Function Of Cd Concentration Research Articles

Structural study of a series of synthetic goethites obtained in aqueous solutions containing cadmium(II) ions

The capacity of goethite for CdIIsubstitution has been explored in a series of synthetic samples prepared from FeIIIand CdIInitrate solutions aged 21 days in alkaline media. The total metal content ([Fe]+[Cd]) was 0.071 M in all preparations. The samples have been characterized by chemical and X-ray diffraction analysis; the morphology of the solids is described. The cell parameters for all samples were obtained by the Rietveld fits to the X-ray diffraction data. Refined structures show that for samples prepared at the final molar ratio μCd≤5.50 (expressed as μCd=100×[Cd]/[Cd]+[Fe]), a (Cd, Fe)-goethite is the only crystalline product. In these samples, the unit cell parameters increased as a function of Cd concentration, indicating Cd incorporation in the structural frame. At the preparative ratio, μCd=7.03, the incorporation of Cd in the goethite structure is drastically reduced and a probable Cd-substituted hematite is formed together with the Fe,Cd-goethite.

A rheological investigation of the complex formation between hydrophobically modified ethyl (hydroxy ethyl) cellulose and cyclodextrin

The thickening effect of a hydrophobically modified polymer in an aqueous solution is dependent on intermolecular hydrophobic associations, and if the polymer concentration is significantly above the overlap concentration also on chain entanglements. In this investigation we have added different cyclodextrins (CD) in order to decouple hydrophobic polymer–polymer associations via inclusion complex formation with the polymer hydrophobic tails. Both size and hydrophobicity of the cavity of the CD-molecules were found to have an effect on the process. In addition, the influence of chemical structure of the polymer hydrophobic tails was investigated. Either a linear C 14-chain or a more bulky nonylphenol group was used. The viscosity as a function of CD-concentration first decreased strongly, and then attained a constant value. At excess CD the viscosity became virtually the same as in a solution of the unmodified parent polymer, provided that complex formation was not sterically hindered. This suggests that all hydrophobic links, originating from the hydrophobic modification process, which influence the rheology could be deactivated. On the other hand, with combinations where the complex formation was hindered to a certain degree the initial decrease was less accentuated, and also, the viscosity leveled out at a significantly higher value. In an attempt to rationalize the data a simple model based on the assumption that each complex formed deactivates one rheologically active link was used. In combination with the Langmuir adsorption model the number of complexes as a function of CD concentration could be obtained. This model also gave a value of the complex formation constant. Furthermore, in solutions where all hydrophobic links could be deactivated the results from the model suggested that all polymer hydrophobic tails were originally active in forming the network.

Mechanisms and Surface Chemical Prediction of Imipramine ‐Induced Hemolysis Suppressed by Modified Cyclodextrins

The suppression of imipramine hydrochloride (IMP)‐ induced hemolysis by native cyclodextrins (α‐, β‐, and γ‐CDs) and β‐CD derivatives is measured as a function of CD concentration and is quantitatively correlated with the surface tension of the solution determined at 37.0 °C. The modified β‐CDs are more or less adsorbed onto the air–water interface and occupy larger areas than the wider rim of β‐CD. The surface tension data at low CD concentrations in the presence of 3 mM IMP allow us to estimate the 1:1 binding constants of IMP with CDs. Both the capabilities of hemolysis suppression and surface tension elevation for 3 mM IMP are strong in the order carboxymethyl‐β‐CD (CM) > β‐CD ≈ 6‐O‐glucosyl‐β‐CD (G1) > γ‐CD > 2‐hydroxypropyl‐β‐CD (HP) > α‐CD ≥ 2,6‐di‐O‐methyl‐β‐CD (DM). The suppression of IMP‐induced hemolysis is ascribed to the decrease in the concentration of free IMP molecules. This concentration can be quantitatively estimated from the surface tension data determined at 37 °C. Therefore, the suppression of IMP‐induced hemolysis by most of the CDs can be quantitatively predicted from these surface tension data, regardless of the kind and concentration of CD. However, α‐CD, HP, and DM are outliers of this prediction. This failure for α‐CD and HP is ascribed to their weaker competitive binding to IMP than to membrane phospholipid. Because DM has a strong hemolytic activity, it does not almost suppress the IMP‐induced hemolysis. © 2001 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1056–165, 2001

Dietary assimilation of cadmium associated with bacterial exopolymer sediment coatings by the estuarine amphipod Leptocheirus plumulosus:effects of Cd concentration and salinity

