/pdf/nanoparticle-pegylation-for-imaging-and-therapy-45vkc0dds0.pdf

Nanoparticle PEGylation for imaging and therapy

http://ideaexchange.uakron.edu/cgi/viewcontent.cgi?article=1230&context=chemengin_ideas

Surface Hydration: Principles and Applications Toward Low-fouling/nonfouling Biomaterials

A review on the adsorption of heavy metals by clay minerals, with special focus on the past decade

Based on its generally accessible I/II redox couple and bioavailability, copper plays a wide variety of roles in nature that mostly involve electron transfer (ET), O2 binding, activation and reduction, NO2− and N2O reduction and substrate activation. Copper sites that perform ET are the mononuclear blue Cu site that has a highly covalent CuII-S(Cys) bond and the binuclear CuA site that has a Cu2S(Cys)2 core with a Cu-Cu bond that keeps the site delocalized (Cu(1.5)2) in its oxidized state. In contrast to inorganic Cu complexes, these metalloprotein sites transfer electrons rapidly often over long distances, as has been previously reviewed.1–4 Blue Cu and CuA sites will only be considered here in their relation to intramolecular ET in multi-center enzymes. The focus of this review is on the Cu enzymes (Figure 1). Many are involved in O2 activation and reduction, which has mostly been thought to involve at least two electrons to overcome spin forbiddenness and the low potential of the one electron reduction to superoxide (Figure 2).5,6 Since the Cu(III) redox state has not been observed in biology, this requires either more than one Cu center or one copper and an additional redox active organic cofactor. The latter is formed in a biogenesis reaction of a residue (Tyr) that is also Cu catalyzed in the first turnover of the protein. Recently, however, there have been a number of enzymes suggested to utilize one Cu to activate O2 by 1e− reduction to form a Cu(II)-O2•− intermediate (an innersphere redox process) and it is important to understand the active site requirements to drive this reaction. The oxidases that catalyze the 4e−reduction of O2 to H2O are unique in that they effectively perform this reaction in one step indicating that the free energy barrier for the second two-electron reduction of the peroxide product of the first two-electron step is very low. In nature this requires either a trinuclear Cu cluster (in the multicopper oxidases) or a Cu/Tyr/Heme Fe cluster (in the cytochrome oxidases). The former accomplishes this with almost no overpotential maximizing its ability to oxidize substrates and its utility in biofuel cells, while the latter class of enzymes uses the excess energy to pump protons for ATP synthesis. In bacterial denitrification, a mononuclear Cu center catalyzes the 1e- reduction of nitrite to NO while a unique µ4S2−Cu4 cluster catalyzes the reduction of N2O to N2 and H2O, a 2e− process yet requiring 4Cu’s. Finally there are now several classes of enzymes that utilize an oxidized Cu(II) center to activate a covalently bound substrate to react with O2.



Figure 1

Copper active sites in biology.





Figure 2

Latimer Diagram for Oxygen Reduction at pH = 7.0 Adapted from References 5 and 6.



This review presents in depth discussions of all these classes of Cu enzymes and the correlations within and among these classes. For each class we review our present understanding of the enzymology, kinetics, geometric structures, electronic structures and the reaction mechanisms these have elucidated. While the emphasis here is on the enzymology, model studies have significantly contributed to our understanding of O2 activation by a number of Cu enzymes and are included in appropriate subsections of this review. In general we will consider how the covalency of a Cu(II)–substrate bond can activate the substrate for its spin forbidden reaction with O2, how in binuclear Cu enzymes the exchange coupling between Cu’s overcomes the spin forbiddenness of O2 binding and controls electron transfer to O2 to direct catalysis either to perform two e− electrophilic aromatic substitution or 1e− H-atom abstraction, the type of oxygen intermediate that is required for H-atom abstraction from the strong C-H bond of methane (104 kcal/mol) and how the trinuclear Cu cluster and the Cu/Tyr/Heme Fe cluster achieve their very low barriers for the reductive cleavage of the O-O bond.

