Of Phenol Red

Ltease test. The enzyme uretwe hydrolyses urea to ammonium carbonate (p. 519). The reaction is sp ific and is frequently used for solu tions of urea to which the biuret test cannot be applied. Add about 5 drops of phenohred to o 2 g. of urea dissolved in 5 ml. of water. To this yellow solution, add 0 2 g. of jack bean meal suspended in 2 ml. of water containing. also 5 drops of phenol-red. The colour changes to red as the solution becomes alkaline. 

Place about 0 2 g. of jack-bean meal in a test-tube, add 2 ml. of water and about 5 drops of phenol-red. Mix thoroughly and allow the faintly yellow solution to stand while the urea solution is being made up. 

Phenolsulphonephthalein (phenol red). Mix 10 g. of o-sulpho-benzoic anhydride (Section VIII,9), 14 g. of pure phenol and 10 g. of freshly fused zinc chloride in a small conical flask. Place a glass rod in the flask and heat gently over a flame to melt the phenol. Then heat the flask containing the well-stirred mixture in an oil bath at 135-140° for 4 hours. Stir from time to time, but more frequently during the first hour if the mixture froths unduly, remove the flask from the bath, cool and then resume the heating. When the reaction is complete, add 50 ml. of water, allow the water to boil and stir to disintegrate the product. Filter the crude dye with suction and wash it well with hot water. Dissolve the residue in the minimum volume of warm (60°) 20 per cent, sodium hydroxide solution, filter, and just acidify the filtrate with warm dilute hydrochloric acid (1 1). Filter the warm solution, wash with water, and dry upon filter paper. The yield of phenol red (a brilliant red powder) is 11 g. 

Add 2-3 drops of phenol red indicator. The solution should be red in color. Place a piece of white paper under the beaker to view the color of the solution better. 

Figure 3 Bromination of phenol red by Laminaria digitata in seawater (see Wever). Beakers from left to right 1) seawater plus phenol red, 2) same as 1 plus H202, 3) same as 1 plus Laminaria 4) same as 2 plus Laminaria Phenol red is converted by the bromination.

Ambrosia elatir, Euphorbia leachates of phenolic red d nodule size no. red d ... 

As the pH increases, the concentration of the base form of phenol red increases, resulting in increased energy transfer from eosin to phenol red and in a diminished fluorescence intensity of eosin. Thus, changes in the absorption of phenol red as a function of pH are detected as a change in the fluorescence signal of eosin. 

The first pH sensor was developed at NIH (Bethesda, Maryland) and made use of phenol red as acid-base indicator, covalently bound to polyacrylamide microspheres10 such microspheres are contained inside a cellulose dialysis tubing (internal diameter 0.3 mm) connected to a 250 pm plastic fibre (Figure 2). The probe was inserted into either the tissue or the... 

Figure 19.24 The conjugation of phenol red to cBSA using the Mannich reaction.

Phenol red immobilized PVA membrane for an optical pH sensor is developed based on the same approach, since the molecular structure of phenol red is similar to that of phenolphthalein. Phenol red was first reacted with the formaldehyde to produce hydroxymethyl groups, and then it was attached to PVA membrane via the hydroxymethyl groups. The changes of spectra characteristics after immobilization, the ionic strength effects, response time, reproducibility and long-term stability of the sensor membrane are discussed by Z. Liu et al. [170],... 

Figure 10.12. Absorption spectra of Phenol Red and emission spectrum of Eosin as potential pH probe based on resonance energy transfer.

Suppose we have a pH indicator like Phenol Red whose absorption spectrum is pH-sensitivewith pKa = 7.6 (Figure 10.12). Phenol Red displays two distinct absorption spectra for protonated form (pH 2.5) and for unprotonated form (pH 10.4). One of the possible donors is an Eosin which displays an emission spectrum that overlaps with the absorption spectra of the protonated and unprotonated forms (acceptors) of Phenol Red (Figure 10.12). The critical distances for energy transfer (R0),(32) calculated from spectral properties of Eosin and Phenol Red, are 28.3 and 52.5 A for protonated and unprotonated forms of Phenol Red, respectively. For randomly distributed acceptors in three dimensions with no diffusion, the donor decay is... 

