With the support from the Chemical Dynamic, Structure and Mechanisms Program at the National Science Foundation, Professor Laren Tolbert of the Georgia Institute of Technology will take advantage of the photophysics of the green fluorescent protein (GFP), which contains an embedded chromophore that exhibits an excited-state proton transfer (ESPT) cascade through a relay mechanism, as well emission quantum yields and vibronic structure that make it a unique probe for its environment. Methods developed in the Tolbert laboratories for excited-state proton transfer (ESPT) will be extended to biology, taking advantage of these properties, using supramolecular constructs to reproduce the GFP fluorescence. These studies will use large-scale synthesis and screening techniques to replace the protective protein barrel in GFP by new hosts, particularly proteins, but also other macromolecules and polymers which turn on fluorescence. Of special interest are a number of proteins, e.g., beta-lactoglobulin, which have "natural" ligands and may be expected to "turn on" in the presence of a chromophore similar to the natural ligand. On the one hand, this activation event serves to make the chromophore a probe for the host. On the other hand, the type of fluorescence, whether proton-transfer mediated or driven by solvent effects, provides clues as to the nature of the host-guest interaction. Whereas other analogous studies have focused on the structure of the host, Tolbert will use the availability of an almost infinite variety of guest molecules, testing various features of the non-bonding interactions within the complex and allowing a direct examination of the how subtle changes in the guest molecule impact the photophysics of the complex. These studies will include the design, synthesis, and exploration of a large variety of new chromophores which are chemically and topologically responsive to their environment. Some are non-emissive in the absence of a host, but can be activated by their environment and thus will create a versatile basis for the wide exploration of the effect of cavity shape, polarity, and acidity on fluorescence.
Tolbert and coworkers will collaborate with scientists in a number of laboratories, and will train a set of future scientists skilled in organic synthesis, spectroscopy, mechanistic chemistry, and collaborative research. The involvement of the investigator and the students in such close interdisciplinary international collaborations will help develop a diverse, globally-engaged, U.S. science and engineering workforce. Several specific outreaches will be pursued, including the involvement of undergraduate students in research, both during the year and during the summer through our Research Experience for Undergraduates Project. First, a group of senior undergraduate students at Georgia Tech will participate in the current project through a senior laboratory as part of their graduation requirement. Second, graduate students in the Tolbert group will participate in high school chemistry teaching in schools with high proportions of students from underrepresented groups.
