Novel Family of Gelators of Organic Fluids and the Structure of Their Gels

Article abstract of DOI:10.1021/ja00197a005

The macroscopic and microscopic properties of a new family of thermally reversible gelators (ALS) of organic fluids and their gels have been investigated by a variety of techniques.Each ALS contains a 2-substituted anthracenyl-type group coupled directly or indirectly to C3 of a steroidal group.Only weak intermolecular interactions (dipolar and van der Waals forces) need hold the gelator networks in place.In spite of this, a gel of 2percent cholesteryl 4-(2-anthryloxy)butanoate (CAB) in 4-heptanol can be retained in a sealed vessel at room temperature for several months.Experiments with a variety of organic fluids demonstrate that specific gelator-solvent interactions are not necessary for the gels to form.Thus, n-alkanes from heptane to hexadecane afford the same gelation temperature (T_g) with CAB.Molecular shape of fluid is an important factor in T_g since methylcyclohexane is gelled by CAB at a lower temperature than are the n-alkanes, and 4-heptanol is gelled at a higher temperature.The kinetics of gel formation and the T_g have been followed by changes in intensities of absorption, fluorescence, and circular dichroism spectra.The intermolecular packing arrangement among neighboring CAB gelator molecules has been probed by using the above spectral techniques in addition to X-ray diffraction and (1)H NMR studies.They indicate a stacked, helical arrangement for CAB molecules with the anthracenyl groups overlapping partially.Optical and electron microscopies have allowed the gelator structure in CAB/1-octanol and CAB/dodecane gels to be elucidated: they consist of molecular domains (several micrometers in diameter) of fibrous bundles; the fibers have rectangular cross sections of 20.9 nm X 10.4 nm (dodecane gel) and 25.3 nm X 8.2 nm (1-octanol gel).Additionally, the fibers of the CAB/1-octanol gel are helically twisted.These results are compared with information from other gel systems in which the gelator forms intertwined fibers.

Full text of DOI:10.1021/ja00197a005

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Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.