I didn't see the figure, but I would not be surprised if cacodylate donates a methyl group to make O-methylserine. Diethylene glycol is quite a bit bigger than a methyl though.
Cacodylate is quite labile and undergoes radiolysis. It should probably not be used for crystallization. If you either grow in a different buffer or harvest into a different buffer before diffraction data collection, what does the electron density map look like? Jim
