Emulsion liquid membrane pertraction of l-cysteine from sodium chloride aqueous solutions mediated by a narrow rim phosphorylated cone-shaped calix[4]arene

Abstract

The transport of l-cysteine (l-cys) from sodium chloride aqueous solutions through emulsion liquid membranes mediated by a cone conformation of calix[4]arene substituted at the narrow rim by two Ph2PO groups named 5,11,17,23-tetra-tert-butyl-25,27-bis(diphenylphosphinoylmethoxy)-26,28-dihydroxycalix[4]arene (CX), into hydrochloric acid solution has been investigated. It is proposed that the process takes place by an ion-pair formation mechanism between [Na·CX]+ complexes and deprotonated l-cysteine species (l-cys−). The influence of pH of the external aqueous phase, kind of the salt used in the aqueous phase, the carrier and surfactant concentration in the membrane, the acid concentration in the receiving phase, the emulsification and mixing speeds on the process efficiency were examined and discussed. A quantitative and highly selective transport of l-cysteine has been occurred under optimized experimental conditions. These conditions were as follows: 1.3 × 10−3 M of the calix[4]arene, liquid paraffin as diluent, 4 % surfactant (non-ionic polyamine surfactant ECA-4360), emulsification rate 11,000 rpm for preparation of the membrane, 30 min of stirring (800 rpm) in the extraction step and using 2 M solution of hydrochloric acid as stripping phase. UV–Vis Spectroscopy and TLC method using ninhydrin, as indicator, were used for amino acid analysis.