What is the affect of pH on crystallization process ?

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Elias Nakouzi

Hello Farah.

The answer depends on the specific system you are working with. For example, calcium carbonate dissolves in acidic solutions, but can re-crystallize if you raise the pH again.

Giorgio Giardina

HI Farah,

what are you trying to crystallize? Small molecules or macromolecules (proteins, DNA ect)? pH is in general one of the many parameters that you should try to optimize, for the obviuos reason that protonation or deprotonation of functional groups will affect the ability of the molecules to pack or not in a certain space group. But please be more precise if you what more useful answers.

Giorgio

Farah Bassam Alqadi

Thanks all...

I am trying to make crystallization for vanadyl complexes...

I had single crystals for other complexes before , but the same general methods for crystallization didn't work for vanadyl complexes , it gave me micro crystals ... So I am tryiny to find a way for a single big good X-ray crystal .

Ok Farah,

that's a bit more information, pH will certainly affect the dissociation constant of your complex. However, if you are getting small crystals your not so far. I don't know which crystallization method you are using, but to go from many small crystals to few big ones, you need to slow-down the nucleation process, that is when your crystals start to form the initial nuclei which will then grow into visible crystals. Lower the complex concentration, and/or the precipitant concentration, and/or the temperature (try 4˚C).