Bacterial extracellular substances (also known as exopolysaccharides, or EPS) may serve as vectors for trophic transfer of metals in benthic systems because these ubiquitous sediment coatings can sorb high concentrations of toxic metals, and because many benthic invertebrates assimilate EPS sediment coatings upon ingestion. We conducted 3 sets of experiments to determine the assimilative bioavailability of EPS-associated Cd to the benthic amphipod Leptocheirus plumulosus as a function of Cd concentration and salinity. Bioavailability was measured as L. plumulosus Cd assimilation efficiency (AE) from EPS-coated silica (EPS-Si) and from uncoated silica (NC-Si) using modified pulse-chase methods with the gamma-emitting radioisotope 109 Cd. Cd AE was significantly greater from NC-Si than from EPS-Si at 7.5‰, but not at 2.5 or 25‰. Overall, Cd AE from EPS-Si was between 15.1 and 21.5%. Because EPS-Si sorbed more Cd than NC-Si, EPS coatings magnified the amount of Cd amphipods accumulated at each salinity by up to a factor of 10. Salinity did not directly affect Cd AE from EPS-Si, but because Cd-EPS partitioning increased with decreasing salinity, amphipods accumulated more Cd from EPS at the lowest Cd-EPS incubation salinity (2.5‰) than at higher salinities (7.5 and 25‰). Finally, Cd concentration in EPS exhibited an inverse relationship with Cd AE at 2.5 ‰, but not at 25 ‰. Specifically, Cd AE was 12 times greater at 1 compared with 10 μg Cd μg -1 EPS. Together, these results show that estuarine benthos can accumulate Cd from EPS sediment coatings, but that the degree to which this phenomenon occurs is dependent upon seawater salinity and Cd concentration in EPS.

Excitonic nonlinearities in wide gap II–VI multiple quantum wells

We report a comprehensive study of excitonic nonlinearities in Zn1−xCdxSeZnSe multiple quantum wells under optical and electrical excitation. The stability of the heavy-hole exciton is studied as a function of Cd concentration by using pump and probe transmission spectroscopy. The heavy-hole exciton absorption peak is investigated as a function of the intensity of the pump beam until the exciton bleaching is reached. The experimental results are fitted with a theoretical model which includes band-gap renormalization, phase space filling and density dependent lifetime broadening. The correlation of these results with stimulated emission measurements performed also in magnetic field up to 8 T, allowed us to elucidate the role of excitons and free carriers in the lasing process in Zn1−xCdxSeZnSe multiple quantum wells. Electric field induced effects are also studied in order to elucidate the role of quantum confined Stark effect on the optical modulation. Further insight in the nonlinear optical properties of excitons has been obtained by photoluminescence measurements under external bias.

Conductivity studies of the molecular encapsulation of sodium perfluoroctanoate by?-cyclodextrin derivatives

The molecular encapsulation of sodium perfluoroctanoate (SPFO) by hydroxypropyl-β-cyclodextrin (HP-β-CD) or 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD) has been analyzed by measuring the conductivity in solution of the ternary systems formed by CD + SPFO + H2O. The studies were carried out at 25 °C using a fully computerized electrical conductivity technique. The measurements were made as a function of CD concentration at various non-micellar concentrations of SPFO, and as a function of CD and SPFO concentrations with [CD]/[SPFO] constant at stoichiometric ratio. The inclusion complexes, HP-β-CD-SPFO and DM-β-CD-SPFO, were characterized through the stoichiometry, which has been found to be 1 : 1 in both cases, and the binding constants, which have been evaluated from the conductivity data with a model proposed by us considering the variation of the ionic molar conductivities with the concentration and the association of the surfactant counterion to the inclusion complex. The resultingK values indicate that the interaction between the CD cavity and the monomeric SPFO is strong and similar in both cases.

The pseudobinary HgTe-CdTe phase diagram

The complete pseudobinary HgTe-CdTe constitutional phase diagram was determined by precision differential-thermal-analysis measurements and used to calculate the segregation coefficient of Cd as a function of Cd concentration and interface temperature. A thorough error analysis was made, and the results are compared with published data. Empirical, analytical-expressions were developed for the liquidus and solidus compositions as functions of temperature to facilitate calculations of phase equilibrium parameters.

Ultraviolet photoelectron spectra of the outer d bands of Ag-In and Ag-Cd alloys

Photoelectron spectra (40.81 eV) of the Ag-Cd and Ag-In alloy systems are presented and are discussed in connection with both d band overlap and crystal-field models. The Ag 4d bands in each system show similar dependences on Ag concentration. This favours the former model. It is not clear which mechanism is responsible for the variation and increase in Cd 4d band splitting over the Cd free-ion value as a function of Cd concentration. The In 4d bands which have large binding energy show little dependence on concentration, apparently due to the small effect of neighbouring atoms.