Low molecular weight organogelators based on a noncholesteryl steroid with a bulky silyl moiety

EDELSZTEIN, VALERIA C.; BURTON, GERARDO; DI CHENNA PABLO H.

Porto de Galinhas, Pernambuco, Brasil

Conferencia; XVth International Sol-Gel Conference; 2009

Sol-Gel society

Molecular gels are constructed from the self-assembly of low molecular weight building blocks. These molecules self-assemble into supramolecular structures (often fibrilar in nature) as a consequence of non covalent interactions such as hydrogen bonds, pi-pi interactions, Van der Waals, etc. Steroids are a class of naturally occurring molecules involved in several biochemical processes; their structural characteristics are a rigid skeleton with a defined asymmetric architecture. Most organogelators of the steroid family are derived from cholesterol or other naturally occurring steroids (such as bile acids) where diversity has been achieved by attaching different molecules (aromatic groups, crown ethers, chelating agents, etc) with linkers at position C-3. Only a few organogelators without the cholesterol skeleton or substituents in other positions were reported in the literature. In this communication we report the synthesis of a new steroidal organogelator 1 and the properties and characterization of the gels. This molecule with a pregnane skeleton and a bulky silyl group at C-3 is capable to gelate non polar solvents like hydrocarbons and ketones to give stable, thermoreversible and transparent gels at low concentrations (0.5 % Wt/vol for n-hexane at 25ºC). We also present the gelation abilities of a series of analogues with different substituents at positions C-3 and C-20. The gels were studied and characterized by microscopy (AFM, TEM), DSC, I.R., X Ray, NMR and molecular modeling. The presence of a complementary hydrogen bond donor and acceptor pair on the a and b faces respectively has proved to be the driving force that leads to the 1D self-assembly.