Silica metal binding

A general lack of effectiveness has been noted for several MCAs in the suppression of GI-uptake of cadmium in mice. In this study the MCAs, the metal-binding capacity was 2-6.8 mM g 1, ranged from DTPA immobilized via amide bond formation to finely divided aminopropyl-silica, xanthates of polyvinylalcohol and various polysaccharides, and a dextran bearing ethylthiol moieties produced by action of ethylenesulphide on dextran209. ... 

Although varying the concentration of salt in the eluent usually modulates the retention of proteins in MIC, the nature of the salt also plays an important role. It was found that stationary phases with chelates of soft and intermediate metals bind protein more strongly in the presence than in the absence of antichaotropic salts [21 ]. In a study using EDDA-silica supports, the elution strength of sodium salts on an Fe " " column was chloride < acetate < formate < phosphate for several proteins, whereas the strength on a Co column was acetate < phosphate <... 

Once introduced into a mammalian biological system, there is no such thing aa an inert particle. Pfirticles of obvious chemical (covalent) inertness, such as hydrophobic talc particles, can manifest a strong physico-chemical reactivity, in aqueous media, on accoimt of their hydrophobic attraction for biopolymers (e.g., proteins cf. van Oss et al., 1995b). hydrophilic particles such as silica also bind proteins, by a different physico-chemical mechanism, as do many other metal oxides (van Oss et al., 1995a, b). 

Effective metal ion adsorbent has been prepai ed by the immobilization of propylthioethyleamine ligand onto the surface of silica gel (SN-SiO,).The effectiveness of this material to bind metal ions has been attributed to the complexation chemistry between the ligand and the metal. We are investigating properties of propylthioethyleamine grafted on the surface of silica and possibility of application of the obtained surface for preconcentration of heavy metals such as zinc, lead, cadmium, copper, etc. from water solutions. 

In 1975, the fabrication of a chiral electrode by permanent attachment of amino acid residues to pendant groups on a graphite surface was reported At the same time, stimulated by the development of bonded phases on silica and aluminia surfaces the first example of derivatized metal surfaces for use as chemically modified electrodes was presented. A silanization technique was used for covalently binding redox species to hydroxy groups of SnOj or Pt surfaces. Before that time, some successful attemps to create electrode surfaces with deliberate chemical properties made use of specific adsorption techniques... 

The reaction of preformed cyanoalkylsilane with silica gel followed by hydrolysis leads to the formation of chemisorbed carboxylic acid groups that are capable of strongly binding metal ions including Cu(II), Mn(II), Ni(II),... 

Of direct interest for photoemission of supported catalysts is that similar increases in the width of d-bands have been observed by Mason in UPS spectra of small metal particles deposited on amorphous carbon and silica substrates [48]. Theoretical calculations by Baetzold et al. [49] indicate that the bulk density of states is reached if Ag particles contain about 150 atoms, which corresponds to a hemispherical particle 2 nm in diameter. Concomitant with the appearance of narrowed d-bands in small particles is the occurrence of an increase in core level binding energies of up to 1 eV. The effect is mainly an initial and only partly a final state effect [48], although many authors have invoked final state - core hole screening effects as the only reason for the increased binding energy. 

The first consideration was the speciation and distribution of the metal in the sediment and water. Benthic organisms are exposed to surface water, pore water and sediment via the epidermis and/or the alimentary tract. Common binding sites for the metals in the sediment are iron and manganese oxides, clays, silica often with a coating of organic carbon that usually accounts for ca. 2% w/w. In a reducing environment contaminant metals will be precipitated as their sulfides. There is not necessarily a direct relationship between bioavailability and bioaccumulation, as digestion affects the availability and transport of the metals in animals, in ways that differ from those in plants. 

Binding of metal ions by amorphous silica. 300 mg Si02 dm-3, [Mej = 10 5 MJ. The fraction of metal ion bound was calculated from peak currents measured with differential pulse polarography. 

The liquid-phase reaction kinetics of doped molecules in silica nanomatrixes was conducted using the metalation of meso-tetra (4-Ai,Ai,Ai-trimethylanilinium) porphyrin tetrachloride (TTMAPP) with Cu(II) as a model. To demonstrate the effect of the silica nanomatrix on the diffusion, pure silica shells with varied thickness were coated onto the same silica cores, which doped the same amount of TTMAPP molecules. The Cu(II) from the suspension could penetrate into the silica nanomatrixes and bind to the TTMAPP. The reaction rate of TTMAPP metalation with Cu(II) was significantly slower than that in a bulk solution. The increase in the thickness of the silica resulted in a consistent decrease of reaction rates (Fig. 8). 

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