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Many molecular biology recipes use MgSO4 (and not MgCl2). Is there indeed a preference? If so, why?

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closed as unclear what you're asking by rg255, fileunderwater, Satwik Pasani, Chris, WYSIWYG Feb 19 '14 at 10:55

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question.If this question can be reworded to fit the rules in the help center, please edit the question.

Can you specify which recipes you mean? I am aware of a number of polymerases like Pfu which prefer $ MgSO_4 $. I haven't found a reference for that now, but its probably the same: The chloride ion interferes with the enzymes reaction. – Chris Feb 18 '14 at 17:38

My guess is its the solubility properties of the anions.

Chloride ions can precipitate with some metals that might appear in a complicated buffer or medium. And yes they could even compete with enzyme binding. Sulfate will remain in solution with just about anything.

There are exceptions, but if you're making a buffer you're probably going to do better if you use the general solubility rules.

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Are you sure about the insoluble chloride salts? I recall only a handfull of them, mostly with ions, which are not common in cells like titanium or silver. For sulphate I agree completely. – Chris Feb 18 '14 at 18:31
Although calcium sulphate is only sparingly soluble. – Alan Boyd Feb 18 '14 at 20:44
added a link... this is chem 101 so nearly every book has a mention of some form of counter-ion solubility rules. – shigeta Feb 18 '14 at 23:21
@AlanBoyd A number of sulphates is nearly insoluble. – Chris Feb 19 '14 at 6:42
@shigeta Thats a good link, thanks for it. – Chris Feb 19 '14 at 8:40

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