Figure 10.13. Dependence of energy transfer on concentration of Phenol Red, for the protonated (Roi = 28.3 A) and unprotonated form (R02 = 52.5 A). The inset shows the pH-dependent energy transfer using an acceptor concentration of 4 x 10 3 M (effect of diffusion is omitted).

Figure 3. Time course of tissue and plasma concentrations of phenol red model predictions vs. experimental results. The lines are model predictions the symbols are experimental data for iv injection of 10 mg/kg into the caudal vein of dogfish sharks. Each symbol represents the average of five to eight female sharks/time point with SD indicated by vertical bars. The limit of sensitivity of the assay was 25,15, and 5 g/g or mL for ( ), kidney (K) Liver (L) and (O), plasma (P),...

Figure 4. Time course of accumulation of phenol red and glucuronide in the bile and urine. The lines are model predictions and the symbols are experimental data ( )> bile (B) (A), urine (V) (9).

Our initial interest was in studying the disposition of phenol red in the shark. This turned out to be a good choice because nearly equal amounts of the model compound appeared in the urine and bile. After solving the body fluid collecting problems, we studied in greater depth, the transport properties of phenol red in both the renal and hepatic systems. 

Phenol red is rapidly cleared biphasically from the plasma compartment with an initial t of about 46 min. (Fig. 3) and a second phase with a t of 8 3 hrs. As early as 10 min. there are detectable levels or phenol red in the kidney. The concentration of drug in kidney peaked at 30 min. and decayed with a half-time of about 9 hrs. There also were detectable levels of phenol red within 10 min. in liver but the values were considerably below those of plasma and kidney. Hepatic levels took longer (ca. 2 hrs.) to peak than did those in kidney, and then decayed with a half-time of about 10 hrs. The glucuronide... 

Consideration of these data in terms of multi-compartmental analysis is found in Fig. 5. The renal compartment never achieved more than 6.3% of the administered dose and declined rapidly after 1 hr. As early as 10 min. the hepatic compartment contained about 18% of the administered compound where a peak value occurred at 2 hrs. and continued to contain large amounts of phenol red for up to 12 hrs. There is only a slight difference between the amount of phenol red handled by the urinary and biliary compartments in 48 hrs., 40% and 48% respectively. In each compartment most of the material is free drug. 

Effects of Interrupted Enterohepatic Circulation on Biliary and Urinary Handling of Phenol Red... 

The values in Table I compare biliary and urinary excretion of phenol red. The intact animal excretes 49% of the administered dose in 48 hrs. into gall bladder bile and of this 20% is excreted... 

Table I. Comparison of Urinary and Biliary Excretion of Phenol Red in Intact and in Fistulized Dogfish Shark3...

Figure 5. Time course of distribution of phenol red in terms of multicompartment analysis (8)...

Concentrated Transfer of Phenol Red into Renal and Hepatic Compartments... 

Attempts to gather evidence that both phenol red and its glucuronide are excreted by saturable transfer processes were made by measuring drug disposition at four different doses of phenol red. Of the four doses studied (j3) only the two extreme doses are shown in Table III. Over this range of doses, there was no evidence of saturation in terms of concentration, of either the plasma or kidney. There was no proportionality between... 

Table III. Effects of Different Doses of Phenol Red on its Distribution in the Dogfish Shark3...

Since probenecid is used extensively as an inhibitor of the urinary and biliary excretion of carboxylic, phenolic and sulphonic acids in many other animals, it was of interest to determine if probenecid would inhibit the urinary and/or biliary transport of phenol red in the shark (Table IV). The plasma levels determined at 4 hrs. after administration of phenol red alone or in combination... 

Tissue or fluid (form of phenol red) Phenol Red mr/r Alone % Dose Phenol Red pr/r + Probenecid % Dose... 

At the dose most commonly employed in the present work (10 mg/kg), 66.6% of phenol red occurred bound as determined by ultrafiltration techniques (8). There were no significant differences in percentage bound at 20 and 40 mg/kg doses whereas there was a slight but significant decrease in the amount of binding by phenol red in the presence of probenecid. 

---