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  1. We summarize recent advances in the design of hybrid nanostructures through the combination of synthetic polymers and plasmonic nanoparticles (NPs). We categorize the synthetic methods of those polymer-coated metal NPs into two main strategies: direct encapsulation and chemical grafting, based on how NPs interact with polymers. In direct encapsulation, NPs with hydrophobic ligands are physically encapsulated into polymer micelles, primarily through hydrophobic interactions. We discuss strategies for controlling the loading numbers and locations of NPs within polymer micelles. On the other hand, polymer-grafted NPs (PGNPs) have synthetic polymers as ligands chemically grafted on NPs. We highlight that polymer ligands can asymmetrically coat metal NPs through hydrophobicity-driven phase segregation using homopolymers, BCPs and blocky random copolymers. This review provides insights into the methodologies and mechanisms to design new nanostructures of polymers and NPs, aiming to enhance the understanding of this rapidly evolving field. 
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    Free, publicly-accessible full text available May 1, 2025
  2. Free, publicly-accessible full text available April 9, 2025
  3. We report a new design of polymer phenylacetylene (PA) ligands and the ligand exchange methodology for colloidal noble metal nanoparticles (NPs). PA-terminated poly(ethylene glycol) (PEG) can bind to metal NPs through acetylide (M-CC-R) that affords a high grafting density. The ligand−metal interaction can be switched between σ bonding and extended π backbonding by changing grafting conditions. The σ bonding of PEG−PA with NPs is strong and it can compete with other capping ligands including thiols, while the π backbonding is much weaker. The σ bonding is also demonstrated to improve the catalytic performance of Pd for ethanol oxidation and prevent surface absorption of the reaction intermediates. Those unique binding characteristics will enrich the toolbox in the control of colloidal surface chemistry and their applications using polymer ligands. 
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    Free, publicly-accessible full text available May 15, 2025
  4. We report a facile method to prepare polymer-grafted plasmonic metal nanoparticles (NPs) that exhibit pH-responsive surface-enhanced Raman scattering (SERS). The concept is based on the use of pH- responsive polymers, such as poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH), as multi- dentate ligands to wrap around the surface of NPs instead of forming polymer brushes. Upon changing the solvent quality, the grafted pH-responsive polymers would drive reversible aggregation of NPs, leading to a decreased interparticle distance. This creates numerous hot spots, resulting in a secondary enhancement of SERS as compared to the SERS from discrete NPs. For negatively charged PAA-grafted NPs, the SERS response at pH 2.5 showed a secondary enhancement of up to 104-fold as compared to the response for discrete NPs at pH 12. Similarly, positively charged PAH-grafted AuNPs showed an oppo- site response to pH. We demonstrated that enhanced SERS with thiol-containing and charged molecular probes was indeed from the pH-driven solubility change of polymer ligands. Our method is different from the conventional SERS sensors in the solid state. With pH-responsive polymer-grafted NPs, SERS can be performed in solution with high reproducibility and sensitivity but without the need for sample pre-con- centration. These findings could pave the way for innovative designs of polymer ligands for metal NPs where polymer ligands do not compromise interparticle plasmon coupling. 
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    Free, publicly-accessible full text available January 3, 2025
  5. Cytochrome P450s (Cyt P450s) and peroxidases are enzymes featuring iron heme cofactors that have wide applicability as biocatalysts in chemical syntheses. Cyt P450s are a family of monooxygenases that oxidize fatty acids, steroids, and xenobiotics, synthesize hormones, and convert drugs and other chemicals to metabolites. Peroxidases are involved in breaking down hydrogen peroxide and can oxidize organic compounds during this process. Both heme-containing enzymes utilize active FeIV[double bond, length as m-dash]O intermediates to oxidize reactants. By incorporating these enzymes in stable thin films on electrodes, Cyt P450s and peroxidases can accept electrons from an electrode, albeit by different mechanisms, and catalyze organic transformations in a feasible and cost-effective way. This is an advantageous approach, often called bioelectrocatalysis, compared to their biological pathways in solution that require expensive biochemical reductants such as NADPH or additional enzymes to recycle NADPH for Cyt P450s. Bioelectrocatalysis also serves as an ex situ platform to investigate metabolism of drugs and bio-relevant chemicals. In this paper we review biocatalytic electrochemical reactions using Cyt P450s including C–H activation, S-oxidation, epoxidation, N-hydroxylation, and oxidative N-, and O-dealkylation; as well as reactions catalyzed by peroxidases including synthetically important oxidations of organic compounds. Design aspects of these bioelectrocatalytic reactions are presented and discussed, including enzyme film formation on electrodes, temperature, pH, solvents, and activation of the enzymes. Finally, we discuss challenges and future perspective of these two important bioelectrocatalytic systems. 
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    Free, publicly-accessible full text available July 31, 2024
  6. This paper reports a robust strategy to catalyze in situ C–H oxidation by combining cobalt (Co) single-atom catalysts (SACs) and horseradish peroxidase (HRP). Co SACs were synthesized using the complex of Co phthalocyanine with 3-propanol pyridine at the two axial positions as the Co source to tune the coordination environment of Co by the stepwise removal of axial pyridine moieties under thermal annealing. These structural features of Co sites, as confirmed by infrared and X-ray absorption spectroscopy, were strongly correlated to their reactivity. All Co catalysts synthesized below 300 °C were inactive due to the full coordination of Co sites in octahedral geometry. Increasing the calcination temperature led to an improvement in catalytic activity for reducing O2, although molecular Co species with square planar coordination obtained below 600 °C were less selective to reduce O2 to H2O2 through the two-electron pathway. Co SACs obtained at 800 °C showed superior activity in producing H2O2 with a selectivity of 82–85% in a broad potential range. In situ production of H2O2 was further coupled with HRP to drive the selective C–H bond oxidation in 2-naphthol. Our strategy provides new insights into the design of highly effective, stable SACs for selective C–H bond activation when coupled with natural enzymes. 
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    Free, publicly-accessible full text available August 30, 2024
  7. Free, publicly-accessible full text available July 11, 2024
  8. We report the hydrophobicity-enhanced reactivity of Cu2+ions as an ester hydrolase.

