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Science

Controlling multicomponent systems is difficult due to convoluted behavior, pathway complexity, and coupled equilibria. Here the authors showed modulation of aggregate morphology in a zinc porphyrin-based supramolecular system via judicious capping with a manganese porphyrin monomer, in which the monomer’s chirality can influence the supramolecular behavior.

supramolecular assembly, tris(pentafluorophenyl)borane, triphenylamine, charge transfer, Chemistry, and QD1-999

Abstract The introduction of a chemical additive to supramolecular polymers holds high potential in the development of new structures and functions. In this regard, various donor- and acceptor-based molecules have been applied in the design of these noncovalent polymers. However, the incorporation of boron–nitrogen frustrated Lewis pairs in such architectures is still rare despite their many intriguing properties in catalysis and materials science. The limited choices of suitable boron derivatives represent one of the main limitations for the advancement in this direction. Here, we examine the use of the commercially available tris(pentafluorophenyl)borane with various triphenylamine derivatives to create supramolecular B–N charge transfer systems. Our results highlight the importance of a proper balance between the donor/acceptor strength and the driving force for supramolecular polymerization to achieve stable, long-range ordered B–N systems. Detailed analyses using electron paramagnetic resonance and optical spectroscopy suggest that tris(pentafluorophenyl)borane displays complex behavior with the amide-based triphenylamine supramolecular polymers and may interact in dimers or larger chiral aggregates, depending on the specific structure of the triphenylamines.

Chemistry and QD1-999

Science

Connecting molecular-level phenomena to larger scales and molecular systems that resemble living systems remains a considerable challenge in supramolecular chemistry. Here, the authors report different self-assembly patterns in a porphyrin structure which can form – depending on the concentration - spirals or toroids.

supramolecular polymers, chain-length control, chain capper, Chemistry, and QD1-999

Abstract In polymer chemistry, modulation of sequence and control over chain length are routinely applied to alter and fine-tune the properties of covalent (co)polymers. For supramolecular polymers, the same principles underlying this control have not been fully elucidated up to this date. Particularly, rational control over molecular weight in dynamic supramolecular polymers is not trivial, especially when a cooperative mechanism is operative. We start this review by summarizing how molecular-weight control has been achieved in seminal examples in the field of supramolecular polymerizations. Following this, we propose to classify the avenues taken to control molecular weights in supramolecular polymerizations. We focus on dynamic cooperative supramolecular polymerization as this is the most challenging in terms of molecular weight control. We use a mass-balance equilibrium model to predict how the nature of the interaction of an additive B with the monomers and supramolecular polymers of component A affects the degree of aggregation and the degree of polymerization. We put forward a classification system that distinguishes between B acting as a chain capper, a sequestrator, a comonomer, or an intercalator. We also highlight the experimental methods applied to probe supramolecular polymerization processes, the type of information they provide in relation to molecular weight and degree of aggregation, and how this can be used to classify the role of B. The guidelines and classification delineated in this review to assess and control molecular weights in supramolecular polymers can serve to reevaluate exciting systems present in current literature and contribute to broaden the understanding of multicomponent systems.

Science

Determining the spatial arrangement of molecules on a nanoparticle’s surface is key to understanding its interactions. Here, the authors use dSTORM imaging and probabilistic modelling to map the distribution of fluorophores on a nanoparticle, finding that ligand coverage is heterogeneous and highly variable between individual particles.

Science

DNA-origami allows the precise recruitment of DNA-protein conjugates but lacks the dynamics found in natural protein assemblies. Here the authors present a synthetic polymer platform that combines the dynamics of supramolecular polymers with the programmability of DNA-mediated protein recruitment.

