Cresol Red

Cresol red (full name: o-cresolsulfonephthalein)^[1] is a triarylmethane dye frequently used for monitoring the pH in aquaria.

Cresol red (pH indicator)
below pH 7.2		above pH 8.8
7.2	⇌	8.8

Cresol Red

Names
Preferred IUPAC name 3,3-Bis(4-hydroxy-3-methylphenyl)-2,1λ6-benzoxathiole-1,1(3H)-dione
Identifiers
CAS Number	1733-12-6 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:86218 N
ChemSpider	65818 Y
ECHA InfoCard	100.015.513
PubChem CID	73013
UNII	839K2R4B8K Y
CompTox Dashboard (EPA)	DTXSID8061929
InChI InChI=1S/C21H18O5S/c1-13-11-15(7-9-18(13)22)21(16-8-10-19(23)14(2)12-16)17-5-3-4-6-20(17)27(24,25)26-21/h3-12,22-23H,1-2H3 Y Key: OBRMNDMBJQTZHV-UHFFFAOYSA-N Y InChI=1/C21H18O5S/c1-13-11-15(7-9-18(13)22)21(16-8-10-19(23)14(2)12-16)17-5-3-4-6-20(17)27(24,25)26-21/h3-12,22-23H,1-2H3 Key: OBRMNDMBJQTZHV-UHFFFAOYAD
SMILES Cc1cc(ccc1O)/C(=C/2C=CC(=O)C(=C2)C)c3ccccc3OS(O)=O
Properties
Chemical formula	C21H17NaO5S
Molar mass	382.43 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Molecular biology

Cresol red can be used in many common molecular biology reactions in place of other loading dyes. Cresol Red does not inhibit Taq polymerase to the same degree as other common loading dyes.

Color marker

Cresol red can also be used as an electrophoretic color marker to monitor the process of agarose gel electrophoresis and polyacrylamide gel electrophoresis. In a 1% agarose gel, it runs approximately at the size of a 125 base pair (bp) DNA molecule (it depends on the concentration of buffer and other component). Bromophenol blue and xylene cyanol can also be used for this purpose.