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Binding of cationic dyes to potassium alginate: A spectrophotometric and dichroic probe

1990; Wiley; Volume: 29; Issue: 12-13 Linguagem: Inglês

10.1002/bip.360291205

1097-0282

Medini Kanta Pal, Nemai Mandal,

Photochromic and Fluorescence Chemistry

Abstract Acridine orange (AO) binds to potassium alginate (KAlg) stoichiometrically as is evidenced from conductometric and spectrofluorometric titrations. However, AO as well as methylene blue (MB) exhibits weak metachromasia and no induced dichroism at any sensible polymer to dye ratio (P / D). KAlg induces large blue shifts (by as much as 125 nm) of the λ max of the strongly aggregating dyes 1, 9‐dimethylmethyleneblue (DMMB) and pinacyanol at reasonable P / D values; KAlg also induces strong dichroism in these dyes. The signs of the induced CD spectra indicate KAlg to have a left‐handed helical conformation. This polymer also induces red‐shifted J band and dichroism in the dye N‐N′‐diethylpseudoisocyanine (PIC) at high P / D under which condition the signs of CD spectra in DMMB reverse with drastic reduction in [θ] values. This reversal of sign of CD or induction of J band in PIC at only high KAlg concentrations does not involve any conformational change in the polymer as indicated by the insensitivity of the UV‐CD spectrum of KAlg as a function of concentration.