Research Interests:
Organic, polymer, materials and
medicinal chemistry -- Organic
chemistry on the nanometer scale with
macromolecules: from catalysis and
chiral recognition to targeted drug
delivery
Most individual projects
in the Fréchet research group
involve organic synthesis applied to
large macromolecules for which chemical
structure, architecture, and reactive
group placement defines function. Our
research covers both fundamental and
applied aspects of organic, polymer,
and materials chemistry. As a result,
most projects involve three stages:
- the design stage with the development
of approaches and the study of
mechanisms;
- the synthetic stage with the
preparation of model compounds
and target molecules;
- the characterization
stage with characterization of
structure and properties, and the
testing of function.
I. Control of molecular architecture at the nanometer scale.
While most common organic molecules - "small molecules" - have sizes well below one nanometer, macromolecules such as proteins or synthetic polymers have sizes in the nanometer range. Within this size range, it is generally very difficult to control the 3-D structure of the molecules. Nature has learned how to achieve this with proteins and DNA but most other large synthetic macromolecules have little shape persistence and precise functional group placement is difficult. During the past decade dendrimers and other dendritic macromolecules have emerged as a major new family of well defined nanoscale building blocks. They are globular, and sometimes almost spherical in shape, and the placement of their functional groups within the molecules can be accurately controlled. Our synthetic work seeks new ways to prepare these molecules and to incorporate catalytic or other active sites. In some cases we organize these reactive sites to achieve cooperative effects, while in other cases we seek to "insulate" these sites from each other, or restrict their access by external moieties, affording novel properties. A
great variety of molecular frameworks
may be used and new, creative ways to
assemble large and precise macromolecules
are being designed and explored.
II. New polymerization mechanisms:
hyperbranched polymers and hybrid copolymers.
Though less precisely defined than dendrimers
in terms of structure, several other families
of synthetic macromolecules derive their
function from a combination of shape and
chemical reactivity. We explore novel approaches for the preparation of such macromolecules. Instead
of a step-by-step approach, we seek new
reaction mechanisms that provide both structural
and functional control in a single step.
III. Separation, molecular recognition, and reactive surfaces.
In order to exploit the power of functional
surfaces in binding, recognition, and catalytic
processes, we develop porous organic materials
that present reactive functionalities over
large contact areas. These materials, which generally take the form of polymer beads or macroporous monoliths, may carry a broad array of functionalities, enabling them to carry out functions such as biocatalysis, separation, or chiral recognition. Their uses in areas such as solid-phase syntheses, combinatorial chemistry, or miniaturized "lab-on-a-chip" are
also explored.
IV. Functional macromolecules and their applications
Much of our research is mission oriented
and many of the functional macromolecules
we prepare are designed for a specific
application. For example, a dendrimer with
laser dyes placed at its periphery can
act as a light-harvesting antenna; the
same molecule fitted with a catalytic site
might perform photosynthesis. A macromolecule may be designed to act as a vector or carrier for a drug specifically "engineered" to avoid side effects, and capable of precise delivery of its "payload" with
the help of targeting and release functionalities.
A reactive polymer may be used for the
sort of precision imaging that is required
in the preparation of today's powerful
microprocessors or optoelectronic devices.
A macroporous polymer bead with pendant
chiral groups may be perfectly suited for
the analysis, recognition, or enantioseparation
of biologically active molecules.
