M. Taha, B. Gupta, I. Khoiroh
Oct 18, 2011
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45
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Journal
Macromolecules
Abstract
Proteins are practically never in a buffer-free solution. We therefore studied the effects of some important biological buffers 2-(N-morpholino)ethanesulfonic acid (MES), 3-(N-morpholino)propanesulfonic acid (MOPS), and 3-morpholino-2-hydroxypropanesulfonic acid (MOPSO) on the lower critical solution temperature (LCST) phase transition of poly(N-isopropylacrylamide) (PNIPAM), an isomer of polyleucine, as a model compound for protein. The results from dynamic light scattering (DLS) analysis showed that the LCST of PNIPAM aqueous solutions were decreased significantly with increasing the buffer concentration, due to the presence of the buffers destroying the hydration structures and subsequent aggregation of PNIPAM. Based on density functional theory (DFT) and molecular mechanics calculations, these buffers are highly polar compounds and, therefore, strongly interact with water molecules, causing buffering out of PNIPAM. The buffer’s affinity to water follows the order MOPS > MES > MOPSO. The LCST values de...