Since metals like zinc, copper cobalt have a tendency to bind to non-specific sites, imidazole chelation may become useful. Magnesium chloride or sulfate 5-100mM Can also be used as a precipitant. It inevitably reduces protein solubility. It can act as an inhibitor. It is very concentration dependent Barium chloride or acetate 1-20mM Same as calcium Heavy Atom Copper sulfate 0.
Some enzymes depend on it.
Erbium or Samarium acetate 0.1-10mM use to replace other divalent metals. Salts are used to precipitate as well as solubilize proteins. Potassium chloride 0.05-2 M alternative to NaCl. NaCl is generally better Lithium chloride 0.05-2 M alternative to NaCl. The differences are worth checking out Sodium Fluoride 20-300mM Inhibitor.