Imidazole lyophilization

Solid state 15N NMR has also been used103 to study lyophilized powders of 15N-enriched histidine and imidazole, prepared from aqueous solutions with pH ranging... 

Buffers for lyophilized formulations need additional consideration. Some buffers like sodium phosphate can crystallize out of the protein amorphous phase during freezing resulting in rather large shifts in pH. Other common buffers such as acetate and imidazole should be avoided since they may sublime or evaporate during the lyophilization process, thereby shifting the pH of formulation during lyophilization or after reconstitution. 

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