Department of Chemistry
Malcolm Forbes

Malcolm Forbes

Professor
mdef@unc.edu
919-962-1696
919-962-2388 (fax)
Caudill 020

 

Research Interests

Spin, Donor-Acceptor and Polymer Degradation Chemistry

Professional Background

Ph.D., Chemistry, The University of Chicago, (1988); M.S., Chemistry, The University of Chicago, (1986); B.S., Chemistry, University of Illinois at Chicago, (1983); IBM Junior Faculty Development Award, (1991); National Science Foundation Young Investigator Award, (1993-1998); Dupont Junior Faculty Development Award, (1994); John Charles Morrow Junior Faculty Development Award, (1994); Japan Society for the Promotion of Science Foreign Fellowship Award, (1998-1999)

Research Synopsis

Research in the Forbes Group falls into three general areas: Spin Chemistry, Polymer Photodegradation and Dynamics, and Electron Donor-Acceptor Chemistry. Because free radicals are produced in nearly all of the systems we study, we rely heavily on the technique of electron paramagnetic resonance (EPR) spectroscopy. Our laser laboratory consists of four EPR spectrometers operating at multiple frequencies, fast detection electronics interfaced to these spectrometers, and high energy pulsed excimer and Nd:YAG laser. This enables us to produce and detect free radicals in the sub-microsecond time range. Since we study organized assemblies such as micelles and biradicals generated from novel triplet ketone precursors, we also have a laboratory dedicated to organic synthesis, outfitted with the usual wet chemistry tools and characterization equipment such as UV-Vis and GC/MS. Many of our students gain experience in the both the physical (instrumentation, magnetic resonance and computational theory) and organic (synthesis, characterization) sides of our research.

In our Spin Chemistry projects we study how the exchange interaction (J) between two unpaired electrons, such as in biradicals or in micellized radical pairs, is influenced by molecular motion. We have found interesting parallels in the dynamics of biradicals and micellized radical pairs. We have also developed a new theoretical model which allows us to simulate these species' EPR spectra and extract diffusion parameters. Work to improve and refine the theory is ongoing, and will include molecular dynamics (MD) calculations which will be performed to further describe and understand micellar environments and the dynamics of molecules inside micelles. The acquisition of experimental data from EPR experiments performed on original surfactants and biradical precursors synthesized in our lab is also continuing so that theory may be tested and challenged. Many of the observed EPR phenomena are field dependent and are therefore studied at more than one frequency of spectrometer.

Polymer Photodegradation and Dynamics can be studied by time-resolved EPR, and the technique is advantageous here as it allows the primary photochemical events to be observed, rather than photolysis of secondary photoproducts or radicals formed by rearrangements. We have investigated the photodegradation of alternating alkyl-CO copolymers, and more recently the degradation of acrylates and methacrylates. We have focused intensely on these latter polymers, since there is much controversy regarding the mechanism of the primary degradation step. Presently we are writing a manuscript detailing our findings. We have also been investigating the differences in plasticization properties between standard agents and gaseous carbon dioxide by conducting steady state EPR studies of nitroxide spin probes doped into several different polymers. Electron Donor-Acceptor Chemistry are also under investigation in our laboratory. Major spin physics and chemistry issues surrounding the photoionization of small molecules such as tyrosine and p-cresol are being studied, and a novel method for producing transient biradicals from short peptides via such photoionization processes has been developed.

The Forbes laboratory also functions as a de facto regional center for EPR spectroscopy, having the largest cluster of spectrometers and the widest variety of experiments available in the entire southeastern U.S. This availability has led to numerous collaborations with many scientists in other fields, and has provided a rich experience for the group as we assist other researchers in collecting data, designing new experiments, and analyzing spectra from systems as diverse as blue copper proteins, color centers in synthetic diamonds, organometallic catalysts, biopolymers, and the surfaces of polymers used for barrier coatings in food packaging.