Science

Dynamic behaviour in supramolecular systems is an important aspect of their functionality. Here, the authors use stochastic optical reconstruction microscopy to unveil structural diversity in self-assembled peptide amphiphile nanofibres, with potential relevance to biomedical applications.

supramolecular polymers, rheology, hydrogels, small-angle X-ray scattering, Biology (General), QH301-705.5, Chemistry, and QD1-999

Hydrogels and, in particular, supramolecular hydrogels show promising properties for application in regenerative medicine because of their ability to adapt to the natural environment these materials are brought into. However, only few studies focus on the structure-property relationships in supramolecular hydrogels. Here, we study in detail both the structure and the mechanical properties of such a network, composed of poly(ethylene glycol), end-functionalized with ureido-pyrimidinone fourfold hydrogen bonding units. This network is responsive to triggers such as concentration, temperature and pH. To obtain more insight into the sol-gel transition of the system, both rheology and small-angle X-ray scattering (SAXS) are used. We show that the sol-gel transitions based on these three triggers, as measured by rheology, coincide with the appearance of a structural feature in SAXS. We attribute this feature to the presence of hydrophobic domains where cross-links are formed. These results provide more insight into the mechanism of network formation in these materials, which can be exploited for tailoring their behavior for biomedical applications, where one of the triggers discussed might be used.

Physics, QC1-999, Chemistry, and QD1-999

We present a computationally efficient approach to account for the non-linear chemistry occurring during the dispersion of ship exhaust plumes in a global 3-D model of atmospheric chemistry (GEOS-Chem). We use a plume-in-grid formulation where ship emissions age chemically for 5 h before being released in the global model grid. Besides reducing the original ship NOx emissions in GEOS-Chem, our approach also releases the secondary compounds ozone and HNO3, produced during the 5 h after the original emissions, into the model. We applied our improved method and also the widely used "instant dilution" approach to a 1-yr GEOS-Chem simulation of global tropospheric ozone-NOx-VOC-aerosol chemistry. We also ran simulations with the standard model (emitting 10 molecules O3 and 1 molecule HNO3 per ship NOx molecule), and a model without any ship emissions at all. The model without any ship emissions simulates up to 0.1 ppbv (or 50%) lower NOx concentrations over the North Atlantic in July than our improved GEOS-Chem model. "Instant dilution" overestimates NOx concentrations by 0.1 ppbv (50%) and ozone by 3–5 ppbv (10–25%), compared to our improved model over this region. These conclusions are supported by comparing simulated and observed NOx and ozone concentrations in the lower troposphere over the Pacific Ocean. The comparisons show that the improved GEOS-Chem model simulates NOx concentrations in between the instant dilution model and the model without ship emissions, which results in lower O3 concentrations than the instant dilution model. The relative differences in simulated NOx and ozone between our improved approach and instant dilution are smallest over strongly polluted seas (e.g. North Sea), suggesting that accounting for in-plume chemistry is most relevant for pristine marine areas.

Physics, QC1-999, Chemistry, and QD1-999

Tropospheric NO2 column retrievals from the Global Ozone Monitoring Experiment (GOME) satellite spectrometer are used to quantify the source strength and 3-D distribution of lightning produced nitrogen oxides (NOx=NO+NO2). A sharp increase of NO2 is observed at convective cloud tops with increasing cloud top height, consistent with a power-law behaviour with power 5±2. Convective production of clouds with the same cloud height are found to produce NO2 with a ratio 1.6/1 for continents compared to oceans. This relation between cloud properties and NO2 is used to construct a 10:30 local time global lightning NO2 production map for 1997. An extensive statistical comparison is conducted to investigate the capability of the TM3 chemistry transport model to reproduce observed patterns of lightning NO2 in time and space. This comparison uses the averaging kernel to relate modelled profiles of NO2 to observed NO2 columns. It exploits a masking scheme to minimise the interference of other NOx sources on the observed total columns. Simulations are performed with two lightning parameterizations, one relating convective preciptation (CP scheme) to lightning flash distributions, and the other relating the fifth power of the cloud top height (H5 scheme) to lightning distributions. The satellite-retrieved NO2 fields show significant correlations with the simulated lightning contribution to the NO2 concentrations for both parameterizations. Over tropical continents modelled lightning NO2 shows remarkable quantitative agreement with observations. Over the oceans however, the two model lightning parameterizations overestimate the retrieved NO2 attributed to lightning. Possible explanations for these overestimations are discussed. The ratio between satellite-retrieved NO2 and modelled lightning NO2 is used to rescale the original modelled lightning NOx production. Eight estimates of the lightning NOx production in 1997 are obtained from spatial and temporal correlation methods, from cloud-free and cloud-covered observations, and from two different lightning parameterizations. Accounting for a wide variety of random and possible systematic errors, we estimate the global NOx production from lightning to be in the range 1.1–6.4 Tg N in 1997.