Preparation and characterization of thermally stabilized Ceria and Ceria containing materials

Ceria, CeO2, is one of the most important catalytic materials that can play multiple roles owing to its ability to release and uptake oxygen under catalytic reaction conditions with the preservation of it fluorite structure. Textural and thermal stability is a critical issue in determining the promoting and metal supporting functions of CeO2 in its catalytic applications in the three way catalysis. Therefore, significant efforts have been made by industry on finding ways to improve the thermal stability of ceria both by modification of the synthesis of CeO2 and by looking at possible stabilizers. In the first part of this work, thermally stable ceria aggregates were obtained via a two-step sol gel process of cerium isopropoxide dispersed in isopropanol by ultrasonic radiation. The first step involved a hydrolysis reaction. In the second step, the resultant dispersions were mixed under stirring with neutral or basic water isopropanol solutions. The ceria powders obtained via neutral and basic media were shown to be composed of aggregates of fine particles. However, it was found that the type of media affected both particle texture and morphology. Specific surface areas of 33.1 and 44.2 m2g-1 respectively, were obtained for the neutral and basic materials, which calcined at 650 °C for 3 hours. Moreover, the oxidative nature of ceria was found to help in the removal of the organic impurities while the hydroxylated surface of ceria facilitated the formation of thermally stable agglomerates. In the second part of this work, ceria supported on silica, ceria/silica, materials of 10 and 20% (w/w) were prepared by calcinations, at 650 °C for 3 h, of the xerogels obtained by the mixing of the corresponding amount of a ceria precursor with freshly prepared sols of spherical silica particles (Stober particles) in their mother liquors. Two different ceria precursors were examined in this investigation. The first was a gel produced by prehydrolysis of cerium (IV)-tetra isopropoxide in isopropanol media, and the second was an aqueous solution of ceric (IV) ammonium nitrate. Different textural and morphological characteristics that developed by calcination, were investigated by TGA, FTIR, XRD, SEM and analyses of N2 adsorption isotherms. The results indicated better ceria dispersion and formation of mesoporous textural composites materials produced by the second precursor, ceric (IV) ammonium nitrate, than the first precursor, prehydrolysed cerium (IV)-tetra isopropoxide. The results show that properties of composite materials are largely related to the preparation method and the precursor type. Moreover, mixing media affect both nucleation and the growth of ceria particles and their protection against sintering upon calcinations at the test temperature

Antibiotic Resistance of Helicobacter pylori Strains in the United Arab Emirates and its Relation to the Gene Associated to Gastric Cancer “Cag A Gene”

Helicobacter pylori is a flagellated corkscrew, slow growing neutrophilic gram negative ureolytic organism. It has an extraordinary ability to establish infection in human stomach that can last for years or decades. Its eradication remains an important public health challenge especially in light of broadening indications and increasing antimicrobial resistance. AIM: i) Identification of H. pylori in UAE patients ii) Determination of the prevalence of antibiotic resistance genes (mutation in 23S rRNA gene in clarithromycin, and deletion in RdxA gene in metronidazole) among H. pylori strains isolated from U.A.E patients by using molecular methods, iii) Ascertain whether Cag A- positive H. pylori strains correlates with the antibiotic resistance strains or not and iv) Screening for new H. pylori strains in UAE through the phylogenetic analysis of the 23S rRNA middle region of the gene. METHODS: The identification of H. pylori in UAE patients was carried on by primary screening for H. pylori using CLO test while the confirmation test were done using PCR technique. The prevalence of antibiotic resistance genes (mutation in 23S rRNA gene in clarithromycin, and deletion in RdxA gene in metronidazole) among H. pylori strains isolated from U.A.E patients and Cag A gene relation between this gene and antibiotic resistant genes were studied by PCR and sequencing technique. Phylogenetic analysis of the 23S rRNA gene was analyzed by using the software ClustalX, version 2. Reference sequences used in the alignment was obtained from NCBI data base for all 23s rRNA from different H. pylori strains. RESULTS: 26 out of 90 biopsy samples were positive for H. pylori using PCR whereas only 22 were positive when tested by CLO test. Resistance to clarithromycin and metronidazole was detected in 9 and 3 of strains, respectively. Of the clarithromycin resistant strains, 2 strains had the A2142G mutation in the 23S rRNA gene, 5 strains in A2143G, 1 strain in A2143C and 1 strain of highly changed in sequence. Of the metronidazole resistant strains, deletion in rdxA gene was detected in 3 strains which were negative for CLO test. DNA sequence phylogenetic analysis of the 23S rRNA middle region of the gene indicates that the strains from UAE harbor a unique 23S rRNA sequences that is common among isolates from the UAE patients and different than other strains published in the NCBI database. CONCLUSION: This study is the first time done in the UAE where a significant proportion of gastric mucosal biopsies obtained in the UAE are positive for Genes associated with Clarithromycin and Metronidazole resistance (mainly in Clarithromycin). A2143G remains the most prevalent point mutation involved, thus suggesting that new therapeutic strategies are neede

Development of Electroanalytical Methods for the Determination of Sialic Acid as a Biomarker for Cancer

