Selina Hollstein

Volume 33, Issue 4, April 2021, Page 71-79
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Communications Chemistry, Published online: 07 August 2020; doi:10.1038/s42004-020-00344-7

Chemical reaction networks (CRNs) are prototypical complex systems because reactions are nonlinear and connected in intricate ways, and they are also essential to understand living systems. Here, the author discusses how recent developments in nonequilibrium thermodynamics provide new insight on how CRNs process energy and perform sophisticated tasks, and describes open challenges in the field.

Volume 32, Issue 4, April 2020, Page 276-286
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A series of acyclic, macrocyclic and mechanically interlocked luminescent anion sensors have been prepared by incorporation of the isophthalamide motif into dipyridylbenzene to obtain cyclometallated complexes of Pt^II and Ru^II. Anion titrations with the ruthenium [2]rotaxane demonstrate a marked increase in chloride binding affinity and indicate the interlocked receptor is capable of chloride recognition even in competitive 30 % aqueous mixtures (see figure).

Abstract

A series of novel acyclic, macrocyclic and mechanically interlocked luminescent anion sensors have been prepared by incorporation of the isophthalamide motif into dipyridylbenzene to obtain cyclometallated complexes of platinum(II) and ruthenium(II). Both the acyclic and macrocyclic derivatives 7⋅Pt, 7⋅Ru⋅PF₆ , 10⋅Pt and 10⋅Ru⋅PF₆ are effective sensors for a range of halides and oxoanions. The near‐infra red emitting ruthenium congeners exhibited an increased binding strength compared to platinum due to the cationic charge and thus additional electrostatic interactions. Intramolecular hydrogen‐bonding between the dipyridylbenzene ligand and the amide carbonyls increases the preorganisation of both acyclic and macrocyclic metal derivatives resulting in no discernible macrocyclic effect. Interlocked analogues were also prepared, and preliminary luminescent chloride anion spectrometric titrations with 12⋅Ru⋅(PF₆)₂ demonstrate a marked increase in halide binding affinity due to the complementary chloride binding pocket of the [2]rotaxane. ¹H NMR binding titrations indicate the interlocked dicationic receptor is capable of chloride recognition even in competitive 30 % aqueous mixtures.

On the move : Thiol–anhydride networks were fabricated and assessed for their dynamic reversible characteristics. Three anhydrides (maleic, succinic, and phthalic) were used to create dynamic thermosets of diverse propensities for thioester anhydride link reversion. An impressive degree of control over their dynamic responsiveness was achieved.

Abstract

The reaction of thiols and anhydrides to form ring opened thioester/acids is shown to be highly reversible and it is accordingly employed in the fabrication of covalent adaptable networks (CANs) that possess tunable dynamic covalent chemistry. Maleic, succinic, and phthalic anhydride derivatives were used as bifunctional reactants in systems with varied stoichiometries, catalyst, and loadings. Dynamic characteristics such as temperature‐dependent stress relaxation, direct reprocessing and recycling abilities of a range of thiol–anhydride elastomers, glasses, composites and photopolymers are discussed. Depending on the catalyst strength, 100 % of externally imposed stresses were relaxed in the order of minutes to 2 hours at mild temperatures (80–120 °C). Pristine properties of the original materials were recovered following up to five cycles of a hot‐press reprocessing technique (1 h/100 °C).

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Nature Communications, Published online: 17 February 2020; doi:10.1038/s41467-020-14665-7

Mass spectrometry (MS) enables identification of modified RNA residues, but high-throughput processing is currently a bottleneck. Here, the authors present a free and open-source database search engine for RNA MS data to facilitate reliable identification of modified RNA sequences.

aza‐BODIPY comes alive! Living supramolecular polymerization was demonstrated by aza‐BODIPY 1 bearing hydrogen‐bond accepting triazole units that can be facilely constructed through click chemistry. The H‐bonding unit of amide‐linked triazole in dye 1 could be employed as a general motif for encoding conformational information and developing polymorphic supramolecular systems.

