6 research outputs found
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 (PÂ(AAm-<i>co</i>-AN-<i>co</i>-AAc) or PÂ(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 PÂ(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 PÂ(AAm-<i>co</i>-AN-<i>co</i>-4VP)-<i>b</i>-PDMA-<i>b</i>-PÂ(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
CO<sub>2</sub>‑Responsive Polymer Single-Chain Nanoparticles and Self-Assembly for Gas-Tunable Nanoreactors
CO<sub>2</sub>-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 polyÂ{(<i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate)-<i>co</i>-4-methyl-[7-(methacryloyl)Âoxy-ethyl-oxy]Âcoumarin} (PÂ(DMAEMA-<i>co</i>-CMA)). When dispersed in aqueous solution, individual
nanoparticles can undergo reversible swelling/shrinking under alternating
CO<sub>2</sub>/N<sub>2</sub> 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>-PÂ(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 CO<sub>2</sub>/N<sub>2</sub> stimulation, the collective swelling/shrinking of SCJNPs within
the micelle results in large, reversible volume change. Both PÂ(DMAEMA-<i>co</i>-CMA) SCNPs and PS-<i>b</i>-PÂ(DMAEMA-<i>co</i>-CMA) SCJNP micelles are explored as gas-tunable nanoreactors
for AuNPs. The rate of AuNP formation increases under CO<sub>2</sub> stimulation and decreases upon N<sub>2</sub> 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 CO<sub>2</sub> 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
CO<sub>2</sub>‑Responsive Polymer Single-Chain Nanoparticles and Self-Assembly for Gas-Tunable Nanoreactors
CO<sub>2</sub>-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 polyÂ{(<i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate)-<i>co</i>-4-methyl-[7-(methacryloyl)Âoxy-ethyl-oxy]Âcoumarin} (PÂ(DMAEMA-<i>co</i>-CMA)). When dispersed in aqueous solution, individual
nanoparticles can undergo reversible swelling/shrinking under alternating
CO<sub>2</sub>/N<sub>2</sub> 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>-PÂ(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 CO<sub>2</sub>/N<sub>2</sub> stimulation, the collective swelling/shrinking of SCJNPs within
the micelle results in large, reversible volume change. Both PÂ(DMAEMA-<i>co</i>-CMA) SCNPs and PS-<i>b</i>-PÂ(DMAEMA-<i>co</i>-CMA) SCJNP micelles are explored as gas-tunable nanoreactors
for AuNPs. The rate of AuNP formation increases under CO<sub>2</sub> stimulation and decreases upon N<sub>2</sub> 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 CO<sub>2</sub> 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 H<sub>1</sub> antagonists