No abstract

Raman spectroscopy is a technique preferably used for studies of water structure because the proportions of intensities of main OH stretching modes are thought to reflect well a network of "intermonomer" hydrogen bonds as well as its disturbance by the presence of some solutes. The work presented herein demonstrates how the intensity ratio of two main components (around 3200 and 3400 cm (-1)) depends on the excitation wavelength in the visible range. Polarized Raman spectra indicate that the component at ca. 3200 cm (-1) is in resonance with light from the red range, which is in agreement with the presence of vibrational overtones in UV-vis absorption spectrum of water. These results are the first report on the occurrence of the Raman resonance effect in liquid water.

We study the conformation and reorientation dynamics of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) under neutral and acidic conditions using a combination of broadband dielectric relaxation spectroscopy and polarization-resolved femtosecond mid-infrared pump-probe spectroscopy. We find that both zwitterionic and cationic GABA adopt nearly linear conformations in aqueous solution, meaning that the two charged functional groups of the GABA zwitterion are hydrated separately.