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|Section2= |Section6= }} 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 g/l in ethanol.〔''Merck Index'', 11th ed., 7213 Phenolsulfonphtalein〕 It is a weak acid with pKa = 8.00 at . A solution of phenol red is used as a pH indicator: its color exhibits a gradual transition from yellow to red over the pH range 6.8 to 8.2. Above pH 8.2, phenol red turns a bright pink (fuchsia) color.〔''Merck Index'', 13th ed., 7329 Phenolsulfonphthalein〕〔Beilstein 5-19-03-00457〕 This solution contains a pH indicator which helps in monitoring of the pH changes in the cell culture. It will change from red to yellow when the pH value decreases. In crystalline 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 H2+PS− and is orange-red. If the pH is increased (pKa = 1.2), the proton from the ketone group is lost, resulting in the yellow, negatively charged ion denoted as HPS−. At still higher pH (pKa = 7.7), the phenol's hydroxide group loses its proton, resulting in the red ion denoted as PS2−. 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.〔〔(【引用サイトリンク】 Phenolsulfonphthalein )〕 However, this cyclic structure could not be confirmed by X-ray crystallography. 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.) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「phenol red」の詳細全文を読む スポンサード リンク
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