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Results for “Cadmium Compounds”

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PubMed2005

Type-II CdSe/CdTe/ZnTe (core-shell-shell) quantum dots with cascade band edges: the separation of electron (at CdSe) and hole (at ZnTe) by the CdTe layer.

The rational design and synthesis of CdSe/CdTe/ZnTe (core-shell-shell) type-II quantum dots are reported. Their photophysical properties are investigated via the interband CdSe-->ZnTe emission and its associated relaxation dynamics. In comparison to the strong CdSe (core only) emission (lambda(max) approximately 550 nm, Phi(f) approximately 0.28), a moderate CdSe-->CdTe emission (lambda(max) approximately 1026 nm, Phi(f) approximately 1.2 x 10(-3)) and rather weak CdSe-->ZnTe interband emission (lambda(max) approximately 1415 nm, Phi(f) approximately 1.1 x 10(-5)) are resolved for the CdSe/CdTe/ZnTe structure (3.4/1.8/1.3 nm). Capping CdSe/CdTe with ZnTe results in a distant electron-hole separation between CdSe (electron) and ZnTe (hole) via an intermediate CdTe layer. In the case of the CdSe/CdTe/ZnTe structure, a lifetime as long as 150 ns is observed for the CdSe-->ZnTe (1415 nm) emission. This result further indicates an enormously long radiative lifetime of approximately 10 ms. Upon excitation of the CdSe/CdTe/ZnTe structure, the long-lived charge separation may further serve as an excellent hole carrier for catalyzing the redox oxidation reaction.

Absorption↗
PubMed2005

Physicochemical evaluation of the hot-injection method, a synthesis route for monodisperse nanocrystals.

The quintessence of the hot-injection method, a synthesis route for monodisperse, highly luminescent semiconductor nanocrystals, is reviewed. The separate stages of nucleation and growth of the nanocrystals are discussed in the framework of classical nucleation theory and an equilibrium model proposed by Debye. We also review the numerous adaptations of the original synthesis that currently provide colloidal nanocrystals with well-defined, size-dependent optical, electrical, and magnetic properties. The availability of these remarkable materials is one of the most promising developments in nanoscience and nanotechnology.

Cadmium Compounds↗
PubMed2006

Shape control of II-VI semiconductor nanomaterials.

Anisotropic II-VI semiconductor nanocrystals and nanoparticles have become important building blocks for (potential) nanotechnological applications. Even though a wide variety of differently shaped nanoparticles of this class can be prepared, the underlying mechanisms are mostly not fully understood. This Review article provides a brief overview of the currently studied shape-evolution mechanisms and the most prominent synthesis methods for such particles, with an aim to provide a fundamental understanding on how different morphologies evolve, and to function as a tool to aid in the preparation of specific nanocrystals.

Anisotropy↗
PubMed2006

Formation of CdS nanoparticle necklaces with functionalized dendronized polymers.

A one-dimensional assembly of cadmium sulfide (CdS) nanoparticles was prepared by using functionalized polymers with pendant Fréchet-type dendritic wedges of different generation. The novel dendronized polymers acted as both nanoreactors for the formation of CdS nanoparticles and a template to arrange the nanoparticles into a necklace. The polymers of different dendron generation were applied to stabilize CdS particles and the effect of dendron size was observed. CdS nanoparticle necklaces were obtained successfully when polymers bearing second-generation dendrons were applied.

Acetates↗
PubMed2006

The empirical correlation between size and two-photon absorption cross section of CdSe and CdTe quantum dots.

The tuning of CdSe quantum dot (QDs) sizes, and consequently their corresponding two-photon absorption (TPA) cross section, has been systematically investigated. As the size (diameter) of the quantum dots increases, the TPA cross section is found to be empirically related via a power-law proportionality of 3.5+/-0.5 and 5.6+/-0.7 to the diameters of CdSe and CdTe QDs, respectively. The results are tentatively rationalized via a theoretical model of two-photon excitation properties in a system incorporating excitons and defects.

Absorption↗
PubMed1984

Potentiation of acetazolamide induced ectrodactyly in SWV and C57BL/6J mice by cadmium sulfate.

CdSO4 and acetazolamide each induce postaxial ectrodactyly in rodents when administered at a critical time in forelimb development. C57BL/6J mice are extremely sensitive to the teratogenic action of both agents, whereas SWV mice are relatively resistant. Additionally, both of these agents can inhibit carbonic anhydrase. In the present study administration of CdSO4 and acetazolamide in combination to either strain of mice potentiates the incidence of forelimb ectrodactyly. These results, in combination with the aforementioned similarities of teratogenesis, suggest a common mechanism of teratogenesis.

Abnormalities, Drug-Induced↗
PubMed1985

Histological changes induced in developing limb buds of C57BL mouse embryos submitted in utero to the combined influence of acetazolamide and cadmium sulphate.

