View source for Phenol red

{{Use dmy dates|date=December 2021}}
{{chembox
| Watchedfields = changed
| verifiedrevid = 477507749
| Name = Phenol red
| ImageFile = Phenol-red-zwitterionic-form-2D-skeletal.png
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| ImageName = Phenol red
| ImageFile1 = Phenol-red-zwitterionic-form-3D-balls.png
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| ImageName1 = Phenol red
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 143-74-8
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = I6G9Y0J1OJ
| PubChem = 4766
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 258921
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 4602
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 31991
| SMILES = O=S2(=O)OC(c1ccccc12)(c3ccc(O)cc3)c4ccc(O)cc4
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI=1S/C19H14O5S/c20-15-9-5-13(6-10-15)19(14-7-11-16(21)12-8-14)17-3-1-2-4-18(17)25(22,23)24-19/h1-12,20-21H
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = BELBBZDIHDAJOR-UHFFFAOYSA-N
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|Section2={{Chembox Properties
| C=19 | H=14 | O=5 | S=1
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|Section6={{Chembox Pharmacology
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'''Phenol red''' (also known as '''phenolsulfonphthalein''' or '''PSP''') is a [[pH indicator]] frequently used in [[cell biology]] laboratories.

==Chemical structure and properties==
Phenol red exists as a red crystal that is stable in air. Its solubility is 0.77 grams per liter (g/L) in water and 2.9&nbsp;g/L in [[ethanol]].<ref name=merck>''[[Merck Index]]'', 11th ed., 7213 Phenolsulfonphtalein</ref> It is a [[weak acid]] with [[pKa|p''K''<sub>a</sub>]] = 8.00 at {{convert|20|C}}.

A solution of phenol red is used as a [[pH]] indicator, often in cell culture. Its color exhibits a gradual transition from yellow ([[Lambda max|λ<sub>max</sub>]] = 443&nbsp;nm<ref name="Saha2015">{{cite journal|last1= Saha|first1=U.|last2= Mukherjea|first2=K. K.|title= Development of a multifunctional biomimicking L-cysteine based oxovanadium(IV) complex: synthesis, DFT calculations, bromo-peroxidation and nuclease activity|journal= RSC Advances|volume= 5|issue= 114|year= 2015|pages= 94462–94473|doi= 10.1039/C5RA19585C|bibcode=2015RSCAd...594462S }}</ref>) to red (λ<sub>max</sub> = 570&nbsp;nm<ref name="Mills2011">{{cite journal|last1= Mills|first1=A.|last2= Skinner|first2=G. A.|title= A novel 'fizziness' indicator|journal= The Analyst|volume= 136|issue= 5|year= 2011|pages= 894–896|doi= 10.1039/c0an00610f|pmid=21210046|bibcode= 2011Ana...136..894M}}</ref>) over the pH range 6.8 to 8.2. Above pH 8.2, phenol red turns a bright pink ([[fuchsia (color)|fuchsia]]) color.<ref name=Merck>''[[Merck Index]]'', 13th ed., 7329 Phenolsulfonphthalein</ref><ref name=Beilstein>Beilstein 5-19-03-00457</ref>
{{pH_indicator template|indicator_name=Phenol red|low_pH=6.8|high_pH=8.2|low_pH_color=yellow|high_pH_color=fuchsia|high_pH_text=white}}

In [[crystal]]line form, and in solution under very acidic conditions (low pH), the compound exists as a [[zwitterion]] as in the structure shown above, with the [[sulfate]] group negatively charged, and the [[ketone]] group carrying an additional proton. This form is sometimes symbolically written as {{chem|H|2|+|PS|−}} and is orange-red. If the pH is increased (p''K''<sub>a</sub> = 1.2), the proton from the ketone group is lost, resulting in the yellow, negatively charged ion denoted as HPS<sup>−</sup>. At still higher pH (p''K''<sub>a</sub> = 7.7), the [[phenol]]'s [[hydroxy group]] loses its proton, resulting in the red ion denoted as PS<sup>2−</sup>.<ref>{{ cite journal | author = Tamura, Z. | author2 = Maeda M. | title = Differences between phthaleins and sulfonphthaleins | journal = Yakugaku Zasshi | date = 1997 | volume = 117 | issue = 10–11 | pages = 764–770 | language = ja | pmid = 9414589 | doi = 10.1248/yakushi1947.117.10-11_764 | doi-access = free }}</ref>

