Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

The interaction of gold atoms with CeO₂ nanocrystals having rod and cube shapes has been examined by cyanide leaching, TEM, TPR, CO IR and X-ray absorption spectroscopy. After deposition?Cprecipitation and calcination of gold, these surfaces contain gold nanoparticles in the range 2?C6 nm. For the ceria nanorods, a substantial amount of gold is present as cations that replace Ce ions in the surface as follows from their first and second coordination shells of oxygen and cerium by EXAFS analysis. These cations are stable against cyanide leaching in contrast to gold nanoparticles. Upon reduction the isolated Au atoms form finely dispersed metal clusters with a high activity in CO oxidation, the WGS reaction and 1,3-butadiene hydrogenation. By analogy with the very low activity of reduced gold nanoparticles on ceria nanocubes exposing the {100} surface plane, it is inferred that the gold nanoparticles on the ceria nanorod surface also have a low activity in such reactions. Although the finely dispersed Au clusters are thermally stable up to quite high temperature in line with earlier findings (Y. Guan and E. J. M. Hensen, Phys Chem Chem Phys 11:9578, 2009), the presence of gold nanoparticles results in their more facile agglomeration, especially in the presence of water (e.g., WGS conditions). For liquid phase alcohol oxidation, metallic gold nanoparticles are the active sites. In the absence of a base, the O?CH bond cleavage appears to be rate limiting, while this shifts to C?CH bond activation after addition of NaOH. In the latter case, the gold nanoparticles on the surface of ceria nanocubes are much more active than those on the surface of nanorod ceria.     

Clinical characteristics and outcome of hyperglycaemic emergencies in Johannesburg Africans

In this prospective analysis we investigated the clinical characteristics of black South African diabetic patients admitted to hospital with hyperglycaemic emergencies. The study cases were selected from the medical admissions to an urbanized, Johannesburg academic hospital over a period of 12 months. Only patients with severe diabetic ketoacidosis (DKA) or hyperosmolar non-ketotic hyperglycaemia (HNKH) as defined in the text were included. Over the study period, we identified 58 patients with severe DKA (M: 32, F: 26) and 24 with HNKH (M: 14, F:10). Thirty-two of the patients with DKA (55.2%) were classified as having non-insulin dependent (Type 2) diabetes mellitus (NIDDM). Compared to the 26 subjects with insulin-dependent (Type 1) diabetes mellitus (IDDM), the NIDDM patients were older (51.7 vs 27.7 years) and had a significantly higher body mass index (BMI) (29.4 vs 23.5 kg m(-2), p = 0.002), and glucose levels 47.5 vs 34 mmol l(-1) p = 0.004). Mortality from DKA was 6.8 % and from HNKH 16.6%. Infection was the leading precipitating factor for both DKA and HNKH, followed by first presentation and noncompliance. We conclude that the majority of urban African patients admitted to hospital with DKA have NIDDM. Mortality from DKA among the black Africans in Johannesburg is low and comparable to the mortality in western Europe.     

The role of collagen in bone apatite formation in the presence of hydroxyapatite nucleation inhibitors

Bone is a composite material in which collagen fibrils form a scaffold for a highly organized arrangement of uniaxially oriented apatite crystals. In the periodic 67 nm cross-striated pattern of the collagen fibril, the less dense 40-nm-long gap zone has been implicated as the place where apatite crystals nucleate from an amorphous phase, and subsequently grow. This process is believed to be directed by highly acidic non-collagenous proteins; however, the role of the collagen matrix during bone apatite mineralization remains unknown. Here, combining nanometre-scale resolution cryogenic transmission electron microscopy and cryogenic electron tomography with molecular modelling, we show that collagen functions in synergy with inhibitors of hydroxyapatite nucleation to actively control mineralization. The positive net charge close to the C-terminal end of the collagen molecules promotes the infiltration of the fibrils with amorphous calcium phosphate (ACP). Furthermore, the clusters of charged amino acids, both in gap and overlap regions, form nucleation sites controlling the conversion of ACP into a parallel array of oriented apatite crystals. We developed a model describing the mechanisms through which the structure, supramolecular assembly and charge distribution of collagen can control mineralization in the presence of inhibitors of hydroxyapatite nucleation.     

Oligonucleotide optimization for DNA synthesis

Large DNA constructs can be synthesized from smaller oligonucleotides using the polymerase chain reaction. The set of oligonucleotides should be designed so that the melting temperature amongst oligonucleotide hybridization pairs do not vary greatly and the length of each oligonucleotide should not exceed 50 nucleotides. A near optimal oligonucleotide set is calculated using reliable gradient optimization methods. This was accomplished by defining a set of discrete arrays that is used to determine the melting temperature of a subset of the larger DNA sequence, depending on the subset start and end positions. These arrays were then incorporated into an objective function, which was optimized using the Broyden‐Fletcher‐Goldfarb‐Shanno method. This method is adjusted slightly to incorporate explicit length and temperature constraints. Experimental results confirmed that the method performs better than similar software programs for the cases investigated and produces suitable oligonucleotide sets for DNA assembly. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Differential induction of systemic resistance in Arabidopsis by biocontrol bacteria

