Metachromasia Induced in Cationic Dyes by Neem (Azadirachta indica) Polysaccharide

Aqueous extract of Neem (Azadirachta indica) tree exudate gum furnishes, a polysaccharide material (NP) having high equivalent weight (10855). NP induces slight spectral shift in toluidine blue (TB, 1x10-5M) and distinct multiple banded metachromasia in more aggregating thiazine dye 1, 9-dimethylmethylene blue (DMMB, 1x10-5M). Weak chromotropic ability of NP is reflected in its failure to induce metachromasia in methylene blue (MB, 1x10-5M). NP induces strong metachromasy (blue shift ~100nm) in dye pinacyanol chloride (PCYN, 1x10-5M). Half plateau values signifying destruction of metachromatic compounds to the extent of 50 % correspond to 25 %, 18 % and 28 % ethanol for DMMB-NP, TB-NP and PCYN-NP systems respectively. Negative S values for the DMMB-NP and PCYN-NP systems indicate the formation of ordered structures during the formation of dye-polysaccharide complexes.