Abstract
A1H NMR chemical shift ( delta ) study of a homologous series of hydrocarbon (hc) (CxH2x+ 1CO2Na, x = 5, 7, 9, 11, 13) surfactants (S) has been carried out in water and in binary solvent (D2O + cyclodextrin (CD)) systems at 22°C. Complementary1H NMR chemical shift ( delta ) data of the cyclodextrins in binary (D2O + S) systems containing hc surfactants have also been obtained. Complex induced shift (CIS) values for selected host or guest protons were found to increase as the alkyl chain (Cx) length of the surfactant increased. The CIS values are found to depend on the following factors: (i) the magnitude of the binding constant (Ki, i = 1:1, 2:1), (ii) the chain length of the surfactant, (iii) the mole ratio of the host to guest species, (iv) the host-guest stoichiometry, and (v) the host-guest inclusion geometry. The CIS values of the CD-S systems have been analyzed using equilibrium models in which 1:1 complexes, 1:1 plus 2:1 complexes, and uncomplexed species are present. Differences in the binding affinity, stoichiometry, and inclusion geometry of the complexes formed between a given hc surfactant and the various cyclodextrins were observed.Key words: cyclodextrin, surfactant, NMR, chemical shift, complex, binding constant.
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