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Electrochemical conversion of CO 2 into value-added chemicals holds promise to enable the transition to carbon neutrality. Enhancing selectivity for a specific hydrocarbon product is challenging, however, due to numerous possible reaction pathways of CO 2 electroreduction. Here we present a Cu–polyamine hybrid catalyst, developed through co-electroplating, that significantly increases the selectivity for ethylene production. The Faradaic efficiency for ethylene production is 87% ± 3% at −0.47 V versus reversible hydrogen electrode, with full-cell energetic efficiency reaching 50% ± 2%. Raman measurements indicate that the polyamine entrained on the Cu electrode results in higher surface pH, higher CO content and higher stabilization of intermediates compared with entrainment of additives containing little or no amine functionality. More broadly, this work shows that polymer incorporation can alter surface reactivity and lead to enhanced product selectivity at high current densities. Electrochemical conversion of CO 2 into value-added chemicals holds promise to enable the transition to carbon neutrality, but enhancing the selectivity toward a specific hydrocarbon product remains a challenging task. Now, the authors present a Cu–polyamine hybrid catalyst that achieves Faradaic efficiency of 87% for ethylene and full-cell energy efficiency of 50%.

Many chemical and biological processes involve the transfer of both protons and electrons. The complex mechanistic details of these proton-coupled electron transfer (PCET) reactions require independent control of both electron and proton transfer. In this report, we make use of lipid-modified electrodes to modulate proton transport to a Cu-based catalyst that facilitates the O 2 reduction reaction (ORR), a PCET process important in fuel cells and O 2 reduction enzymes. By quantitatively controlling the kinetics of proton transport to the catalyst, we demonstrate that undesired side products such as H 2 O 2 and O 2 − arise from a mismatch between proton and electron transfer rates. Whereas fast proton kinetics induce H 2 O 2 formation and sluggish proton flux produces O 2 − , proton transfer rates commensurate with O–O bond breaking rates ensure that only the desired H 2 O product forms. This fundamental insight aids in the development of a comprehensive framework for understanding the ORR and PCET processes in general. Controlling proton-coupled electron transfer reactions—an important process for fuel cells—can be challenging. Lipid-modified electrodes are now used to modulate proton transport to a Cu-based catalyst that facilitates oxygen reduction reactions.

This review summarizes part of the author’s research in the area of supramolecular chemistry, beginning with his early life influences and early career efforts in molecular recognition, especially molecular tweezers. Although designed to complex DNA, these hosts proved more applicable to the field of host–guest chemistry. This early experience and interest in intercalation ultimately led to the current efforts to develop small molecule therapeutic agents for myotonic dystrophy using a rational design approach that heavily relies on principles of supramolecular chemistry. How this work was influenced by that of others in the field and the evolution of each area of research is highlighted with selected examples.

This work describes the rational design, synthesis, and study of a ligand that selectively complexes CUG repeats in RNA (and CTG repeats in DNA) with high nanomolar affinity. This sequence is considered a causative agent of myotonic dystrophy type 1 (DM1) because of its ability to sequester muscleblind-like (MBNL) proteins. Ligand 1 was synthesized in two steps from commercially available compounds, and its binding to CTG and CUG repeats in oligonucleotides studied. Isothermal titration calorimetry studies of 1 with various sequences showed a preference toward the T-T mismatch (Kd of 390 ± 80 nM) with a 13-, 169-, and 85-fold reduction in affinity toward single C-C, A-A, and G-G mismatches, respectively. Binding and Job analysis of 1 to multiple CTG step sequences revealed high affinity binding to every other T-T mismatch with negative cooperativity for proximal T-T mismatches. The affinity of 1 for a (CUG)₄ step provided a Kd of 430 nM with a binding stoichiometry of 1:1. The preference for the U-U in RNA was maintained with a 6-, >143-, and >143-fold reduction in affinity toward single C-C, A-A, and G-G mismatches, respectively. Ligand 1 destabilized the complexes formed between MBNL1N and (CUG)₄ and (CUG)₁₂ with IC₅₀ values of 52 ± 20 μM and 46 ± 7 μM, respectively, and Ki values of 6 ± 2 μM and 7 ± 1 μM, respectively. These values were only minimally altered by the addition of competitor tRNA. Ligand 1 does not destabilize the unrelated RNA-protein complexes the U1A-SL2 RNA complex and the Sex lethal-tra RNA complex. Thus, ligand 1 selectively destabilizes the MBNL1N-poly(CUG) complex.

Developing highly active, multivalent ligands as therapeutic agents is challenging because of delivery issues, limited cell permeability, and toxicity. Here, we report intrinsically cell-penetrating multivalent ligands that target the trinucleotide repeat DNA and RNA in myotonic dystrophy type 1 (DM1), interrupting the disease progression in two ways. The oligomeric ligands are designed based on the repetitive structure of the target with recognition moieties alternating with bisamidinium groove binders to provide an amphiphilic and polycationic structure, mimicking cell-penetrating peptides. Multiple biological studies suggested the success of our multivalency strategy. The designed oligomers maintained cell permeability and exhibited no apparent toxicity both in cells and in mice at working concentrations. Furthermore, the oligomers showed important activities in DM1 cells and in a DM1 liver mouse model, reducing or eliminating prominent DM1 features. Phenotypic recovery of the climbing defect in adult DM1 Drosophila was also observed. This design strategy should be applicable to other repeat expansion diseases and more generally to DNA/RNA-targeted therapeutics.

