The specific pI of the target protein can be used to model the process around and the compound can then be purified from the rest of the mixture.
At high pH values, the net charge of most proteins is negative, where they bind to the positively-charged matrix in anion exchangers.
[4] For an amino acid with only one amine and one carboxyl group, the pI can be calculated from the mean of the pKas of this molecule.
[6] Glycine may exist as a zwitterion at the isoelectric point, but the equilibrium constant for the isomerization reaction in solution is not known.
The other example, adenosine monophosphate is shown to illustrate the fact that a third species may, in principle, be involved.
For instance, within the model proposed by Bjellqvist and co-workers, the pKs were determined between closely related immobilines by focusing the same sample in overlapping pH gradients.
[7] Some improvements in the methodology (especially in the determination of the pK values for modified amino acids) have been also proposed.
[8][9] More advanced methods take into account the effect of adjacent amino acids ±3 residues away from a charged aspartic or glutamic acid, the effects on free C terminus, as well as they apply a correction term to the corresponding pK values using genetic algorithm.
[10] Other recent approaches are based on a support vector machine algorithm[11] and pKa optimization against experimentally known protein/peptide isoelectric points.
The isoelectric points (IEP) of metal oxide ceramics are used extensively in material science in various aqueous processing steps (synthesis, modification, etc.).
The exact value can vary widely, depending on material factors such as purity and phase as well as physical parameters such as temperature.
[27] Mixtures of titania (TiO2) and zirconia (ZrO2) were studied and found to have an isoelectric point between 5.3–6.9, varying non-linearly with %(ZrO2).
[29] Thus, the isoelectric point is the value of pH at which the colloidal particle remains stationary in an electrical field.
Jolivet uses the intrinsic surface equilibrium constants, pK− and pK+ to define the two conditions in terms of the relative number of charged sites: For large ΔpK (>4 according to Jolivet), the predominant species is MOH while there are relatively few charged species – so the PZC is relevant.
For small values of ΔpK, there are many charged species in approximately equal numbers, so one speaks of the IEP.