PEO−[M(CN)₅NO]^x- (M = Fe, Mn, or Cr) Interaction as a Driving Force in the Partitioning of the Pentacyanonitrosylmetallate Anion in ATPS: Strong Effect of the Central Atom

Abstract

The partitioning behavior of pentacyanonitrosilmetallate complexes[Fe(CN) 5 NO] (2-), [Mn(CN) 5 NO] 3(-), and [Cr(CN) 5 NO] 3(-)has been studied in aqueous two-phase systems (ATPS) formed by adding poly(ethylene oxide) (PEO; 4000 g mol (-1)) to an aqueous salt solution (Li2 SO4, Na2 SO4, CuSO4, or ZnSO4). The complexes partition coefficients ( K complex) in each of these ATPS have been determined as a function of increasing tie-line length (TLL) and temperature. Unlike the partition behavior of most ions, [Fe(CN) 5 NO] 2(-) and [Mn(CN) 5 NO] 3(-) anions are concentrated in the polymer-rich phase with K values depending on the nature of the central atom as follows: K [Fe(C N) 5 NO] 2 - >> K [ Mn (CN 5 NO] 3 - > K [C r (C N) 5 NO ]3 - . The effect of ATPS salts in the complex partitioning behavior has also been verified following the order Li2 SO 4 > Na2 SO 4 > ZnSO4. Thermodynamic analysis revealed that the presence of anions in the polymer-rich phase is caused by an EO-[M(CN) 5 NO] ( x- ) (M = Fe, Mn, or Cr) enthalpic interaction. However, when this enthalpic interaction is weak, as in the case of the [Cr(CN) 5 NO]3(-) anion ( K [Cr(CN 5 NO] 3 - < 1), entropic driving forces dominate the transfer process, then causing the anions to concentrate in the salt-rich phase.

Phase diagrams, densities and refractive indexes of poly(ethylene oxide)+organic salts+water aqueous two-phase systems: Effect of temperature, anion and molar mass

“…Aqueous two-phase system (ATPSs) have been used for the extraction, separation and purification of solutes such as proteins [1], enzymes [2], amino acids [3], antibiotics [4], nucleic acids [5], ions [6][7][8][9], nanomaterials [10], and organic molecules [11][12][13].…”

Ion-polymer interaction analysis: an inversion of NMR spin echo experimental data

“…An specific enthalpic interaction among poly(ethylene oxide) segments and [Fe(CN) 5 NO] 2− anion has been demonstrated, using FTIR measurements and phase partitioning behavior in Aqueous Two Phase Systems. [26] The initial dipole-dipole interaction between the PEO protons is perturbed by salt addition. Since the NP salt contains Fe (III), the electron-nucleus dipolar interaction is a more effective mechanism, causing a reduction in relaxation time of the PEO protons, as can be seen in equation (9).…”

Block copolymer micellization induced microphase mass transfer: Partition of Pd(II), Pt(IV) and Rh(III) in three-liquid-phase systems of S201–EOPO–Na2SO4–H2O

“…The salting-out induced aggregation and micellization of EOPO molecules account for the microphase mass transfer of PtCl into separated EOPO phase. According to previous reports [24,[35][36][37], only small amount of oxygen atoms in C-O-C of PEO chain interacted with salt cations such as Na + or H + to form so-called pseudopolycations [38,46], which were capable of interacting with negatively charged PGMs species. Here, we call the oxygen atoms interacting with salt cations or H + activity sites.…”

“…The change in phase volumes of EOPO-Na 2 SO 4 ATPS can be attributed to the variation in microphase aggregation structure of block copolymer due to molecular hydration or dehydration, conformation change or transfer of water molecules across the interfaces [35][36][37][38]. The amphiphilic EOPO block copolymer molecules would spontaneously form micelles, a compact inner hydrophobic core constructed by PPO segments and a corona hydrophilic shell composed of PEO segments, with the increase in salt concentration in ambient aqueous solutions.…”