Bromophenol blue

Bromophenol blue, chemically known as 3′,3″,5′,5″-tetrabromophenolsulfonphthalein (BPB), is a versatile compound widely used in scientific research and various applications due to its color-changing properties under different pH conditions. It serves as a pH indicator, an electrophoretic color marker, and a dye[1].

pH Indicator

As a pH indicator, bromophenol blue exhibits a useful range between pH 3.0 and 4.6. It changes color from yellow at pH 3.0 to blue at pH 4.6, with this reaction being reversible. This property makes it valuable for monitoring pH changes in various chemical and biological experiments[1].

Electrophoretic Color Marker

In the context of agarose gel electrophoresis and polyacrylamide gel electrophoresis, bromophenol blue is employed as a color marker. Due to its slight negative charge at moderate pH levels, it migrates in the same direction as DNA or proteins during electrophoresis. The migration rate of bromophenol blue varies depending on the gel density and buffer composition. For instance, in a typical 1% agarose gel using either 1X TAE or TBE buffer, bromophenol blue migrates at a rate comparable to a DNA fragment of approximately 300 base pairs. In a 2% agarose gel, it corresponds to around 150 base pairs[1].

Dye

Bromophenol blue also finds use as a dye. At neutral pH, it absorbs red light most strongly and transmits blue light, with its peak absorbance at 590 nm occurring at a basic pH of 12. Consequently, solutions of the dye appear blue. At low pH, the dye absorbs ultraviolet and blue light most strongly, making the solution appear yellow. Interestingly, at pH 3.6, which is within its transition range, bromophenol blue exhibits a characteristic green-red color, with the apparent color shifting based on the concentration or path length through which the solution is observed. This phenomenon is known as dichromatic color, and bromophenol blue has the highest known value of Kreft's dichromaticity index, indicating a significant change in color hue with variations in thickness or concentration of the observed sample[1].

In summary, bromophenol blue's multifunctional properties as a pH indicator, electrophoretic color marker, and dye, along with its unique color-changing abilities, make it a valuable tool in scientific research and various applications.

Citations:

[1] https://en.wikipedia.org/wiki/Bromophenol_blue

[2] https://www.sigmaaldrich.com/US/en/product/sial/b0126

[3] https://pubchem.ncbi.nlm.nih.gov/compound/Bromophenol-Blue

[4] https://www.abmgood.com/bromophenol-blue-g114.html

[5] https://www.thermofisher.com/order/catalog/product/A18469.18

[6] https://www.emdmillipore.com/US/en/product/Bromophenol-blue,MDA_CHEM-108122

[7] https://www.caymanchem.com/product/14331

[8] https://lab.honeywell.com/shop/bromophenol-blue-32712