Much of the insight available into these mechanisms in Cu biochemistry has come from the application of a wide range of spectroscopies and the correlation of spectroscopic results to electronic structure calculations. Thus we start with a tutorial on the different spectroscopic methods utilized to study mononuclear and multinuclear Cu enzymes and their correlations to different levels of electronic structure calculations.

/pdf/copper-active-sites-in-biology-lhhabv47if.pdf

Copper Active Sites in Biology

Wildland fire ash: Production, composition and eco-hydro-geomorphic effects

Evaluating the adsorptive capacity of montmorillonitic and calcareous clays on the removal of several heavy metals in aqueous systems

Radioactive soil particles several tens of micrometers in size were collected from litter soil in the radiation contaminated area by the Fukushima nuclear plant accident and characterized using electron and X-ray microanalyses. The radioactive particles were discriminated by autoradiography using imaging plates (IP) on which microgrids were formed by laser ablation in order to find the particles under microscopy. Fifty radioactive particles were identified and classified into three types from their morphology and chemical composition, namely: (1) aggregates of clay minerals, (2) organic matter containing clay mineral particulates, and (3) weathered biotite originating from local granite. With respect to the second type, dissolution of the organic matter did not reduce the radiation, suggesting that the radionuclides were also fixed by the clay minerals. The weathered biotite grains have a plate-like shape with well-developed cleavages inside the grains, and kaolin group minerals and goethite filling the c...

/pdf/speciation-of-radioactive-soil-particles-in-the-fukushima-3ljfknpv99.pdf

Speciation of Radioactive Soil Particles in the Fukushima Contaminated Area by IP Autoradiography and Microanalyses

The crystal structure of whewellite [Ca(C2O4)·H2O] and the dehydration mechanism of caoxite [Ca(C2O4)·3H2O] have been studied by means of differential thermal analysis, X-ray diffraction (powder and single-crystal) analysis and infrared analysis. The first and second analyses confirmed the direct transformation of caoxite into whewellite without an intermediate weddellite [Ca(C2O4)·2H2O] stage. Infrared spectra obtained from caoxite, weddellite and whewellite emphasize the similarity of the O–H-stretching band and O–C–O-stretching band in whewellite and caoxite and the unique bands of weddellite. The structure refinement at low temperature (123 K) reveals that all the hydrogen atoms of whewellite form hydrogen bonds and the two water molecules prop up the crystal structure by the hydrogen bonds that cause a strong anisotropy of the displacement parameter. Comparing the structural features of whewellite with those of weddellite and caoxite suggests that caoxite and whewellite have a sheet structure consisting of Ca2+ ions and oxalate ions although weddellite does not. It is additionally confirmed that the sheets of caoxite are corrugated by hydrogen bonds but whewellite has flat sheets. The corrugated sheets of caoxite would be flattened by dehydration so the direct transformation of caoxite into whewellite would not occur via weddellite. Essential for this transformation is the dehydration of interlayered water molecules in caoxite leading to the building of the crystal structure of whewellite on its intralayered water molecules. The difference in conformation of water molecules between those two crystal structures may explain the more common occurrence of whewellite than of caoxite in nature.

Re-investigation of the crystal structure of whewellite [Ca(C2O4)·H2O] and the dehydration mechanism of caoxite [Ca(C2O4)·3H2O]

