Adsorption of cytosine and aza derivatives of cytidine on Au single crystal surfaces

The adsorption of cytosine on the Au(111) and Au(110) surfaces has been studied using both aqueous deposition and evaporation in vacuum to prepare the samples. Soft X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) were used to determine the electronic structure and orientation of the adsorbates. In addition, three derivatives of cytosine, 6-azacytosine, 6-azacytidine and 5- azacytidine, were studied. Monolayer films of the latter three samples were adsorbed on Au(111) from aqueous solution, and the nature of bonding was determined. Spectra have been interpreted in the light of published calculations of free cytosine molecules and new ab initio calculations of the other compounds. Surface core level shifts of Au 4f imply that all of these compounds are chemisorbed. Cytosine adsorbs as a single tautomer, but in two chemical states with different surface-molecule bonding. For deposition in vacuum, a flat-lying molecular state bonded through the N(3) atom of the pyrimidine ring dominates, but a second state is also present. For deposition from solution, the second state dominates, with the molecular plane no longer parallel to the surface. This state also bonds through the N(3) atom, but in addition interacts with the surface via the amino group. Two tautomers of 6-azacytosine were observed, and they and 6-azacytidine adsorb with similar geometries, chemically bonding via the azacytosine ring. The ribose ring does not appear to perturb the adsorption of azacytidine compared with azacytosine. The azacytosine ring is nearly but not perfectly parallel to the surface, like 5-azacytidine, which adsorbs as an imino tautomer. ...Comment: 40 pages, 3 tables and 8 figure

Potent E. coli M‑17 Growth Inhibition by Ultrasonically Complexed Acetylsalicylic Acid−ZnO−Graphene Oxide Nanoparticles

A single-step ultrasonic method (20 kHz) is demonstrated for the complexation of acetylsalicylic acid (ASA)−ZnO− graphene oxide (GO) nanoparticles with an average size of <70 nm in aqueous solution. ASA−ZnO−GO more e ffi ciently inhibits the growth of probiotic Escherichia coli strain M-17 and exhibits enhanced antioxidant properties than free ASA and ASA−ZnO in neutralization of hydroxyl radicals in the electro-Fenton process. This improved function of ASA in the ASA −ZnO GO can be attributed to the well-de fi ned cone-shaped morphology, the surface structure containing hydroxyl and carboxylate groups of ZnO−GO nanoparticles, which facilitated the complexation with ASA

Direct Conversion of Methane to Methanol on Ni-Ceria Surfaces: Metal-Support Interactions and Water-Enabled Catalytic Conversion by Site Blocking

[EN] The transformation of methane into methanol or higher alcohols at moderate temperature and pressure conditions is of great environmental interest and remains a challenge despite many efforts. Extended surfaces of metallic nickel are inactive for a direct CH → CHOH conversion. This experimental and computational study provides clear evidence that low Ni loadings on a CeO(111) support can perform a direct catalytic cycle for the generation of methanol at low temperature using oxygen and water as reactants, with a higher selectivity than ever reported for ceria-based catalysts. On the basis of ambient pressure X-ray photoemission spectroscopy and density functional theory calculations, we demonstrate that water plays a crucial role in blocking catalyst sites where methyl species could fully decompose, an essential factor for diminishing the production of CO and CO, and in generating sites on which methoxy species and ultimately methanol can form. In addition to water-site blocking, one needs the effects of metal-support interactions to bind and activate methane and water. These findings should be considered when designing metal/oxide catalysts for converting methane to value-added chemicals and fuels.The work carried out at Brookhaven National Laboratory was supported by the U.S. Department of Energy (Chemical Sciences Division, DE-SC0012704). S.D.S. is supported by a U.S. Department of Energy Early Career Award. This research used resources of the Advanced Light Source (Beamline 9.3.2),which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. Authors acknowledge contribution of Dr. Ethan Crumlin for assistance with AP-XPS measurements. M.V.G.-P. acknowledges the financial support of the /Ministry of Economy and Competitiveness MINECO-Spain (Grant No. CTQ2015-78823-R) and P.G.L. that of the Agencia Nacional de Promocion Científiica y Tecnologica-Argentina (Grant No. PICT-2016-2750). Computer time provided by the BIFI-ZCAM, RES at the Marenostrum and La Palma nodes, SNCAD (Sistema Nacional de Computación de Alto Desempeño, Argentina), and the DECI resources BEM based in Poland at WCSS and Archer at EPCC with support from the PRACE aislb, is acknowledged. M.V. thanks the Ministry of Education, Youth and Sports of the Czech Republic for financial support under Project LH15277. R.M.P. was partially funded by the AGEP-T (Alliance for Graduate Education and the Professoriate−Transformation) which is funded by the National Science Foundation, award #131131

Sonochemical Formation of Copper/Iron-modified Graphene Oxide Nanocomposites for Ketorolac Delivery

A feasible sonochemical approach is described for the preparation of copper/iron-modified graphene oxide nanocomposites by using ultrasound (20 kHz, 18 W/cm2) in aqueous solution containing copper and iron ion precursors. Unique copper-, copper/iron- and iron-modified graphene oxide nanocomposites have a submicron size that is smaller than pristine GO and a higher surface area enriched with Cu2O, CuO, Fe2O3 of multiform phases (α-, β-, ε- or γ), FeO(OH) and sulfur- or carbon-containing compounds. These nanocomposites are sonochemically intercalated with the nonsteroidal anti-inflammatory drug ketorolac resulting in formation of nanoscale carriers. Ketorolac monotonically disintegrates from these nanoscale carriers in aqueous solution adjusted to pH from 1 to 8. The disintegration of ketorolac proceeds at a slower rate from the copper/iron-modified graphene oxide at increased pH, but at a faster rate from the iron-modified graphene oxide starting from acidic conditions

Ultrasonic Formation of Copper/Iron Graphene Oxide for Ketorolac Delivery

New accessible sonochemical methods were developed for the functionalization of synthesized graphene oxide (GO) with copper/iron compounds and drug intercalation into their structure in aqueous solution at ambient conditions by using ultrasound (20 kHz) treatment. The sonochemical formation mechanism of a new nanomaterial was revealed through the structural analysis of three types of nanocomposites: (i) copper@graphene oxide, (ii) copper/iron@-graphene oxide and (iii) iron@graphene oxide. Unique copper/iron-modied graphene oxide nanocomposites can be used as nanocarriers for the anti-in°ammatory drug (ketorolac) delivery in aqueous solution due to the reduced submicron size and enlarged surface area. Disintegration of the ultrasonically intercalated ketorolac followed the exponential decay curve fit at higher pH values of the aqueous solution with a higher decay constant observed in copper/iron-modifed graphene oxide nanocomposites

Ultrastructural demonstration of glucose-6-phosphatase activity and glycogen in skeletal muscles of newborn piglets with the splayleg syndrome

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