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We studied surface plasmon-coupled emission (SPCE) of semiconductor quantum dots (QDs). These QDs are water-soluble ZnS-capped CdSe nanoparticles stabilized using lysine cross-linked mercaptoundecanoic acid. The QDs were spin-coated from 0.75% PVA solution on a glass slide covered with 50 nm of silver and a 5-nm protective SiO(2) layer. Excited QDs induced surface plasmons in a thin silver layer. Surface plasmons emitted a hollow cone of radiation into an attached hemispherical glass prism at a narrow angle of 48.5 degrees. This directional radiation (SPCE) preserves the spectral properties of QD emission and is highly p-polarized irrespective of the excitation polarization. The SPCE spectrum depends on the observation angle because of the intrinsic dispersive properties of SPCE phenomenon. The remarkable photostability can make QDs superior to organic fluorophores when long exposure to the intense excitation is needed. The nanosize QDs also introduce a roughness near the metal layer, which results in a many-fold increase of the coupling of the incident light to the surface plasmons. This scattered incident illumination transformed into directional, polarized radiation can be used simultaneously with SPCE to develop devices based on both quantum dot emission and light scattered from surface plasmons on a rough surface.
ZnSCdS:Ag was evaluated as a radiographic image receptor and was compared with Gd2O2S:Tb and Y2O2S:Tb phosphors often used in radiography. The evaluation of a radiographic receptor was modelled as a three-step process: (i) determination of light output intensity as related to the input radiation dose, (ii) determination of visible light characteristics with respect to radiographic optical detectors, and (iii) determination of image information transfer efficiency. The light intensity emitted per unit of x-ray exposure rate was measured and theoretically calculated for laboratory prepared screens with coating thicknesses from 20 to 220 mg cm-2 and tube voltages from 50 to 250 kVp. ZnSCdS:Ag light intensity was higher than that of Gd2O2S:Tb or Y2O2S:Tb for tube voltages less than 70 and 80 kVp respectively. ZnSCdS:Ag displayed the highest x-ray to light conversion efficiency (0.207) and had optical properties close to those of Gd2O2S:Tb and Y2O2S:Tb, and its emission spectrum was well matched to optical detectors. The image information transfer properties described by the modulation transfer function, the quantum noise transfer function, and the detective quantum efficiency were calculated for both general radiographic and mammographic conditions and were found to be intermediate between those of Gd2O2S:Tb and Y2O2S:Tb screens. Conclusively, ZnSCdS:Ag is an efficient phosphor well suited to radiography.
This article presents a general infrared spectroscopic method that enables the monitoring of the adsorption of surfactants and polyelectrolytes on high surface area silica particles from aqueous solution. The method is based on the use of a ZnSe internal reflection element (IRE) coated with a layer of titania particles. The titania surface is the converted to silica using atomic layer deposition with sequential addition of an amine catalyst, gaseous SiCl4, and water vapor. A minimum of three cycles is needed to produce a surface that mimics silica, as evidenced by the reaction of hexamethyldisilazane and zeta potential measurements. It is shown that the silicacoated titania particles on the ZnSe crystals are stable to flowing aqueous solutions below pH = 8 and can be used to study the dynamics of polymer/surfactant adsorption on silica.
