Bo Zhang

In living cells, the conversion of squalene to lanosterol requires two dedicated enzymes and proceeds through 2,3-oxidosqualene as an essential intermediate. We show that water microdroplets contacting immiscible organic solvents accomplish this same multistep transformation without enzymatic catalysis. We propose that the oriented electric field across the water–organic interface generates reactive oxygen species that epoxidize squalene and then initiates acid-catalyzed ring-opening of the epoxide followed by a cationic polyene cyclization cascade to yield lanosterol. H218O labeling traced oxygen from water into TEMPO-derived and peroxyacetate ions observed by real-time mass spectrometry. LC–HRMS/MS further revealed C18–C30 reaction products with spectral matches to oxygenated terpenoid and steroid-like structures. We find that ethyl acetate is the most effective organic solvent because it generates peroxyacetic acid at the interface. Simulations show that a preformed protonated 2,3-oxidosqualene model remains hydrated and oriented after placement at the ethyl acetate–water interface, and calculations on microsolvation models indicate that an interfacial water configuration preferentially stabilizes the epoxidation transition state relative to the reactant by approximately 3 kcal mol–1. These results establish a plausible, abiotic pathway for steroid emergence and diversification at water–organic interfaces.

Biomineralization enables living systems to construct hybrid materials by controlling the location, orientation, and polymorph of inorganic crystals with proteins and other biomolecules. Despite decades of study, the molecular principles underlying these processes remain difficult to harness in engineered materials, in part because native biomineralization proteins are often intrinsically disordered, heterogeneous, or insoluble. Here we show that de novo designed protein interfaces can be assembled into reconfigurable two-dimensional arrays which template calcite nanocrystals. By fine-tuning RFdiffusion2 on repeat protein scaffolds, we further enable the design of protein architectures which selectively form aragonite, a metastable polymorph of calcium carbonate, in nucleation conditions that otherwise result in a mixture of phases. Extending beyond inorganics found in biological systems, we show that lattice-matched protein designs template cobalt carbonate formation: a flat helical repeat protein interface promotes unconfined growth, whereas soluble D3 cage assemblies yield more homogenous cobalt carbonate nanocrystals confined to the interior of the cage. These protein-cage cobalt carbonate hybrid materials function as electrocatalysts for alkaline water splitting. Our results demonstrate the potential of deep learning-based methods to unlock the structural and functional activity of protein-mineral composites.

Herein, we report the dynamic nucleation and growth behavior of individual hydrogen microbubbles on a thin-film Pt ultramicroelectrode (UME). By depositing and patterning a thin layer of platinum metal on a transparent, conductive, but electrocatalytically inert indium-tin oxide (ITO) substrate, we are able to obtain individual Pt UMEs and use them to image hydrogen microbubbles formed by the hydrogen evolution reaction (HER) in an acid solution. The use of reflection microscopy and the semitransparent Pt UME allows us to observe hydrogen microbubbles as they nucleate on the UME surface, track their growth with time, and image their movement and bubble-bubble interaction on the electrode. Our results show that H₂ microbubbles formed on a Pt UME tend to move toward the center of the microelectrode as they grow bigger in size and extend their contact area on the electrode. Our results suggest multiple microbubbles forming on the same electrode compete with each other for bubble growth, following a mechanism similar to Ostwald ripening.

We report a mechanistic study of the electrocatalytic response of single Pt nanoparticles (NPs) on a carbon ultramicroelectrode (UME) in a hydrazine (N₂H₄) solution. Using a NP collision approach, our study shows their catalytic response is characterized by a sharp, 2H₄ molecules preadsorbed onto the NP surface, while the step current reflects the continuous catalytic oxidation of protonated hydrazine (N₂H₅⁺), which goes through a deprotonation and adsorption step on Pt. Since each N₂H₅⁺ molecule releases five H⁺ upon complete oxidation, a drastic decrease in local pH can be expected in the vicinity of the NP. This pH shift in turn limits the rate of adsorption and the steady-state oxidation current one can observe from each colliding particle. Our study reveals the key importance of molecular adsorption and the changing local chemical environment (e.g., pH) to the observed catalytic response of single NPs and highlights that steady-state currents in their measurement may be chemically or mass-transport limited.

A robust and detailed physicochemical description of electrochemically generated surface nanobubbles and their effects on electrochemical systems remains at large. Herein, we report the development and utilization of an off-axis, dark-field microscopy imaging tool for probing the dynamic process of generating single H₂ nanobubbles at the surface of a carbon nanoelectrode. A change in the direction of the incident light is made to significantly reduce the intensity of the background light, which enables us to image both the nanoelectrode and nanobubble on the electrode surface or the metal nanoparticles in the vicinity of the electrode. The correlated electrochemical and optical response provides novel insights regarding bubble nucleation and dissolution on a nanoelectrode previously unattainable solely from its current-voltage response.

Here we report the use of a Langmuir isotherm model to analyze and better understand the dynamic adsorption and desorption behavior of single fluorophore molecules at the surface of a hydrogen nanobubble supported on an indium tin oxide (ITO) electrode. Three rhodamine dyes, rhodamine 110 (R110, positively charged), rhodamine 6G (R6G, positively charged), and sulforhodamine G (SRG, negatively charged) were chosen for this study. The use of the Langmuir isotherm model allows us to determine the equilibrium constant and the rate constants for the adsorption and desorption processes. Of the three fluorophores used in this study, SRG was found to have the greatest equilibrium constant. No significant potential dependence was observed on the adsorption characteristics, which suggests the nanobubble size, geometry, and surface properties are relatively constant within the range of potentials used in this study. Our results suggest that the use of the Langmuir isotherm model is a valid and useful means for probing and better understanding the unique adsorption behavior of fluorophores at surface-supported nanobubbles.