Polyethylene glycol (PEG-8000, Lot# SLBW6815) with molecular weight (Mw) of 8000 Da, polypropylene glycol (PPG-400, Lot# BCBT9613) with Mw of 400 Da, and polyvinylpyrrolidone (PVP-40,000 Lot# WXBD4555V and Lot# WXBB3898V) with Mw of 40,000 Da were obtained from Sigma-Aldrich (St. Louis, MO, USA). Polyacrylamide (PAM-10,000, Lot# A804225) with Mw of 10,000 Da (50% wt. in water solution) was purchased from Polysciences, Inc. (Warrington, PA, USA). Ucon 50-HB-5100 (Ucon-3930, Lot# SJ1955S3D2), a random copolymer of 50% ethylene oxide and 50% propylene oxide, with Mw of 3930, was purchased from Dow-Chemical (Midland, MI, USA). Sodium sulfate, sodium phosphate monobasic, sodium phosphate dibasic, and KCl of analytical reagent grade were purchased from Fisher Scientific (Waltham, MA, USA) and used without further purification. Ultrapure water purified using a Millipore Milli-Q lab water system was used for preparation of all solutions.
Dinitrophenylated (DNP-) amino acids (DNP-alanine, DNP-norvaline, DNP-norleucine, and DNP-α-amino-N-octanoic acid) were purchased from Sigma-Aldrich. The sodium salts of the DNP-amino acids were prepared by titration.
Dinitrophenylated (DNP-) amino acids (DNP-alanine, DNP-norvaline, DNP-norleucine, and DNP-α-amino-N-octanoic acid) were purchased from Sigma-Aldrich. The sodium salts of the DNP-amino acids were prepared by titration.