After the collapse on 25 Apr. 1998 of the Aznalcóllar mine tailings dike in southwestern Spain, 45 km2 of the Guadiamar valley were covered by a pyritic sludge containing up to 2% sphalerite (ZnS). Later, the sludge was mechanically removed and calcium carbonate was plowed into the soil to immobilize heavy metals. By June 2001 more than 60% of the sulfides in the residual sludge had oxidized and soil Zn contents reached locally phytotoxic levels. Therefore, the oxidative dissolution of sphalerite in the sludge and other pyritic samples was examined. Flow-through oxidation experiments showed that: (i) about 5 and 17% of the sludge Fe and Zn were in soluble form, respectively, because the sludge sample had been partly oxidized in the field; (ii) the oxidation rates of the residual pyrite and sphalerite were similar; (iii) the overall sulfide oxidation rate was relatively unaffected by the addition of calcite; and (iv) poorly crystalline Fe (hydr)oxides containing Zn in occluded form and Zn (hydroxi)carbonates were formed in the presence of calcite. The rate of oxidation of reference sphalerite greatly increased when it was incorporated in the sludge or in a reference pyrite matrix. This enhancement was due to galvanic interaction because pyrite oxidation was depressed in the presence of sphalerite. Oxidation by Fe3+ ions was less important because the oxidation rates of native sphalerite were not greater at low than at high pH. The fast oxidation rate of sphalerite in the Aznalcóllar sludge indicates a need for quick adoption of remediation measures in similar accidents elsewhere. The use of calcite amendments has little influence on the oxidation rate but does result in the accumulation of Zn in relatively insoluble forms.
Benzocycloheptapyridine tricyclic compounds with piperazine or substituted piperidine moieties extending either from the 5- or 6-position of the tricyclic bridgehead exhibited enhanced FTase activity: this resulted from favorable binding of the ligand nitrogen with the catalytic zinc found in the FTase. A single isomer at C-11 with piperazine adduct extending from the 6-position, compound 24, exhibited excellent FTase activity with IC50 = 0.007 microM, soft agar IC50 = 72 nM, and Rat AUC(PO, 10 mpk) = 4.0 microM x h. X-ray of (-)-[8-chloro-6-(1-piperazinyl)-1H-benzo[5,6]]cyclohepta[1,2-b]pyridine-11-yl]-1-(methylsulfonyl)piperidine 24 bound to Ftase revealed favorable interaction between piperazine nitrogen and catalytic zinc atom.
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Polaprezinc, N-(3-aminopropionyl)-L-histidinatozinc, has been shown to stimulate the production of insulin-like growth factor-1 (IGF-1) in mesenchymal cells, the polypeptide playing a role in the gastric epithelial wound repair. The present study was performed to examine the effect of polaprezinc on the impaired healing of chronic gastric ulcers in adjuvant-induced arthritic rats, in relation to IGF-1. Arthritis was induced in male Dark Agouti (DA) rats by a single injection of Freund's complete adjuvant (FCA), and the gastric ulcers were induced by thermal cauterization (70 degrees C for 30 sec) 7 days after FCA injection. Omeprazole (30 mg/kg) was administered p.o. once daily, while recombinant human IGF-1 (rhIGF-1) (30 micrograms/kg, s.c.) or polaprezinc (3-10 mg/kg, p.o.) was administered twice daily, starting from 3 days after ulceration for 14 days. The healing of gastric ulcers was significantly delayed in arthritic rats as compared to normal rats on day 10 and 17 following ulceration. The expression of IGF-1 mRNA was markedly increased in the ulcerated mucosa, but this response was apparently attenuated in arthritic rats. Repeated administration of polaprezinc accelerated the healing of gastric ulcers in both normal and arthritic rats, in a dose-dependent manner, and this effect was more pronounced in arthritic rats. Likewise, treatment with omeprazole also significantly promoted the healing of gastric ulcers in both normal and arthritic rats. On the other hand, rhIGF-1 significantly promoted the gastric ulcer healing in arthritic rats without any effect on that in normal rats. These results suggest that the impaired healing of chronic gastric ulcers in arthritic rats is, at least partly, accounted for by less expression of IGF-1, and the polaprezinc improves the delayed healing of gastric ulcers in arthritic rats, probably through an increase in IGF-1 production.
