INTERACTIONS BETWEEN SULFONATED AZO DYES AND BIOMOLECULES - ORANGE-G ADENINE AND ORANGE-G CYTOSINE SALTS

The disulfonated azo dye Orange G [the disodium salt of 7-hydroxy-8-(phenylazo)-1,3-naphthalene-disulfonic acid] forms salts with adenine and cytosine on co-crystallization from aqueous HCl. The 1:2 dye:adenine crystal, 2C5H6N5+.C16H10N2O7S2(2-).-5H2O, is a pentahydrate and the 1:2 dye:cytosine crystal, 2C4H6N3O+.C16H10N2O7S2(2-).H2O, is a monohydrate. In the solid state the dye is found to exist predominantly as the hydrazo, rather than the azo, tautomer. In both structures, one of the protonated nucleotide bases approaches close to a sulfonate group of the dye in an 'edge-on' fashion. Molecules in the Orange G/adenine structure lie in segregated layers, but molecules in the Orange G/cytosine structure lie in mixed stacks.