Hydroxyapatite

Hydroxyapatite for TI-CHA chromatography is a form of calcium phosphate, formed by high temperature calcination of porous spherical material, is a pure inorganic chromatography medium specially designed for the purification of biomolecules, through a variety of mechanisms with biomolecules.

1. the phosphate root is negatively charged, and can be combined with positively charged biomolecules by the formation of ionic bonds;
2. the calcium ions can be combined by the formation of metal chelating bondsbinding to biomolecules with free carboxyl groups, imidazole rings, and other electron donors;
3. hydroxyl groups on hydroxyapatite can bind biomolecules by forming hydrogen bonds with hydroxyl groups on biomolecules.

Spherical hydroxyapatite calcined at lower temperatures has smaller pores and a relatively large specific surface area, known as type A hydroxyapatite, which has a higher binding capacity for smaller molecular weight biomolecules and is mainly used to purify most proteins (molecular weights below 100 kd). Type B hydroxyapatite calcined at a higher temperature forms larger internal pores, which have a higher binding load for larger biomolecules such as antibodies and nucleic acids, making it suitable for the purification of antibodies. Meanwhile, type B has a greater retention of nucleic acids, and is able to discriminate between single- and double-stranded, super-helical, and other kinds of structural DNA, and thus is also suitable for the purification of nucleic acids.

Since the crystal structures formed at different temperatures vary, the binding specificity for biomolecules is significantly different.