Molecular-Weight Inorganic Anions

A number of low-molecular-weight inorganic ligands are involved in metal binding in metalloproteins. These include HCO) and P04, as ligands to Fe in proteins involved in iron transport, in association with amino acid residues of the protein. We will discuss the role of CN and CO as ligands to Fe in bacterial hydrogenases, where they are part of more complex metal centres in a later section. 

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Dowex 1-X8 1.2 0.75 Strongly basic anion exchanger with S-DVB matrix for separation of inorganic and organic anions with molecular weight exclusion < 1000. 100-200 mesh is standard for analytical separations. 

Anionic extractants are commonly based on high molecular weight amines. Metal anions such as MnO or ReO can be exchanged selectively with inorganic anions such as Cl or The equiHbrium for a quaternary onium compound of organic radicals R for two anion species A and B ... 

A semi-permeable membrane, which is unequally permeable to different components and thus may show a potential difference across the membrane. In case (1), a diffusion potential occurs only if there is a difference in mobility between cation and anion. In case (2), we have to deal with the biologically important Donnan equilibrium e.g., a cell membrane may be permeable to small inorganic ions but impermeable to ions derived from high-molecular-weight proteins, so that across the membrane an osmotic pressure occurs in addition to a Donnan potential. The values concerned can be approximately calculated from the equations derived by Donnan35. In case (3), an intermediate situation, there is a combined effect of diffusion and the Donnan potential, so that its calculation becomes uncertain. 

Researchers found that zeolite particles can be treated with high-molecular-weight surfactants [such as hexadecyltrimethylammonium (HDTMA)]. HDTMA does not penetrate into the internal pore structure of the zeolite, but coats the outer surface. The outer surface then develops hydrophobic anionic exchange properties, while the inner surface retains the capacity to adsorb cations. Researchers claim that SMZ can be used for the three major classes of water contaminants inorganic cations, inorganic anions, and nonpolar organics. 

For the purpose of this discussion, milk salts are considered as ionized or ionizable substances of molecular weight 300 or less. Ionizable groups of proteins are not included here, although, of course, they must be taken into account in a complete description of ionic balance and equilibria. Trace elements, some of which are ionized or partially so in milk, are considered in a later section of this chapter. Milk salts include both inorganic and organic substances thus they are not equivalent to either minerals or ash. The principal cations are Na, K, Ca, and Mg, and the anionic constituents are phosphate, citrate, chloride, carbonate, and sulfate. Small amounts of amino cations and organic acid anions are also present. 

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