SALT EFFECT ON THE HYDROPHOBIC BINDING OF P-TOLUIDINO NAPHTHALENE SULFONATE WITH CYCLODEXTRINS

Lithium chloride, lithium perchlorate, cesium bromide, tetra-n-butyl a mmonium bromide (TBBr) and guanidine hydrochloride (GnCl) affect the f luorescence properties of 2,6-p-toluidino naphthalene sulphonate (TNS) bound to alpha- and beta-cyclodextrins (CD) in strikingly different w ays. This indicates that the salts have considerable influence on the hydrophobic binding of TNS molecules with CDs. The salting-in agents ( LiClO4, CsBr and GnCl) markedly reduce the fluorescence quantum yield (phi(f)) and lifetime (tau(f)) of CD-bound TNS anion. It is suggested that they directly interact with the bound TNS ions. The salting-in ag ent TBBr increases phi(f) and tau(f). This fluorescence enhancement in dicates that the local polarity is reduced by wrapping the four n-buty l groups around the CD-bound TNS ions. The salting-out agent LiCl caus es 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; t he fluorescence yield of TNS increases sixfold. This is attributed to clustering of TB cations around the TNS anion.