Operando X-ray absorption experiments and density functional theory (DFT) calculations are reported that elucidate the role of copper redox chemistry in the selective catalytic reduction (SCR) of NO over Cu-exchanged SSZ-13. Catalysts prepared to contain only isolated, exchanged Cu(II) ions evidence both Cu(II) and Cu(I) ions under standard SCR conditions at 473 K. Reactant cutoff experiments show that NO and NH3 together are necessary for Cu(II) reduction to Cu(I). DFT calculations show that NO-assisted NH3 dissociation is both energetically favorable and accounts for the observed Cu(II) reduction. The calculations predict in situ generation of Brønsted sites proximal to Cu(I) upon reduction, which we quantify in separate titration experiments. Both NO and O2 are necessary for oxidation of Cu(I) to Cu(II), which DFT suggests to occur by a NO2 intermediate. Reaction of Cu-bound NO2 with proximal NH4(+) completes the catalytic cycle. N2 is produced in both reduction and oxidation half-cycles.

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Chemical penetration enhancers (CPEs) are present in a large number of transdermal, dermatological, and cosmetic products to aid dermal absorption of curatives and aesthetics. This wide spectrum of use is based on only a handful of molecules, the majority of which belong to three to four typical chemical functionalities, sporadically introduced as CPEs in the last 50 years. Using >100 CPEs representing several chemical functionalities, we report on the fundamental mechanisms that determine the barrier disruption potential of CPEs and skin safety in their presence. Fourier transform infrared spectroscopy studies revealed that regardless of their chemical make-up, CPEs perturb the skin barrier via extraction or fluidization of lipid bilayers. Irritation response of CPEs, on the other hand, correlated with the denaturation of stratum corneum proteins, making it feasible to use protein conformation changes to map CPE safety in vitro. Most interestingly, the understanding of underlying molecular forces responsible for CPE safety and potency reveals inherent constraints that limit CPE performance. Reengineering this knowledge back into molecular structure, we designed >300 potential CPEs. These molecules were screened in silico and subsequently tested in vitro for molecular delivery. These molecules significantly broaden the repertoire of CPEs that can aid the design of optimized transdermal, dermatological, and cosmetic formulations in the future. stratum corneum ͉ spectroscopy ͉ skin irritation ͉ lipid C urrently, hypodermic needles are the only available mode for systemic delivery of macromolecular drugs into humans. Transdermal delivery offers an attractive alternative to needlebased drug administration. However, evolved to impede the flux of exogenous molecules, stratum corneum (SC), the topmost layer of the skin, provides a strong barrier to molecular delivery. This is especially problematic for relatively large drugs (molecular mass Ͼ 500 Da), which represent a large majority of active agents for therapeutic applications (1). Over 350 molecules, termed chemical penetration enhancers (CPEs), have been identified to perturb the SC barrier to facilitate molecular delivery. However, incorporation of CPEs into products has been mitigated by safety concerns related to the health of the skin membrane (2-4). Accordingly, overcoming the skin barrier in a safe and effective way still remains the bottleneck of transdermal and topical therapies.Identification of chemicals to increase skin permeability has been an area of high activity in the last three decades (5-7). After an initial rise in the number of CPEs in the 1980s, the active pool of CPEs has reached a plateau in the last decade. In an era where new chemical entities are being discovered at an exponential rate (as indicated by the entries in the Chemical Abstract Service), the plateau in the number of CPE molecules is rather surprising (only 1 in 100,000 known molecules represents a CPE). This anomaly originates from the slow rates of syntheses of CPEs when compar...

Au/TiO(2) catalysts used in the water-gas shift (WGS) reaction at 120 °C, 7% CO, 22% H(2)O, 9% CO(2), and 37% H(2) had rates up to 0.1 moles of CO converted per mole of Au per second. However, the rate per mole of Au depends strongly on the Au particle size. The use of a nonporous, model support allowed for imaging of the active catalyst and a precise determination of the gold size distribution using transmission electron microscopy (TEM) because all the gold is exposed on the surface. A physical model of Au/TiO(2) is used to show that corner atoms with fewer than seven neighboring gold atoms are the dominant active sites. The number of corner sites does not vary as particle size increases above 1 nm, giving the surprising result that the rate per gold cluster is independent of size.