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My current research involves supersonic-jet spectroscopy of anthranilic acid, a molecule which is used
as a fluorescent label in studies of biological systems. One advantage of using anthranilic acid as a
fluorescent label is that it is a small molecule, which reduces the perturbation induced by the presence of
anthranilic acid. Other advantageous properties of anthranilic acid include its large quantum yield and the
ease with which it is incorporated into common techniques used for peptide synthesis. In some studies, a change
in the fluorescent properties of anthranilic acid is used to indicate a change in the local environment of protein
under study1. When the protein moves from aqueous solution to a
nonpolar
environment, the quantum yield of anthranilic acid increases and its fluorescence emission undergoes
a blue shift. It has also been observed that the quantum yield of anthranilic acid decreases by an
order of magnitude when it is attached to specific amino
acids.2 The
reasons behind these observed
properties of anthranilic acid are not well understood. To gain further insight into these problems,
we have performed supersonic-jet spectroscopy of this molecule.
Thus far, I have obtained fluorescence excitation, dispersed emission, and two-color, resonantly enhanced two-photon ionization (R2PI) spectra of anthranilic acid. These spectra have indicated the presence of multiple conformers of anthranilic acid in the jet. The structure of this molecule indicates the possibility of at least two conformers; one of which would be expected to possess an intramolecular hydrogen bond. The presence of this hydrogen bond allows for the possibility of proton transfer, although no evidence for this has been seen in the spectra we have collected. The structure of anthranilic acid also allows for the production of hydrogen-bonded dimers. The presence of these dimers was detected by our R2PI experiments, and the spectral features of the dimers have been assigned.
These experiments are ongoing, and we intend to pursue several other avenues. One of these involves collaboration with Tim Zwier's group at Purdue University. This laboratory has the capability of performing hole-burning experiments and a technique referred to as resonant ion-dip infrared spectroscopy (RIDIRS). The hole-burning experiments will allow us to determine the number of conformers present and the spectral features belonging to the various conformers. The RIDIRS experiments will produce ground state IR spectra of anthranilic acid, allowing us to further probe the hydrogen-bonding characteristics of this molecule. Other future studies include the examination of water clusters of anthranilic acid to examine the effect of solvation on the fluorescent properties of this molecule
(1) Turchiello, R. F.; Lamy-Freund, M. T.; Hirata, I. Y.; Juliano, L.; Ito, A. S. Biophys. Chem. 1998, 73, 217.
(2)Ito, A. S.; Turchiello, R. F.; Hirata, I. Y.; Cezari, H. S.; Meldal, M.; Juliano, L. Biospectroscopy 1998, 4, 395.
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