Dynamics of Solvating Water As a Probe of Polymers and Supramolecular Structures

The (bio)chemical reaction dynamics of polymers and supramolecular systems are intimately related to the conformational dynamics of these systems. A relatively new approach to studying the structure and structural dynamics of large (bio)molecular systems in aqueous solution is the measurement of the dynamics of the solvating water molecules. A suitable technique to measure the reorientation dynamics of solvating water molecules is polarization-resolved femtosecond mid-infrared pump-probe spectroscopy (PR-fs-IR). PR-fs-IR measures the full orientation correlation function of the water molecules in solution and is capable of distinguishing water molecules that are bulk-like and that are in direct (solvation) contact with hydrophobic, hydrophilic, and ionic groups of the solute. In this review, we show how the measurement of the reorientation of the solvating water can provide information on the structures of micelles, water-oil emulsions, and large polymers. We also discuss how the measurement of the water reorientation provides information on the origin of the temperature sensitivity of hydrogels and the folding of proteins. We compare the results obtained with PR-fs-IR with the results obtained with other experimental techniques, such as nuclear magnetic resonance (NMR), terahertz Fourier-transform infrared (THz-FTIR), Raman-multivariate curve resolution (Raman-MCR), dielectric relaxation (DR), and time-resolved optical Kerr effect (OKE) spectroscopy.