Dichlorphenolindophenol

2,6-dichlorophenolindophenol, ( DCPIP ) is a blue chemical compound used as a redox dye. Oxidized DCPIP is blue, reduced DCPIP is colorless.

The rate of photosynthesis can be measured by the rate at which this dye is broken down (reduced) when exposed to light in a photosynthetic system. This reaction is reversible, as colorless DCPIP can be reoxidized to blue. It is often used in measurements of the electron transport chain in plants because of its higher [affinity] for electrons than ferredoxin. For example, it is possible to compare rates of photosynthesis with DCPIP. Due to the reductions that occur during the light reactions, DCPIP can be substituted for NADPH, the final electron carrier in the light reactions. The light reactions will reduce the DPIP and turn it colorless. As DCPIP is reduced and becomes colorless, the following increase in light transmittance can be measured by a spectrophotometer.



DCPIP
DCPIP is a redox dye commonly used as a monitor of the light reactions in photosynthesis because it is an electron acceptor that is blue when oxidized and colourless when reduced. DPIP is commonly used as a substitute for NADP+. The dye changes color when it is reduced, due to its chemical structure. The nitrogen atom in the center of the molecule is the atom that accepts electrons, and it changes the double N-C bond to a single bond, which forces bonds between carbons in the entire left ring to change. This microscopic shift in the DCPIP structure causes the macroscopic change in colour, from dark blue to colourless.

The rate of photosynthesis light-dependent reaction can be measured with this property of DCPIP, because one of the stages of the light reaction is an electron transport chain that normally ends with the reduction of NADP+. When DCPIP is present, it also gets reduced by the light reaction. The amount of DCPIP reduced can be found by measuring the solution's light transmittance with a spectrophotometer.

Using DCPIP to determine the concentration of ascorbic acid or Vitamin C in a solution.

DCPIP is commonly used as an indicator for Vitamin C. If vitamin C, which is a good reducing agent is present, the blue dye, which turns pink in acid conditions and is reduced to a colourless compound by ascorbic acid.


 * DCPIP (blue) + H+   -->    DCPIPH (pink)
 * DCPIPH (pink) + VitC --> DCPIPH2 (colourless)
 * C6H8O6 + C12H7NCl2O2 --> C6H6O6 + C12H9NCl2O2

In a titration, when all the ascorbic acid in the solution has been used up, there will not be any electrons available to reduce the DCPIPH and the solution will remain pink due to the DCPIPH. The end point is a pink colour that persists for 10 seconds or more.