No abstract

The interaction of an X-ray-modified self-assembled monolayer with a mixture of atomic and molecular oxygen (O/O 2 ) has been studied using in situ X-ray photoelectron spectroscopy. Initially the reaction dynamics are dominated by the incorporation of new oxygen containing functionality at the vacuum/film interface. At intermediate O/O 2 exposures, when a steady-state concentration of C-O, CdO, and O-CdO groups has been established, the production of volatile carbon-containing species, including CO 2 , is responsible for etching the hydrocarbon film. Upon prolonged O/O 2 exposures, O atoms penetrate to the film/substrate interface, producing Au 2 O 3 and sulfonate (RSO 3 ) species. Under steady-state conditions, the thickness of the hydrocarbon film was reduced with an efficiency of ≈7.4 × 10 -4 Å/impingent O atom while the average penetration depth of O atoms within the hydrocarbon film was determined to be ≈5.5 Å.

The nucleoside analog 5-aza-2′-deoxycytidine (Decitabine, DAC) is one of several drugs in clinical use that inhibit DNA methyltransferases, leading to a decrease of 5-methylcytosine in newly replicated DNA and subsequent transcriptional activation of genes silenced by cytosine methylation. In addition to methyltransferase inhibition, DAC has demonstrated toxicity and potential mutagenicity, and can induce a DNA-repair response. The mechanisms accounting for these events are not well understood. DAC is chemically unstable in aqueous solutions, but there is little consensus between previous reports as to its half-life and corresponding products of decomposition at physiological temperature and pH, potentially confounding studies on its mechanism of action and long-term use in humans. Here we have employed a battery of analytical methods to estimate kinetic rates and to characterize DAC decomposition products under conditions of physiological temperature and pH. Our results indicate that DAC decomposes into a plethora of products, formed by hydrolytic opening and deformylation of the triazine ring, in addition to anomerization and possibly other changes in the sugar ring structure. We also discuss the advantages and problems associated with each analytical method used. The results reported here will facilitate ongoing studies and clinical trials aimed at understanding the mechanisms of action, toxicity, and possible mutagenicity of DAC and related analogs.

The low-temperature (<150 K) oxidation of nitrided iron surfaces exposed to oxygen and water was probed using X-ray photoelectron spectroscopy (XPS), reflection absorption infrared spectroscopy (RAIRS), and mass spectrometry (MS). During exposure of nitrided iron surfaces to oxygen, iron oxynitride (Fe x N y O z ), nitrosonium ions (NO+), as well as nitrite/nitrito- and nitrate-type species were observed. The production of nitrite/nitrito and nitrate species is taken as evidence for the existence of oxygen insertion chemistry into the iron nitride lattice under these low-temperature oxidation conditions. No molecular nitrogen was produced during reactions with oxygen or water in contrast to oxidation studies on other transition metal nitrides. Upon annealing the oxidized overlayer, nitrogen desorbs exclusively as nitric oxide (NO) between 250 and 400 K. In contrast to oxygen, the reactivity of nitrided iron surfaces toward water was limited to the production of adsorbed N−O species.

BACKGROUND: In this study the effects of ampicillin and aqueous garlic extract on Escherichiacoli (ATCC 9637) and Staphylococcus aureus (ATCC 25923) were compared. Atomic force microscopy (AFM) was used to study the possible mechanisms of membrane disruption.