The Novel Ferrocene Cholesterol Derivatives Synthesis And Gelation Behavior

Recently, increasing interest has been paid to organogels based on low-molecular-mass compounds. This is not only because various superamolecular networks can be formed due to self-assembly of the gelator molecules in the medium, but also because they are soft materials with special properties. Low-molecular-mass gels belong to physical gels and they are formed and maintained by weak interactions including hydrogen bonding, van der Waals interactions,π-πstacking, electrostatic interactions, coordination interactions, and dipole-dipole interactions, ect. Therfore, these systems usually possess better thermo-reversibility. Furthermore, introduction of some functional groups in low-molecular-mass gelators may result in stimulus-responsive properties, in which the stimuli can be irradiation, electron or charge transfer, host-guest interaction, oxidative/reductive reaction, and shearing force, etc. It is because of these reasons that low-molecular-mass gels have promising potential applications in sensors and actuators, drug delivery, protection of historical relics, as templates for preparing micro/nano-materials, oil recovery, mild separation and purification, etc.It is known that cholesterol possesses a rigid skeleton, several sterogenic centers, and a strong tendency to form aggregates via van der Waals interaction. These structural characteristics make it an ideal component for designing various potential low-molecular-mass organic gelators (LMOGs) and in fact cholesteryl derivatives are efficient LMOGs. Ferrocene (Fc), a typical organometallic compound, possesses cataytic, magnetic, electrical activity and nonlinear optical properties., As a result, its derivatives have been widly applied in asymmetric catalysis, in the development of molecular electronic materials, in light stabilizer, electrochemical sensor, etc. As the continuation of our work on the studies of LMOGs, Fc has been intentionally introduced into three specially designed LS2 type di-cholesteryl derivatives as a pendant structure, where L denotes a linker and S stands for a steroidal unit. Their gelation behaviors are investigated and water-in-oil (W/O) gel-emulsions have been obtained. This distation is maily composed of the follow ing two parts:In the frist part, three compounds denoted as 1,2, and 3, respectively, are designed and sytheszied by varying the number of hydrogen-bonding sites in the linkers. The structures and compositions of all these compounds are characterized by 1H NMR, FT-IR spectroscopy, elemental analysis, and satisfied results have been obtained. The gelation properties of the three compounds in common solvents are studied systematically. It is found that that 1 gels none of the 34 solvents tested, 2 gels some of the alkanes, and 3 gels 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 (Fig.1). The micro-morphologies of some xerogels are investigated by SEM. Concentration dependent of the morphology of the xerogel was also intentionally investigated in order to examine the evolution process of the microstructures of the xerogels. FT-IR,XRD and 1H NMR studies revealed the formation mechanism of the organogel. At last, a structural mode has been proposed to describe the fundamental assembly of 2 in n-decane.In the second part, compound 2 as a stabilizer was used to prepare the water in oil gel emulsion as a continuation of the frist part. Frist, the systems of 2/n-decane/water with different water contents were adopted as example systems to look for the effect of the water content on phase behavior. For the system of 2/n-decane/water, the maximum volume ratio of water (dispersed phase) is 97%(v/v). Optical microscopy measurements confirmed the foam-like structures of the gel emulsions. Rheological measurements demonstrated that the 2/n-decane/water gel emulsions possess good mechanical stability, and exhibit typical viscoelastic properties. It was found that the storage modulus (G') and the yield stress of the gel emulsions increase along with increasing the volume ratio of the dispersed phase, a result consistent with the result of the traditional gel emulsions. At the same time, the system of 2/tert-butyl methacrylate/water gel emulsion was created (Fig.2). Tert-butyl methacrylate was successfully polymerized by free redical polymerization in this gel emulsion to get porous and low-density material (Fig.2).