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Deep Hydration: Poly(ethylene glycol) Mw 2000-8000 Da Probed by Vibrational Spectrometry and Small-Angle Neutron Scattering and Assignment of {Δ}G° to Individual Water Layers.



Kenneth A. Rubinson, Curtis W. Meuse


Aquesous solutions of poly9ethylene glycol) (PEG) exhibit some remarkable properties, among which is the small changes in water activity compared to the volumes occupied by the PEG: For example, the water in a 20 % w/w solution of 600 Da PEG has an activity of 0.9939. We have investigated PEGs with molecular weights 200, 400, 1000, 2000, 4000, and 8000 Da in the concentration range 1% w/w to 17% w/w at neutral pH and with added KCl concentrations of 10 mM in aqueous solutions-conditions near those for promoting protein crystallization. These solutions exhibit a structural change at around 6% w/w as seen in the solution viscosities, compressibilities, and infrared spectra. Raman spectroscopy shows that the PEGs remain in the same structural form over the concentration range, and the infrared spectra indicate that the change must be due to a local shift in the water structure. Modeling of the results from Small-Angle Neutron Scattering (SANS) on the solutions suggest that the structures of PEGs in the molecular mass range 2000 Da to 8000 Da are paired in the solution, and the separation distance decreases with increasing PEG concentration. From the structure, it becomes clear that the small effect on water activity occurs because of screening by the more weakly bound outer layers. From the bulk measurement of aw}/I} and with reasonable assumptions, a free energy {Δ}G° can be assigned to each of the fourth, third, and second hydration layrs.


SANS, poly(ethylene glycol), Infrared, Raman, water structure, hydration


Rubinson, K. and Meuse, C. (2013), Deep Hydration: Poly(ethylene glycol) M<sub>w</sub> 2000-8000 Da Probed by Vibrational Spectrometry and Small-Angle Neutron Scattering and Assignment of {&#916;}G&#176; to Individual Water Layers., Polymers, [online], (Accessed July 22, 2024)


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Created January 24, 2013, Updated February 19, 2017