In several sources, the structure of phenol red is shown with the [[sulfur]] atom being part of a cyclic group, similar to the structure of [[phenolphthalein]].<ref name=merck/><ref>{{ cite web | url = https://pubchem.ncbi.nlm.nih.gov/compound/4766 | title = Phenolsulfonphthalein | work = [[PubChem]] | publisher = NIH }}</ref> However, this cyclic structure could not be confirmed by [[X-ray crystallography]].<ref>{{ cite journal | author = Yamaguchi, K. | author2 = Tamura, Z. | author3 = Maeda, M. | title = Molecular Structure of the Zwitterionic Form of Phenolsulfonphthalein | journal = Analytical Sciences | date = 1997 | volume = 13 | issue = 3 | pages = 521–522 | doi = 10.2116/analsci.13.521 | doi-access = free }}</ref>

Several indicators share a similar structure to phenol red, including [[bromothymol blue]], [[thymol blue]], [[bromocresol purple]], [[thymolphthalein]], and phenolphthalein. (A table of other common chemical indicators is available in the article on [[pH indicators]].)

== Uses ==

=== Phenolsulfonphthalein test ===
Phenol red was used by [[Leonard Rowntree]] and John Geraghty in the '''phenolsulfonphthalein test''' to estimate the overall blood flow through the [[kidney]] in 1911.<ref>{{cite journal |last1=GERAGHTY |first1=J. T. |last2=ROWNTREE |first2=L. G. |title=The Phenolsulphonephthalein Test for Estimating Renal Function |journal=Journal of the American Medical Association |date=2 September 1911 |volume=LVII |issue=10 |pages=811 |doi=10.1001/jama.1911.04260090033014|url=https://zenodo.org/record/1836345 }}</ref> It was the first test of kidney function and was used for almost a century but is now obsolete.

The test is based on the fact that phenol red is excreted almost entirely in the urine. Phenol red solution is administered [[intravenous]]ly; the [[urine]] produced is collected. By measuring the amount of phenol red excreted [[colorimetry|colorimetrically]], kidney function can be determined.<ref>{{ cite encyclopedia | encyclopedia = [[Encyclopædia Britannica]] | url = http://www.britannica.com/eb/article-9059617/phenolsulfonphthalein-test | title = Phenolsulfonphthalein Test }}</ref>

=== Indicator for cell cultures ===
[[File:Phenol red pH 6,0 - 8,0.jpg|thumb|Phenol red, 40&nbsp;μM: colors in cell culture medium at a pH range from 6.0 to 8.0.]]

Most [[biological tissue|living tissues]] prosper at a near-neutral pH—that is, a pH close to 7. The pH of [[blood]] ranges from 7.35 to 7.45, for instance. When [[Cell (biology)|cells]] are grown in [[tissue culture]], the medium in which they grow is held close to this physiological pH. A small amount of phenol red added to this growth medium will have a pink-red color under normal conditions. Typically, 15&nbsp;mg/L are used for cell culture.

In the event of problems, waste products produced by dying cells or overgrowth of contaminants will cause a change in pH, leading to a change in indicator color. For example, a culture of relatively slowly dividing [[mammal]]ian cells can be quickly overgrown by [[bacteria]]l contamination. This usually results in an [[acid]]ification of the medium, turning it yellow. Many [[biologist]]s find this a convenient way to rapidly check on the health of tissue cultures. In addition, the waste products produced by the mammalian cells themselves will slowly decrease the pH, gradually turning the solution orange and then yellow. This color change is an indication that even in the absence of contamination, the medium needs to be replaced (generally, this should be done before the medium has turned completely orange).

