Water Structure around Hydrophobic Solutes by Femtosecond 2DVibrational Spectroscopy

1
Water Structure around Hydrophobic Solutes by
Femtosecond 2D-Vibrational Spectroscopy

• Mark A. Berg, Department of Chemistry and
  Biochemistry, University of South Carolina

Solutes in water create distortions of the
hydrogen-bond network. The distortions drive
hydrophobic effects, solubility, self-assembly
and protein folding. A new type of
multiple-pulse spectroscopy is being developed to
measure the structure of the distorted water next
to a solute a vibrational IR pulse excites a
solute vibration a near IR pulse uses a
proximity-induced transition to transfer
coherence to a nearby water molecule coherent
Raman scattering of a visible pulse yields the
Raman spectrum of the solute-perturbed water.
coherentRaman signal
Near IR pulse
Visible pulse
Vibrational IR pulse
In the first phase of this project, a new method
was developed to detect the coherent Raman signal
with femtosecond pulses. In the second phase of
the project, a new set-up has been built to
generate the three excitation pulses and to bring
them to the sample with the correct relationships
in time, space and polarization. These
requirements are challenging because the pulses
are spread over very different spectral regions
vibrational IR, near IR and visible. The X-FROG
traces to the left show success in combing these
pulses at the sample while retaining good pulse
properties.