The reason for the odd K/Na combination is solubility - mixed phosphate is more soluble than either of the individual ones.
I try to avoid high phosphate conditions as the Plague. It's great for molecular biology but horrible for crystallization because phosphate + a variety of other ions = lovely salt crystals. It all usually ends up in tears. If you absolutely must make phosphate buffers - just open up any basic practical biochemistry book, there are standard ratios (both by weight and by volumes of molar solutions) that produce specified pH in a wide range. Artem > Dear all, > > Quite a few crystallisation conditions in the screens feature > 'sodium/potassium phosphate'. I'm curious to know why such a Na/K mix > is there. As the pH is mostly determined by the (H2PO4)- to (HPO4)2- > ratio, is there such a need to have both cations? If so, is the Na to > K ratio important? > > On the more practical side of things, if you want to explore an > initial hit based on sodium/potassium phosphate, how would you go > about it - e.g. what phosphate buffers would you make and at what > ratio would you mix them? > > Thanks in advance, > Geoffrey Kong >
