Ligand-enforced geometric constraints and associated reactivity in p-block compounds.

The geometry at an element centre can generally be predicted based on the number of electron pairs around it using valence shell electron pair repulsion (VSEPR) theory. Strategies to distort p-block compounds away from these predicted geometries have gained considerable interest due to the unique structural outcomes, spectroscopic properties or reactivity patterns engendered by such distortion. This review presents an up-to-date group-wise summary of this exciting and rapidly growing field with a focus on understanding how the ligand employed unlocks structural features, which in turn influences the associated reactivity. Relevant geometrically constrained compounds from groups 13-16 are discussed, along with selected stoichiometric and catalytic reactions. Several areas for advancement in this field are also discussed. Collectively, this review advances the notion of geometric tuning as an important lever, alongside electronic and steric tuning, in controlling bonding and reactivity at p-block centres.

Planar bismuth triamides: a tunable platform for main group Lewis acidity and polymerization catalysis.

Geometric deformation in main group compounds can be used to elicit unique properties including strong Lewis acidity. Here we report on a family of planar bismuth(iii) complexes (cf. typically pyramidal structure for such compounds), which show a geometric Lewis acidity that can be further tuned by varying the steric and electronic features of the triamide ligand employed. The structural dynamism of the planar bismuth complexes was probed in both the solid and solution phase, revealing at least three distinct modes of intermolecular association. A modified Gutmann-Beckett method was used to assess their electrophilicity by employing trimethylphosphine sulfide in addition to triethylphosphine oxide as probes, providing insights into the preference for binding hard or soft substrates. Experimental binding studies were complemented by a computational assessment of the affinities and dissection of the latter into their intrinsic bond strength and deformation energy components. The results show comparable Lewis acidity to triarylboranes, with the added ability to bind two bases simultaneously, and reduced discrimination against soft substrates. We also study the catalytic efficacy of these complexes in the ring opening polymerization of cyclic esters ε-caprolactone and rac-lactide. The polymers obtained show excellent dispersity values and high molecular weights with low catalyst loadings used. The complexes retain their performance under industrially relevant conditions, suggesting they may be useful as less toxic alternatives to tin catalysts in the production of medical grade materials. Collectively, these results establish planar bismuth complexes as not only a novel neutral platform for main group Lewis acidity, but also a potentially valuable one for catalysis.

A review of the mechanisms of by-product PCB formation in pigments, dyes and paints.

There has been an increased awareness of paints and pigments as a source of by-product PCBs in the environment. The majority of existing work has focused only on reporting the presence of the main PCBs in different products with a specific focus on the most PCB congeners, PCB11 and PCB209. This gives the impression that only a handful of PCBs are found in paints. However, this is not the case. PCB profiles in paints and pigments can be just as complex as commercial technical mixtures. This review identified the presence of 149 different PCBs in paint samples. For reference, only 141 different PCBs have been reported in all of the 5 main commercial Aroclor formulations (A1016, A1242, A1248, A1254 (early & late) and A1260). The total PCB concentrations in some paint samples can be substantial, with concentrations as high as 919 mg kg-1 reported in azo pigments. When trying to identify sources of PCBs in the environment, pigments, dyes and paints are often overlooked. In this manuscript, we have compiled congener profiles from 140 different samples from the available scientific literature and presented this in the supplementary information as valuable resource for others to use in source identification applications. We have also proposed detailed mechanisms for the formation of PCBs in pigments, dyes and paints. In many cases, the PCB congeners predicted by these mechanisms provide an excellent match for what has been observed in the scientific literature. We have also identified several additional classes of pigments that are expected to contain PCBs but have yet to be verified by experimental data.

Bioionic Liquid Conjugation as Universal Approach To Engineer Hemostatic Bioadhesives.

Adhesion to wet and dynamic surfaces is vital for many biomedical applications. However, the development of effective tissue adhesives has been challenged by the required combination of properties, which includes mechanical similarity to the native tissue, high adhesion to wet surfaces, hemostatic properties, biodegradability, high biocompatibility, and ease of use. In this study, we report a novel bioinspired design with bioionic liquid (BIL) conjugated polymers to engineer multifunctional highly sticky, biodegradable, biocompatible, and hemostatic adhesives. Choline-based BIL is a structural precursor of the phospholipid bilayer in the cell membrane. We show that the conjugation of choline molecules to naturally derived polymers (i.e., gelatin) and synthetic polymers (i.e., polyethylene glycol) significantly increases their adhesive strength and hemostatic properties. Synthetic or natural polymers and BILs were mixed at room temperature and cross-linked via visible light photopolymerization to make hydrogels with tunable mechanical, physical, adhesive, and hemostatic properties. The hydrogel adhesive exhibits a close to 50% decrease in the total blood volume loss in tail cut and liver laceration rat animal models compared to the control. This technology platform for adhesives is expected to have further reaching application vistas from tissue repair to wound dressings and the attachment of flexible electronics.