Ultrafast two-dimensional infrared (2D IR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and electronic structure calculations were used to probe the structural and dynamic characteristics of divalent and trivalent metal coordination by ethylenediaminetetraacetic acid (EDTA) and ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA). EDTA and EGTA are common chelating agents used in science, medicine, and industry. We present ultrafast spectroscopic measurements of structure, vibrational relaxation, and energy exchange in the ion-coordinating carboxylate groups of EDTA and EGTA as they are bound to a series of divalent and trivalent ions. These measurements reveal ion-dependent changes in structure and dynamics on the picometer length- and sub-picosecond time-scales, well outside the temporal and spatial resolution of structural methods such as X-ray diffraction and NMR spectroscopy. Spectroscopic data is interpreted using estimates of intramolecular energy transfer and intramolecular vibrational redistribution derived from electronic structure calculations, showing that vibrational energy transfer within EDTA and EGTA is sensitive to the nature of the bound ion and correlates with complex stability. Our results demonstrate that 2D IR spectroscopy is a powerful tool for probing metal complex structure and dynamics, and is sensitive to aspects of structural fluctuation and intramolecular energy exchange that remain invisible to other methods.

Probing ion coordination and energy exchange in chelate complexes with ultrafast vibrational spectroscopy

256th National Meeting (2018)

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