Catalytic behavior of alkali-treated Pt/HMOR n-hexane hydroisomerization

Bifunctional Pt-HMOR catalysts were prepared by incipient wetness impregnation of various desilicated MOR obtained by alkaline treatment using NaOH concentrations ranging from 0.1 to 0.5 M. The zeolite structural changes upon modification were investigated by several techniques including powder X-ray diffraction,Al-27 and Si-29 MAS-NMR spectroscopy, N-2 adsorption, pyridine adsorption followed by infrared spectroscopy and the catalytic model reaction of m-xylene transformation. For low alkaline concentration the zeolite acidity is preserved, along with a slight increase of the volume correspondent to the larger micropores due to the removal of extra-framework debris already existent at the parent zeolite. At higher NaOH concentrations there is a significant loss of crystalinity and acidity as well as the formation of mesoporosity. The characterization of the metal function shows similar patterns for Pt-HMOR and Pt-M/0.1 samples, with Pt particles located mainly inside the inner porosity. In contrast, large Pt particles become visible at the intercrystalline mesoporosity of MOR crystals developed during the desilication treatments at severe alkaline conditions. The catalytic results obtained for n-hexane hydroisomerization showed an improved selectivity for dibranched over monobranched isomers for Pt-M/0.1 sample, likely due to the preservation of the support acidity and the slight enlargement of the micropores. This work is a new example in which the mesoporous development does not improve the catalytic efficiency of the zeolites, whereas mild alkaline desilication might be considered as an effective solution to produce customized catalysts with enhanced performance for a given application. (C) 2014 Elsevier B.V. All rights reserved.

Pt/Carbon materials as Bi-Functional catalysts for N-decane hydroisomerization

The activity and selectivity of bi-functional carbon-supported platinum catalysts for the hydroisomerization of n-alkanes have been studied. The influence of the properties of the carbon support on the performance of the catalysts were investigated by incorporating the metallic function on a series of carbons with varied porosity (microporous: GL-50 from Norit, and mesoporous: CMK-3) and surface chemistry (modified by wet oxidation). The characterization results achieved with H-2 chemisorption and TEM showed differences in surface metal concentrations and metal-support interactions depending on the support composition. The highest metal dispersion was achieved after oxidation of the carbon matrix in concentrated nitric acid, suggesting that the presence of surface functional sites distributed in inner and outer surface favors a homogeneous metal distribution. On the other hand, the higher hydrogenating activity of the catalysts prepared with the mesoporous carbon pointed out that a fast molecular traffic inside the pores plays an important role in the catalysts performance. For n-decane hydroisomerization of long chain n-alkanes, higher activities were obtained for the catalysts with an optimized acidity and metal dispersion along with adequate porosity, pointing out the importance of the support properties in the performance of the catalysts.

Catálise de hydrocraking baseado em zeólitos

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia Química

Insights into cell wall synthesis and cell division in Staphylococcus aureus

Dissertation presented to obtain the Ph.D degree in Biology

HOMO-raising strategies in aminocatalysis, from Enamine to Tetraenamine

Dissertação para obtenção do Grau de Mestre em Bioorgânica

DOTA-based Ga(III) and Gd(III) chelates for medical imaging (PET, SPECT and MRI)

PhD Thesis in Sciences Specialization in Chemistry

Poly(2-hydroxyethyl methacrylate): A new star polymer

Multiarm star polymers are attractive materials due to their unusual bulk and solution properties. They are considered analogues of dendrimers with a wide range of applications, such as drug delivery, membranes, coatings and lithography.1 The advent of controlled polymerization made possible the existence of this unique class of organic nanoparticles (ONPs).2 Two major synthetic strategies are usually employed in the preparation of star polymers, the core-first and arm-first approaches. The core-first approach involves a controlled living polymerization using a multiarm initiator core while the arm-first methodology is based in the quenching of living polymers with multifunctional coupling agent or bifunctional vinyl compounds. Herein, we present the synthesis and characterization of a new star polymer, the multiarm star poly(2-hydroxyethyl methacrylate). The tetra-armed star polymer was prepared by reversible addition fragmentation chain-transfer (RAFT) polymerization using the core-first approach. The RAFT chain-transfer agent (RAFT CTA) pentaerythritol tetrakis[2-(dodecylthiocarbonothioylthio)-2-methylpropionate] was used as multiarm initiator core were 2-hydroxyethyl methacrylate (HEMA) was polymerized using AIBN as radical initiator. Structural characterization was performed by 1H NMR and FTIR. The new polymer is able to uptake large quantities of organic solvents, forming gels. The rheological behavior of these gels was also investigated.