Selected nonpathogenic, root-colonizing bacteria are able to elicit induced systemic resistance (ISR) in plants. To elucidate the molecular mechanisms underlying this type of systemic resistance, an Arabidopsis-based model system was developed in which Pseudomonas syringae pv. tomato and Fusarium oxysporum f. sp. raphani were used as challenging pathogens. In Arabidopsis thaliana ecotypes Columbia and Landsberg erecta, colonization of the rhizosphere by P. fluorescens strain WCS417r induced systemic resistance against both pathogens. In contrast, ecotype RLD did not respond to WCS417r treatment, whereas all three ecotypes expressed systemic acquired resistance upon treatment with salicylic acid (SA). P. fluorescens strain WCS374r, previously shown to induce ISR in radish, did not elicit ISR in Arabidopsis. The opposite was found for P. putida strain WCS358r, which induced ISR in Arabidopsis but not in radish. These results demonstrate that rhizosphere pseudomonads are differentially active in eliciting ISR in related plant species. The outer membrane lipopolysaccharide (LPS) of WCS417r is the main ISR-inducing determinant in radish and carnation, and LPS-containing cell walls also elicit ISR in Arabidopsis. However, mutant WCS417rOA-, lacking the O-antigenic side chain of the LPS, induced levels of protection similar to those induced by wild-type WCS417r. This indicates that ISR-inducing bacteria produce more than a single factor that trigger ISR in Arabidopsis. Furthermore, WCS417r and WCS358r induced protection in both wild-type Arabidopsis and SA-nonaccumulating NahG plants without activating pathogenesis-related gene expression. This suggests that elicitation of an SA-independent signaling pathway is a characteristic feature of ISR-inducing biocontrol bacteria.     

Microarray analysis reveals a mechanism of phenolic polybrominated diphenylether toxicity in zebrafish

Polybrominated diphenylethers (PBDEs) are ubiquitous in the environment, with the lower brominated congener 2,2',4,4'-tetrabromodiphenylether (BDE47) among the most prevalent. The phenolic PBDE, 6-hydroxy-BDE47 (6-OH-BDE47) is both an important metabolite formed by in vivo metabolism of BDE47 and a natural product produced by marine organisms such as algae. Although this compound has been detected in humans and wildlife, including fish, virtually nothing is known of its in vivo toxicity. Here we report that 6-OH-BDE47 is acutely toxic in developing and adult zebrafish at concentrations in the nanomolar (nM) range. To identify possible mechanisms of toxicity, we used microarray analysis as a diagnostic tool. Zebrafish embryonic fibroblast (PAC2) cells were exposed to 6-OH-BDE47, BDE47, and the methoxylated metabolite 6-MeO-BDE47. These experiments revealed that 6-OH-BDE47 alters the expression of genes involved in proton transport and carbohydrate metabolism. These findings, combined with the acute toxicity, suggested that 6-OH-BDE47 causes disruption of oxidative phosphorylation (OXPHOS).Therefore, we further investigated the effect of 6-OH-BDE47 on OXPHOS in zebrafish mitochondria. Results show unequivocally that this compound is a potent uncoupler of OXPHOS and is an inhibitor of complex II of the electron transport chain. This study provides the first evidence of the in vivo toxicity and an important potential mechanism of toxicity of an environmentally relevant phenolic PBDE of both anthropogenic and natural origin. The results of this study emphasize the need for further investigation on the presence and toxicity of this class of polybrominated compounds.     

Reduction of nitric oxide at a platinum cathode in an acidic solution

The reduction of nitric oxide at a platinum electrode in 4 M H₂SO₄ was investigated by the measurement of potential/current relations and by the determination of the current efficiencies for the hydroxylamine, nitrous oxide, ammonia, hydrazine and hydrogen formation at fixed potentials in the potential range from 0 to ?400 mV vs sce.The potential/current curve for the reduction of nitric oxide has two waves, of which the limiting currents depend strongly on the potential and the time of the pretreatment of the electrode and on the direction of the potential change during the measurements. In the potential range of the first wave (viz ? > ?30 mV) nitric oxide is reduced only to nitrous oxide. In the whole potential range of the second wave (viz from ?50 to ?250 mV) nitric oxide is reduced to hydroxylamine, ammonia and nitrous oxide. Formation of hydrazine has not been detected.From the literature and from the relations of the current efficiencies a possible mechanism is proposed for the reduction of nitric oxide.     

From divided to integrated city?

Good urban governance results in economic efficiency, social equity, gender-aware policies, overall sustainability and ultimately, improved living conditions of not only the urban poor but all city residents. […] Good urban governance is not merely a matter of efficient management; it also has political dimensions related to democracy, human rights and civic participation in decision-making processes. (UNCHS, 2001: 211, emphasis in original) The Commission proposes the urgent establishment of a City Development Partnership to enable the development and implementation of a shared development agenda. This partnership must be about concerted action and must be co-owned by the Council, other government agencies, parastatals, the private sector, labour and civil society organisations. The emphasis of the city development partnership will be on a highly focussed campaign or campaigns which can mobilise the commitment, energy and resources of a wide range of stakeholders but which substantively address our core issues of a divided city, dysfunctional communities, and a dual economy. (Unicity Commission, 2000: 9) Previous versions of this paper were prepared for a conference on urban governance in Boston during September 2000, under the aegis of the National Academy of Sciences, and the “Urbanizing World and UN Human Habitat II” Conference, 4–6 June 2001, Columbia University, New York.