Ptn-Ov synergistic sites on MoOx/γ-Mo2N heterostructure for low-temperature reverse water-gas shift reaction.

In heterogeneous catalysis, the interface between active metal and support plays a key role in catalyzing various reactions. Specially, the synergistic effect between active metals and oxygen vacancies on support can greatly promote catalytic efficiency. However, the construction of high-density metal-vacancy synergistic sites on catalyst surface is very challenging. In this work, isolated Pt atoms are first deposited onto a very thin-layer of MoO3 surface stabilized on γ-Mo2N. Subsequently, the Pt-MoOx/γ-Mo2N catalyst, containing abundant Pt cluster-oxygen vacancy (Ptn-Ov) sites, is in situ constructed. This catalyst exhibits an unmatched activity and excellent stability in the reverse water-gas shift (RWGS) reaction at low temperature (300 °C). Systematic in situ characterizations illustrate that the MoO3 structure on the γ-Mo2N surface can be easily reduced into MoOx (2 < x < 3), followed by the creation of sufficient oxygen vacancies. The Pt atoms are bonded with oxygen atoms of MoOx, and stable Pt clusters are formed. These high-density Ptn-Ov active sites greatly promote the catalytic activity. This strategy of constructing metal-vacancy synergistic sites provides valuable insights for developing efficient supported catalysts.

Iron Carbides: Control Synthesis and Catalytic Applications in COx Hydrogenation and Electrochemical HER.

Catalytic transformation of COx (x = 1, 2) with renewable H2 into valuable fuels and chemicals provides practical processes to mitigate the worldwide energy crisis. Fe-based catalytic materials are widely used for those reactions due to their abundance and low cost. Novel iron carbides are particularly promising catalytic materials among the reported ferrous catalysts. Recently, a series of strategies has been developed for the preparation of iron carbide nanoparticles and their nanocomposites. Control synthesis of FeCx -based nanomaterials and their catalytic applications in COx hydrogenation and electrochemical hydrogen evolution reaction (HER) are reviewed. The discussion is focused on the unique catalytic activities of iron carbides in COx hydrogenation and HER and the correlation between structure and catalytic performance. Future synthesis and potential catalytic applications of iron carbides are also summarized.

Characterization of Parallel ß-Sheets at Interfaces by Chiral Sum Frequency Generation Spectroscopy.

Characterization of protein secondary structures at interfaces is still challenging due to the limitations of surface-selective optical techniques. Here, we address the challenge of characterizing parallel ß-sheets by combining chiral sum frequency generation (SFG) spectroscopy and computational modeling. We focus on human islet amyloid polypeptide aggregates and a de novo designed short polypeptide at lipid/water and air/glass interfaces. We find that parallel ß-sheets adopt distinct orientations at various interfaces and exhibit characteristic chiroptical responses in the amide I and N-H stretch regions. Theoretical analysis indicates that the characteristic chiroptical responses provide valuable information on the symmetry, orientation, and vibrational couplings of parallel ß-sheet at interfaces.

Membrane permeation induced by aggregates of human islet amyloid polypeptides.

Several neurodegenerative diseases such as Alzheimer's and Parkinson's diseases as well as nonneuropathic diseases such as type II diabetes and atrial amyloidosis are associated with aggregation of amyloid polypeptides into fibrillar structures, or plaques. In this study, we use molecular dynamics simulations to test the stability and orientation of membrane-embedded aggregates of the human islet amyloid polypeptide (hIAPP) implicated in type II diabetes. We find that in both monolayers and bilayers of dipalmitoylphosphatidylglycerol (DPPG) hIAPP trimers and tetramers remain inside the membranes and preserve their ß-sheet secondary structure. Lipid bilayer-inserted hIAPP trimers and tetramers orient inside DPPG at 60° relative to the membrane/water interface and lead to water permeation and Na(+) intrusion, consistent with ion-toxicity in islet ß-cells. In particular, hIAPP trimers form a water-filled ß-sandwich that induce water permeability comparable with channel-forming proteins, such as aquaporins and gramicidin-A. The predicted disruptive orientation is consistent with the amphiphilic properties of the hIAPP aggregates and could be probed by chiral sum frequency generation (SFG) spectroscopy, as predicted by the simulated SFG spectra.

Chiral sum frequency generation for in situ probing proton exchange in antiparallel ß-sheets at interfaces.

Studying hydrogen/deuterium (H/D) exchange in proteins can provide valuable insight on protein structure and dynamics. Several techniques are available for probing H/D exchange in the bulk solution, including NMR, mass spectroscopy, and Fourier transform infrared spectroscopy. However, probing H/D exchange at interfaces is challenging because it requires surface-selective methods. Here, we introduce the combination of in situ chiral sum frequency generation (cSFG) spectroscopy and ab initio simulations of cSFG spectra as a powerful methodology to probe the dynamics of H/D exchange at interfaces. This method is applied to characterize H/D exchange in the antiparallel ß-sheet peptide LK7ß. We report here for the first time that the rate of D-to-H exchange is about 1 order of magnitude faster than H-to-D exchange in the antiparallel structure at the air/water interface, which is consistent with the existing knowledge that O-H/D dissociation in water is the rate-limiting step, and breaking the O-D bond is slower than breaking the O-H bond. The reported analysis also provides fundamental understanding of several vibrational modes and their couplings in peptide backbones that have been difficult to characterize by conventional methods, including Fermi resonances of various combinations of peptide vibrational modes such as amide I and amide II, C-N stretch, and N-H/N-D bending. These results demonstrate cSFG as a sensitive technique for probing the kinetics of H/D exchange in proteins at interfaces, with high signal-to-noise N-H/N-D stretch bands that are free of background from the water O-H/O-D stretch.

Amphiphilic adsorption of human islet amyloid polypeptide aggregates to lipid/aqueous interfaces.

Many amyloid proteins misfold into ß-sheet aggregates upon interacting with biomembranes at the onset of diseases, such as Parkinson's disease and type II diabetes. The molecular mechanisms triggering aggregation depend on the orientation of ß-sheets at the cell membranes. However, understanding how ß-sheets adsorb onto lipid/aqueous interfaces is challenging. Here, we combine chiral sum frequency generation (SFG) spectroscopy and ab initio quantum chemistry calculations based on a divide-and-conquer strategy to characterize the orientation of human islet amyloid polypeptides (hIAPPs) at lipid/aqueous interfaces. We show that the aggregates bind with ß-strands oriented at 48° relative to the interface. This orientation reflects the amphiphilic properties of hIAPP ß-sheet aggregates and suggests the potential disruptive effect on membrane integrity.