title: Temperature-dependent behavior of a symmetric long-chain bolaamphiphile with phosphocholine headgroups in water: from hydrogel to nanoparticles.
abstract: The temperature-dependent self-assembly of the single-chain bolaamphiphile dotriacontan-1,1'-diyl-bis[2-(trimethylammonio)ethyl phosphate] (PC-C32-PC) was investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), X-ray scattering, rheological measurements, and dynamic light scattering (DLS). At room temperature this compound, in which two phosphocholine headgroups are connected by a C(32) alkyl chain, proved to be capable of gelling water very efficiently by forming a dense network of nanofibers (Kohler et al. Angew. Chem., Int. Ed. 2004, 43, 245). A specific feature of this self-assembly process is that it is not driven by hydrogen bonds but solely by hydrophobic interactions of the long alkyl chains. The nanofibers have a thickness of roughly the molecular length and show a helical superstructure. A model for the molecular structure of the fibrils which considers the extreme constitution of the bolaamphiphile is proposed. Upon heating the suspensions three different phase transitions can be detected. Above 49 degrees C, the temperature of the main transition where the alkyl chains become "fluid", a clear low-viscosity solution is obtained due to a breakdown of the fibrils into smaller aggregates. Through mechanical stress the gel structure can be destroyed as well, indicating a low stability of these fibers. The gel formation is reversible, but as a drastic rearrangement of the molecules takes place, metastable states occur.
authors.affiliation: MLU Halle-Wittenberg, Institut für Physikalische Chemie, Mühlpforte 1, 06108 Halle/Saale, Germany.
authors.forename: Karen
authors.initials: K
authors.lastname: Köhler
authors.forename: Günter
authors.initials: G
authors.lastname: Förster
authors.forename: Anton
authors.initials: A
authors.lastname: Hauser
authors.forename: Bodo
authors.initials: B
authors.lastname: Dobner
authors.forename: Ulrich F
authors.initials: UF
authors.lastname: Heiser
authors.forename: Friederike
authors.initials: F
authors.lastname: Ziethe
authors.forename: Walter
authors.initials: W
authors.lastname: Richter
authors.forename: Frank
authors.initials: F
authors.lastname: Steiniger
authors.forename: Markus
authors.initials: M
authors.lastname: Drechsler
authors.forename: Heiko
authors.initials: H
authors.lastname: Stettin
authors.forename: Alfred
authors.initials: A
authors.lastname: Blume
mesh_terms: D000935:Antifungal Agents / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D020100:Hydrogels / Q000737:chemistry*; D008958:Models, Molecular; D049329:Nanostructures / Q000737:chemistry*; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000737:chemistry; D012212:Rheology; D012542:Scattering, Radiation; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D014867:Water / Q000737:chemistry*; D014965:X-Rays
chemical_list: D000935:Antifungal Agents; D020100:Hydrogels; D014867:Water; D010767:Phosphorylcholine