The molecular biology of histochemical staining by cationic phthalocyanin dyes: the design of replacements for Alcian Blue

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Abstract
Four cationic copper phthalocyanin dyes are compared with Alcian Blue 8G for specificity of interaction with a range of natural and synthetic polyanions. The CEC system is used to estimate dye-substrate affinities. The results support the hypothesis that the tissue staining pattern of Alcian Blue is determined by (a) exclusion of the dye from polynucleotide stacked base pairs by steric hindrance due to bulky substituents on the chromophore and (b) the presence of pendant quaternary charges whose affinity for negative sites on polyanionic substrates is without regard for the precise chemical nature of the anion. These conclusions, and practical considerations lead to the choice of quaternized Astra Blue 6GLL as a replacement for Alcian Blue (now no longer manufactured). It is superior to Alcian Blue in pH range, and stability in solution. It is easily prepared from a readily available precursor.