Jordan W. Bye , Stefano Meliga , Denis Ferachou ,
Gianfelice Cinque , J Axel Zeitler , and Robert John Falconer
J. Phys. Chem. A, Just Accepted Manuscript
DOI: 10.1021/jp407410g
Publication Date (Web): December 11, 2013
Copyright © 2013 American Chemical Society
Terahertz spectroscopy was used to study the absorption of bovine serum albumin (BSA) in water. The Diamond Light Source operating in a low alpha mode generated coherent synchrotron radiation that covered a useable spectral bandwidth of 0.3-3.0 THz (10-100 cm-1). As the BSA concentration was raised there was a non-linear change in absorption. At low BSA concentrations (0-1 mM) the absorption remained constant or rose slightly. Above a concentration of 1 mM BSA a steady decrease in absorption was observed which was followed by a plateau that started at 2.5 mM. We propose that water molecules that are interacting with apolar amino acid side chains exhibit lower absorption than bulk water due to a change in its relaxational dynamics and that the levelling of the decrease in absorption that was observed at high BSA concentrations originated from an overlap of the hydration layers. The apolar-associated hydration layer was estimated to extend to approximately 15 Å away from the protein. Alternative explanations are also discussed.
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