Mechanism by which Tungsten Oxide Promotes the Activity of Supported V2 O5 /TiO2 Catalysts for NOX Abatement: Structural Effects Revealed by 51 V MAS NMR Spectroscopy.

The selective catalytic reduction (SCR) of NOx with NH3 to N2 with supported V2 O5 (-WO3 )/TiO2 catalysts is an industrial technology used to mitigate toxic emissions. Long-standing uncertainties in the molecular structures of surface vanadia are clarified, whereby progressive addition of vanadia to TiO2 forms oligomeric vanadia structures and reveals a proportional relationship of SCR reaction rate to [surface VOx concentration]2 , implying a 2-site mechanism. Unreactive surface tungsta (WO3 ) also promote the formation of oligomeric vanadia (V2 O5 ) sites, showing that promoter incorporation enhances the SCR reaction by a structural effect generating adjacent surface sites and not from electronic effects as previously proposed. The findings outline a method to assess structural effects of promoter incorporation on catalysts and reveal both the dual-site requirement for the SCR reaction and the important structural promotional effect that tungsten oxide offers for the SCR reaction by V2 O5 /TiO2 catalysts.

Nature of Active Sites and Surface Intermediates during SCR of NO with NH3 by Supported V2O5--WO3/TiO2 Catalysts.

Time-resolved in situ IR was performed during selective catalytic reduction of NO with NH3 on supported V2O5-WO3/TiO2 catalysts to examine the distribution and reactivity of surface ammonia species on Lewis and Brønsted acid sites. While both species were found to participate in the SCR reaction, their relative population depends on the coverage of the surface vanadia and tungsta sites, temperature, and moisture. Although the more abundant surface NH4+,ads intermediates dominate the overall SCR reaction, especially for hydrothermally aged catalysts, the minority surface NH3,ads intermediates exhibit a higher specific SCR activity (TOF). The current study serves to resolve the long-standing controversy about the active sites for SCR of NO with NH3 by supported V2O5-WO3/TiO2 catalysts.

Investigating the influences of redox buffer compositions on the amyloid fibrillogenesis of hen egg-white lysozyme.

More than twenty different human proteins have been found to fold abnormally resulting in the formation of pathological deposits and several lethal degenerative diseases. Despite extensive investigations on amyloid fibril formation, the detailed molecular mechanism remained rather elusive. The present study is aimed at exploring the effect of the ratio of cysteine and cystine in the buffer on the fibrillation of hen egg-white lysozyme. Our results revealed that the inhibition of lysozyme amyloid formation by cysteine in the redox buffer followed a concentration-dependent fashion. Cystine, the oxidized form of cysteine, nevertheless, did not influence the final level of fibrillation although it lengthened the lag period of fibril formation. Moreover, the effect of the ratio of cysteine to cystine in the buffer on the fibrillogenesis of hen lysozyme was found to be greatly associated with the formation of mixed disulfide derivatives. Finally, a possible reaction mechanism was proposed to explain our experimental results. Our study shows that the concentration of mixed disulfide derivative was inversely correlated with the level of lysozyme fibrillogenesis. The results from this work may aid in comprehending the molecular mechanism(s) of amyloid fibrillogenesis for disulfide bonded proteins and the development of effective therapeutics for amyloidogenic diseases.

Effects of copolypeptides on amyloid fibrillation of hen egg-white lysozyme.

The fibrillation of hen egg-white lysozyme (HEWL) in the absence and presence of simple, unstructured D,L-lysine-co-glycine (D,L-Lys-co-gly) and D,L-lysine-co-L-phenylalanine (D,L-Lys-co-Phe) copolypeptides was studied by using a variety of analytical techniques. The attenuating and decelerating effects on fibrillation are significantly dependent on the polypeptide concentration and the composition ratios in the polypeptide chain. Interestingly, D,L-Lys-co-gly and D,L-Lys-co-Phe copolypeptides with the same composition ratio have comparable attenuating effects on fibrillation. The copolypeptide with highest molar fraction of glycine residue exhibits the strongest suppression of HEWL fibrillation. The copolypeptide has the highest hydrophobic interacting capacity due to the more molar ratio of apolar monomer in the polymer backbone. The major driving forces for the association of HEWL and copolypeptides are likely to be hydrogen bonding and hydrophobic interactions, and these interactions reduce the concentration of free protein in solution available to proceed to fibrillation, leading to the increase of lag time and attenuation of fibrillation. The results of this work may contribute to the understanding of the molecular factors affecting amyloid fibrillation and the molecular mechanism(s) of the interactions between the unstructured polypeptides and the amyloid proteins.

Efficient and stable enzyme immobilization in a block copolypeptide vesicle-templated biomimetic silica support.

We report the immobilization of a model enzyme, papain, within silica matrices by combining vesiclization of poly-l-lysine-b-polyglycine block copolypeptides with following silica mineralization. Our novel strategy utilizes block polypeptide vesicles to induce the condensation of orthosilicic acid while trapping an enzyme within and between vesicles. The polypeptide mediated silica-immobilized enzyme exhibits enhanced pH and thermal stability and reusability, comparing with the free and vesicle encapsulated enzyme. The enhanced enzymatic activity in the immobilized enzyme is due to the confinement of the enzyme in the polypeptide mediated silica matrices. Kinetic analysis shows that the enzyme functionality is determined by the structure and property of silica/polypeptide matrices. The proposed novel strategy provides an alternative route for the synthesis of a broad range of functional bionanocomposites entrapped within silica nanostructures.