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Self-assembling properties of ionisable amphiphilic drugs in aqueous solution

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  • Christina Efthymiou, Uppsala University
  • ,
  • L. Magnus Bergström, Uppsala University
  • ,
  • Jannik Nedergaard Pedersen
  • ,
  • Jan Skov Pedersen
  • Per Hansson, Uppsala University

Hypothesis: Common amphiphilic drug molecules often have a more rigid nonpolar part than conventional surfactants. The rigidity is expected to influence the self-assembling properties and possibly give rise to aggregation patterns different from that of regular surfactants. Experiments: We have investigated self-assembling properties of the hydrochloride salts of adiphenine (ADP), pavatrine (PVT), and amitriptyline (AMT) at concentrations up to 50 wt% using small-angle x-ray scattering, dynamic light scattering, cryo-transmission electron microscopy, and surface tension measurements. Findings: All drugs form small micelles of oblate spheroidal shape at concentrations above the critical micelle concentrations (CMC). The micelles grow weakly in size up to about 20 wt%, where the aggregation number reaches a maximum followed by a slight decrease in size at higher drug concentrations. We observe a correlation between the decrease in micelle size at high concentrations and an increasing charge of the micelles, as the degree of ionization increases with increasing drug concentration and decreasing pH. In contrast to what has previously been reported, the aggregation behavior of all studied drugs resembles the closed association behavior of conventional surfactants with a short aliphatic chain as hydrophobic tail group i.e. the micelles are always small in size and lack a second CMC. CMC values were determined with surface tension measurements, including also lidocaine hydrochloride (LDC) and chlorpromazine hydrochloride (CHL).

TidsskriftJournal of Colloid and Interface Science
Sider (fra-til)701-710
Antal sider10
StatusUdgivet - okt. 2021

Bibliografisk note

Funding Information:
We thank the Faculty of Pharmacy at Uppsala University for financial support, and Sana Tirgani for technical assistance.

Publisher Copyright:
© 2021 Elsevier Inc.

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