for the reliable assembly of carbon-only aromatic systems into predictable supramolecular architectures: not through non-directional π-stacking, but via specific and directional halogen bonding. We present a systematic experimental, theoretical and database study of halogen bonds to carbon-only π-systems (C-I⋯πC bonds), focusing on the synthesis and structural analysis of cocrystals with diversely-sized and -shaped non-derivatised arenes, from one-ring (benzene) to 15-ring (dicoronylene) polycyclic atomatic hydrocarbons (PAHs), and fullerene C60, along with theoretical calculations and a systematic analysis of the Cambridge Structural Database. This study establishes C-I⋯πC bonds as directional interactions to arrange planar and curved carbon-only aromatic systems into predictable supramolecular motifs. In &gt;90% of herein presented structures, the C-I⋯πC bonds to PAHs lead to a general ladder motif, in which the arenes act as the rungs and halogen bond donors as the rails, establishing a unique example of a supramolecular synthon based on carbon-only molecules. Besides fundamental importance in the solid-state and supramolecular chemistry of arenes, this synthon enables access to materials with exciting properties based on simple, non-derivatised aromatic systems, as seen from large red and blue shifts in solid-state luminescence and room-temperature phosphorescence upon cocrystallisation.</p

Azo dye polyelectrolyte multilayer films reversibly re-soluble with visible light

Polymeric multilayer films were prepared using a layer-by-layer (LBL) technique on glass surfaces, by repeated and sequential dipping into dilute aqueous solutions of various combinations of water-soluble polyanions (polyacrylic acid (PAA)), polycations (polyallylamine hydrochloride (PAH) or chitosan (CS)), with bi-functional water-soluble cationic azo dyes bismark brown R bismarck brown red or bismark brown Y (BBY), or anionic azo dyes allura red (ALR) or amaranth (AMA), as ionic cross-linkers. The electrostatically-assembled ionically-paired films showed good long-term stability to dissolution, with no re-solubility in water. However, upon exposure to low power visible light under running water, the films photo-disassembled back to their water-soluble constituent components, via structural photo-isomerization of the azo ionic crosslinkers. The relative rate of the disassembly (RRD) of the films was established using UV-Vis spectroscopy, demonstrating that these assemblies can in principle represent fully recyclable, environmentally structurally degradable materials triggered by exposure to sunlight, with full recovery of starting components. A density functional theory treatment of the allura red azo dye rationalizes the geometrical isomerization mechanism of the photo-disassembly and provides insight into the energetics of the optically-induced structural changes that trigger the disassembly and recovery

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Plastic Microbead Accumulation in our Freshwaters: North American Great Lakes Assessments and Perspective

The authors review recent studies conducted across the Great Lakes of North America to assess the quantity and type of microplastic waste found in these waters, sediments, and beaches. Findings from their own studies are shared, sampling plastic pollution from remote and secluded Nature Reserves in Lake Erie (ON), and the Ottawa River watershed (QC), showing significant accumulation of microbeads. Spherical ‘microbeads’ made of plastics are now ubiquitous in a wide range of personal healthcare and cleansing products, used by the average North American consumer now at upwards of quadrillions per day. Designed to be flushable, these plastic microbeads inevitably end up in municipal wastewater streams, and then to a large extent leak into our freshwater ecosystems. Recent studies throughout the important Great Lakes system of North America have reported microbeads at essentially all locations examined. On the shorelines, in surface waters, throughout water columns, and in sediments of these freshwater systems, microbeads are now ever-present, and are accumulating in significant amounts. Their small and stable shape and composition, and limited pathways to degradation produce a long lifespan, with the capacity to remain in the freshwater environment for potentially hundreds of years. This review collects and compares initial microbead studies between 2013–2021 in the Great Lakes region to provide a snapshot of the current levels and locations, and to serve as a baseline for future tracking to assess progress as the microbead contamination and accumulation problem is addressed. We as well present findings from our own local study of microplastic/bead accumulation downstream of the Great Lakes, in the St. Lawrence and Ottawa rivers near Montreal. Aspects of microbead contamination represent a unique subset of the worldwide microplastic problem, in that much control remains over their life cycle and eventual fate. Consequently, the power to address this microbead problem can rest with polymer chemists and engineers, who, armed with a better understanding of the relevant physical polymer properties of the beads that govern their movement into the aquatic environment, hold the ability to rationally redesign microbead composition and develop removal techniques

Crystal structure of octane-1,8-diaminium 4,4′-(diazene-1,2-diyl)dibenzoate monohydrate

The title salt, C8H22N22+·C14H8N2O42−·H2O, represents a pseudo-polymer ionic material, resulting from the self-organizing behavior of 4,4′-azinodibenzoate dianions and doubly protonated, 1,8-diaminium-octane cations in aqueous solution. The asymmetric unit consists of two halves of octane 1,8-diaminium cations (the complete cations are both generated by crystallographic inversion symmetry), a 4,4′-azinodibenzoate anion [dihedral angle between the aromatic rings = 10.22 (4)°] and a water molecule of crystallization. One of the cations is in a fully extended linear conformation while the second one has a terminal C—C—C—N gauche conformation. In the crystal, the cations, anions and water molecules are linked into a three-dimensional network via a complex pattern of charge-assisted N—H...O and O—H...O hydrogen bonds

Direct mechanocatalysis using Resonant Acoustic Mixing (RAM)

We demonstrate the first example of direct mechanocatalysis by Resonant Acoustic Mixing (RAM), an emerging mechanochemical methodology that eliminates the need for bulk solvent and milling media. By using a simple copper coil as a catalyst, RAM enables the effective one-pot, 2-step synthesis of triazoles via a combination of benzyl azide formation and copper-catalyzed alkyne-azide click-coupling (CuAAC), on a wide scope of reagents, providing excellent control over reaction stoichiometry, and enabling a simple synthesis of the anticonvulsant drug Rufinamide

Bleaching the Record: After 200 Years, Single Crystal X-Ray Crystallography Reveals the Structure and Hydrogen-Bonding Properties of Hypochlorite and Hypobromite Ions in the Solid State

We report the first single crystal structures of hypochlorite and hypobromite salts, including hydrated sodium hypochlorite - a ubiquitous bleaching and disinfection agent in use for almost 200 years. The structures represent the first characterization of fundamentally important hypochlorite and hypobromite anions in the solid state, by X-ray crystallography and are supported by Raman spectroscopy on individual crystals. The structural analysis provides insight into supramolecular chemistry of the hypohalite ions in the hydrated environment of the NaOCl.5H2O and NaOBr.5H2O solid salts, and reveals measured Cl-O and Br-O bond lengths of 1.69 A and 1.82 A, respectively, which are significantly longer than those for corresponding higher-valence oxoanions, and in agreement with the values spectroscopically determined for hypohalous acids and corresponding oxides in the gas phase.</div