Scale chelating agents

Sca.Ie nd Sta.in Controllers. Polyacrjiates (low molecular weight) and organic phosphonates, eg, (l-hydroxyethyhdene)diphosphonic acid, prevent or control precipitation of CaCO by acting as chelating agents (qv) or dispersants (qv) to prevent excessive formation of hard scale by promoting crystal distortion. 

In 1956 it was found that when pyridine is refluxed with a modified Raney-nickel catalyst, 2,2 -bipyridine (1) is formed in satisfactory yield. The isomeric bipyridines could not be detected, and the product was readily purified. Similar heterocyclic biaryls have been formed in the same way from substituted pyridines and from some related compounds, the yield being dependent on the nature of the compound. The reaction has become the method of choice for the preparation of 2,2 -bipyridine, and it is now used on an industrial scale. Bipyridyls are of particular importance as chelating agents. 

Thennodynamic inhibitors are complexing and chelating agents, suitable for specific scales. For example, for scale inhibition of barium sulfate, common chemicals are ethylenediaminetetraacetic acid (EDTA) andnitrilotriacetic acid. The solubility of calcium carbonate can be influenced by varying the pH or the partial pressure of carbon dioxide (CO2). The solubility increases with decreasing pH and increasing partial pressure of CO2, and it decreases with temperature. 

Scale deposits are converted to dispersed particles which can be circulated out of the wellbore. A chelating agent such as ethylenediamine tetraacetic acid can aid in dissolving calcium sulfate deposits. Hydrochloric acid following the basic treatment can also be used to dissolve calcium sulfate (167). 

Renn, O., and Meares, C.F. (1992) Large scale synthesis of the bifunctional chelating agent 2-p-nitroben-zyl-l,4,7,10-tetraazacyclododecane-N,N, N"N" -tetraacetic acid and the determination of its enantiomeric purity by chiral chromatography. Bioconjugate Chem. 3, 563-569. 

For the subculture of adherent cells, removal of culture medium and the detachment of cells from the monolayer are necessary. This detachment is usually performed with trypsin, but other proteases, such as pronase, dispase, and collagenase, can be employed. In general, a chelating agent, such as EDTA, is also added to capture the Ca2+ ions involved in the cell adhesion process. Some cell lines bind weakly to surfaces and, in small-scale cultures, can be removed mechanically by gently tapping or hitting the culture flask by hand. 

A type of hydroxycarboxylic acid that is used as a chelating agent is gluconic acid. It is produced on a commercial scale by bacterial fermentative oxidation of glucose. The reaction can be represented by Eq. 16.7 ... 

Immobilized metal affinity chromatography has been shown to be effective for isolating proteins from crude mixtures, as well as for selective separations of closely related proteins [2]. With respect to separation efficiency, IMAC compares well with biospecific affinity chromatography and the immobilized metalion complexes are much more robust than antibodies or enzymes. These factors make IMAC particularly well suited for scale-up to process scale chromatography. The main scale-up points to be aware of are the degree to which the column is metal saturated, the chelating agent content of the sample, and the potential of leached metal (or its interactions) within the product eluate. 

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