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Which buffer will be suitable for NHS-ester coupling if I need a pH 5.5-6.5

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Biotech78:
Hi
I know the optimal pH for NHS-ester (activated by EDC/NHS) crosslinking with amines is around 8. But I have a specific need where I need to conduct this experiment at slightly acidic pH.
I also need MgCl2 and NaCl in the buffer. In other words, I am looking for a PBS pH below 7.

Borek:

--- Quote from: Biotech78 on February 12, 2024, 02:32:20 PM ---I am looking for a PBS pH below 7.
--- End quote ---

PBS is a poor choice for these pH. Not to mention the fact Mg2+ is a sure way to interfere with phosphates and to precipitate.

Perhaps look for some other buffer? Citrate?

Babcock_Hall:
I suggest looking into Good's buffers, such as MES, which has a pKa near 6.  Many of these buffers are non-nucleophilic (MES is a tertiary amine), which means that they won't compete with the intended nucleophile in a coupling reaction.

Biotech78:
MES with 150mM NaCl and 1mM MgCl2 is what I think will be most suitable in this case. I can test pH 5.5 to 6.5

Biotech78:
Appears that I don't have MES readily available. What could be other options? I need a pH range 5.5-6.5, want to add NaCl (100-150mM) and 1mM MgCl2. I know NHS ester crosslinking is most efficient around pH 8 but I have a specific need where I have to conduct experiment at slightly acidic pH

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