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Ions_in_absorption_spectra-21.pdf (3.44 MB)
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The Effect of Ions on the Optical Absorption Spectra of Aqueously Solvated Chromophores

preprint
submitted on 17.05.2019 and posted on 20.05.2019 by Sapana Soni, Tim J. Zuehlsdorff, Michael J. Servis, Christine Isborn, Aurora Clark
In the condensed phase, ions often create heterogeneous local environments around a solute, which may impart chemical reactivity or perturbations to physico-chemical properties. Although the former has been the subject of some study, the latter - particularly as is pertains to optical absorption spectroscopy - is much less understood. In this work, the computed UV-Vis absorption spectrum is examined for the aqueously solvated chromophore anion of green fluorescent protein for different local ion configurations. The strong ability of water to screen the ions from the chromophore results in little change in excitation energy compared to a purely aqueous environment. However, upon forming a contact ion pair with a sodium ion at either of the two electronegative oxygen sites of the chromophore, there is a spectral shift to either higher or lower energies. Surprisingly, our analysis suggests that the cause of the spectral shift is dominated not by the electrostatic presence of the ion, but instead by ion disruption of the hydrogen bond network at the oxygen contact ion pair site.

History

Email Address of Submitting Author

sapnavshedge@gmail.com

Institution

University of California Merced

Country

United states of America

ORCID For Submitting Author

0000-0003-0159-8940

Declaration of Conflict of Interest

No conflict of interest

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