The role of the mammalian DNA end-processing enzyme polynucleotide kinase 3'-phosphatase in spinocerebellar ataxia Type 3 pathogenesis

DNA strand-breaks (SBs) with non-ligatable ends are generated by ionizing radiation, oxidative stress, various chemotherapeutic agents, and also as base excision repair (BER) intermediates. Several neurological diseases have already been identified as being due to a deficiency in DNA end-processing activities. Two common dirty ends, 3'-P and 5'-OH, are processed by mammalian polynucleotide kinase 3'-phosphatase (PNKP), a bifunctional enzyme with 3'-phosphatase and 5'-kinase activities. We have made the unexpected observation that PNKP stably associates with Ataxin-3 (ATXN3), a polyglutamine repeat-containing protein mutated in spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph Disease (MJD). This disease is one of the most common dominantly inherited ataxias worldwide; the defect in SCA3 is due to CAG repeat expansion (from the normal 14-41 to 55-82 repeats) in the ATXN3 coding region. However, how the expanded form gains its toxic function is still not clearly understood. Here we report that purified wild-type (WT) ATXN3 stimulates, and by contrast the mutant form specifically inhibits, PNKP's 3' phosphatase activity in vitro. ATXN3-deficient cells also show decreased PNKP activity. Furthermore, transgenic mice conditionally expressing the pathological form of human ATXN3 also showed decreased 3'-phosphatase activity of PNKP, mostly in the deep cerebellar nuclei, one of the most affected regions in MJD patients' brain. Finally, long amplicon quantitative PCR analysis of human MJD patients' brain samples showed a significant accumulation of DNA strand breaks. Our results thus indicate that the accumulation of DNA strand breaks due to functional deficiency of PNKP is etiologically linked to the pathogenesis of SCA3/MJD.

Preparació de materials híbrids orgànico-inorgànics a partir de sals d'imidazoli

Estudi elaborat a partir d’una estada a l’ Ecole Nationale Supérieure de Chimie de Montpellier, França, durant 2006. S’han sintetitzat materials híbrids orgànico-inorgànics mitjançant el procés sol-gel i altres estratègies sintètiques. En alguns casos, s’ha intentat estructurar aquests materials, ja sigui per autoestructuració o per mitjà de tensioactius. Com a catalitzadors de les reaccions d'hidròlisi i policondensació s’han utilitzat àcids, bases i fluorurs. Els materials obtinguts s’han caracteritzat mitjançant diferents tècniques: BET (Brunauer-Emmett-Teller), TEM (microscopia electrònica de transmissió), SEM (microscòpia electrònica de rastreig), raigs X en pols , IR i RMN (ressonància magnètica nuclear) en estat sòlid. Amb aquests materials es pretén preparar catalitzadors heterogenis de Pd per reaccions d’acoblament creuat, i de Ru per reaccions de metàtesi. També s’han sintetitzat sals d'imidazoli amb cadenes hidrocarbonades llargues amb l'objectiu de preparar gels de sílice amb aquestes molècules atrapades dins la matriu inorgànica. Aquests materials s’utilitzaran com a organocatalitzadors i també es prepararan els corresponents catalitzadors de Pd per reaccions de Heck, Suzuki i Sonogashira. Les sals d’imidazoli s’han utilitzat com a tensioactius en la preparació de gels de sílice estructurats. Aquestes molècules han resultat ser cristalls líquids i s’han caracteritzar mitjançant DSC (differential scanning calorimetry), microscopia òptica i raigs X.

Functional analysis of pyochelin-/enantiopyochelin-related genes from a pathogenicity island of Pseudomonas aeruginosa strain PA14.

