BODIPY-Derived Polymeric Chemosensor Appended with Thiosemicarbazone Units for the Simultaneous Detection and Separation of Hg(II) Ions in Pure Aqueous Media

Developing a simple and cheap analytical method for the selective detection and quantitative separation of toxic ions present in aqueous media is the biggest challenge faced by the chemosensing research community. Here, a 5,5-difluoro-1,3,7,9-tetramethyl-10-phenyl-5H-dipyrrolo-diazaborinine-derived water-soluble polymer integrated with thiosemicarbazone units was rationally designed and synthesized for the simultaneous detection and separation of Hg­(II) ions in pure aqueous solution. The water-soluble polymer scaffold poly­(N,N′-dimethyl acrylamide-co-5,5-difluoro-1,3,7,9-tetramethyl-10-phenyl-5H-dipyrrolo-diazaborinine-2-carbaldehyde) was synthesized by reversible addition–fragmentation chain transfer polymerization, followed by post-polymerization modification with thiosemicarbazide, leading to the formation of the target probe, P1. The nonemitting P1 exhibited bright yellow emission upon exposure to Hg­(II) ions, with a limit of detection as low as 0.37 μM. This turn-on emission behavior triggered by Hg­(II) ions might originate from the suppression of isomerization around the CN bond of the thiosemicarbazone moiety caused by the formation of a coordination complex between P1 and Hg­(II) ions. In addition, P1 displayed excellent selectivity toward Hg­(II) ions over other metal cations. Finally, the selective removal of Hg­(II) ions from an aqueous solution containing various metal ions was achieved by precipitation, which is probably caused by the fact that coordination complexes whereby Hg­(II) ions acted as bridgeheads between P1 molecules had formed

Remarkable Swelling Capability of Amino Acid Based Cross-Linked Polymer Networks in Organic and Aqueous Medium

This work reports design and synthesis of side chain amino acid based cross-linked polymeric gels, able to switch over from organogel to hydrogel by a simple deprotection reaction and showing superabsorbancy in water. Amino acid based methacrylate monomers, <i>tert</i>-butoxycarbonyl (Boc)-l/d-alanine methacryloyloxyethyl ester (Boc-l/d-Ala-HEMA), have been polymerized in the presence of a cross-linker via conventional free radical polymerization (FRP) and the reversible addition–fragmentation chain transfer (RAFT) technique for the synthesis of cross-linked polymer gels. The swelling behaviors of these organogels are investigated in organic solvents, and they behave as superabsorbent materials for organic solvents such as dichloromethane, acetone, tetrahydrofuran, etc. Swollen cross-linked polymer gels release the absorbed organic solvent rapidly. After Boc group deprotection from the pendant alanine moiety, the organogels transform to the hydrogels due to the formation of side chain ammonium (−NH₃⁺) groups, and these hydrogels showed a significantly high swelling ratio (∼560 times than their dry volumes) in water. The morphology of organogels and hydrogels is studied by field emission scanning electron microscopy (FE-SEM). Amino acid based cross-linked gels could find applications as absorbents for oil spilled on water as well as superabsorbent hydrogels

CdS Quantum Dots Doped Tuning of Deswelling Kinetics of Thermoresponsive Hydrogels Based on Poly(2-(2-methoxyethoxy)ethyl methacrylate)

Thermoresponsive poly­(2-(2-methoxyethoxy)­ethyl methacrylate) (PMEO₂MA) based hybrid nanocomposite hydrogels (NCH) were synthesized by dispersing preformed cadmium sulfide (CdS) quantum dots (QDs) in the reaction mixture followed by polymerization via reversible addition–fragmentation chain transfer (RAFT) technique. High doping capacity and negligible QDs leakage were observed for hydrophilic QDs doped hydrogels (hpl-NCH) due to H-bonding interactions between QDs and pendant groups of hydrogel network. The hpl-NCH networks showed improved structural/orientational order and swelling ratios with increasing doping concentration compared to the organic hydrogel (OH). Opposite trends were observed for bulk-CdS (NCH-bulk) and 1-dodecanethiol capped CdS (NCH-DDT) doped hydrogels. Swelling induced linear retardance and quenching of photoluminescence (PL) intensity for hydrogels were exploited to study the deswelling kinetics respectively by Mueller matrix polarimetry and solid state fluorimetry, which were further corroborated with gravimetric analysis. For all the NCH, deswelling process significantly decreased with increasing temperature, which followed the order: 30 > 45 > 60 °C. Slower deswelling was observed for NCH-bulk and hpl-NCH compared to the OH, and also with increase in doping concentration due to the formation of skin layer. However, NCH-DDT exhibited accelerated deswelling process and the order was reversed with respect to doping concentration due to DDT mediated enhanced hydrophobic aggregation and water leakage channels created by long hydrophobic free-mobile nature of QDs surface tethered DDT molecules. The presented methodology provides tunable deswelling of PMEO₂MA based hydrogels by doping with hydrophilically/hydrophobically modified CdS QDs

Polyisobutylene-Based pH-Responsive Self-Healing Polymeric Gels

This work demonstrates the successful application of dynamic covalent chemistry for the construction of self-healing gels from side-chain primary amine leucine pendant diblock copolymers of polyisobutylene (PIB) ((P­(H₂N-Leu-HEMA)-<i>b</i>-PIB)) in the presence of PIB based dialdehyde functionalized cross-linker (HOC–PIB–CHO) through imine (−HCN−) bond formation without aiding any external stimuli. Gels were synthesized in 1,4-dioxane at room temperature at varied wt % of gelator concentration, [H₂N]/[CHO] ratios and molecular weight of the block segments. The mechanical property of gels was examined by rheological measurements. We observed higher value of storage modulus (<i>G</i>′) than the loss modulus (<i>G</i>″) within the linearity limits of deformation, indicating the rheological behavior in the gel is dominated by an elastic property rather than a viscous property. The <i>G</i>′ values significantly depend upon the extent of cross-linking in the gel network. To establish self-healing property of the gels, rheology analysis through step-strain measurements (strain = 0.1 to 200%) at 25 °C was performed. The polymeric gel network shows reversible sol–gel transition for several cycles by adjusting the pH of the medium with the help of hydrochloric acid (HCl) and triethylamine (Et₃N) triggers. FT-IR spectroscopy established formation of imine bonds in the gel network and these gels showed poor swelling behavior in various organic solvents because of the small interstitial porosity, confirmed by field emission-scanning electron microscopy (FE-SEM)