The structures of n-alkanoic acid monolayers (CH3(CH2) m CO2H, m = 5, 6, 11, 13−22) self-assembled on gold premodified by electrodeposition of a silver or copper adlayer are studied by contact angle measurements, IRAS (infrared reflectance−absorption spectroscopy), and XPS (X-ray photoelectron spectroscopy). Prior to immersion into the fatty acid-containing solutions, the substrates are prepared by underpotential deposition (upd), resulting in a sub-monolayer or full monolayer of silver or copper on gold. The adlayer promotes anchoring of carboxylate headgroup and assembly of n-alkanoic acids, which would otherwise exhibit no chemisorption on bare gold. The results show that the monolayers exhibit low wettability, all-trans methylene conformation, and a bidentate binding scheme of the carboxylate headgroups onto the upd-modified substrate. The odd−even effect of alternating peak intensity of the methyl-stretching modes is significant for monolayers on silver upd surface and, to a less extent, yet notably, for those on copper upd surface. These features are distinctly different from structures of n-alkanoic acid SAMs on bulk copper containing native oxides. We attribute the difference to the degree of surface oxide formation indicated by XPS which reveals that in ambient conditions the upd-modified surface is less oxidized by dioxygen than the corresponding bulk substrate.
We present an alternative to self-assembled monolayers (SAMs) of ω-functionalized alkanethiols on gold. Substrates utilized here are gold modified by electrochemical deposition of silver or copper monolayers. The metal adlayers promote anchoring of carboxylate headgroups and assembly of ω-alkanoic acids, which would otherwise exhibit no chemisorption on bare gold. Infrared reflectance absorption spectroscopy shows that the films exhibit general characteristics of SAMs. The binding scheme is different from SAMs of alkanethiols on gold and alkanoic acids on silver or copper surfaces. Wetability results obtained from contact angle measurements indicate that such films are more reproducible than SAMs of alkanoic acids on bulk silver and copper.
The enteric pathogen enterohemorrhagic Escherichia coli (EHEC) is responsible for outbreaks of bloody diarrhea and hemolytic uremic syndrome (HUS) worldwide. Several molecular mechanisms have been described for the pathogenicity of EHEC; however, the role of bacterial metabolism in the virulence of EHEC during infection in vivo remains unclear. Here we show that aerobic metabolism plays an important role in the regulation of EHEC virulence in Caenorhabditis elegans. Our functional genomic analyses showed that disruption of the genes encoding the succinate dehydrogenase complex (Sdh) of EHEC, including the sdhA gene, attenuated its toxicity toward C. elegans animals. Sdh converts succinate to fumarate and links the tricarboxylic acid (TCA) cycle and the electron transport chain (ETC) simultaneously. Succinate accumulation and fumarate depletion in the EHEC sdhA mutant cells were also demonstrated to be concomitant by metabolomic analyses. Moreover, fumarate replenishment to the sdhA mutant significantly increased its virulence toward C. elegans. These results suggest that the TCA cycle, ETC, and alteration in metabolome all account for the attenuated toxicity of the sdhA mutant, and Sdh catabolite fumarate in particular plays a critical role in the regulation of EHEC virulence. In addition, we identified the tryptophanase (TnaA) as a downstream virulence determinant of SdhA using a label-free proteomic method. We demonstrated that expression of tnaA is regulated by fumarate in EHEC. Taken together, our multi-omic analyses demonstrate that sdhA is required for the virulence of EHEC, and aerobic metabolism plays important roles in the pathogenicity of EHEC infection in C. elegans. Moreover, our study highlights the potential targeting of SdhA, if druggable, as alternative preventive or therapeutic strategies by which to combat EHEC infection.
The effects of heat-treatment ͑before and after anodization͒ on the microstructure and electrochemical characteristics of anodized aluminum oxide films formed in 85°C aqueous ammonium adipate electrolyte were investigated. The morphology and crystal structure of the anodized oxide were examined by transmission electron microscopy. The capacitance, relative dielectric constant, electrochemical impedance spectroscopy, and I-V behavior of the oxide film were also determined. Both pre-and post-heattreatment at 500°C could induce the formation of crystalline ␥Ј-Al 2 O 3 in the outer layer of anodized oxide and consequently increase the relative dielectric constant of the film. The differences in the morphology and crystalline characteristics between the anodized oxide subjected to pre-and/or post-heat-treatments led to variations in the electrochemical properties. The pre-heattreatment could economize the required charge to anodize the oxide and retard the growth of film thickness during anodizing. Thermal-induced phase transformation from amorphous to crystalline oxide of the anodized film due to post-heat-treatment, could leave some defects and substantially decrease the electrical resistance of the oxide layer. The reanodization further developed and extended the crystalline oxide formation, which subsequently increased the relative dielectric constant of the oxide film.Barrier aluminum oxide finds many applications in the integrated circuit process, 1 thin film transistor/liquid crystal display fabrication, 2 metal-insulator-metal cathodes for electron-beam lithography, and electrolytic capacitors. 3 Depending on the anodizing conditions, either amorphous or crystalline barrier aluminum oxide can be formed. Because the crystalline oxide can sustain a higher voltage, 4 has a higher relative dielectric constant, 5,6 and possesses a lower ionic conductivity than that of the amorphous oxide film, work on developing an anodized film with a high degree of crystallinity is of continuous interest to researchers. 7 Crystalline oxide growth may be promoted by the presence of a thin layer of thermal oxide on the surface of aluminum. 5,[8][9][10][11][12] The thermal oxide, which contains ␥-Al 2 O 3 13,14 crystals, becomes incorporated into the growing barrier oxide and acts as nuclei for the amorphous to ␥Ј-Al 2 O 3 transformation. 10,11 But the development, during the anodization, of ␥Ј-Al 2 O 3 within the anodized oxide film formed on aluminum covered with a thin thermal oxide is strongly influenced by the nature of the anion species of the electrolytes. 15 Although the film morphology, crystalline characteristics, and growing mechanism of dielectric oxides anodized in borate and phosphate electrolytes had been extensively reported, 10-12,15-17 those formed in ammonium adipate solution, a common medium to anodize the aluminum for use in lowvoltage electrolytic capacitors, were rarely explored.In a recent study, the dependence of the microstructure of aluminum anodized film on the forming voltage in ammonium adipate solution...
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