The Effect of NaCl on the Conformational Behavior of Acenaphthylene Labeled Poly( N , N ‐diethylacrylamide) in Dilute Aqueous Solution

Summary: The effect of salts on the conformational behavior of acenaphthylene labeled poly( N , N ‐diethylacrylamide) (PDEA/ACE) has been investigated in dilute aqueous solution using UV‐vis and fluorescence spectroscopy. It is demonstrated here that the effectiveness of various salts in changing the lower critical solution temperature ( T LCS ) of the PDEA/ACE solution followed the Hoffmeister series. The addition of NaCl linearly lowered the T LCS . In dilute aqueous solution, the PDEA/ACE adopted a loose coil conformation below its T LCS . The PDEA/ACE adopted a compact globule conformation above the temperature at which the coil to globule transition (CGT) was completed. A fluorescence anisotropy investigation suggested that a molten globule conformation existed during the CGT of the PDEA/ACE solution. In all of the above three conformations, the PDEA/ACE was more compact in the presence of NaCl than in the absence of any salt.Temperature and NaCl concentration dependence of fluorescence anisotropy of a PDEA/ACE solution. Inset: thermodynamically stable states of PDEA/ACE.