trans- Cinnamic Acid–α-Cyclodextrin System as Studied by Solubility, Spectral, and Potentiometric Techniques

摘要: Complex formation in aqueous solutions of trans-cinnamic acid or trans-cinnamate ion (the substrate, S) and α-cyclodextrin ligand, L) can be described quantitatively as the 1:1 1:2 complexes, SL SL2. The solubility, spectral, potentiometric data over a wide range ligand conccntrations yielded consistent estimates complex association constants. For cinnamic at 25°, K11 = 2260 M−1, ΔH°11 −9.3 kcal/mole, ΔS°11 −8 e.u.; K12 60 ΔH°12 −12 ΔS°12 −26 e.u. cinnamate 110 −9 +11 15 −15 (all entropy changes are unitary quantities). Thermodynamic cycles for using solubility data, reveal that solid phase is thermodynamically spontaneous but stability greater solution than phase.