Can a Dye Base Penetrate into Living Cells from a Relatively Strongly Basic Dye Solution?

Abstract

The color of azure B begins to alter from blue to violet at about pH 10 (the more the higher the pH) until at about pH 13 it turns red. These color changes are instantaneous and readily reversible on appropriately lowering the pH values; they are not progressive on standing for 3 hours. They are due to tautomeric change from the dissociated blue dye salt to the undissociated red dye base. The half-way point in the color change from blue to red occurs roughly in the neighborhood of pH 12. These results show that azure B is a relatively strong base existing chiefly in the form of salt in the pH range available for living cells of Nitella (roughly between pH 6 and pH 9).

On shaking the azure B solution at pH 9.4 and pH 8.5 with carbon tetrachloride the red dye base is extracted by the latter, the more the higher the pH value. The ratio of the apparent absorption coefficients¹ is roughly (K_ap at pH 9.4)(K_ap at pH 8.5)=1.3/0.15=8.7. This ratio agrees with the ratio (percent of dye base at pH 9.4) (percent of dye base at pH 8.5 = 2.44 0.31 = 8, when the basic dissociation constant of the dye is K_b = 10^-3. Such a ratio at higher pH values might show whether the dissociation constant is K_b = 10^-3 or higher, but owing to the color change this determination is not possible by this method. These results show that azure B is strongly basic but the dye base has a high absorption coefficient between carbon tetrachloride and water so that it can be extracted on shaking the mixture in spite of its low percentage in the aqueous phase at these pH values.