Since the color of phenol red can interfere with some [[spectrophotometry|spectrophotometric]] and [[fluorimetry|fluorescent]] assays, many types of tissue culture media are also available without phenol red.

=== Estrogen mimic ===
[[File:Swimming Pool Test Kit.jpg|thumb|240x240px|A commercial test kit for swimming pools with phenol red and an [[Tolidine|orthotolidine]] [[PH indicator|indicator]] solution ]]
Phenol red is a weak [[estrogen]] mimic, and in cell cultures can enhance the growth of cells that express the estrogen receptor.<ref>{{ cite journal | author = Berthois, Y. | author2 = Katzenellenbogen, J. A. | author3 = Katzenellenbogen, B. S. | title = Phenol red in tissue culture media is a weak estrogen: Implications concerning the study of estrogen-responsive cells in culture | journal = Proceedings of the National Academy of Sciences of the United States of America | date = 1986 | volume = 83 | issue = 8 | pages = 2496–2500 | pmid = 3458212 | pmc = 323325 | doi=10.1073/pnas.83.8.2496| bibcode = 1986PNAS...83.2496B | doi-access = free }}</ref> It has been used to induce [[ovaries|ovarian]] [[epithelial]] cells from post-menopausal women to [[differentiation (cellular)|differentiate]] into cells with properties of [[oocyte]]s (eggs), with potential implications for both [[fertility treatment]] and stem cell research.<ref>{{ cite journal | author = Bukovsky, A. | author2 = Svetlikova, M. | author3 = Caudle, M. R. | title = Oogenesis in Cultures Derived from Adult Human Ovaries | journal = Reproductive Biology and Endocrinology | date = 2005 | volume = 3 | issue = 5 | page = 17 | doi = 10.1186/1477-7827-3-17 | pmid = 15871747 | pmc = 1131924 | url = http://www.rbej.com/content/pdf/1477-7827-3-17.pdf | doi-access = free }}</ref>

=== Use in swimming pool test kits ===
Phenol red, sometimes labelled with a different name, such as "Guardex Solution #2", is used as a pH indicator in home [[swimming pool]] test kits.<ref>[https://web.archive.org/web/20040326143901/http://www.mnsu.edu/bldgserv/msds/guardex_solution_2.pdf Guardex Solution 2 – Phenol Red Material Safety Data Sheet]</ref>

[[Chlorine]] can result in the bleaching of the dye in the absence of [[thiosulfate]] to inhibit the oxidizing chlorine. High levels of [[bromine]] can convert phenol red to [[bromophenol red]] (dibromophenolsulfonephthalein, whose lowered [[Acid dissociation constant|p''K''<sub>a</sub>]] results in an indicator with a range shifted in the acidic direction – water at pH 6.8 will appear to test at 7.5). Even higher levels of bromine (>20 ppm) can result in the secondary conversion of bromophenol red to [[bromophenol blue]] with an even lower p''K''<sub>a</sub>, erroneously giving the impression that the water has an extremely high pH despite being dangerously low.<ref>[http://easypools.com.au/pool-maintenance/131-effect-of-bromine-on-phenol-red-in-ph-tests?format=pdf Effect of Bromine on Phenol Red in pH Tests]</ref>

==References==
{{commons category}}
{{reflist}}

==External links==
*[http://video.google.com/videoplay?docid=9209311783284955887 Video of phenol red activity demonstration and medium preparation]

{{Purinergics}}

[[Category:PH indicators]]
[[Category:Triarylmethane dyes]]
[[Category:4-Hydroxyphenyl compounds]]
[[Category:Benzenesulfonates]]