Thermodynamics of micellisation: Sodium dodecyl sulfate/sodium deoxycholate with polyethylene glycol and model drugs

Abstract

Variations in the critical micelle concentration (CMC) have been determined for sodium dodecyl sulfate and sodium deoxycholate (NaDC) in the presence of five drugs and polyethylene glycol (PEG) at 298.2, 304.2 and 310.2 K. From these data, thermodynamic parameters associated with the micellisation process (∆G mic , ∆H mic and ∆S mic ) were calculated. In the presence of some drug-based compounds the CMC of SDS was affected, for example the presence of PEG dramatically reduced the CMC in all cases. Furthermore, PEG appeared to reduce the enthalpy of micellisation for all scenarios with only comparatively minor variations in the change in Gibbs free energy for the processes observed. For NaDC, the calorimetric results were far less predictable. A primary aggregation event recorded at a comparatively low concentration failed to appear for NaDC in the presence of a secondary compound, such as a drug or PEG. For NaDC, the presence of PEG had little effect on the CMC and corresponding thermodynamic data.

Characterizing Drug-Polymer Bead Interactions Using Isothermal Titration Calorimetry

“…Previous work from our group and other researchers has confirmed that isothermal titration calorimetry (ITC) is an appropriate analytical technique to determine the binding interaction of several drug-based systems, such as those based on micelles, 10,11 cyclodextrins, [12][13][14] and polymer aggregates. 15 More recently, polymer beads have been studied using one drug, namely doxorubicin, with one bead type, namely DC BeadM1™ (a sulfonate-modified polyvinylalcohol hydrogel bead termed PVA-AMPS), and found the drug to binding sites on the bead ratio to be far lower than anticipated when compared with previously established binding data.…”