Research Interests
My research interests are focused in the relatively new area of organogels. Although
gels have been known since the early 1800’s, they were poorly understood and therefore
easier to recognize than to define. The empirical definitions were based on macroscopic
observations. In the last 15-20 years, researchers have been working toward a better
understanding of the nature of organogels, and although much has been learned regarding
the structure and properties of organogels, many questions still remain.
Three ongoing projects in my laboratory are:
 Synthesis of Biphenyl-Cholesterol Derivatives: The Effect of the
Spacer Length on their Gelation Ability.
 Study of Biphenyl-Cholesterol Gels: Chirality Influence on C-3 in
the Cholesterol Moiety.
 Styryl Naphthalene Cholesterol Derivatives: Synthesis, Gelation
Ability, Aggregate Structure and Photophysical
Characterization.
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.
O (CH 2)n
O
O
n = 1-7
Study of Biphenyl-Cholesterol Gels: Chirality Influence on C-3 in the Cholesterol
Moiety.
The purpose of this project is to understand the relationship between the structure
of the gelator and its gelation ability. For this purpose, we investigate several biphenyl
derivatives connected by an ester linkage to the C-3 of a cholesterol moiety. We have
synthesized biphenyl-cholesterol compounds with an S and R configuration at C3. In
some compounds the biphenyl is connected directly to the cholesterol. In some other
gelators, there are eight methylene units in between the biphenyl and cholesterol. 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.
O
O
C O
(S)
O
O
O
O
(S)
O
C O
(R)
O
O
O
(R)
Styryl Naphthalene Cholesterol Derivatives: Synthesis, Gelation Ability, Aggregate
Structure and Photophysical Characterization.
In an effort to probe the relative importance of the different factors which may
control the self-assembly of aromatic amphiphiles and therefore gelation ability in some
organic solvents, we have focused our studies on styrylnaphthalene chromophores. Both
 and styrylnaphathalene fatty acids derivatives investigated, have similar absorption
spectra and photophysics in dilute solutions. From simple modeling considerations we
recognized that amphiphiles constructed by attaching a fatty acid chain to the para
position of the phenyl ring of  and  trans-styrylnaphthalene should result in molecules
having very different shapes. The -isomer is anticipated to exist preferentially in an
extended configuration. In contrast, the -isomer is anticipated to have a bent shape.
Analysis of the packing modes for these different amphiphiles has been studied in other
organized media, such as L-B films. Our studies focus on the synthesis and photopysical
characterization of the following aromatic-cholesterol derivatives, to gain a better
understanding of structure/gelation relationship.
O
COOH
O
O
COOH
COOH
O
COOH
Research Students: Fall 2002
Charles Constantine
Ryan Holand
Joe Laakso