Calorimetric Study of Sodium n-Alkanoate−Modified Cyclodextrin−Water Ternary Systems

Abstract

Enthalpies of dilution of sodium n-alkanoate and cyclodextrin aqueous solutions with water as functions of their concentration were measured at 298 K. The enthalpy of transfer (ΔH t) of cyclodextrin (≈0.02 mol kg-1) from water to the aqueous solutions of the substrates was determined as a function of the substrate concentration. The cyclodextrins are hydroxypropyl-α-cyclodextrin (HP-α-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), and hydroxypropyl-γ-cyclodextrin (HP-γ-CD). The substrates (C n CO2Na) are sodium acetate to sodium decanoate. From the experimental data of the binary systems, the apparent molar relative enthalpies were calculated. The trends of ΔH t versus substrate concentration in the premicellar region were rationalized in terms of the substrate−cyclodextrin inclusion complex formation. The latter was not evidenced for HP-γ-CD with C3CO2Na and C5CO2Na and for HP-β-CD with C3CO2Na. The standard free energy for the complex formation decreases with the number of carbon atoms in the alkyl chain. Both enthalpy and entropy favor the HP-α-CD−substrate complex formation while governs the HP-β-CD−substrate and HP-γ-CD + C7CO2Na complex formation. For a given substrate, , and increase with the cavity size. The ΔH t versus f S m S trends for the micellar substrate solutions were interpreted in terms of the substrate−cyclodextrin complex formation and the shift of the micellization equilibrium.

Temperature-controlled poly(propylene) glycol hydrophobicity on the formation of inclusion complexes with modified cyclodextrins. A DSC and ITC study

“…18 Q CD agrees with the exothermic enthalpy of dilution of HP-b-CD with water reported elsewhere. 33 Fig. 3 reports the curves of the heat of interaction per mol of CD (DH i ) as functions of the cyclodextrin/polymer moles ratio (R CD : P ) for all the investigated cyclodextrins at 25 1C.…”

“…Nevertheless, from this qualitative inspection one cannot extract insights on the role of temperature on the inclusion complex equilibrium because DH i is a differential enthalpy and its dependence on R CD : P is a function of both the equilibrium constant and the stoichiometry of the inclusion complex. This is a limit of such a technique compared to other calorimetric methods that provide enthalpy functions like, for instance, the enthalpy of transfer 33 of the guest from the water to the water + host mixture, which gives a more straight description of the system. Therefore, in the case of ITC curves, it is even more necessary to interpret properly the DH i data by means of thermodynamic models to draw conclusions.…”

“…This occurred for HP-b-CD/fluorinated compounds 26 and HP-a-CD/sodium alkanoates. 33 For these systems, one calculates a single value (0.80) of the ratio between the cross sections of the HP-CD cavity and that of the guest. For HP-b-CD/PPG the value of this ratio is 0.97 (the diameter of HP-b-CD cavity is 6.2 A ˚) that allows us to expect relevant negative contributions to DH1 IC .…”

Use of dye complexation dynamics to determine α‐cyclodextrin host:guest stability constants

“…Surfactant inclusion complexes have been characterized by a wide variety of techniques including conductance, NMR chemical shifts, 1 H NMR self‐diffusion, fluorescence probe methods, surfactant selective electrode, surface tension, potentiometry, sound velocity, calorimetry, density, heat capacity, and kinetic methods . The reported binding constants for equivalent systems often vary considerably.…”

(Surfactant+polymer) interaction parameter studied by (liquid+liquid) equilibrium data of quaternary aqueous solution containing surfactant, polymer, and salt

“…Determination of (polymer + surfactant) interaction can be done by calorimetry and voltametry method [19][20][21][22][23], but in this work, we have used LLE of aqueous quaternary system containing surfactant, polymer, and salt for determination of (polymer + surfactant) interaction parameter. In the present work the FloryHuggins model has been used for correlation and prediction of the behavior of the quaternary aqueous systems.…”