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The isoelectric point (pI, pH(I), IEP), is the pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean. The standard nomenclature to represent the isoelectric point is pH(I). [1] However, pI is also used. [2] For brevity, this article uses pI.
From the titration of protonatable group, one can read the so-called pK a 1 ⁄ 2 which is equal to the pH value where the group is half-protonated (i.e. when 50% such groups would be protonated). The pK a 1 ⁄ 2 is equal to the Henderson–Hasselbalch pK a (pK HH a) if the titration curve follows the Henderson–Hasselbalch equation. [14]
[72] [73] [74] The isoelectric point of a given molecule is a function of its pK values, so different molecules have different isoelectric points. This permits a technique called isoelectric focusing , [ 75 ] which is used for separation of proteins by 2-D gel polyacrylamide gel electrophoresis .
The two dimensions that proteins are separated into using this technique can be isoelectric point, protein complex mass in the native state, or protein mass. [citation needed] The separation by isoelectric point is called isoelectric focusing. Thereby, a pH gradient is applied to a gel and an electric potential is applied across the gel, making ...
The iso-electric point is the pH value at which the zeta potential is approximately zero. At a pH near the iso-electric point (± 2 pH units), colloids are usually unstable; the particles tend to coagulate or flocculate. Such titrations use acids or bases as titration reagents. Tables of iso-electric points for different materials are available ...
A typical titration curve of a diprotic acid, oxalic acid, titrated with a strong base, sodium hydroxide.Both equivalence points are visible. Titrations are often recorded on graphs called titration curves, which generally contain the volume of the titrant as the independent variable and the pH of the solution as the dependent variable (because it changes depending on the composition of the ...
Isoelectric focusing (IEF), also known as electrofocusing, is a technique for separating different molecules by differences in their isoelectric point (pI). [ 1 ] [ 2 ] It is a type of zone electrophoresis usually performed on proteins in a gel that takes advantage of the fact that overall charge on the molecule of interest is a function of the ...
For this reason, phosphate esters are often quoted with a single pKa, but the ionization is for the second deprotonation, typical pK a 6-6.5 HOPO 2-OR + H 2 O ↔ OPO 2 2-OR + H 3 O + The quoted pK a s for 5'-AMP are 0.9, 3.8, 6.1, and should be attributed as pKa 1 = 0.9 - first phosphoric ester ionization pKa 2 = 3.8 - deprotonation from ...