Microscopic defects in limb buds of C57BL mouse embryos after the combined teratogenic action of acetazolamide plus cadmium sulphate administered on day 9 of gestation were studied in serial sections. Postaxial deficiencies observed in 12-15-day embryos and affecting preferentially the right forelimbs were classified in nine morphological types according to increasing amounts of missing parts. Type X defect consists of a nearly complete amelia in which all four limbs are represented only by the girdle and proximal end of the stylopod. Type XI abnormality appears as an intermediate reduction affecting the area of digit IV. In addition to modifications of the forelimb bud shape detected from the 10-day stage onwards, observations made 24 and 48 hr after treatment confirmed that the postaxial defects result from an absolute lack of postaxial mesoderm occurring without cell necrosis as a consequence of a postaxial shortening of the apical ectodermal ridge (aer). In 10-day embryos, the latter appears shortened and hypertrophied; it is later fragmented into alternate thick and thin portions in 11-day affected limb buds. These ectodermal changes might account for the genesis of all types of defects observed. Untreated 9-day embryos with 12-25 pairs of somites display a number of asymmetries between their right and left forelimb territories: Until the 19-somite stage, the vascular supply to that area is provided exclusively by the umbilical vein, which is larger on the right side; the initial amount of somatopleural limb mesoderm is greater in the right rudiment and the genesis of its aer is slightly protracted as compared to the left one. These asymmetries might contribute to the right side predominance of the forelimb defects induced by acetazolamide and cadmium.

Abnormalities, Drug-Induced↗
PubMed1994

Zinc and other divalent cations inhibit purified leukotriene A4 hydrolase and leukotriene B4 biosynthesis in human polymorphonuclear leukocytes.

Leukotriene A4 hydrolase is a bifunctional metalloenzyme that contains 1 mol of zinc per mole of protein. The primary function of the metal is catalytic and zinc is thus necessary for both its peptidase and its epoxide hydrolase activity. However, at concentrations of zinc exceeding a 1:1 molar ratio (metal:enzyme), we found that zinc acted as an inhibitor with IC50 values of 10 microM for the epoxide hydrolase activity, i.e., the conversion of leukotriene A4 to leukotriene B4, and 0.1 microM for the peptidase activity. The inhibition of both enzyme activities could be reversed by treating the enzyme with chelating agents such as EDTA or dipicolinic acid. Several divalent cations, other than zinc, were also found to inhibit leukotriene A4 hydrolase although with different specificity and potency for the two enzyme activities. Thus, CdSO4 and HgCl2 were effective inhibitors (IC50 approximately 10 microM) of the epoxide hydrolase activity, whereas CoCl2 or MnCl2 were not inhibitory even at concentrations of 1 mM. On the other hand, the peptidase activity was inhibited by CdSO4, NiSO4, HgCl2, MnCl2, CoCl2, and PbNO3, listed in decreasing order of potencies (IC50 0.5-10 microM). In addition, zinc in micromolar concentrations inhibited leukotriene B4 formation in intact human polymorphonuclear leukocytes stimulated by the calcium ionophore A23187 and cell homogenates incubated with arachidonic acid. However, this effect was not related to inhibition of leukotriene A4 hydrolase but rather to a direct or indirect inhibitory effect on the enzyme 5-lipoxygenase in isolated leukocytes. In these cells, 15-lipoxygenase activity was also inhibited by zinc (IC50 5 microM), whereas leukotriene C4 synthase activity in human platelets and rat basophilic leukemia cells was significantly affected only at concentrations > or = 1 mM.

Animals↗
PubMed2000

Time-resolved spectral observations of cadmium-enriched cadmium sulfide nanoparticles and the effects of DNA oligomer binding.

We measured the steady-state and time-resolved fluorescence spectral properties of cadmium-enriched nanoparticles (CdS-Cd2+). These particles displayed two emission maxima, at 460 and 580 nm. The emission spectra were independent of excitation wavelength. Surprisingly, the intensity decays were strongly dependent on the observation wavelength, with longer decay times being observed at longer wavelengths. The mean lifetime increased from 150 to 370 ns as the emission wavelength was increased from 460 to 650 nm. The wavelength-dependent lifetimes were used to construct the time-resolved emission spectra, which showed a growth of the long-wavelength emission at longer times, and decay-associated spectra, which showed the longer wavelength emission associated with the longer decay time. These nanoparticles displayed anisotropy values as high as 0.35, depending on the excitation and emission wavelengths. Such high anisotropies are unexpected for presumably spherical nanoparticles. The anisotropy decayed with two correlation times near 5 and 370 ns, with the larger value probably due to overall rotational diffusion of the nanoparticles. Addition of a 32-base pair oligomer selectively quenched the 460-nm emission, with less quenching being observed at longer wavelengths. The time-resolved intensity decays were minimally affected by the DNA, suggesting a static quenching mechanism. The wavelength-selected quenching shown by the nanoparticles may make them useful for DNA analysis.

Biopolymers↗
PubMed1994

Role of CdS quantum crystallites in cadmium resistance in Candida glabrata.

Glutathione-related peptides (gamma-Glu-Cys)nGly, trivially known as phytochelatins (PCs), sequester Cd(II) and other heavy metals in all plants and some yeasts. However, the metal resistance levels may depend on factors such as the PC concentrations, their chain length and ability to incorporate labile sulfide. We show here that a highly Cd(II)-resistant mutant of yeast Candida glabrata exhibited Cd(II)-dependent formation of extremely high levels of PC-coated CdS quantum crystallites. The CdS crystallites were formed in the cytosol but finally accumulated in the vacuoles. Cd(II)-stimulated sulfide production required sulfate and was inhibited by both cysteine and methionine. GSH synthesis inhibition sensitized the resistant strain to Cd(II) indicating that GSH still provided primary defense against the metal ion.

Cadmium↗