Self-assembly of chromotropic acid – a plausible explanation for monodisperse oligomer formation

The sodium salt of 4,5-dihydroxy-2,7-naphthalene disulphonic acid (chromotropic acid, DCA) self-assembles in aqueous media above its critical aggregate concentration (above 11 mM) to form organized aggregates as confirmed by conductometric, pH-metric and densitometric techniques. The molecular size of the aggregate was determined from gel filtration chromatographic studies. The molecular weight obtained in the postaggregate concentration region (100 mM) is about 1,660. The molecular weight of the aggregate indicates that four molecules of DCA constitute the aggregate. The results suggest that aggregate formation at high concentrations could explain the monodisperse spontaneous oligomerization in phenolic compounds.