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  9. We report the use of polymer N -heterocyclic carbenes (NHCs) to control the microenvironment surrounding metal nanocatalysts, thereby enhancing their catalytic performance in CO 2 electroreduction. Three polymer NHC ligands were designed with different hydrophobicity: hydrophilic poly(ethylene oxide) (PEO–NHC), hydrophobic polystyrene (PS–NHC), and amphiphilic block copolymer (BCP) (PEO- b -PS–NHC). All three polymer NHCs exhibited enhanced reactivity of gold nanoparticles (AuNPs) during CO 2 electroreduction by suppressing proton reduction. Notably, the incorporation of hydrophobic PS segments in both PS–NHC and PEO- b -PS–NHC led to a twofold increase in the partial current density for CO formation, as compared to the hydrophilic PEO–NHC. While polymer ligands did not hinder ion diffusion, their hydrophobicity altered the localized hydrogen bonding structures of water. This was confirmed experimentally and theoretically through attenuated total reflectance surface-enhanced infrared absorption spectroscopy and molecular dynamics simulation, demonstrating improved CO 2 diffusion and subsequent reduction in the presence of hydrophobic polymers. Furthermore, NHCs exhibited reasonable stability under reductive conditions, preserving the structural integrity of AuNPs, unlike thiol-ended polymers. The combination of NHC binding motifs with hydrophobic polymers provides valuable insights into controlling the microenvironment of metal nanocatalysts, offering a bioinspired strategy for the design of artificial metalloenzymes. 
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    Free, publicly-accessible full text available August 1, 2024
  10. Abstract

    Chirality plays a significant role in the manufacture of pharmaceuticals and fine chemicals. The use of chemical catalysts to control stereoselectivity relies on the use of chiral catalysts with labor–intensive synthesis and purification. Natural enzymes offer inherent stereoselectivity, making them attractive catalysts for this purpose. We report here chiral biocatalytic oxidations in microemulsions driven by horseradish peroxidase coupled with a synthetic Cu2+‐polymer catalyst. This hybrid system features crosslinked layer–by–layer (LBL) films composed of polyions with Cu2+‐containing pyrene–labelled poly(2‐hydroxy‐3‐dipicolylamino) propyl methacrylate (Py−PGMADPA) to drive oxygen reduction to form hydrogen peroxide. Peroxide in turn activates horseradish peroxidase (HRP) crosslinked in LbL films on magnetic particle beads to biocatalytically oxidize styrene, ethylbenzene, and methyl phenylacetate to chiral products. R‐stereoisomers of these reactants were selectively formed with a high enantiomeric excess of ≥80 % at 90 °C. The enzyme films show high thermal stability at 90 °C in cetyltrimethylammonium bromide microemulsion. Reactions at 90 °C were essentially complete in 2 hr. This hybrid approach opens a door to new designs of biocatalytic syntheses using a separate electrocatalyst for enzyme activation.

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