Chemical Properties
Bromophenol Blue is pink or red powder, soluble in ethanol, benzene, ether and other organic solvents, slightly soluble in water, the aqueous solution is yellow, and blue-purple in alkaline solution. It is mainly used as an acid-base indicator, the pH discoloration range is 3.0 to 4.6, and the color changes from yellow to green to blue-violet.
Uses
Bromophenol blue is used as a tracking dye in electrophoresis, as a color marker in gel electrophoresis and polyacrylamide gel electrophoresis. As a biological stain, it plays an important role to stain proteins and nucleic acids. It acts an intermediate and an acid-base indicator in the pH range 3.0 to 4.6.
Definition
ChEBI: Bromophenol blue is 3H-2,1-Benzoxathiole 1,1-dioxide in which both of the hydrogens at position 3 have been substituted by 3,5-dibromo-4-hydroxyphenyl groups. It is used as a laboratory indicator, changing from yellow below pH 3 to purple at pH 4.6, and as a size marker for monitoring the progress of agarose gel and polyacrylamide gel electrophoresis. It has also been used as an industrial dye. It has a role as a two-colour indicator, an acid-base indicator and a dye. It is a sultone, an arenesulfonate ester, a 2,1-benzoxathiole, a member of phenols and an organobromine compound.
Preparation
Bromophenol Blue is prepared by slow addition of excess bromine to a hot solution of phenolsulfonphthalein in glacial acetic acid.
Synthesis steps: Dissolve phenol red in glacial acetic acid, add a solution of bromine in glacial acetic acid with stirring, pour into 60°C hot water after stirring for a few minutes, cool to room temperature, and place overnight. Filter, wash the filter cake with glacial acetic acid and benzene in turn, and air dry to obtain bromophenol blue.
Biotechnological Applications
Bromophenol blue is present as a sulfonated hydroxyquinone in acidic aqueous solutions. It is also known as tetrabromophenolsulfonphthalein. Bromophenol Blue is a pH indicator and a dye appears a strong blue color. It has a slightly negative charge and will migrate in the same direction as DNA, allowing the user to monitor the progress of molecules moving through the gel. The rate of migration varies with gel composition.
Bromophenol Blue is used as a tracking dye in DNA, RNA (agarose) and protein (polyacrylamide) gel electrophoresis. It has been used in the preparation of protein samples for western blotting analysis. Bromophenol blue migrates at approximately the same rate as 300-500bp DNA in agarose gel and at the buffer front in protein polyacrylamide gels.It has also been known for its use as a vital stain to probe the blood-brain barrier.
Purification Methods
Crystallise the dye from *C6H6 or Me2CO/AcOH, and dry it in air. It is an indicator: at pH 3.0 it is yellow and it is purple at pH 4.6. [Beilstein 19/3 V 458.]
