Tris
Tris is an abbreviation of the organic compound known as tris(hydroxymethyl)aminomethane, with the formula (HOCH2)3CNH2. Tris is extensively used in biochemistry and molecular biology.[1] In biochemistry, tris is widely used as a component of buffer solutions, such as in TAE and TBE buffer, especially for solutions of nucleic acids. It is a primary amine and thus undergoes the reactions associated with typical amines, e.g. condensations with aldehydes.
Buffering features
Tris has a pKa of 8.06, which implies that the buffer has an effective pH range between 7.0 and 9.2.
Buffer details
- The pKa declines approximately 0.03 units per degree Celsius rise in temperature.
- Silver-containing single-junction pH electrodes are incompatible with Tris (Ag-Tris precipitation clogs the junction). Double-junction electrodes are resistant to this problem, and non-silver containing electrodes are immune.
- It is toxic to mammalian cells.
- A common variant of tris (aka tris base) is tris-HCl, the acid salt. When titrated to a specific pH with the corresponding counter ion (OH- for tris-HCl, H+ for tris base) they are equivalent. However, the molecular weights are different and must be correctly accounted for in order to arrive at the expected buffer strength.
Preparation
Tris is prepared in two steps from nitromethane via the intermediate (HOCH2)3CNO2 . Reduction of the latter gives tris(hydroxymethyl)aminomethane.[2]
Uses
The useful buffer range for Tris (7-9) coincides with the typical physiological pH of most living things. This, and its low cost, make Tris one of the most common buffer elements in use in the biology/biochemistry lab.