My research interests are focused in the relatively new area of organogels. Some of the projects we are currently investigating are:
Synthesis of Biphenyl-Cholesterol Derivatives: The Effect of the Spacer Length on their Gelation Ability.
Among the types of gelators found by different investigators thus far are single molecules or two component systems. The introduction of two components increases the aggregation ability and the formation of super gels--gels formed at concentrations lower than 1% (w/w). We have synthesized several biphenyl fatty acids and connect them to cholesterol compounds by an ester link. We are interested in finding out what effect, if any, the length of the connecting chain has on the gelation ability of these compounds.
The stability of these gels and the relationship between structure/scaffold/gelation is analyzed by studying the phase transition temperatures and absorption and emission behavior.
Study of Biphenyl-Cholesterol Gels: Chirality Influence on C-3 in the Cholesterol Moiety.
The purpose of this project is to understand the effect of stereochemistry on the structure of some biphenyl-cholesterol derivatives and their gelation ability in several organic solvents. For this purpose, we have synthesized four biphenyl derivatives connected by an ester linkage to the C-3 of a cholesterol moiety. Cholesterol in its natural configuration contains the hydroxyl group positioned in an S-configuration. We have synthesized two biphenyl-cholesterol compounds with an S-configuration at C3 and two other with and R-configuration. In two of the compounds the biphenyl is connected directly to the cholesterol. In the other two compounds, there are eight methylene units in between the two components. By molecular modeling simulations, we observe different packing arrangements for these compounds. By emission, absorption and circular dichroism spectroscopy, we investigate the nature of the aggregates formed.
Synthesis and Gelation Studies of a Dicholesterol-Biphenyl Derivative
The formation of a gel depends on the relationship of the gelatorís structure and the nature of the solvent involved in gelation among other factors. One important aspect of the structure is the ability to self assembly. Fibrous aggregates of low-molecular weight compounds formed by noncovalent interactions are responsible for such aggregation. It is well known that aromatic compounds can form aggregates due to the p-p interaction of the benzene rings, also certain cholesterol derivatives can form stable gels due to the helical stacking of the cholesterol units. We envision a more powerful gelator consisting of an aromatic part connected by a methylene chain to two cholesterol moities. By having three driving forces leading to self assembly this compound could be a super gelator, i.e., a compound capable to form gels at less than 0.5% (w/w) concentration. We propose the total synthesis of dicholesteryl-4,4í-biphenoxyoctanoate, the gelation studies and photophysical characterization of this compound in gels, isotropic state and in dilute solutions.
Dan Galka- ACS meeting, San Francisco, March 2006
†††††††††† Magdalene Assimon††††††††††††††††† †††††††††††††††††††††††††††††††††††††††††Sara Villani
††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† Spencer Varney