Ultrasensitive pH-Induced Water Solubility Switch Using UCST Polymers

For some thermosensitive polymers, the absence of an upper critical solution temperature (UCST) in water in an accessible temperature range (say, 5–90 °C) can be attributed to the influence of charged groups in the polymer structure. This property was exploited in the present study to achieve ultrasensitive pH-induced water solubility switch of UCST polymers in physiological medium. By incorporating either acrylic acid (AAc) or 4-vinylpyridine (4VP) comonomer units in the random copolymer of acrylamide and acrylonitrile (P­(AAm-<i>co</i>-AN-<i>co</i>-AAc) or P­(AAm-<i>co</i>-AN-<i>co</i>-4VP)), the pH-induced shift of UCST was investigated by monitoring the solution cloud point. The results revealed an unusually large shift of the cloud point upon pH variation over a small range. In particular, one P­(AAm-<i>co</i>-AN-<i>co</i>-4VP) sample exhibited a cloud point drop from 72 °C at pH 4.75 to 15 °C at pH 4.50 (i.e., 57 K shift over 0.25 pH units), and its transition from soluble to insoluble state at room temperature was visually observable over a pH change as little as 0.05 unit. Using this sample as macromolecular chain transfer agent to polymerize dimethylacrylamide (DMA) through RAFT, an ABA-type triblock copolymer of P­(AAm-<i>co</i>-AN-<i>co</i>-4VP)-<i>b</i>-PDMA-<i>b</i>-P­(AAm-<i>co</i>-AN-<i>co</i>-4VP) was obtained, and it showed an even larger cloud point switch from 71 to 10 °C with pH decreasing from 4.75 to 4.50. Consequently, the micelle formed by this block copolymer was stable at 37 °C with pH from 7.00 down to 4.75 but abruptly dissolved at pH 4.50 due to the water solubility switch. This study demonstrates a new UCST polymer-based approach to polymer assemblies that can sense a very small pH change by undergoing straightforward water solubility switch

CO₂‑Responsive Polymer Single-Chain Nanoparticles and Self-Assembly for Gas-Tunable Nanoreactors

CO₂-responsive polymer single-chain nanoparticles (SCNPs) and self-assembled micellar aggregates are investigated as gas-controlled, rate- and size-tunable nanoreactors of gold nanoparticles (AuNPs). On one hand, SCNPs are prepared from a random copolymer of poly­{(<i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate)-<i>co</i>-4-methyl-[7-(methacryloyl)­oxy-ethyl-oxy]­coumarin} (P­(DMAEMA-<i>co</i>-CMA)). When dispersed in aqueous solution, individual nanoparticles can undergo reversible swelling/shrinking under alternating CO₂/N₂ stimulation as a result of the reversible protonation/deprotonation of tertiary amine groups. On the other hand, tadpole-like single-chain “Janus” nanoparticles (SCJNPs) are prepared using an amphiphilic diblock copolymer of PS-<i>b</i>-P­(DMAEMA-<i>co</i>-CMA) (PS is hydrophobic polystyrene). This type of SCJNPs can self-assemble into core–shell micellar aggregates in aqueous solution. Under CO₂/N₂ stimulation, the collective swelling/shrinking of SCJNPs within the micelle results in large, reversible volume change. Both P­(DMAEMA-<i>co</i>-CMA) SCNPs and PS-<i>b</i>-P­(DMAEMA-<i>co</i>-CMA) SCJNP micelles are explored as gas-tunable nanoreactors for AuNPs. The rate of AuNP formation increases under CO₂ stimulation and decreases upon N₂ bubbling, which makes it possible to tune the reaction rate up and down (on/off switching) by using the two gases. Moreover, using the micelles of SCJNPs, whose volume can be controlled over a wide range by adjusting the CO₂ stimulation strength, variable-size AuNPs and their aggregates are obtained with continuous redshift of the surface plasmon resonance (SPR) into the long-wavelength visible light region

CO₂‑Responsive Polymer Single-Chain Nanoparticles and Self-Assembly for Gas-Tunable Nanoreactors

CO₂-responsive polymer single-chain nanoparticles (SCNPs) and self-assembled micellar aggregates are investigated as gas-controlled, rate- and size-tunable nanoreactors of gold nanoparticles (AuNPs). On one hand, SCNPs are prepared from a random copolymer of poly­{(<i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate)-<i>co</i>-4-methyl-[7-(methacryloyl)­oxy-ethyl-oxy]­coumarin} (P­(DMAEMA-<i>co</i>-CMA)). When dispersed in aqueous solution, individual nanoparticles can undergo reversible swelling/shrinking under alternating CO₂/N₂ stimulation as a result of the reversible protonation/deprotonation of tertiary amine groups. On the other hand, tadpole-like single-chain “Janus” nanoparticles (SCJNPs) are prepared using an amphiphilic diblock copolymer of PS-<i>b</i>-P­(DMAEMA-<i>co</i>-CMA) (PS is hydrophobic polystyrene). This type of SCJNPs can self-assemble into core–shell micellar aggregates in aqueous solution. Under CO₂/N₂ stimulation, the collective swelling/shrinking of SCJNPs within the micelle results in large, reversible volume change. Both P­(DMAEMA-<i>co</i>-CMA) SCNPs and PS-<i>b</i>-P­(DMAEMA-<i>co</i>-CMA) SCJNP micelles are explored as gas-tunable nanoreactors for AuNPs. The rate of AuNP formation increases under CO₂ stimulation and decreases upon N₂ bubbling, which makes it possible to tune the reaction rate up and down (on/off switching) by using the two gases. Moreover, using the micelles of SCJNPs, whose volume can be controlled over a wide range by adjusting the CO₂ stimulation strength, variable-size AuNPs and their aggregates are obtained with continuous redshift of the surface plasmon resonance (SPR) into the long-wavelength visible light region

Enantioselective Hydrogenation of β‑Ketophosphonates with Chiral Ru(II) Catalysts

Highly effective asymmetric hydrogenation of β-ketophosphonates in the presence of Ru–(<i>S</i>)-SunPhos as catalyst was realized; good to excellent enantioselectivities (up to 99.9% ee) and excellent diastereoselectivities (96:4) were obtained

Photoresponsive Coumarin Polyesters That Exhibit Cross-Linking and Chain Scission Properties

The synthesis and properties of a new class of photoresponsive coumarin polyesters are described. Incorporation of the coumarin chromophore in the polymer chain provides interesting properties such as polymer chain cross-linking upon irradiation at 350 nm and chain un-cross-linking when irradiated at 254 nm. In addition, irradiation at 254 nm also results in polymer chain scission. The cross-linking, un-cross-linking, and chain scission properties were studied by ssNMR, ATR-IR, and GPC measurements. These properties enable the fabrication of 2D surfaces having complementary micropatterned features. Also, initial biocompatibility profiles of the polymers and their irradiation products were demonstrated using MTT assays

Ruthenium-Catalyzed Enantioselective Hydrogenation of Aryl-Pyridyl Ketones

Various substituted aryl-pyridyl ketones were hydrogenated in the presence of Ru-XylSunPhos-Daipen bifunctional catalytic system with enantiomeric excesses up to 99.5%. Upon introduction of a readily removable <i>ortho</i>-bromo atom to the phenyl ring, enantiomerically enriched 4-chlorophenylpyridylmethanol was obtained by hydrogenation method with 97.3% ee, which provided an important chiral intermediate for some histamine H₁ antagonists