Molecular switches gate many fundamental processes in natural and artificial systems. Here, we report the development of an electrochemical platform in which a proton carrier switches the activity of a catalyst. By incorporating an alkyl phosphate in the lipid layer of a hybrid bilayer membrane, we regulate proton transport to a Cu-based molecular oxygen reduction reaction catalyst. To construct this hybrid bilayer membrane system, we prepare an example of a synthetic Cu oxygen reduction reaction catalyst that forms a self-assembled monolayer on Au surfaces. We then embed this Cu catalyst inside a hybrid bilayer membrane by depositing a monolayer of lipid on the self-assembled monolayer. We envisage that this electrochemical system can give a unique mechanistic insight not only into the oxygen reduction reaction, but into proton-coupled electron transfer in general. Molecular switches regulate many fundamental processes in natural and artificial systems. An electrochemical platform in which a proton carrier switches the activity of a catalyst is now presented. A hybrid bilayer membrane allows the regulation of proton transport to a Cu-based molecular oxygen reduction reaction catalyst.

Synthetic host systems capable of selectively binding guest molecules are of interest for applications ranging from separations and chemical or biological sensing to the development of biomedical materials. Such host systems can be efficiently prepared by ‘imprinting’ polymers or inorganic materials with template molecules, which, upon removal, leave behind spatially arranged functional groups that act as recognition sites 1 , 2 , 3 , 4 . However, molecularly imprinted polymers have limitations, including incomplete template removal, broad guest affinities and selectivities, and slow mass transfer 5 , 6 , 7 , 8 . An alternative strategy for moulding desired recognition sites uses combinatorial libraries of assemblies that are made of a relatively small number of molecules, interconverting in dynamic equilibrium; upon addition of a target molecule, the library equilibrium shifts towards the best hosts 9 , 10 , 11 . Here we describe the dynamic imprinting of dendritic macromolecules with porphyrin templates to yield synthetic host molecules containing one binding site each. The process is based on our general strategy to prepare cored dendrimers 12 , 13 , and involves covalent attachment of dendrons to a porphyrin core, cross-linking of the end-groups of the dendrons, and removal of the porphyrin template by hydrolysis. In contrast to more traditional polymer imprinting, our approach ensures nearly homogeneous binding sites and quantitative template removal. Moreover, the hosts are soluble in common organic solvents and amenable to the incorporation of other functional groups, which should facilitate further development of this system for novel applications.

Although a variety of acid‐generating molecules have been developed, the formation of toxic byproducts and the need for light‐activation or temperatures that may be incompatible with physiological conditions leave room for the optimization of biocompatible acid‐generators. Herein, we report 4‐hydroxybenzyl chloride derivatives that generate hydrochloric acid via hydrolysis at the benzylic position at room temperature in the absence of light. Utilizing the acetal protected 4‐hydroxybenzyl chloride scaffold, we access a myriad of compounds that generate acid at different rates. A series of 4‐chloromethylphenyl acetals have been prepared and studied as thermal acid generators in water. Simple mechanistic studies show that a potential acid amplified pathway involving acetal hydrolysis and quinone methide formation is out‐competed by a simple hydrolysis pathway. The rate of thermal acid generation can be tuned through substituent effects and by incorporating the small molecule into a ROMP polymer.

Single-molecule fluorescence techniques have emerged as a powerful approach to understanding complex biological systems. However, a challenge researchers still face is the limited photostability of nearly all organic fluorophores, including the cyanine and Alexa dyes. We report a new, monovalent probe that emits in the far-red region of the visible spectrum with properties desirable for single-molecule optical imaging. This probe is based on a ring-fused boron-dipyrromethene (BODIPY) core that is conjugated to a polyglycerol dendrimer (PGD). The dendrimer makes the hydrophobic fluorophore water-soluble. This probe exhibits excellent brightness, with an emission maximum of 705 nm. We have observed strikingly long and stable emission from individual PGD–BODIPY probes, even in the absence of anti-fading agents such as Trolox, a combined oxidizing–reducing agent often used in single-molecule studies for improving the photostability of common imaging probes. These interesting properties greatly simplify use of the fluorophore. A far-red-fluorescent probe based on a ring-fused BODIPY core that is conjugated to a polyglycerol dendrimer is now reported. The most notable feature of this probe is its long-lasting fluorescence emission with a strikingly low level of blinking in single-molecule-imaging experiments, even in the absence of anti-fading agents such as Trolox.

A major challenge in developing recyclable polymeric materials is the inherent conflict between the properties required during and after their life span. In particular, materials must be strong and durable when in use, but undergo complete and rapid degradation, ideally under mild conditions, as they approach the end of their life span. We report a mechanism for degrading polymers called cyclization-triggered chain cleavage (CATCH cleavage) that achieves this duality. CATCH cleavage features a simple glycerol-based acyclic acetal unit as a kinetic and thermodynamic trap for gated chain shattering. Thus, an organic acid induces transient chain breaks with oxocarbenium ion formation and subsequent intramolecular cyclization to fully depolymerize the polymer backbone at room temperature. With minimal chemical modification, the resulting degradation products from a polyurethane elastomer can be repurposed into strong adhesives and photochromic coatings, demonstrating the potential for upcycling. The CATCH cleavage strategy for low-energy input breakdown and subsequent upcycling may be generalizable to a broader range of synthetic polymers and their end-of-life waste streams.Extensive crosslinking in thermosetting polymers provides their desirable durability but makes them difficult to recycle. Now acetal-based monomers containing nucleophilic pendant groups have been incorporated into polyurethanes, which are stable in aqueous acid yet degradable at room temperature under organic acidic conditions. The degradation products were upcycled into higher-value, long-lasting materials.