Catalysis by metallic nanoparticles is certainly among the most intensely studied problems in modern nanoscience. However, reliable tests for catalytic performance of such nanoparticles are often poorly defined, which makes comparison and benchmarking rather difficult. We tackle in this tutorial review a subset of well-studied reactions that take place in aqueous phase and for which a comprehensive kinetic analysis is available. Two of these catalytic model reactions are under consideration here, namely the reduction of (i) p-nitrophenol and (ii) hexacyanoferrate (III), both by borohydride ions. Both reactions take place at the surface of noble metal nanoparticles at room temperature and can be accurately monitored by UV-vis spectroscopy. Moreover, the total surface area of the nanoparticles in solution can be known with high precision and thus can be directly used for the kinetic analysis. Hence, these model reactions represent cases of heterogeneous catalysis that can be modelled with the accuracy typically available for homogeneous catalysis. Both model reactions allow us to discuss a number of important concepts and questions, namely the dependence of catalytic activity on the size of the nanoparticles, electrochemistry of nanoparticles, surface restructuring, the use of carrier systems and the role of diffusion control.

The counterions neutralizing the charges on polyelectrolytes such as DNA or heparin may dissociate in water and greatly influence the interaction of such polyelectrolytes with biomolecules, particularly proteins. In this Review we give an overview of studies on the interaction of proteins with polyelectrolytes and how this knowledge can be used for medical applications. Counterion release was identified as the main driving force for the binding of proteins to polyelectrolytes: Patches of positive charge become multivalent counterions of the polyelectrolyte and lead to the release of counterions from the polyelectrolyte and a concomitant increase in entropy. This is shown from investigations on the interaction of proteins with natural and synthetic polyelectrolytes. Special emphasis is paid to sulfated dendritic polyglycerols (dPGS). The Review demonstrates that we are moving to a better understanding of charge–charge interactions in systems of biological relevance. Research along these lines will aid and promote the design of synthetic polyelectrolytes for medical applications.

We present a thermodynamic study of the adsorption of lysozyme on a negatively charged core–shell microgel at pH 7.2. The carrier particles consist of a polystyrene core onto which a charged poly(N-isopropylacrylamide-co-acrylic acid) network is attached. Isothermal titration calorimetry (ITC) is used to investigate the temperature and salt dependence of lysozyme binding. Our ITC analysis unequivocally shows that the adsorption of lysozyme onto the charged gel is driven by entropy. The addition of salt strongly decreases the binding affinity, indicating significant electrostatic contributions to the adsorption process. However, at high salt concentrations, substantial protein binding with unaltered entropies is still observed pointing to large contributions from hydrophobic interactions. Furthermore, the calorimetric analysis suggests that protonation of lysozyme takes place upon binding. This is directly shown by analysis of the enzymatic activity of adsorbed lysozyme. It was found that the activity is enhanced about ∼3.5 times, indicating that lysozyme has taken up approximately one proton when entering the gel. The entire set of data demonstrates that core–shell microgels present “smart” colloidal carriers for lysozyme that enhance its activity.

Evidence is strengthening to suggest that the novel SARS‐CoV‐2 mutant Omicron, with its more than 60 mutations, will spread and dominate worldwide. Although the mutations in the spike protein are known, the molecular basis for why the additional mutations in the spike protein that have not previously occurred account for Omicron's higher infection potential, is not understood. We propose, based on chemical rational and molecular dynamics simulations, that the elevated occurrence of positively charged amino acids in certain domains of the spike protein (Delta: +4; Omicron: +5 vs. wild type) increases binding to cellular polyanionic receptors, such as heparan sulfate due to multivalent charge‐charge interactions. This observation is a starting point for targeted drug development.

We present a detailed study of the catalytic activity of Au/Pd nanoalloys with Au : Pd molar ratio 75 : 25 synthesized using spherical polyelectrolyte brushes (SPB) as carrier system. The reduction of 4-nitrophenol (Nip) by sodium borohydride (BH₄ ⁻) has been used as a model reaction. This reaction proceeds in two steps: 4-nitrophenol is first reduced to 4-hydroxylaminophenol which in a second step is reduced to the final product 4-aminophenol. Both steps of the reaction proceed on the surface of the nanoparticles (Langmuir–Hinshelwood-mechanism). We use this model to analyze the experimental data obtained by catalysis with the Au/Pd-nanoalloys. Good agreements between theory and experiments were found up to 30% conversion of Nip. The kinetic parameters were compared with the data derived from neat Au and Pd nanoparticles immobilized in the same SPB carrier system. The addition of 25% molar ratio of Pd to the nanoalloys increases the reaction rate of the first step nearly 10 times compared with that of SPB-Au and 60 times compared with that of SPB-Pd. Analysis of the nanoalloy by high-resolution transmission electron microscopy suggests that the surface defects of the nanoalloys play an important role for the enhanced catalytic activity.