Lead EXAFS spectroscopy

Manceau A, Boisset M-C, Sarret G, et al. 1996. Direct determination of lead speciation in contaminated soils by EXAFS spectroscopy. Environ Science Technology 30(5) 1540-1552. 

The EXAFS spectroscopy results strongly confirm the existence of local order in the mineral part of lead isooctane reverse micelles in dodecane and reveal quantitative information concerning the first and second coordination shells. The radial distribution functions (RDFs) exhibit peaks at around 0.19 nm, corresponding to the first shell of oxygen atoms and at around 0.35 nm corresponding to the shell of lead. Analytical transmission electron microscopy (ATEM) indicates the size of the mineral core of the micelles (1-1.5 nm) and the discoid shape of the particles when the micelles aggregate (Mansot et al. 1994). 

Sulfate formation and coke deposition were often excluded as reasons for deactivation, using EXAFS spectroscopy. The formation of larger clusters in the zeolite, which can also lead to destruction of the host structure, can be observed by an increase in the coordination number of the Cu—Cu scattering contribution to the EXAFS. 

EXAFS spectroscopy, as well as magnetic properties turns to be very sensitive to the fixation of two ammonia molecules (Fig. 11b, d) increased complexity of the spectrum, particularly for Peaks 2 and 3, at both Cu and Br edges, reduced intensity of the Cu—Br Peak 4. These observations can be related simply to a site distortion of the square CuO entity, leading to a copper surroundings with 4 short bonds (2 Cu—N... 

At this point it should be stressed that the application of quantitative modeling using the TP Model and EXAFS spectroscopy as well as the performance of calculations based on DFT may lead to an improvement or to a slight modification of the tentative local structures proposed in this work. 

Manceau A (1995) The mechanism of anion adsorption on iron oxides evidence for the bonding of arsenate tetrahedra on free Fe(0,OH)6 edges. Geochim Cosmocliim Acta 59 3647-3653 Manceau A, Boisset MC, Sarret G, Hazemann J-L, Mench M, Cambier P, Prost R (1996) Direct determination of lead speciation in contaminated soils by EXAFS spectroscopy. Environ Sci Technol 30 1540-1552... 

In addition to lead, the form of zinc in the Fe plaque of Phalaris arundinacea was also examined by fluorescence microtomography and EXAFS spectroscopy (Fig. 27, Hansel et al. 2001). Unlike lead, which was clearly associated with Fe (oxyhydr)oxides and inferred to be complexed to organic molecules, zinc was clearly correlated to manganese. On the basis of Mn-0 (2.20 A) and Zn-0 (1.96 A, 2.06 A, 2.08 A, 2.15 A) EXAFS distances, Mn was assumed to be speciated as rhodochrosite (MnC03) and Zn as hydrozincite (Zn5(0H)6(C03)2). While this study documented for the first time the combined use of fluorescence microtomography and EXAFS spectroscopy, and... 

Ryan JA, Zhang P, Hesterberg DA, Chou J, Sayers DE (2001) Formation of chloropyromorphite in lead-contaminated soil amended with hydroxyapatite. Env Sci Tech 35 3798-3803 Sarret G, Manceau A, Spadini L, Roux JC, Hazemann JL, Soldo Y, Eybert-Berard L, Menthonnex JJ (1998) Structural determination of Zn and Pb binding sites in Penicillium chrysogenum cell wall by EXAFS spectroscopy. Env Sci Tech 32 1648-1655. 

Sobanska S, Ricq N, Laboudigue A, Guillermo R, Btemard C, Lauteyns J, Merlin JC, Wignacourt JP (1999) Microchemical investigations of dust by a lead smelter. Env Sci Tech 33 1334-1339 Spadini L, Manceau A, Schindler PW, Charlet L (1994) Structure and stability of Cd2+ surface complexes on ferric oxides. I. Results from EXAFS spectroscopy. J Coll Interf Sci 168 73-86. 

What insights into lead coordination chemistry can be gained from EXAFS spectroscopy that are not available from X-ray crystal structures ... 

Taking into account the curvature of the wavefront of the electron emitted by the ionized atom leads to the effective dependence of the scattering amplitude on the interatomic distance. In this review we will not discuss this question in more detail, because it has already been successfully solved in EXAFS spectroscopy [63-68]. 

The introduction of redox activity through a Co11 center in place of redox-inactive Zn11 can be revealing. Carboxypeptidase B (another Zn enzyme) and its Co-substituted derivative were oxidized by the active-site-selective m-chloroperbenzoic acid.1209 In the Co-substituted oxidized (Co111) enzyme there was a decrease in both the peptidase and the esterase activities, whereas in the zinc enzyme only the peptidase activity decreased. Oxidation of the native enzyme resulted in modification of a methionine residue instead. These studies indicate that the two metal ions impose different structural and functional properties on the active site, leading to differing reactivities of specific amino acid residues. Replacement of zinc(II) in the methyltransferase enzyme MT2-A by cobalt(II) yields an enzyme with enhanced activity, where spectroscopy also indicates coordination by two thiolates and two histidines, supported by EXAFS analysis of the zinc coordination sphere.1210... 

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