Tuning metal–support interaction has been considered as an effective approach to modulate the electronic structure and catalytic activity of supported metal catalysts. At the atomic level, the understanding of the structure–activity relationship still remains obscure in heterogeneous catalysis, such as the conversion of water (alkaline) or hydronium ions (acid) to hydrogen (hydrogen evolution reaction, HER). Here, we reveal that the fine control over the oxidation states of single-atom Pt catalysts through electronic metal–support interaction significantly modulates the catalytic activities in either acidic or alkaline HER. Combined with detailed spectroscopic and electrochemical characterizations, the structure–activity relationship is established by correlating the acidic/alkaline HER activity with the average oxidation state of single-atom Pt and the Pt–H/Pt–OH interaction. This study sheds light on the atomic-level mechanistic understanding of acidic and alkaline HER, and further provides guidelines for the rational design of high-performance single-atom catalysts.
The growth of atomically dispersed metal catalysts (ADMCs) remains a great challenge owing to the thermodynamically driven atom aggregation. Here we report a surface-limited electrodeposition technique that uses site-specific substrates for the rapid and room-temperature synthesis of ADMCs. We obtained ADMCs by the underpotential deposition of a non-noble single-atom metal onto the chalcogen atoms of transition metal dichalcogenides and subsequent galvanic displacement with a more-noble single-atom metal. The site-specific electrodeposition enables the formation of energetically favorable metal–support bonds, and then automatically terminates the sequential formation of metallic bonding. The self-terminating effect restricts the metal deposition to the atomic scale. The modulated ADMCs exhibit remarkable activity and stability in the hydrogen evolution reaction compared to state-of-the-art single-atom electrocatalysts. We demonstrate that this methodology could be extended to the synthesis of a variety of ADMCs (Pt, Pd, Rh, Cu, Pb, Bi, and Sn), showing its general scope for functional ADMCs manufacturing in heterogeneous catalysis.
T-cell receptor-CD3 complex (TCR) is a versatile signaling machine that can initiate antigen-specific immune responses based on various biochemical changes of CD3 cytoplasmic domains, but the underlying structural basis remains elusive. Here we developed biophysical approaches to study the conformational dynamics of CD3ε cytoplasmic domain (CD3ε CD ). At the single-molecule level, we found that CD3ε CD could have multiple conformational states with different openness of three functional motifs, i.e., ITAM, BRS and PRS. These conformations were generated because different regions of CD3ε CD had heterogeneous lipid-binding properties and therefore had heterogeneous dynamics. Live-cell imaging experiments demonstrated that different antigen stimulations could stabilize CD3ε CD at different conformations. Lipid-dependent conformational dynamics thus provide structural basis for the versatile signaling property of TCR.
Molecular
self-assembly provides a chemical strategy for the synthesis
of nanostructures by using the principles of nature, and peptides
serve as the promising building blocks to construct adaptable molecular
architectures. Recently, a series of heptapeptides with alternative
hydrophobic and hydrophilic residues were reported to form amyloid-like
structures, which are capable of catalyzing acyl ester hydrolysis
with remarkable efficiency. However, information remains elusive about
the atomic structures of the fibrils. What is the origin of the sequence-dependent
catalytic activity? How is the ester hydrolysis catalyzed by the fibrils?
In this work, the atomic structures of the aggregates were determined
by using molecular modeling and further validated by solid-state NMR
experiments, where the fibril with high activity adopts twisted parallel
configuration within each layer, and the one with low activity is
in flat antiparallel configuration. The polymorphism originates from
the interactions between different regions of the building block peptides,
where the delicate balance between rigidity and flexibility plays
an important role. We further show that the p-nitrophenylacetate
(pNPA) hydrolysis reactions catalyzed by two different
fibrils follow a similar mechanism, and the difference in microenvironment
at the active site between the natural enzyme and the present self-assembled
fibrils should account for the discrepancy in catalytic activities.
The present work provides understanding of the structure and function
of self-assembled fibrils formed with short peptides at an atomic
level and thus sheds new insight on designing aggregates with better
functions.
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