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Salt effect on the hydrophobic binding ofp-toluidino naphthalene sulphonate with cyclodextrins

Chemical Physics Letters
Publication Date
DOI: 10.1016/0009-2614(94)00021-2
  • Physics


Abstract Lithium chloride, lithium perchlorate, cesium bromide, tetra- n-butyl ammonium bromide (TBBr) and guanidine hydrochloride (GnCl) affect the fluorescence properties of 2, 6- p-toluidino naphthalene sulphonate (TNS) bound to α- and β-cyclodextrins (CD) in strikingly different ways. This indicates that the salts have considerable influence on the hydrophobic binding of TNS molecules with CDs. The salting-in agents (LiClO 4, CsBr and GnCl) markedly reduce the fluorescence quantum yield (Φ f) and lifetime (τ f) of CD-bound TNS anion. It is suggested that they directly interact with the bound TNS ions. The salting-in agent TBBr increases Φ f and τ f. This fluorescence enhancement indicates that the local polarity is reduced by wrapping the four n-butyl groups around the CD-bound TNS ions. The salting-out agent LiCl causes a marginal increase (< 15%) and that at a high concentration (7 M). In the absence of CD in aqueous solution on addition of 0.1 M TBBr; the fluorescence yield of TNS increases sixfold. This is attributed to clustering of TB cations around the TNS anion.

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