1 research outputs found
Macromolecular Crowding Modifies the Impact of Specific Hofmeister Ions on the Coil–Globule Transition of PNIPAM
Macromolecular crowding alters many
biological processes ranging
from protein folding and enzyme reactions in vivo to the precipitation
and crystallization of proteins in vitro. Herein, we have investigated
the effect of specific monovalent Hofmeister salts (NaH<sub>2</sub>PO<sub>4</sub>, NaF, NaCl, NaClO<sub>4</sub>, and NaSCN) on the coil–globule
transition of polyÂ(<i>N</i>-isopropylacrylamide) (PNIPAM)
in a crowded macromolecular environment as a model for understanding
the specific-ion effect on the solubility and stability of proteins
in a crowded macromolecular environment. It was found that although
the salts (NaH<sub>2</sub>PO<sub>4</sub>, NaF, and NaCl) and the macromolecular
crowder (polyethylene glycol) lowered the transition temperature almost
independently, the macromolecular crowder had a great impact on the
transition temperature in the case of the chaotropes (NaClO<sub>4</sub> and NaSCN). The electrostatic repulsion between the chaotropic anions
(ClO<sub>4</sub><sup>–</sup> or SCN<sup>–</sup>) adsorbed
on PNIPAM may reduce the entropic gain of water associated with the
excluded volume effect, leading to an increase in the transition temperature,
especially in the crowded environment. Furthermore, the affinity of
the chaotropic anions for PNIPAM becomes small in the crowded environment,
leading to further modification of the transition temperature. Thus,
we have revealed that macromolecular crowding alters the effect of
specific Hofmeister ions on the coil–globule transition of
PNIPAM