C. Solís

Lead levels in Mexican human teeth from different historical periods using PIXE

Abstract Human teeth from pre-Columbian, colonial and contemporary population groups have been analyzed by PIXE in order to evaluate the elemental changes, particularly those related to lead contents in the inhabitants of Mexico city. Minor changes of the Me Ca ratios for Mn, Fe, Cu, Zn and Sr for the three populations were detected. In contrast, Pb contents showed significant differences among the three groups. In pre-Columbian teeth no lead was found. Colonial teeth showed higher lead levels than contemporary ones. This result suggests that the glaze pottery introduced by the Spaniards was the main source of lead in the colonial period.

Tillandsia usneoides L, a biomonitor in the determination of Ce, La and Sm by neutron activation analysis in an industrial corridor in Central Mexico.

The atmosphere of the Tula Industrial Corridor in Central Mexico is contaminated due to several industries including oil refining while station monitoring in this area are limited. Lanthanides are considered fingerprint of oil refinery activities, and La, Ce and Sm have been previously detected in this area using filters. The suitability of T. usneoides as a biomonitor assessing the La, Ce and Sm concentrations in Particulate Matter is evaluated by NAA. Results of both biomonitor and filters are highly correlated.

PIXE ANALYSIS OF ZN ENZYMES

Abstract Zinc is a necessary component in the action and structural stability of many enzymes. Some of them are well characterized, but in others, Zn stoichiometry and its association is not known. PIXE has been proven to be a suitable technique for analyzing metallic proteins embedded in electrophoresis gels. In this study, PIXE has been used to investigate the Zn content of enzymes that are known to carry Zn atoms. These include the carbonic anhydrase, an enzyme well characterized by other methods and the cytoplasmic pyrophosphatase of Rhodospirillum rubrum that is known to require Zn to be stable but not how many metal ions are involved or how they are bound to the enzyme. Native proteins have been purified by polyacrylamide gel electrophoresis and direct identification and quantification of Zn in the gel bands was performed with an external proton beam of 3.7 MeV energy.

A theoretical and experimental evaluation of imidazolium-based ionic liquids for atmospheric mercury capture

AbstractIn this work, the capacity of three different imidazolium-based ionic liquids (ILs) for atmospheric mercury capture has been evaluated. Theoretical calculations using monomer and dimer models of ILs showed that [BMIM]+[SCN]− and [BMIM]+[Cl]− ionic liquids capture gaseous Hg0, while [BMIM]+[PF6]− shows no ability for this purpose. These findings are supported by experimental data obtained using particle induced X-ray emission (PIXE) trace element analysis. Experimental and theoretical infrared data of the ILs were obtained before and after exposure to Hg. In all cases, no displacement of the bands was observed, indicating that the interaction does not significantly affect the force constants of substrate bonds. This suggests that van der Waals forces are the main forces responsible for mercury capture. Since the anion-absorbate is the driving force of the interaction, the largest charge-volume ratio of [Cl]− could explain the higher affinity for mercury sequestration of the [BMIM]+[Cl]− salt. FigureMercury capture by [BMIM]+[PF6]−, [BMIM]+[SCN]−and [BMIM]+[Cl]−double pair ionic liquids

Development of a non-thermal accelerated pulsed UV photolysis assisted digestion method for fresh and dried food samples

A simple, fast digestion procedure for fresh and dried foods, using high-power pulsed UV photolysis in the presence of hydrogen peroxide, is being developed. The homogenized food samples were mixed with H2O2 or with a mixture of H2O2 and HNO3, and irradiated for short times with a 248-nm UV excimer laser. After centrifugation, a clear, colorless solution was obtained and aliquots were deposited on Teflon filters for XRF and/or PIXE analyses. Standard reference materials (NIST Peach Leaves; Typical Diet) were also analyzed to compare recoveries and detection limits. Improvements in detection limits were observed, but a few trace elements (<1 ppm) were not reproducibly detected (Fe, Sr). This method proved to be practical for the accelerated digestion of food samples and preparing analytes in short-time intervals. In combination with PIXE and XRF, it allows high-sensitivity multi-elemental analyses for screening the nutritional elements and for food safety purposes regarding the potential presence of toxic elements. Further development to optimize and validate this procedure for a broader range of analytes is in progress.