The zinc finger structure that is found in the nucleocapsid protein of nearly all retroviruses has been proposed as a target for antiviral therapy. Since compounds that chemically attack the cysteines of the finger have been shown to inactivate both human immunodeficiency virus type 1 (HIV-1) and murine leukemia virus (MuLV) in vitro, 14 of these compounds were tested in an MuLV-induced Friend disease model to assess their ability to inhibit retroviral replication in vivo. Of the 14 compounds tested, only Aldrithiol-2 clearly exhibited anti-retroviral activity as measured indirectly by the delay of Friend disease onset (P < 0.05). These results were confirmed by quantitative competitive polymerase chain reaction studies which monitored viral spread by measuring the level of viral DNA in the peripheral blood mononuclear cells of treated mice. Comparison of treated mice with untreated mice revealed that Aldrithiol-2 produced a greater than 2-log reduction in virus levels. These results functionally demonstrate that a zinc finger-attacking compound can inhibit viral replication in vivo. Since only 1 of the 14 compounds studied was effective, this study also shows the importance of in vivo testing of these types of antiviral compounds in an animal model. Given the strict conservation of the metal-coordinating cysteine structure within HIV-1 and MuLV zinc fingers, our results support the proposal that anti-retroviral drugs which target the nucleocapsid zinc finger may be clinically useful against HIV-1.
The brain of young domestic chicks was investigated using a Timm sulfide silver method. Serial Vibratome sections were analyzed under the light microscope, and the localization of zinc-positive structures in selected areas was determined at the ultrastructural level. Both strong and differential staining was visible in the avian telencephalon whereas most subtelencephalic structures showed a pale reaction. The highest staining intensity was found in the nonprimary sensory regions of the telencephalon such as the hyperstriatum dorsale, hyperstriatum ventrale, hippocampus, palaeostriatum augmentatum, lobus parolfactorius and caudal parts of neostriatum. There was an overall gradient of staining intensity in neostriatal areas from rostral to caudal with the heaviest zinc deposits in the caudal neostriatum. Primary sensory projection areas, such as the ectostriatum (visual), hyperstriatum intercalatum superius (visual), nucleus basalis (beak representation), the input layer L2 of the auditory field L and the somatosensory area rostral to field L were selectively left unstained. Fiber tracts throughout the brain were free of zinc deposits except for glial cells. In electron micrographs of stained regions, silver grains were localized in some presynaptic boutons of asymmetric synpases (Gray type I), within the cytoplasm of neuronal somata and sporadically in the nucleus. The possible involvement of zinc in synaptic transmission and other processes is discussed.
In the cellular environment, the sulfur ligands in zinc/thiolate coordination sites of proteins can be oxidized with concomitant mobilization of zinc. The characterization of such "redox zinc switches" requires the determination of three species, i.e., the zinc-containing complex and the zinc-free complex with the thiolate ligands either reduced or oxidized. Differential chemical modification of thiol groups in the presence and absence of either reducing or chelating agents allows the analytical speciation of such systems as demonstrated here for the characterization of the redox and metal-binding states of mammalian metallothionein. Thiol derivatization with 6-iodoacetamidofluorescein in the presence and absence of the reducing agent tris(2-carboxyethyl)phosphine, high-performance liquid chromatographic separation, and photometric detection are employed to determine the reduced and oxidized protein. Because the holoprotein reacts only in the presence of a chelating agent such as ethylenediaminetetraacetate (EDTA) its amount can be determined as the difference between measurements in the presence and the absence of EDTA. This method is applied to the study of the chemical and enzymatic oxidation of metallothionein/thionein. It should also greatly facilitate the characterization of the redox and metal-binding properties of zinc/thiolate coordination environments of other proteins such as zinc finger proteins.
A series of mononuclear zinc thiolate complexes have been prepared and fully characterized. The reactions of the complexes with alkyl halides, leading to zinc halides and the corresponding thioethers, have been examined by kinetic methods. In toluene, the reactions obey a second-order rate law displaying activation parameters consistent with a S(N)2 attack of the zinc-bound thiolate on the carbon electrophile. Intramolecular hydrogen bonding of an amide NH to the thiolate sulfur reduces the nucleophilicity and consequently, the rate of alkylation more than 30-fold at 25 degrees C. The H-bonding shows an inverse HD isotope effect of 0.33 (60 degrees C) ascribed to differential H-bonding for the two isotopomers due to zero point energy differences. These model studies provide quantitative evaluation of H-bonding on reaction rates relevant to zinc thiol-activating proteins.
