X-RAY SPECTROSCOPY

Author: VALLS VIDAL NURIA.
Year: 2004.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: AULA D'AUDIOVISUALS DEL DEPT. D'ENGINYERIA QUÍMICA.
Place of preparation: ETSEIB, EDIFICI H PLANTA 4 Campus SUD.

Summary: n the present thesis we have carried out structural studies on DNA. The main purpose was the determination in a detailed way of the interactions between DNA and some intercalating drugs as well as with transition metals. Both, intercalating drugs and transition metals, can influence the properties and structure of DNA. This characteristic can be used in order to improve the therapeutic applications of the drugs. On the other hand, specific interactions between DNA and transition metals are known, and they can be used to design new structures of DNA (Valls et al., 2004). The main technique used has been X-ray crystallography, which allows studying structures in great detail, but also other techniques have been used as for example footprinting, fluorescence or viscosity assays. These techniques can give information about the drugs, they can predict whether a drug is going to intercalate in the DNA and also if they are specific for a particular sequence. The drugs used are aromatic systems, anthraquinone and acridine derivatives with different substituents covalently linked, most of them amino acids. Our studies confirm that in general, the drugs used have no sequence specificity. Crystallographic studies also show that drugs are not specific because in most of the structures solved, the drug could not be detected. Twelve different oligonucleotides, between six and twelve base pairs, have been tested. Those contain CG steps (typical intercalating step) and AA/TT steps. There is only one structure known in the literature where a drug intercalates in an AA/TT step (Malinina et al., 2002) and we have been trying to induce this intercalation again with different oligonucleotides. Many crystallisation assays have been done in order to obtain DNA-drug complexes and finally, five different structures with four different olignucleotides have been solved. Only two of these structures contain the intercalated drug, this is the sequence d(CGTACG) that has been crystallized with two different drugs, an acridine and an anthraquinone derivative. The decamer d(CGCAATTGCG) has been crystallised in the space group I212121, showing an isomorphic structure of the same sequence previously described by Spink et al. (1995). This decamer has been crystallised as five different structures in four different space groups. All these structures allowed a comparative study between all of them, analysing the differences and the effect of the crystallisation conditions. The first structure of a B-DNA with a cubic symmetry has also been solved with the sequence d(GAATTCG). It is the first time this sequence has been crystallised and the most important feature of this structure are the great cavities of solvent contained in each cell, only 24% of the crystal is occupied by DNA atoms. Also the first structure of the decamer d(CAATTAATTG) has been solved in the space group P3221. The fact that contains a large quantity of A and T bases (80%) suggested analysing in detail the conformation of the decamer. There is a group of isomorphic structures with different sequences already described in the literature (Goodsell et al., 1995). All five structures have been crystallised in the presence of Co2+ or Ni2+ ions. Both ions normally form specific interactions with the N7 atoms of guanines and they have a very imortant role in the stabilisation of the crystals. Other ions such Ba2+ and Na+ have also been detected in the structures.

Author: CASTRO SASTRE M. ÁNGELES.
Year: 2006.
University: LEÓN [www.unileon.es].
Place of defense: FACULTAD DE CIENCIAS BIOLÓGICAS Y AMBIENTALES.
Place of preparation: UNIVERSIDAD DE LEÓN.

Summary: The presence of heavy metals, on numerous occasions, is an environmental problem with serious health consequences due to their toxicity. A typical example is arsenic, hence the determination of his interest in environmental samples. For his determination have used different techniques, usually being the electrothermal atomic absorption spectroscopy technique chosen, mainly because of its high sensitivity, and the small volume of sample required for analysis. However, this technique is not without problems, and that leads to major problems analytical determining arsenic. These problems are related to the presence in the environmental samples species that generate significant interferences such as sulfates and chlor-alkali and alkaline, and the interference due to aluminum (in the form of chloride and nitrate). These problems have attempted to correct in numerous publications using different factors being the chemical modifiers more employees, perhaps because they are an essential part in the electrothermal atomic absorption spectroscopy. Despite the progress made in the studies carried out on the interference by using different chemical modifiers still concerns about the possible interfering species, their possible correction, and the mechanisms of action of modifying chemical sobare them. Therefore, this thesis has focused on evaluating the behavior of several species interfering (sulphates and chlor-alkali and alkaline, chloride and nitrate aluminum) and chemical modifiers (itorio, zirconium and palladium) using different analysis techniques surface, which help address these problems from a different perspective. The resutlados obtained focus on developing an analytical method to determine arsenic in fly ash, which presented its parent aluminum and silicon, as major components. First, interference is studied and the results obtained permitieorn establish as possible species interfering metal sulphides. Moreover, in the case of beryllium sulfate, also involves metallic oxide. With regard to the interfering related chlorides. One can say that they are all chlorides being gassed, as well as the corresponding oxides in the cases of beryllium and aluminum. The interference of aluminum was corrected using activated carbon, and may establish as a species interfering the subóxido aluminum (Al2O). Then, we evaluate the thermal behavior of chemical modifiers, as well as its mechanism of action with the analyte, and the majority of matrix components. (Al, Si). The results showed that the chemical modifiers were able to retain arsenic, thus avoiding losses during the same heating electrotérmico, forming oxides with zirconium and thorium, and with an alloy metal palladium. All chemical modifiers had a positive effect on the analytical signal of arsenic, increased stability and sensitivity of the same when acting in conjunction with the proton, while the thorium was the most effective chemical modifier. This method was validated using certified samples of fly ash, and the results demonstrate the accuracy of the method, since the values are similar to those certificates. There was also extended the method to the determination of arsenic in samples certified citrus leaves and rice flour.