Tris
IUPAC name	2-Amino-2-hydroxymethyl-propane-1,3-diol
Other names	TRIS, Tris, Tris base, Tris buffer, TrizmaTM, Trisamine, THAM, Tromethamine, Trometamol, Tromethane
Identifiers
CAS number	[77-86-1]
RTECS number	TY2900000
SMILES	C(C(CO)(CO)N)O
Properties
Molecular formula	C4H11NO3
Molar mass	121.14 g mol-1
Appearance	White crystalline powder
Melting point	>175-176°C (448-449 K)
Boiling point	219°C (492 K)
Solubility in water	~50 g/100 ml (25°C) in water
Acidity (pKa)	8.1
Hazards
MSDS	External MSDS
Main hazards	Irritant
NFPA 704	0 2 0
R-phrases	R36, R37, R38.
S-phrases	S26, S36.
Flash point	Non-flammable
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

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 pK_a declines approximately 0.03 units per degree Celsius rise in temperature.
• Silver-containing single-junction pH electrodes (e.g., silver chloride electrode) 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.

References

1. ^ Gomori, G., Preparation of Buffers for Use in Enzyme Studies. Methods Enzymology., 1, 138-146 (1955).
2. ^ Sheldon B. Markofsky “Nitro Compounds, Aliphatic” Ullmann's Encyclopedia of Industrial Chemistry 2002 by Wiley-VCH, Wienheim, 2002. DOI: 10.1002/14356007.a17_401.