Abstract

An aza‐BODIPY dye 1 bearing two hydrophobic fan‐shaped tridodecyloxybenzamide pendants through 1,2,3‐triazole linkages was synthesized by a click reaction and characterized. ¹H NMR studies indicated that dye 1 exhibited variable conformations through intramolecular H‐bonding interaction, which is beneficial for the polymorphism of aggregation. The thermodynamic, structural, and kinetic aspect of the supramolecular polymerization of dye 1 was investigated by UV/Vis absorption spectroscopy, IR spectroscopy, AFM, TEM, and SEM. Biphasic aggregation pathways of dye 1, leads to the formation of off‐pathway, metastable Agg. I and thermodynamically stable Agg. II with distinct H‐aggregation spectra and nanoscale morphology. The living manner of the supramolecular polymerization of dye 1 was demonstrated in seeded polymerization experiments with temperature‐modulated successive cooling–heating cycles.

Nature Chemistry, Published online: 13 January 2020; doi:10.1038/s41557-019-0388-5

Carbon capture technologies are poised to play an important role in reducing CO2 emissions to mitigate global warming, but their cost prevents their extensive use. Now, CO2 capture and utilization have been combined using a triple-level dynamic combinatorial approach. CO2 was spontaneously captured by industrial polyamines to create libraries of ligands that can be used for the separation and recovery of metals.

Motorized catalysis: A photoresponsive chiral catalyst based on an oligotriazole‐functionalized unidirectional molecular motor has been developed for stereodivergent anion binding catalysis. The motor function controls the helical chirality of supramolecular assemblies with chloride anions.

Abstract

A photoresponsive chiral catalyst based on an oligotriazole‐functionalized unidirectional molecular motor has been developed for stereodivergent anion binding catalysis. The motor function controls the helical chirality of supramolecular assemblies with chloride anions, which by means of chirality transfer enables the enantioselective addition of a silyl ketene acetal nucleophile to oxocarbenium cations. Reversal of stereoselectivity (up to 142 % Δee) was achieved through rotation of the motor core induced by photochemical and thermal isomerization steps.

Volume 32, Issue 2, February 2020, Page 112-118
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Soft matter, hard shell: pH‐responsive hydrogels that can chelate Fe³⁺ were prepared from guanosine‐5′‐hydroxamic acid (HA). At high pH, the hydrogel binds thiazole orange, signaled by enhanced fluorescence. The HA units can also act as a supramolecular siderophore to form red complexes with Fe³⁺, which allowed the patterning of the hydrogel surface with FeCl₃.

Abstract

Guanosine‐5′‐hydroxamic acid (3) forms hydrogels when mixed with guanosine (1) and KCl. The 5′‐hydroxamic acid (HA) unit is pH‐responsive and also chelates Fe³⁺. When gels are prepared under basic conditions, the 5′‐HA groups are deprotonated and the anionic hydrogel binds cationic thiazole orange (TO), signaled by enhanced fluorescence. The HA nucleoside 3, when immobilized in the G‐quartet gel, acts as a supramolecular siderophore to form red complexes with Fe³⁺. We patterned the hydrogel's surface with FeCl₃, by hand and by using a 3D printer. Patterns form instantly, are visible by eye, and can be erased using vitamin C. This hydrogel, combining self‐assembled G‐quartet and siderophore–Fe³⁺ motifs, is strong, can be molded into different shapes, and is stable on the bench or under salt water.

Communications Chemistry, Published online: 09 December 2019; doi:10.1038/s42004-019-0241-1

Amphiphilic block co-polymer vesicles have emerged as attractive artificial systems. Here the authors employ a continuously stirred tank reactor for the polymerization-induced self-assembly of giant polymer vesicles, mediated by radicals generated by an oscillating Belousov-Zhabotinsky reaction.