Effect of sodium chloride on solute–solvent interactions in aqueous polyethylene glycol–sodium sulfate two-phase systems

Abstract

Partition behavior of eight small organic compounds and six proteins was examined in poly(ethylene glycol)-8000-sodium sulfate aqueous two-phase systems containing 0.215M NaCl and 0.5M osmolyte (sorbitol, sucrose, TMAO) and poly(ethylene glycol)-10000-sodium sulfate-0.215M NaCl system, all in 0.01M sodium phosphate buffer, pH 6.8. The differences between the solvent properties of the coexisting phases (solvent dipolarity/polarizability, hydrogen bond donor acidity, and hydrogen bond acceptor basicity) were characterized with solvatochromic dyes using the solvatochromic comparison method. Differences between the electrostatic properties of the phases were determined by analysis of partitioning of sodium salts of dinitrophenylated (DNP-) amino acids with aliphatic alkyl side-chain. The partition coefficients of all compounds examined (including proteins) were described in terms of solute-solvent interactions. The results obtained in the study show that solute-solvent interactions of nonionic organic compounds and proteins in polyethylene glycol-sodium sulfate aqueous two-phase system change in the presence of NaCl additive.

Effects of sodium chloride and sodium perchlorate on properties and partition behavior of solutes in aqueous dextran-polyethylene glycol and polyethylene glycol-sodium sulfate two-phase systems

“…Aqueous two-phase systems were prepared as described previously [20,21]. Stock solutions of PEG 8000 (50 wt.%), PEG-10000 (50 wt.%) and Na 2 SO 4 (20.3 wt.%) were prepared in water.…”

“…All solvatochromic measurements in the phases of ATPSs used were performed as described previously [20,21]. The detailed description of the protocols used is provided in SI B.…”

“…Partitioning of the homologous series of Na-salts of dinitrophenylated (DNP-) amino acids was examined in order to estimate the difference between the relative hydrophobic and electrostatic properties of the phases as described previously [5,20,21]. Partition coefficients of Na-salts of DNP-amino acids with the aliphatic alkyl side-chains of the increasing length (alanine, norvaline, norleucine, and ␣-amino-n-octanoic acid) in the ATPS under study are listed below in Tables 1-3 and Tables A1-A3 and shown graphically as functions of the equivalent number of methylene groups representing the length of the alkyl side-chain in Fig.…”

“…where K DNP-AA is the partition coefficient of a sodium salt of DNPamino acid with aliphatic side-chain; superscript (i) denotes the particular i th ATPSs used for the partition experiments; N C is equivalent number of CH 2 groups in the aliphatic alkyl side-chain of a given DNP-amino acid; E is an average logK increment per CH 2 group; C represents the total contribution of the non-alkyl part of the structure of a DNP-amino acid into logK DNP-AA and used to char- acterize the difference between the electrostatic properties of the coexisting phases as described previously [5,20,21]. The differences between the hydrophobic and electrostatic properties of the phases characterized by the C and E values are listed for all the ATPSs under comparison in Table 4.…”

“…(1) as described in SI A are also present in Table 4. It has been shown previously [5,20,21] that partition behavior of solutes in any given ATPS is affected by the solvent features of the coexisting phases, such as the solvent dipolarity/polarizability (*) characterizing the ability of water to participate in dipoledipole and dipole-induced dipole interactions with a solute, solvent hydrogen bond donor acidity (␣), and hydrogen bond acceptor basicity (␤). The differences between these solvent features of the phases determined as described in SI B are also listed in Table 4.…”