Sialic acid (SA) is a general term for a family composed of 43 derivatives of neuraminic acid. Whereas N-acetylneuraminic acid (NANA) is the most commonly occurring sialic acid in human. There has been a great interest in the determination of SA in humans because variations in SA level was linked to different medical conditions and diseases. In particular, serum SA are elevated in several types of cancers. SA also exists in Erythropoietin (EPO), a hormone, which induces the production of red blood cells and hence used in the treatment of anemia. Although of the great physiological significance of SA and the attractive merits offered by the electrochemical techniques, there was a notable absence of literature describing electrochemical methods for the determination of SA. This surprising observation triggered this project to develop and to evaluate the first flow injection analysis (FIA) system as well as the first biosensor - based on amperometric transduction - for simple, fast, direct, and reliable determination of SA for clinical applications. The principle of the present work is based on a sequence of two enzyme,s i.e., Nacetylneuraminic acid aldolase (NANA-aldolase) and pyruvate oxidase (PO) which catalyze a two-step conversion of SA into H2O2, which could be detected by anodic amperometry using platinum electrode polarized 0.6 V vs Ag/AgCI. The first phase of the current project was to investigate the effect of different experimental variables on the generation of hydrogen peroxide by the sequence action of the two enzymes. This initial study is carried out using the two enzymes in the soluble form (i.e., homogenous enzyme catalysis). The obtained optimum experimental conditions for hydrogen peroxide generation and detection are 0.1 M phosphate buffer pH 6.3 at 37°C, using NANA-aldolase/PO activity ratio of 1.5 and a thiamine pyrophosphate (TPP) cofactor concentration of 0.5-2 mM. The second phase aimed to construct an FIA system based on an immobilized enzyme reactor (IER) and an amperometric detector for the generated hydrogen peroxide. The IER is prepared by co-immobilization of the two enzymes on controlled pore glass beads activated with glutaraldehyde and packed in a glass tube (3-5 cm in length). A tubular platinum detector of large surface area is suggested in this work and proved efficient to enhance the sensitivity of SA determination by the proposed FIA system. The entire FIA system is evaluated under the optimum conditions obtained from the initial investigation. The obtained linear range, analysis time, and sensitivity could be easily tuned to meet the required performance characteristics by controlling the carrier buffer flow rate, and the injected sample volume. The determination of SA in real samples using the proposed FIA system is presented as well. The third phase is devoted to the most challenging task in this project, i.e., to construct a prototype SA biosensor which necessitated co-immobilization of the two enzymes as well as their integration in a close proximity of platinum electrode surface. Although, three methods are tested for enzyme immobilization, the method based on glutaraldehyde crosslinking with BSA proved the most efficient. A novel microporous polyester membrane is used as a substrate for the enzyme layer, which provided high adhesion and reproducible fabrication of the enzyme layer. The optimum pH of the crosslinked enzyme system is ~ 1 pH higher (~ pH 7.3) than that obtained with homogenous catalysis. Careful optimization of enzyme layer composition and thickness allowed stable and fast response with detection limit of less than 10 µM SA .. Protection of the platinum surface with an inner electropolymeric layer enhanced the selectivity of the SA biosensor in the presence of interfering oxidizable species such as ascorbic and uric acids and acetaminophen. The favorable performance characteristics of the developed SA biosensor allowed its successful application in the determination of SA in simulated serum sample and real biological samples. The obtained performance characteristics of the newly developed electrochemical methods suggest their wide use in the numerous clinical applications and in particular as a non-specific tumor marker and to monitor tumor therapy

Structural Studies of the Role of Iron Oxide in Environmental Catalysis

This thesis presents several fundamental studies of structure-reactivity relationships between pure iron oxides, supported and composite oxides specifically in relation to the decomposition of carbon tetrachloride, CCI4. A series of iron oxides were synthesized and characterized using infrared (FT-IR) spectroscopy to establish their composition spectroscopically, using BET surface area measurements to determine their surface areas and X-ray diffraction powder (XRD) experiments to measure their structural parameters. A new method was then developed to decompose CCl4 at a lower temperature than previously found, choosing the optimum catalyst. The effects of varying the temperature on the CCl4 decomposition was then studied in this work. Some suggested possible structural inferences were explored based on the empirical results obtained via surface area measurements and FT-IR methods of characterization. The optimum catalyst was found to be Fe2O3/ Al2O3 with a high surface area. Small amount of CCl4 decomposed at 100°C which then increased as the temperature increased progressively with a concomitant decrease in the amount of COCl2. In this work, binary systems generally showed higher reactivity, especially the Fe2O3/ Al2O3 system than pure iron oxides. Among the pure iron oxides, magnetite showed the highest reactivity and an ability to adsorb water which could be the main reason behind its reactivity. Tentative reaction mechanisms were suggested, based on the new empirical results, outlining what may be taking place structurally on the surface. In the final part of this work, some of the characteristics of metal oxides in general, including both main-group and transition metal oxides were firstly considered. Recently reported structural models (2002) from the literature were then examined, specifically in relation to iron oxides and the role of carbon tetrachloride on the surface, which has been the example chosen for this work. Specifically in the case of magnetite (Fe3O4), the products were found to be significantly different. The major observed products were CO2, COCl2, C2Cl4 and small traces of CO and HCI. This different behavior may indicate a different reaction mechanism due to different structures. However, further continued work using advanced structural techniques (not available at UAEU) need to be carried out to ascertain these observations. This work may pave the way for the future development of a newer and simpler technique for the treatment of carbon tetrachloride, which has huge implications environmentally, if fully exploited and developed at a later stage