Genomic islands are foreign DNA blocks inserted in so-called regions of genomic plasticity (RGP). Depending on their gene content, they are classified as pathogenicity, symbiosis, metabolic, fitness or resistance islands, although a detailed functional analysis is often lacking. Here we focused on a 34-kb pathogenicity island of Pseudomonas aeruginosa PA14 (PA14GI-6), which is inserted at RGP5 and carries genes related to those for pyochelin/enantiopyochelin biosynthesis. These enantiomeric siderophores of P. aeruginosa and certain strains of Pseudomonas protegens are assembled by a thiotemplate mechanism from salicylate and two molecules of cysteine. The biochemical function of several proteins encoded by PA14GI-6 was investigated by a series of complementation analyses using mutants affected in potential homologs. We found that PA14_54940 codes for a bifunctional salicylate synthase/salicyl-AMP ligase (for generation and activation of salicylate), that PA14_54930 specifies a dihydroaeruginoic acid (Dha) synthetase (for coupling salicylate with a cysteine-derived thiazoline ring), that PA14_54910 produces a type II thioesterase (for quality control), and that PA14_54880 encodes a serine O-acetyltransferase (for increased cysteine availability). The structure of the PA14GI-6-specified metabolite was determined by mass spectrometry, thin-layer chromatography, and HPLC as (R)-Dha, an iron chelator with antibacterial, antifungal and antitumor activity. The conservation of this genomic island in many clinical and environmental P. aeruginosa isolates of different geographical origin suggests that the ability for Dha production may confer a selective advantage to its host.

Characterization of the Aspergillus nidulans biotin biosynthetic gene cluster and use of the bioDA gene as a new transformation marker.

The genes involved in the biosynthesis of biotin were identified in the hyphal fungus Aspergillus nidulans through homology searches and complementation of Escherichia coli biotin-auxotrophic mutants. Whereas the 7,8-diaminopelargonic acid synthase and dethiobiotin synthetase are encoded by distinct genes in bacteria and the yeast Saccharomyces cerevisiae, both activities are performed in A. nidulans by a single enzyme, encoded by the bifunctional gene bioDA. Such a bifunctional bioDA gene is a genetic feature common to numerous members of the ascomycete filamentous fungi and basidiomycetes, as well as in plants and oömycota. However, unlike in other eukaryota, the three bio genes contributing to the four enzymatic steps from pimeloyl-CoA to biotin are organized in a gene cluster in pezizomycotina. The A. nidulans auxotrophic mutants biA1, biA2 and biA3 were all found to have mutations in the 7,8-diaminopelargonic acid synthase domain of the bioDA gene. Although biotin auxotrophy is an inconvenient marker in classical genetic manipulations due to cross-feeding of biotin, transformation of the biA1 mutant with the bioDA gene from either A. nidulans or Aspergillus fumigatus led to the recovery of well-defined biotin-prototrophic colonies. The usefulness of bioDA gene as a novel and robust transformation marker was demonstrated in co-transformation experiments with a green fluorescent protein reporter, and in the efficient deletion of the laccase (yA) gene via homologous recombination in a mutant lacking non-homologous end-joining activity.

Mutational analysis of class A and class B penicillin-binding proteins in Streptococcus gordonii.

High-molecular-weight (HMW) penicillin-binding proteins (PBPs) are divided into class A and class B PBPs, which are bifunctional transpeptidases/transglycosylases and monofunctional transpeptidases, respectively. We determined the sequences for the HMW PBP genes of Streptococcus gordonii, a gingivo-dental commensal related to Streptococcus pneumoniae. Five HMW PBPs were identified, including three class A (PBPs 1A, 1B, and 2A) and two class B (PBPs 2B and 2X) PBPs, by homology with those of S. pneumoniae and by radiolabeling with [3H]penicillin. Single and double deletions of each of them were achieved by allelic replacement. All could be deleted, except for PBP 2X, which was essential. Morphological alterations occurred after deletion of PBP 1A (lozenge shape), PBP 2A (separation defect and chaining), and PBP 2B (aberrant septation and premature lysis) but not PBP 1B. The muropeptide cross-link patterns remained similar in all strains, indicating that cross-linkage for one missing PBP could be replaced by others. However, PBP 1A mutants presented shorter glycan chains (by 30%) and a relative decrease (25%) in one monomer stem peptide. Growth rate and viability under aeration, hyperosmolarity, and penicillin exposure were affected primarily in PBP 2B-deleted mutants. In contrast, chain-forming PBP 2A-deleted mutants withstood better aeration, probably because they formed clusters that impaired oxygen diffusion. Double deletion could be generated with any PBP combination and resulted in more-altered mutants. Thus, single deletion of four of the five HMW genes had a detectable effect on the bacterial morphology and/or physiology, and only PBP 1B seemed redundant a priori.

