Conformational and thermal behavior of a pH-sensitive bolaform hydrogelator

Karen Köhler; Annette Meister; Günter Förster; Bodo Dobner; Simon Drescher; Friederike Ziethe; Walter Richter; Frank Steiniger; Markus Drechsler; Gerd Hause; Alfred Blume

doi:10.1039/B514163J

Conformational and thermal behavior of a pH-sensitive bolaform hydrogelator

Karen Köhler,†^a Annette Meister,^a Günter Förster,^a Bodo Dobner,^b Simon Drescher,^b Friederike Ziethe,^b Walter Richter,^c Frank Steiniger,^c Markus Drechsler,‡^d Gerd Hause^e and Alfred Blume*^a

Author affiliations

* Corresponding authors

^a MLU Halle-Wittenberg, Institut für Physikalische Chemie, Mühlpforte 1, 06108 Halle, Germany

^b MLU Halle-Wittenberg, Institut für Pharmazeutische Chemie, Wolfgang-Langenbeck-Str. 4, 06120 Halle, Germany

^c Klinikum der FSU Jena, Elektronenmikroskopisches Zentrum, Ziegelmühlenweg 1, 07740 Jena, Germany

^d FSU Jena, Institut für Pharmazie, Philosophenweg 14, 07743 Jena, Germany

^e MLU Halle-Wittenberg, Biozentrum, Weinbergweg 22, 06120 Halle, Germany

Abstract

The phase behavior of the symmetric long-chain bolaamphiphile dotriacontan-1,1′-diyl-bis[2-(dimethylammonio)ethyl phosphate] (Me₂PE-C32-Me₂PE) was investigated in aqueous suspensions of different pH by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FT-IR). At pH 5 the compound exhibits excellent properties as a hydrogelator by forming a dense network of helically structured nanofibrils with a diameter of 3–4 nm. The phase behavior of Me₂PE-C32-Me₂PE is compared with the previously examined trimethylammonio analogue PC-C32-PC, whose self-assembly process seems to be exclusively driven by hydrophobic interactions. At pH 5, Me₂PE-C32-Me₂PE can form intermolecular hydrogen bonds between the headgroups, which causes a significantly higher stability of the nanofibrils up to at least 75 °C. In contrast, no pronounced gelling properties are observed at pH 10. Obviously, the negatively charged headgroups seem to prevent the suspension from gelling. Nevertheless, nanofibrils are formed, but at 75 °C a fragmentation into smaller aggregates occurs due to the lack of stabilizing effect of intermolecular hydrogen bonds and the destabilizing effect of the negatively charged headgroups.

Soft Matter

Conformational and thermal behavior of a pH-sensitive bolaform hydrogelator

Abstract

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