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Photoremovable Protecting Groups.
In the past decade a series of useful molecular systems
known as phototriggers, photoswitches, photocaging groups,
or photoremovable protecting groups (PRPGs) have been used
in a wide variety of applications, including the release of
fragrances from household goods, as an aid in multi-step
syntheses, and in drug and gene delivery. PRPGs also make it
possible for biochemists to release bioactive compounds in
living tissue with both high temporal and spatial accuracy,
thus making it possible to study physiological events such
as enzyme activity, ion channel permeability, and muscle
contraction by ATP hydrolysis. The choice of PRPG is
critical, depends on the system under investigation, and
must be tailored to the application. Thus, there is a need
for new PRPGs that can satisfy the diverse requirements of
numerous applications.
We have designed several new photoprotecting groups and
studied the mechanism for the photorelease. Understanding
the reaction mechanism for the photorelease has allowed us
to design the next generation of PRPGs that can be tailored
towards specific applications.
We have designed PRPGs that use photoenolization to initiate
release of alcohols. These systems release their alcohols
moiety independent of the reaction medium and can take place
in thin films in the presence of oxygen and are therefore
excellent to release fragrance in house-goods. (see more
details 1 and
2)
Currently, we are using
molecular
rearrangement and intramolecular H-atom
bonding to achieve photorelease in high quantum yields and
to control the rate of release.
We thank ACS-PRF for their financial support of this project.
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Reactive Intermediates.
Fundamental research in chemistry has laid the foundations
for the discovery and design of new materials with
fascinating magnetic, electrical and optical properties,
prompting inventions anywhere from faster computers to
lighter long-range planes. Magnets have been used by humans
for the last thousand years. The earliest magnets were made
from a lodestone, a mineral rich in iron ore. Currently,
commercial magnets are still mainly based on
transition-metal and their oxides. Recently, however,
magnets have been reported that are based on unpaired
electrons in p,
p, or s orbitals of organic molecules. The quest for new
organic materials with magnetic properties arises from them
being potentially both more cost effective and lighter than
the more traditional metal magnets. The pursuit of organic
magnetic materials has sparked renewed interest in triplet
nitrenes, which are ideal candidates because of their high
spin properties.
We have shown that triplet alkyl nitrenes can be formed
selectively in solutions and the solid-state. Furthermore,
alkyl nitrenes are highly unreactive because they do not
abstract H-atom from the solvent or react with their
precursors. (See more details:
1,
2, 3,
4 and 5)
Currently, we are investigating the reactivity of vinyl
nitrenes
in solution and in the solid-state. Our goal is rendering
the nitrene unreactive so they can be used as building
blocks for organic magnets.
We are grateful to NSF for fund this research.
Auroras reflect earth's magnetic field
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Polymer Modification.
The thermal and physical properties of polymers can be
altered by forming cross-links between the polymers strands.
Cross-linking agent can also be used to modify the surface
of the polymer or introduce specific functional groups.
Since singlet aryl nitrenes are highly reactive and insert
non-discriminating into the surrounding chemical bounds,
they are ideal to cross-link polymers.
We have used singlet aryl nitrenes to cross-link polyaniline
to increase the thermal stability of the polymer. (See
more details)
Currently, we are designing di-nitrenes and identifying the
reaction conditions that lead to maximum cross-linking of
polymers.
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