Preparation of novel organometallic derivatives of cholesterol and their gel-formation properties

Ferrocene (Fc) as a pendant structure has been intentionally introduced into three dicholesteryl derivatives of a LS2 type structure, where L denotes a linker and S stands for a steroidal unit. The compounds as designed are denoted as 1, 2 and 3 according to the number of hydrogen-bonding sires in the linkers. Gelation tests revealed that 1 gelates none of the 34 solvents tested, 2 gelates some of the alkanes, and 3 gelates only cyclohexane and DMSO. Importantly, the gel system of 2/n-decane exhibits a sol-gel phase transition upon thermal, ultrasonic, mechanical or even chemical treatments. FTIR, temperature- and concentration-dependent H-1 NMR spectroscopy measurements revealed that intermolecular hydrogen-bonding is one of the driving forces for gel formation. XRD analysis demonstrated that 2 exists in a stretched conformation and aggregates into layered structure in its n-decane and cyclohexane gels. Far from that expected, introduction of Fe unit does not bring the redox responsive properties to the gel systems. (C) 2010 Elsevier B.V. All rights reserved.