Skip to content
Login Register

#phenol red

2 public questions tagged with this topic.

Animal Tissue Culture 1

Phenol red in culture media is used as:

Visual pH monitoring without invasive electrodes that breach sterility risking bacterial contamination is accomplished via chemical indicator phenol red also called phenolsulfonphthalein, molecular weight 354.38 daltons, pKa 7.9 at 37°C making transition range 6.8 to 8.2 overlapping physiological pH of culture. Structure triphenylmethane dye exists in equilibrium between protonated yellow form absorbing maximally 430 nanometers and deprotonated red anionic form with extensive conjugated quinone system absorbing 560 nanometers, isosbestic point near 480 nanometers. At physiological pH mixture appears pink to red due to presence both forms allowing quick visual assessment under phase contrast microscope without opening dish lid to preserve sterility and gas phase. Concentration optimized five to fifteen milligrams per liter provides visible color intensity while minimizing potential estrogenic activity because phenolic ring structurally similar to 17-beta estradiol aromatic A ring can bind estrogen receptor alpha ligand binding domain with low affinity Kd micromolar stimulating proliferation of estrogen responsive cell lines MCF-7 breast cancer and affecting reporter assays for endocrine disruptors.

Ref: Freshney 7th ed phenol red pKa 7.9 indicator nontoxic; Sigma media phenolsulfonphthalein yellow red transition estrogenic caution.

View Details
Basic Applied Biology

Phenol red in culture media acts as:

Phenol red chemically phenolsulfonphthalein, sulfonephthalein class dye, serves as visual pH indicator deliberately incorporated at 5 to 15 mg per L in many mammalian culture media including Dulbecco Modified Eagle Medium, RPMI 1640 and Minimum Essential Medium to allow non-invasive monitoring of acid-base status. Color transition results from protonation equilibrium with pKa approximately 7.9 at 37 Celsius and ionic strength of media: acidic protonated form absorbs at 430 nanometer appearing yellow below pH 6.8, partially deprotonated neutral form appears orange-red around pH 7.4 physiological condition, fully deprotonated di-anion absorbs at 560 nanometer appearing fuchsia-purple above pH 8.2 alkaline indicating CO2 deficiency or ammonia accumulation. Rapid yellowing suggests lactate build-up from glycolysis or bacterial contamination producing acids. Although generally considered non-toxic at standard concentrations, studies by Berthois et al. 1986 revealed weak estrogenic activity via binding to estrogen receptor, stimulating proliferation of MCF-7 breast cancer cells, prompting development of phenol red-free formulations for endocrine research. No nutritional, antibiotic or growth factor role exists; sole function remains optical pH sentinel preventing hidden acidosis harming viability.

Ref: Freshney Ch indicators; Berthois et al. Proc Natl Acad Sci USA 1986 phenol red estrogen; NCBI media formulation guide.

View Details