Membranes Metal complexes

In this work ion-exchange and gel-permeation chromatography coupled with membrane filtration, photochemical oxidation of organic metal complexes and CL detection were applied to the study of the speciation of cobalt, copper, iron and vanadium in water from the Dnieper reservoirs and some rivers of Ukraine. The role of various groups of organic matters in the complexation of metals is established. 

Ionic liquids have already been demonstrated to be effective membrane materials for gas separation when supported within a porous polymer support. However, supported ionic liquid membranes offer another versatile approach by which to perform two-phase catalysis. This technology combines some of the advantages of the ionic liquid as a catalyst solvent with the ruggedness of the ionic liquid-polymer gels. Transition metal complexes based on palladium or rhodium have been incorporated into gas-permeable polymer gels composed of [BMIM][PFg] and poly(vinyli-dene fluoride)-hexafluoropropylene copolymer and have been used to investigate the hydrogenation of propene [21]. 

Membrane, 141, 178 Mercury electrodes, 62, 108 Mercury film electrode, 76, 110 Metals, 75, 81 Metal complexes, 64 Methyl viologen, 43 Michaelis-Menten kinetics, 175 Microbalance, 52, 53 Microcells, 102 Microchip, 194, 195... 

Ramaraj, R and Kaneko, M Metal Complex in Polymer Membrane as a Model for Photosynthetic Oxygen Evolving Center. Vol. 123 pp. 215-242. 

Tetra(o-aminophenyl)porphyrin, H-Co-Nl TPP, can for the purpose of electrochemical polymerization be simplistically viewed as four aniline molecules with a common porphyrin substituent, and one expects that their oxidation should form a "poly(aniline)" matrix with embedded porphyrin sites. The pattern of cyclic voltammetric oxidative ECP (1) of this functionalized metal complex is shown in Fig. 2A. The growing current-potential envelope represents accumulation of a polymer film that is electroactive and conducts electrons at the potentials needed to continuously oxidize fresh monomer that diffuses in from the bulk solution. If the film were not fully electroactive at this potential, since the film is a dense membrane barrier that prevents monomer from reaching the electrode, film growth would soon cease and the electrode would become passified. This was the case for the phenolically substituted porphyrin in Fig. 1. 

There are two general classes of naturally-occurring antibiotics which influence the transport of alkali metal cations through natural and artificial membranes. The first category contains neutral macrocyclic species which usually bind potassium selectively over sodium. The second (non-cyclic) group contains monobasic acid functions which help render the alkaline metal complexes insoluble in water but soluble in non-polar solvents (Lauger, 1972 Painter Pressman, 1982). The present discussion will be restricted to (cyclic) examples from the first class. 

In 1977, Parshall and co-workers published their work on the separation of various homogeneous catalysts from reaction mixtures.[46] Homemade polyimide membranes, formed from a solution of polyamic acid were used. After reaction the mixture was subjected to reverse osmosis. Depending on the metal complex and the applied pressure, the permeate contained 4-40% of the original amount of metal. This publication was the beginning of research on unmodified or non-dendritic catalysts separated by commercial and homemade membranes. 

In the early 1970 s, Bayer et al. reported the first use of soluble polymers as supports for the homogeneous catalysts. [52] They used non-crosslinked linear polystyrene (Mw ca. 100 000), which was chloromethylated and converted by treatment with potassium diphenylphosphide into soluble polydiphenyl(styrylmethyl)phosphines. Soluble macromolecular metal complexes were prepared by addition of various metal precursors e.g. [Rh(PPh3)Cl] and [RhH(CO)(PPh3)3]. The first complex was used in the hydrogenation reaction of 1-pentene at 22°C and 1 atm. H2. After 24 h (50% conversion in 3 h) the reaction solution was filtered through a polyamide membrane [53] and the catalysts could be retained quantitatively in the membrane filtration cell. [54] The catalyst was recycled 5 times. Using the second complex, a hydroformylation reaction of 1-pentene was carried out. After 72 h the reaction mixture was filtered through a polyamide membrane and recycled twice. 

Partitioning of metal complexes into the lipid bilayer of membranes is only significant for hydrophobic species. FA and HA, and their metal complexes, are not expected to enter to a significant extent into the lipid bilayer, due to their large molecular size. Uptake of hydrophobic metal species by diffusion across... 

Nonpolar compounds, including the majority of xenobiotic chemicals and some metal complexes [249-252], generally diffuse passively through the lipid portions of the membrane by simple diffusion [21,246,253,254]. In this case, internalisation rates are reflected by compound permeability in the bilipid membrane [254,255] and can be predicted by Fick s law [254,256] ... 

Many experimental variations are possible when performing uptake studies [246]. In a simple experiment for which the cells are initially free of internalised compound, the initial rates of transmembrane transport may be determined as a function of the bulk solution concentrations. In such an experiment, hydrophilic compounds, such as sugars, amino acids, nucleotides, organic bases and trace metals including Cd, Cu, Fe, Mn, and Zn [260-262] have been observed to follow a saturable uptake kinetics that is consistent with a transport process mediated by the formation and translocation of a membrane imbedded complex (cf. Pb uptake, Figure 6 Mn uptake, Figure 7a). Saturable kinetics is in contrast to what would be expected for a simple diffusion-mediated process (Section 6.1.1). Note, however, that although such observations are consistent... 

Use of ultrafiltration membranes after complexation of the heavy metal ions. 

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