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1. Do polymer ligands block the catalysis of metal nanoparticles? Unexpected importance of binding motifs in improving catalytic activity

   https://doi.org/10.1039/D0TA03906C  

   Zhang, Lei; Wei, Zichao; Meng, Michael; Ung, Gaël; He, Jie (August 2020, Journal of Materials Chemistry A)

   null (Ed.)

   Metal nanoparticles (NPs) tethered by synthetic polymers are of broad interest for self-assembly, nanomedicine and catalysis. The binding motifs in polymer ligands usually as the end functional groups of polymers are mostly limited to thiolates. Since the binding motif only represents a tiny fraction of many repeating units in polymers, its importance is often ignored. We herein report the uniqueness of polymeric N-heterocyclic carbene (NHC) ligands in providing oxidative stability and promoting the catalytic activity of noble metal NPs. Two “grafting to” methods were developed for polymer NHCs for pre-synthesized metal NPs in various solvents and with different sizes. Remarkably, imidazolium-terminated polystyrene can modify gold NPs (AuNPs) within 2 min while reaching a similar grafting density to polystyrene-thiol (SH) requiring 6 h modification. We demonstrate that polymer NHCs are extremely stable at high temperature in air. Interestingly, the binding motifs of polymer ligands dominate the catalytic activity of metal NPs. Polymer NHC modified metal NPs showed improved activity regardless of the surface crowdedness. In the case of AuNPs, AuNPs modified with polystyrene NHCs are approximately 5.2 times more active than citrate-capped ones and 22 times more active than those modified with polystyrene thiolates. In view of ligand-controlled catalytic properties of metal NPs, our results illustrate the importance of binding motifs that has been overlooked in the past. 

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2. Comparing experimental and computational approaches for studying the binding of N-heterocyclic carbenes

   Santos, A; Simpson, S (March 2024, ACS Spring 2024)

   N-heterocyclic carbenes (NHCs) have grown in popularity in recent years due to their superior surface stability on metal nanoparticles and surfaces. This stability is often characterized experimentally by studying the σ-donation and π-backbonding as measured through NHC-selenium adduct NMR and the Huynh Electronic Parameter (HEP), respectively. However, recent work with NHCs on metal clusters suggests that the ligands can adopt a variety of orientations on the surface. Thus, the surface may have a pronounced impact on the σ-donation and π-backbonding observed for these NHCs. In this work, we aim to determine how well these experimental characterizations compare to trends observed via bond decomposition analysis. 

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3. Polymer Ligands with Quaternary Ammonium Binding Motifs on Metal Nanoparticles Enable Selective Ion Transport for CO ₂ Electroreduction

   https://doi.org/10.1002/ange.202516071  

   Muhuri, Debasmita; Sarkar, Manthan; Duan, Hanyi; Hanson, Lindsey A; He, Jie (September 2025, Angewandte Chemie)

   Abstract We report a new class of hydrophobic polymer ligands with quaternary ammonium head groups for surface modification of noble metal nanoparticles (NPs). Quaternary ammonium ligands bind NPs through non‐covalent electrostatic interactions, producing polymer‐grafted NPs with high colloidal and chemical stability. These polymers having charged head groups offer powerful strategies to tailor the structure and function of metal‐electrolyte interfaces in electrocatalytic systems. The ammonium head groups serve as ionic reservoirs that preconcentrate bicarbonate counterions at the surface of nanocatalysts, while the hydrophobic polymer backbones restructure local hydrogen‐bonding networks, modulating water and ion transport dynamics. These interfacial effects promote CO₂electroreduction, particularly under diffusion‐limited conditions, resulting in a CO Faradaic efficiency (FE) exceeding 90%. 

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4. N-Heterocyclic carbene-stabilized gold nanoparticles and luminescent quantum dots

   https://doi.org/10.1117/12.2610485  

   Arabzadeh Nosratabad, Neda; Jin, Zhicheng; Du, Liang; Mattoussi, Hedi (March 2022, Colloidal Nanoparticles for Biomedical Applications XVII)

   Osiński, Marek; Kanaras, Antonios G. (Ed.)

   N-heterocyclic carbenes (NHCs) have attracted tremendous attention over the past decade, as it is expected to form strong coordination to transition metal complexes and surfaces. Here, we investigate the interactions between colloidal gold nanoparticles (AuNPs), or luminescent quantum dots (QDs) and a multidentate NHC-based polymer ligand. The ligand design relies on the nucleophilic addition reaction between several NHC anchoring groups, short polyethylene glycol (PEG) blocks, and a polymer chain. We find that such NHC-decorated ligands rapidly coordinate onto both sets of nanocrystals, which is attributed to the inherent σ-donating nature (soft Lewis base) of NHC groups combined with the soft Lewis acidic character of nanocrystal surfaces. We combine NMR spectroscopy, fluorescence spectroscopy, high-resolution transmission electron microscopy and dynamic light scattering to characterize the NHCstabilized nanocrystals and gain insights into the nature of the binding interactions. In particular, we find that the newly coated nanocrystals exhibit long-term colloidal stability over a broad range of conditions with no sign of degradation or aggregation build up, while preserving their photophysical properties, for at least one year of storage. 

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5. Polymers on plasmonic metal nanoparticles: From symmetric coating to asymmetric surface patterning

   https://doi.org/10.1016/j.polymer.2024.127115  

   Duan, Hanyi; Muhuri, Debasmita; He, Jie (May 2024, Polymer)

   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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