Aim of the present study was the development of a bioassay which enables the detection of genotoxic effects of heavy metal contaminated soils. In the first part of the present study, the data base on metal effects in plant bioassays was extended. Four metal salts, namely Cr(VI)O3, Cr(III)Cl3, Ni(II)Cl2 and Sb(III)Cl3 were tested comparatively in MN tests with pollen tetrad cells of Tradescantia clone #4430 and in meristematic root tip cells of Vicia faba. With Cr6+ and Ni2+, clear-cut dose-effects were observed in a range between 0.75 and 10.0 mM, whereas this was not the case with Cr3+ (range tested 1.25-10 mM) and Sb3+ (range 0.30-5.25 mM). In Vicia, negative results were obtained with the four metal salts under all conditions of test. To compare the mutagenic potencies of the metals, the increases of the regression curves (k-values) were calculated, they indicate the number of MN induced per mM in 100 tetrad cells. The corresponding values for Cr6+ and Ni2+ are 0.87 and 1.05, respectively. It appears that the Tradescantia system is in particular sensitive towards those metal species which cause DNA damage in animals and man such as Cr6+, Cd2+, Ni2+, and Zn2+, whereas no clear positive results were obtained with less harmful metal ions such as Cu2+, Cr3+ or Sb3+. In the second part of the study, the mutagenic effects of four metal contaminated soils and two types of standardized leachates (pH 4.0 and pH 7.0) of these soils were tested in Tradescantia and in Vicia. In addition, chemical analyses were carried out to determine the metal concentrations in the soils and in the extracts. Two of the samples contained highly elevated levels of a number of metals (Zn, Pb, Cu, Cd, Sb, As), one soil came from the Central Austrian Alps and contained high As levels only. Direct exposure of the Tradescantia plants in the soils resulted in a drastic increase of the MN frequencies over the background. The lowest effect was seen with the Slovakian soil which contained in particular Sb and As (4.5-fold increase over the background), with the other soils, the induced frequencies were 11-15-fold over the control values. On the contrary, negative results were obtained upon exposure of Tradescantia cuttings in the leachates and upon implantation of germinated Vicia beans in the soils. The results of the present study indicate that Trad-MN assays with direct exposure of intact plants is an appropriate method which enables to detect genotoxic effects of metal contaminated soils in situ. This simple and fast biomonitoring assays might be a valuable supplement to analytical analyses of contaminated soils.
Municipal wastewater effluent contains ligands that form Hg(II) complexes that are inert in the presence of glutathione (GSH) during competitive ligand exchange experiments. In this study, the strong ligands in wastewater effluent were further characterized by comparing their behavior with sulfide-containing ligands in model solutions and by measuring their concentration after exposing them to oxidants. The strong Hg(II) complexes in wastewater effluent and the complexes formed when Hg(II) was added to S(-II) were retained during C18 solid-phase extraction (SPE) and did not dissociate in the presence of up to 100 microM GSH. In contrast, Hg(II) complexes with dissolved humic acid were hydrophilic and dissociated in the presence of GSH. The combination of sulfide and humic acid resulted in formation of Hg(II) complexes that were inert to GSH and were only partially retained by C18-SPE, indicating that NOM interacted with the Hg-sulfide complexes. When wastewater effluent samples and model solutions of free sulfide, Zn-sulfide, and Fe-sulfide were exposed to 0.14 mM NaOCl for 1 h (to mimic conditions encountered during chlorine disinfection), the strong Hg(II)-complexing ligands were completely removed. Exposure of the wastewater effluent and the model ligands to oxygen for 2 weeks resulted in approximately 60% to 75% loss of strong ligands. The strong ligands that remained in the oxygen-oxidized samples were resistant to further oxidation by chlorine, indicating that oxidation of S(-II) results in the formation of other sulfur-containing ligands such as S8 that form strong complexes with Hg(II).
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