phenol red dianion

What is phenol red dianion

Phenol red dianion is a widely used pH indicator and biological dye, known for its distinct color change in response to varying pH levels. It transitions from yellow (acidic conditions, pH < 6.8) to red (neutral, pH ~7.4) and finally to pink or magenta (alkaline conditions, pH > 8.2). This property makes it invaluable in cell culture media, where it helps monitor pH changes and ensure optimal growth conditions. Additionally, phenol red dianion is utilized in biochemical assays, diagnostic tests, and as a tracer in medical research. Its stability, sensitivity, and non-toxic nature have established it as a reliable tool in both laboratory and clinical settings.

Preparation Process: To prepare phenol red dianion, dissolve phenol red (C19H14O5S) in a polar aprotic solvent like dimethyl sulfoxide (DMSO) or dimethylformamide (DMF). Add a strong base, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), in excess (≥2 equivalents) to deprotonate both phenolic hydroxyl groups. Stir the mixture at room temperature for 1–2 hours until the solution turns deep red, indicating dianion formation. Monitor the reaction by UV-Vis spectroscopy (λmax ~ 560 nm for the dianion). Isolate the product by precipitation with a nonpolar solvent (e.g., diethyl ether) or via column chromatography. Dry under vacuum to obtain the pure dianion.

Usage Scenarios: Phenol red dianion is primarily used as a pH indicator in biological and chemical applications due to its distinct color change from yellow (acidic, pH <6.8) to red (neutral, pH ~7.4) and pink (basic, pH >8.2). It is widely employed in cell culture media to monitor pH changes, ensuring optimal growth conditions. In microbiology, it helps detect acid production in fermentation tests. Additionally, it serves as a tracer in environmental studies to track water flow and contamination. Its low toxicity and high visibility make it useful in physiological experiments, such as assessing kidney function or measuring extracellular pH in tissues.

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