Metachromatic interactions of dimethylmethylene blue with some poly anionic polysaccharidest

Abstract

1,9-Dimethylmethylene blue (DMMB) exhibits stronger metachromatic ability than methylene blue (MB) and toluidine blue (TB). Unlike MB and TB, DMMB undergoes metachromatic spectral shift in presence of Bael (<em>Aegle marmelos</em>) exudate gum polysaccharide (BP), a polyanion with relatively low charge density (0.19 per monosaccharide unit), and Bael (fruit) gum polysaccharide, a polyacid polysaccharide (AMA) of still lower charge density (0.074). Dextran sulphate (OS), a sulphated polysaccharide with very high charge density (2.0), induces very sharp and stable metachromasia in DMMB in its dilute aqueous solution (cone. ~ 10^-⁵ <em>M</em>) at a low polymer to dye ratio (P/D) (0.75). Increased stability of metachromatic compound of DMMB-DS system is reflected in its disruption to the extent of only ~ 50 per cent by high ethanol concentration (~ 60%). High urea concentration (8 <em>M</em>) does not lead to the half-plateau value. The corresponding metachromatic compounds of DS with TB and MB get destroyed at lower ethanol or urea concentrations.