Limestone beds of the Late Cretaceous Abiod formation (Campanian-Maastrichtian system) are fundamentally important for the economic growth of the raw material sector in Tunisia. However, little attention has been paid to the detailed physical and chemical properties of the Abiod limestone. Nine limestone samples collected from the Abiod formation outcropping in the areas of Bizerte, Gafsa and Gabes, Tunisia, as well as their separated clay fractions, were characterized using different techniques, such as XRF, XRD, FTIR and TG/DTA. XRF showed the chemical composition of the limestone in which calcium carbonate was the main constituent, and silica, iron and magnesium were the impurities. XRD also confirmed the presence of small amounts of clay minerals and quartz along with sharp peaks of calcite. FTIR spectra indicated that the limestone was mainly composed of CaCO3 in the form of calcite, as identified by its main characteristic absorption bands. These data were in agreement with XRD and XRF analysis data. The TG/DTA curves of the limestone samples, showing a close similarity to that of pure calcium carbonate, exhibited an endothermic peak between 600 and 760°C, with the maximum near 750°C. Moreover, FTIR spectra of clay fraction samples indicated high silica content in some samples. Especially the samples SD1 and SD2 collected in the northern area showed higher amounts of silica compared with those of AS1, AS2, CHB, ZNC, SND, MKM and GBS collected from southern districts. However, among the latter seven samples, one could recognize two groups based on the clay mineral investigations: (1) limestone with minor amounts of smectite and mixed layer minerals of smectite/illite (AS1 and 2, CHB, ZNC, SND and GBS) and (2) limestone with smectite, kaolinite and apatite (SND and MKM). Differences in these mineralogical and chemical characteristics should be considered when limestone from the Abiod formation is utilized as a medium for heavy metal removal from wastewater.

Mineralogical and spectroscopic characterization, and potential environmental use of limestone from the Abiod formation, Tunisia

Light-induced degradation in realgar (arsenic sulfide) has been studied by means of four-circle single-crystal X-ray diffraction and X-ray photoelectron spectroscopy. Because of the alteration of realgar exposed to light, the a lattice parameter and c sinβ value increase linearly from 9.327 to 9.385 A and from 6.320 to 6.364 A, respectively. In contrast, the b lattice parameter remains substantially constant. Anisotropic variations of the lattice parameters engender a continuous increase of the unit-cell volume from 799.5 to 810.4 A3. Nevertheless, no correlation exists between the continuous increase of the unit-cell volume and the bond distance variations in As4S4 molecules because the As4S4 molecule in the unit cell expands very little during light exposure. The most pronounced change was in the distance between centroids in As4S4 cages. The spread of As4S4 intermolecular distances increases continuously from 5.642 to 5.665 A, which directly affects the unit-cell volume expansion of realgar. In addition, the O1s peak increases rapidly after light exposure. The result substantiates the following reaction proposed by Bindi et al. (2003): 5As4S4 + 3O2 → 4As4S5 + 2As2O3. That is, realgar is transformed into pararealgar if oxygen exists and produces the As4S5 molecule. The additional S atom contributes to anisotropic expansion for the a and c axes because the direction of the additional S atom points toward [414] in the unit cell. Furthermore, an S atom in the As4S5 molecule is released from one of the equivalent As-S-As linkages in As4S5 which becomes the As4S4 molecular of pararealgar. After the As4S5 molecule is divided into an S atom (radical) and the As4S4 (pararealgar type) molecule, the free S atom is re-attached to another As4S4 (realgar type) molecule, and reproduces an As4S5 molecule. The reproduced As4S5 molecule is again divided into an S atom (radical) and an As4S4 (pararealgar type) molecule. This cycle whereby realgar is indirectly transformed into pararealgar via the As4S5 molecule is promoted by light and repeated during light exposure.

/pdf/light-induced-degradation-dynamics-in-realgar-in-situ-25qcopadnw.pdf

Light-induced degradation dynamics in realgar: in situ structural investigation using single-crystal X-ray diffraction study and X-ray photoelectron spectroscopy

Tamao Hatta

Papers

Evaluating the adsorptive capacity of montmorillonitic and calcareous clays on the removal of several heavy metals in aqueous systems

Speciation of Radioactive Soil Particles in the Fukushima Contaminated Area by IP Autoradiography and Microanalyses

Re-investigation of the crystal structure of whewellite [Ca(C2O4)·H2O] and the dehydration mechanism of caoxite [Ca(C2O4)·3H2O]

Mineralogical and spectroscopic characterization, and potential environmental use of limestone from the Abiod formation, Tunisia

Light-induced degradation dynamics in realgar: in situ structural investigation using single-crystal X-ray diffraction study and X-ray photoelectron spectroscopy