PIXE ANALYSIS OF PROTEINS FROM A PHOTOCHEMICAL CENTER

Abstract In oxygen evolving photosynthetic organisms, light is absorbed and its energy used for the conversion of chemical products in two photosystems: PSI and PSII. Each photosystem is composed of a protein core which binds a pigment antenna and a Reaction Center (RC). RC of PSI is considered an “Iron-Sulfur” type. There are six components that participate in the charge separation after light absorption occurs in PSI: the center chlorophyll P700, two acceptors A 0 and A 1 and three FeS centers F X , F A and F B . However, the exact number of polypeptides, their exact molecular weight, their relative abundances and the active components associated to those polypeptides remain still to be completely characterized. In particular the FeS centers have been difficult to detect in a direct way in a gel band, because the amount of centers involved is under the detection limits of the conventional techniques. This study has been under-taken to explore the capability of particle induced X-ray emission (PIXE) to detect in a qualitative way the presence of Fe in some of the protein bands obtained by Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) from the PSI complex. The complex was isolated from membranes of thermophilic cyanobacteria: Synechochoccus sp. The polyacrylamide gel electrophoresis of the complex shows eight subunits of 66, 60–65, 14, 13, 9, 8 and 7 KDa. In-air PIXE was performed at 2 MeV and proved to be an adequate tool for direct identification of the iron present in the gel bands.

Metal/protein ratio determination in the Rhodobacter capsulatus cytoplasmic pyrophosphatase enzyme by particle induced X-ray emission

Inorganic pyrophosphatases are divided in two families, which differ both in structure and mechanism. All of them incorporate in its structure divalent metal cations. In 2003, it was reported for the first time that Rhodobacter capsulatus cytoplasmic pyrophosphatase belongs to family II. It is expected then, that this enzyme contains metal elements in its structure; however, this characterization has not been carried out yet. A fine application of accelerators is the use of proton beams to induce X-ray emission (PIXE) for analyzing the composition of biological macromolecules. The purpose of this work is to complement R. capsulatus cytoplasmic pyrophosphatase characterization by determining the presence of metal elements in its structure. Three different strategies were used: PAGE-PIXE, PAGE-Digestion-PIXE, and Dialysis-PIXE and when metals were found the metal/enzyme ratio was calculated. Only cobalt was found to be associated to the enzyme chemical structure in a ratio 3 Co/enzyme.

Chemical diagenesis in fossil shells from Baja California, México studied using PIXE and mass spectrometry

Abstract In this work we present elemental composition determined by PIXE, and 13 C and 18 O stable isotope concentrations determined using mass spectrometry for recent and Late Miocene-Pliocene marine shells deposits in Baja California, Mexico. Recent and fossil mollusk shells show large variations in trace element content along growth lines. Diagenesis in fossils mollusks has resulted in different degrees of depletion in Sr, 13 C and 18 O. An enrichment in Mn, Fe and Zn due to the diagenesis process was not clearly observed.

26Al production: The Allende meteorite (Chihuahua) stellar nucleosynthesis and solar models

In 1969 a meteorite fell near the small town of Allende, state of Chihuahua in the north of Mexico. Its study yielded information that changed the current understanding of the solar model. In particular traces of 26Al were found. Abundances of that isotope had been seen in the universe and were related to regions of active heavy nucleosynthesis. Its presence on the solar system was unexpected.It is now understood that cosmic rays induce nuclear reactions on materials to produce 26Al, on Earth this is well known and it is the basis of many environmental studies, so it is not only the product of some high metalicity star collapse.Taking advantage of the recently reinforced laboratory infrastructure of the Instituto de Fisica, at UNAM in Mexico City, we proposed to measure the cross section for 26Al production via some of the most likely reactions, from the nuclear physics point of view (highest Q-values).In this paper the study of the 28Si(d,α)26 Al nuclear reaction is shown.A target is prepared by a mixtur...

Elemental analyses of marine skeletons

Abstract Detailed elemental analyses along the growth lines of a recent shell (of the mollusk Trachycardium sp. ) and two fossil shells (of the brachiopod Eogryphus sp. and of the mollusk Ostrea sp. ) have been performed using PIXE. A number of differences among the three shells could be seen. These differences are likely due to the different degrees of shell preservation. A comparsion of the metal distributions along two close parallel growth lines in the fossil brachiopod, indicates that the observed variations can not be attributed to seasonal changes but more likely to diagenesis.