Ionization Constants of Basic Dyes in Relation to Gastric Secretion.

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Abstract
The ionization constants of 14 basic dyes belonging to 5 chemical classes, azo, azines, xanthenes, oxazines and thiazines, each containing 2-4 compounds, were detd. spectrophotometrically in buffered 50% alcoholic solns. The dyes were those which Ingraham and Visscher have found to be secreted by the stomach. Fairly good agreement for the ionization constants by 3 different methods (spectrophotometric in buffered 50% alcohol, titration in water and in 50% unbuffered alcohol) is obtained for Nile Blue A, Bismarck Brown Y, Rhodamine B, Chrysoidin Y, Neutral Red and Pyronine B. With the exception of Acridine Red these are all the weaker bases. Higher values were found for Neutral Violet, Methylene Green, Brilliant Cresyl Blue, Toluidine Blue O, Thionin, Safranin O, and Methylene Blue by the spectrophotometric method. The spectrophotometric pKa values paralleled the buffer benzene ratios. The order of basicity varies in different media. It was not possible to correlate satisfactorily the secretion of dyes in a biological system with their ionization constants in aqueous or buffered 50% alcoholic soln.

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