No abstract

Iron complexes of tetra-amido macrocyclic ligands are important members of the suite of oxidation catalysts known as TAML activators. TAML activators are known to be fast homogeneous water oxidation (WO) catalysts, producing oxygen in the presence of chemical oxidants, e.g., ceric ammonium nitrate. These homogeneous systems exhibited low turnover numbers (TONs). Here we demonstrate immobilization on glassy carbon and carbon paper in an ink composed of the prototype TAML activator, carbon black, and Nafion and the subsequent use of this composition in heterogeneous electrocatalytic WO. The immobilized TAML system is shown to readily produce O2 with much higher TONs than the homogeneous predecessors.

Random heteropolymers (RHPs) are an interesting class of materials useful in many theories and applications. While previous studies typically focused on simplified RHP systems, here we explore a more complex scenario inspired by highly heterogeneous molecules like proteins. Our system consists of four monomers mimicking different classes of amino acids. Using Molecular Dynamics simulations and Small-Angle X-Ray Scattering, we explore dynamical and structural features of these RHPs in solution.Our results show the RHPs assemble with heterogeneous interfaces reminiscent of protein surfaces. The polymer backbones appear frozen at room temperature on the nano-to micro-second timescale with molten-globule morphology, albeit their conformational space has multiple metastable conformations for a given sequence, drawing comparison to Intrinsically Disordered Proteins. Local connectivity and chemistry are also shown to have substantial impact on polymer solvation. The work presented here indicates that RHPs share similarities with proteins to be leveraged in bio-mimetic and bio-inspired applications.

Biological fluids, the most complex blends, have compositions that constantly vary and cannot be molecularly defined1. Despite these uncertainties, proteins fluctuate, fold, function and evolve as programmed2–4. We propose that in addition to the known monomeric sequence requirements, protein sequences encode multi-pair interactions at the segmental level to navigate random encounters5,6; synthetic heteropolymers capable of emulating such interactions can replicate how proteins behave in biological fluids individually and collectively. Here, we extracted the chemical characteristics and sequential arrangement along a protein chain at the segmental level from natural protein libraries and used the information to design heteropolymer ensembles as mixtures of disordered, partially folded and folded proteins. For each heteropolymer ensemble, the level of segmental similarity to that of natural proteins determines its ability to replicate many functions of biological fluids including assisting protein folding during translation, preserving the viability of fetal bovine serum without refrigeration, enhancing the thermal stability of proteins and behaving like synthetic cytosol under biologically relevant conditions. Molecular studies further translated protein sequence information at the segmental level into intermolecular interactions with a defined range, degree of diversity and temporal and spatial availability. This framework provides valuable guiding principles to synthetically realize protein properties, engineer bio/abiotic hybrid materials and, ultimately, realize matter-to-life transformations.

Synthetic random heteropolymers (RHPs) with high chemical heterogeneity can self-assemble into single-chain nanoparticles that exhibit features reminiscent of natural proteins, such as conformational polymorphism. Using all-atom molecular dynamics simulations, this work investigates the structure and single-chain mechanical unfolding of a library of four-component RHPs in water, studying the effects of sequence, composition, configuration, and molecular weight. Results show that compactified RHPs can have highly dynamic unfolding behaviors, which are dominated by complex side-chain interactions and prove markedly different from their homopolymer counterparts. For a given sequence, an RHP's native backbone conformation can strongly impact its unfolding response, hinting at the importance of topological design in the nanoscale mechanics of heteropolymers. In addition, we identify enthalpically driven reconfiguration upon unfolding, observing a solvent-shielding protection mechanism similar to protein stabilization by PEGylation. This work provides the first computational evidence for the force-induced unfolding of protein-inspired multicomponent heteropolymers.

This work demonstrates the remodeling of single‐chain nanoparticles (SCNPs) upon a transition to organic solvent through molecular dynamics simulations. Methacrylate‐based random heteropolymers (RHPs), assembled via transient noncovalent linkages in water, have shown promise in an assortment of applications that harness their bio‐inspired properties. While their molecular behavior has been broadly characterized in aqueous environments, many newer applications include the use of organic solvent rather than bio‐mimetic conditions. The polymer assemblies, typically driven by the hydrophobic effect in water, are less well understood in nonaqueous solution. Here, a specific RHP system is examined which forms compact globular morphologies in highly polar or highly nonpolar environments while adopting extended conformations in solvents of intermediate polarity. The pivotal role of electrostatic interactions between charge groups in low dielectric mediums is also observed. Finally, high temperature anneal cycles are compared to room temperature transformations to illuminate barriers to remodeling upon environmental changes.

No abstract

Synthetic random heteropolymers (RHPs) with high chemical heterogeneity can self-assemble into single-chain nanoparticles that exhibit features reminiscent of natural proteins, such as topological polymorphism. Using all-atom molecular dynamics simulations, this work investigates the structure and single-chain mechanical unfolding of a library of four-component RHPs in water, studying the effects of sequence, composition, configuration, and molecular weight. Results show that compactified RHPs can have highly dynamic unfolding behaviors which are dominated by complex side-chain interactions and prove markedly different from their homopolymer counterparts. For a given sequence and conformation, an RHP’s backbone topology can strongly impact its unfolding response, hinting at the importance of topological design in the nanoscale mechanics of heteropolymers. In addition, we identify enthalpically-driven reconfiguration upon unfolding, observing a solvent-shielding protection mechanism similar to protein stabilization by PEGylation. This work provides the first computational evidence for the force-induced unfolding of protein-inspired multicomponent heteropolymers.