New Insights into the Partitioning of Phenothiazine Dyes in Aqueous Two-Phase Systems

Yara Coelho,Luis Da Silva,Gabriel Ferreira,Alan De Castro,Guilherme Ferreira,Eliara Hudson,Ana Clarissa Pires,Álvaro Agudelo

doi:10.21577/0103-5053.20200056

Abstract

Aqueous two-phase systems (ATPSs) have proven to be efficient and environmentally safe methods for extracting chemical species. However, the driving forces behind the partition of solutes in these systems are still little understood. A complete thermodynamic partitioning of phenothiazine dyes was investigated in poly(ethylene oxide) (PEO) + salt + water ATPSs. Standard transfer parameters (Gibbs free energy change (ΔtrGo), enthalpy change (ΔtrHo) and entropy change (TΔtrSo)) were evaluated, and their dependence on the dye structure, electrolyte nature and tie line length (TLL). All phenothiazine dyes are concentrated predominantly in the polymer enriched phase, with ΔtrGo values ranging from -4.1 up to -13.4 kJ mol-1. Due to the dye-PEO attractive interactions that occur mainly via benzene condensed ring present in the structures of phenothiazine dyes, the partitioning of these dyes was enthalpically driven, with -11.4 ≥ ΔtrHo ≥ -52 kJ mol-1 and -4.93 ≥ TΔtrSo ≥ -38 kJ mol-1.

Highlights

Since 1958 with the pioneering work of Albertson,[1] aqueous two-phase systems (ATPS) have proven to be efficient and environmentally safe methods for the extraction and purification of a great number of chemical species, such as enzymes,[2] proteins,[3] metals,[4,5] nanoparticles,[6] carbon nanotubes,[7] and synthetic[8,9,10,11,12,13] and natural[14,15,16] dyes
The ΔtrHo values for methylene blue (MB), azure B (AZB) and azure A (AZA) in each tie line length (TLL) were obtained through the following steps: the energy associated with the dilution process ( ) was determined by filling the reference and the sample cells with 1.80 mL of the bottom phase, and titrating the sample solution with fifteen consecutive injections of 15 μL of dye at a concentration of 0.5 mmol kg−1 injected into the bottom phase of the Aqueous two-phase systems (ATPSs)
The use of MB, AZB, AZA, and thionin acetate (TA) as probes for studying the driving forces behind the process of cationic dye transfer in different ATPSs was presented in this work for the first time

Summary

Introduction

Since 1958 with the pioneering work of Albertson,[1] aqueous two-phase systems (ATPS) have proven to be efficient and environmentally safe methods for the extraction and purification of a great number of chemical species, such as enzymes,[2] proteins,[3] metals,[4,5] nanoparticles,[6] carbon nanotubes,[7] and synthetic[8,9,10,11,12,13] and natural[14,15,16] dyes. The ΔtrHo values for MB, AZB and AZA (calorimetric experiment for the dye TA was not possible due to its precipitation in the system) in each TLL were obtained through the following steps: the energy associated with the dilution process ( ) was determined by filling the reference and the sample cells with 1.80 mL of the bottom (or top) phase, and titrating the sample solution with fifteen consecutive injections of 15 μL of dye at a concentration of 0.5 mmol kg−1 injected into the bottom (or top) phase of the ATPS.

Results

Conclusion