Water-Soluble Polymeric Probe for the Selective Sensing and Separation of Cu(II) Ions in Aqueous Media: pH-Tunable Detection Sensitivity and Efficient Separation by Thermal Precipitation

Abstract

A thiosemicarbazone-based water-soluble polymeric probe was developed for the selective colorimetric detection of Cu­(II) ions with pH-tunable sensitivity. The successful separation of Cu­(II) ions from several alkali and transition metal cations by thermal precipitation was demonstrated. N , N -Dimethylacrylamide (DMA) and 3-vinylbenzaldehyde (VBA) were copolymerized by reversible addition–fragmentation chain transfer (RAFT) polymerization to produce p­(DMA-co-VBA), herein P1. The aldehyde group of P1 was reacted with 4-phenyl­thiosemicarbazide to yield poly­{DMA-co-[N-phenyl-2-(3-vinylbenzylidene)­hydrazine­carbothioamide]}, [p­(DMA-co-PVHC)], herein P2. Upon the addition of Cu­(II) ions to an aqueous solution of P2, the color of the solution turned from colorless to yellow due to the formation of a coordination complex between the Cu­(II) ions and phenylthio­semicarbazone units of P2, herein P2–Cu­(II). The availability of the electron-rich imino nitrogen in the thiosemicarbazone units allowed P2 to show excellent sensing behavior toward Cu­(II) ions. P2 has remarkable pH-switchable sensing properties toward Cu­(II) ions. Although efficient colorimetric sensing was observed at neutral or high pH, no appreciable color change appeared at low pH. Protonation of the imino nitrogen at low pH prevented the formation of coordination complexes. Cu­(II) ions were separated successfully from various alkali and transition metal cations by thermal precipitation due to the thermoresponsive property of P2–Cu­(II).

Use of Core-Cross-Linked Polymeric Micelles Induced by the Selective Detection of Cu(II) Ions for the Sustained Release of a Model Drug

“…Furthermore, the originally colorless solution became yellow due to the formation of coordination complexes between Cu(II) ions and the phenylthiosemicarbazone units of p(DMA-b-PVHC) micelles. 36,45 As previously reported, p(DMA-b-PVHC) exhibited good selectivity toward Cu(II) ions in the presence of several alkali and transition metal cations (Figure 2b). Interestingly, the Cu(II) ion detection process is time-dependent.…”

“…The gradual decrease in intensity of the absorption maximum at 318 nm and the gradual increase in absorbance at 390 nm, which contains the onset of the greenish-yellow color, coupled with the overall broadening of the absorption band were observed upon the addition of the Cu­(II) ion solution. Furthermore, the originally colorless solution became yellow due to the formation of coordination complexes between Cu­(II) ions and the phenylthiosemicarbazone units of p­(DMA- b -PVHC) micelles. , As previously reported, p­(DMA- b -PVHC) exhibited good selectivity toward Cu­(II) ions in the presence of several alkali and transition metal cations (Figure b). Interestingly, the Cu­(II) ion detection process is time-dependent.…”

“…28−35 We recently reported a method for the selective colorimetric sensing of Cu(II) ions in aqueous media based on the use of polymeric probes with phenylthiosemicarbazone units as ligands. 36 In recent years, efforts have been made to merge advances in sensor technology with those in drug delivery systems because the continuous monitoring of specific target species is often needed to achieve efficient disease treatment. The integration of sensing and drug delivery systems is an efficient approach to control drug release.…”

“…A postpolymerization modification reaction was conducted as previously reported. 36 Briefly, p(DMA-b-VBA) (0.179 g, 0.135 mmol per VBA repeating unit) and 4-phenylthiosemicarbazide (45.2 mg, 0.270 mmol) were added to a round-bottom flask and dissolved in THF (50 mL); the resulting solution was then heated at 80 °C overnight. The solution was concentrated and precipitated in diethyl ether.…”

“…Recently, the selective detection of transition metal ions has become increasingly important. In particular, sensing Cu­(II) ions have attracted special attention because these ions have both positive and negative effects on human health and the environment. , While numerous methods have been developed to detect Cu­(II) ions effectively, colorimetric detection via the formation of complexes between ligands and Cu­(II) ions has been proposed by many researchers. − We recently reported a method for the selective colorimetric sensing of Cu­(II) ions in aqueous media based on the use of polymeric probes with phenylthiosemicarbazone units as ligands …”