Synthesis of chemically functionalized superparamagnetic nanoparticles as delivery vectors for chemotherapeutic drugs.

Superparamagnetic iron oxide nanoparticles (SPIONs) are in clinical use for disease detection by MRI. A major advancement would be to link therapeutic drugs to SPIONs in order to achieve targeted drug delivery combined with detection. In the present work, we studied the possibility of developing a versatile synthesis protocol to hierarchically construct drug-functionalized-SPIONs as potential anti-cancer agents. Our model biocompatible SPIONs consisted of an iron oxide core (9-10 nm diameter) coated with polyvinylalcohols (PVA/aminoPVA), which can be internalized by cancer cells, depending on the positive charges at their surface. To develop drug-functionalized-aminoPVA-SPIONs as vectors for drug delivery, we first designed and synthesized bifunctional linkers of varied length and chemical composition to which the anti-cancer drugs 5-fluorouridine or doxorubicin were attached as biologically labile esters or peptides, respectively. These functionalized linkers were in turn coupled to aminoPVA by amide linkages before preparing the drug-functionalized-SPIONs that were characterized and evaluated as anti-cancer agents using human melanoma cells in culture. The 5-fluorouridine-SPIONs with an optimized ester linker were taken up by cells and proved to be efficient anti-tumor agents. While the doxorubicin-SPIONs linked with a Gly-Phe-Leu-Gly tetrapeptide were cleaved by lysosomal enzymes, they exhibited poor uptake by human melanoma cells in culture.

Sandwich enzyme immunoassay using three monoclonal antibodies against different epitopes of carcinoembryonic antigen (CEA).

Purified monoclonal antibodies (Mab) produced by 3 hybridomas and reacting with 3 different epitopes of carcinoembryonic antigen (CEA) were used in a solid phase enzyme immunoassay. Two Mabs were physically adsorbed to polystyrene balls and the third Mab was coupled to alkaline phosphatase using the bifunctional reagent N-succinimidyl-3-(2-pyridyldithio)-propionate. During a first incubation, CEA from heat-extracted serum samples was immunoadsorbed to the antibody coated balls. After washing of the balls, bound CEA was detected by a second incubation with the enzyme coupled Mab. The sensitivity of the assay was 0.6 ng per ml of serum. A total of 196 serum samples from patients with various types of carcinoma, with liver cirrhosis, or from healthy blood donors with or without smoking habits, were tested. The results obtained with the monoclonal enzyme immunoassay (M-EIA) were compared with those obtained with perchloric acid extracts of the same serum samples tested by an inhibition radioimmunoassay using conventional goat anti-CEA antiserum. There was an excellent correlation between the two assays. In particular, the new M-EIA gave good results for the detection of tumor recurrences in the follow-up of colon carcinoma patients. However, despite the use of exclusively monoclonal antibodies the new assay detected a similar percentage of slightly elevated CEA values as the conventional assay in patients with non-malignant disease, suggesting that the CEA associated with non-malignant diseases is immunologically identical to the CEA released by colon carcinoma.

Surface-functionalized ultrasmall superparamagnetic nanoparticles as magnetic delivery vectors for camptothecin.

Drug-nanoparticle conjugates: The anticancer drug camptothecin (CPT) was covalently linked at the surface of ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) via a linker, allowing drug release by cellular esterases. Nanoparticles were hierarchically built to achieve magnetically-enhanced drug delivery to human cancer cells and antiproliferative activity.The linking of therapeutic drugs to ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) allowing intracellular release of the active drug via cell-specific mechanisms would achieve tumor-selective magnetically-enhanced drug delivery. To validate this concept, we covalently attached the anticancer drug camptothecin (CPT) to biocompatible USPIOs (iron oxide core, 9-10 nm; hydrodynamic diameter, 52 nm) coated with polyvinylalcohol/polyvinylamine (PVA/aminoPVA). A bifunctional, end-differentiated dicarboxylic acid linker allowed the attachment of CPT to the aminoPVA as a biologically labile ester substrate for cellular esterases at one end, and as an amide at the other end. These CPT-USPIO conjugates exhibited antiproliferative activity in vitro against human melanoma cells. The intracellular localization of CPT-USPIOs was confirmed by transmission electron microscopy (iron oxide core), suggesting localization in lipid vesicles, and by fluorescence microscopy (CPT). An external static magnetic field applied during exposure increased melanoma cell uptake of the CPT-USPIOs.