Postdoctoral Associate

Ph.D. in Chemistry, 2002, University of California at Berkeley

B.A. in Physics and Chemistry, 1992, Cornell University, Ithaca, NY

Solvated electron systems are remarkable in many ways. The lightest room-temperature liquids are formed from solvated electrons in ammonia. These deep blue solutions exemplify the very strong absorption found in many other solvated electron systems. In water, solvated electrons have a conductivity greater than any ion except H⁺, and many of their reactions occur at or near the diffusion-limited rate. These and other unusual properties have captured the attention of experimentalists and theorists alike.

The general problems that are illuminated by study of the hydrated electron include the solvent structure in the vicinity of a charge and aqueous solvent dynamics. The understanding of these problems has implications that extend far beyond the realm of physical chemistry. For example, life depends upon the extremely rapid transport of ions through channels within a cellular membrane. Current studies of the structures of these channels(see ref. 1, below) highlight that ionic transport depends upon the energetics and structure of the water-cation complexation both at the exterior of the cellular membrane, as well as inside the channel that traverses it. In a second example, one hardly needs to read beyond the title of the most recent X-ray crystallographic study of rhodopsin "Functional role of internal water molecules in rhodopsin revealed by X-ray crystallography" (ref. 2) to realize the paramount importance of water in the function of the visual pigment! The study provides convincing evidence that water molecules near the charged retinal Schiff base are critical for regulating the absorption characteristics and function of the most well-studied G-protein coupled receptor. Together, these two examples emphasize that essential processes of nature depend upon the mechanism of aqueous solvation of charged sites and ions.

Our work aims to answer the following question: What are the structure and functional dynamics of water molecules in the vicinity of the aqueous solvated electron? Our use of pump-probe resonance Raman spectroscopy and fluorescence emission measurements comprise the first quantitative measurements of the vibrational and emission spectra of the aqueous solvated electron.(refs 3 and 4) The analysis of these spectra has contributed new insights into the structure of the solvated electron at room temperature, and the dynamics of solvation immediately following photoexcitation.(ref. 5)

Figure 1: Resonance Raman Spectra of solvated electrons generated by UV photolysis of ferrocyanide Fe(CN)₆^4-

Figure 1. (Upper panel) Pump + probe spectra of 1.80 mM potassium ferrocyanide in D₂O (a) and H₂O (b). Pump-only spectra for the H₂O solution (c) and D₂O (d) and probe-only spectra are presented as (e) and (f) respectively. (Lower panel) Solvated electron spectra resulting from the difference (pump+probe)-(pump only) - K*(probe only). The e-(D₂O) spectrum is normalized to account for the different concentration-length measurements which are 8.0 and 9.4 mM-cm for electrons in H₂O and D₂O, respectively. The maximum subtraction of the probe-only spectra which does not result in a subtraction anomaly in the OH/OD stretch region is K = 0.70. Interpolated baseline fits to the lowest points of the Raman spectra are shown as dashed lines.

Figure 2: Schematic representation of the aqueous solvated electron.

Figure 2. Schematic representation of molecules in the first and second coordination shells around the solvated electron. First shell molecules are shown hydrogen bonded to the electron. Hydrogen bonds between molecules of 1st and 2nd shells are disrupted.

References & Publications

1) Zhou, Y.; Morais-Cabral, J. H.; Kaufman, A.; MacKinnon, R. Nature 2001, 414, 43.

2) Okada, T.; Fujiyoshi, Y.; Silow, M.; Navarro, J.; Landau, E. M.; Shichida, Y. Proc. Natl. Acad. Sci. USA 2002, 99, 5982.

3) Tauber, M. J.; Mathies, R. A. "Fluorescence and resonance Raman spectra of the aqueous solvated electron" J. Chem. Phys. A v105 n49, 10952-10960 (2001).
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4) Tauber, M. J.; Mathies, R. A. "Resonance Raman spectra and vibronic analysis of the aqueous solvated electron" Chem. Phys. Lett. v354, 518-526 (2002).
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5) Tauber, M. J., and Mathies, R. A. "Structure of the Aqueous Solvated Electron from Resonance Raman Spectroscopy: Lessons from Isotopic Mixtures"J. Amer. Chem. Soc., 125, 1394-1402 (2003).
[Abstract] [Full text in HTML] [Full text in PDF]