Fluorescence in poly(ethylene glycol) (PEGs 400-12000) solutions is reported here for the first time. PEG solutions form a vesicular organization with the hydrophilic groups attached at both ends which arrange themselves beyond a particular concentration and offer electron-dense regions at the center of the vesicle. These vesicles provide an inherent site for fluorescence generation in PEG solutions. Fluorescence emission was observed at ~380 nm with an excitation wavelength of 300 nm. PEG of molecular weight 6000 was found to show maximum emission intensity at a particular concentration. The formation of PEG vesicles (~1 nm size) was confirmed by dynamic light scattering (DLS) and confocal laser microscopy. On addition of metal ions the polymeric vesicle breaks up to monomeric PEG, and hence, the fluorescence intensity decreases with a red shift. Fluorescence lifetime measurements indicate the nature of complexation of the metals with PEG. Since PEGs are used as one of the phases in aqueous biphasic systems (ABS) of liquid-liquid extractions, the nature of the fluorescence emission spectrum of the PEG phase after extraction was studied. Metal extraction in the PEG-rich phase of an ABS leads to quenching of fluorescence in PEG.

The present study aims at the generation of a triblock copolymer vs sodium sulfate aqueous biphasic system (ABS), its application toward extraction of molybdenum species, and finally purification and regeneration of the block copolymer. The ABS was characterized for its biphasic region by constructing the phase diagram using turbidometric titration methods. Extractions were monitored using the spectrophotometric method directly in the block copolymer medium. Complete extraction of molybdenum species was observed in this method. Interference from other closely related metal ions in the extraction process was found to be negligible excepting oxo and polyoxometallates of vanadium and tungsten. Regeneration of the polymer was done using a thermoseparation technique followed by successive treatment with ion exchange resins. ∼87% of the pure triblock copolymer could be regenerated as a result of such treatment.

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A carbohydrate-based aqueous biphasic system (ABS) has been designed by adding an aqueous solution of sugar alcohols (D-mannitol and glycerol) to poly(propylene glycol) (PPG#400). The phase diagrams of the ABSs have been constructed using the turbidometric titration method at 309 K. The tie-line lengths and the slope of tie lines of the system have been obtained using the gravimetric method. The use of sugar alcohol to replace the salt-rich phase for phase separation makes the ABS apt for extracting different molecules of biological relevance. Using one of these newly constructed eco-friendly ABSs, D-mannitol vs PPG#400, the extraction behaviors of Ivermectin and Doxycycline (which have been extensively used to treat COVID-19 patients) were studied at different pH values. About 90% of Ivermectin and 70% of Doxycycline has been extracted to the polymer-rich phase of ABS at pH 7 in single extraction. The extraction patterns of these two drugs remain almost the same even in the presence of Lascorbic acid and zinc acetate, which are also administered as combination drugs in the treatment of COVID-19. We have also studied the extraction behavior of Prednisolone, a corticosteroid, which also is widely recommended to particularly treat the severity of the cytokine storm that arises in many patients at the third phase of COVID-19. Complete extraction of Prednisolone has been achieved at pHs 3 and 5, and ∼97% of extraction has been achieved at pH 7. The objective of such extraction is to design cleaner methods of remediation of these drugs to minimize their exposure to the environment that may lead to drug resistance in the environment. We have also recovered the polymer using thermoseparation and adsorption techniques after extraction experiments to make the method environmentally as well as economically viable.