A series of enantiomerically enriched tertiary phosphine oxides have been prepared via the Pd‐catalyzed cross‐coupling reactions of enantiomerically pure tert‐butylphenylphosphine oxide, with a variety of aryl iodides and bromides. This new protocol under optimized reaction conditions [toluene, 110 0C, Pd(PPh3)4, K2CO3 (or Et3N)] afforded highly functionalized P‐chiral phosphine oxides with a yield of 78% to 95% and with enantiomeric excesses above 98%. The stereoretentive outcome of the cross‐coupling reactions was proved by X‐ray crystallography of selected phosphine oxides: (S)‐(2‐aminophenyl)(tert‐butyl)(phenyl)phosphine oxide (3a) and (S)‐anthracen‐9‐yl(tert‐butyl)(phenyl)phosphine oxide (3i). When attempting to convert the enantiomerically pure phosphine oxide 3a to the corresponding borane by the treatment with the borane dimethyl sulfide complex partial stereoerosion at a stereogenic phosphorus atom was observed. Racemic tert‐butyl (2‐(dimethylamino)phenyl)(phenyl)phosphine (7a) was isolated in a quantitative yield upon deprotection of the corresponding borane (8a) and converted to a palladium crystalline complex (9), the structure of which has been proved by X‐ray crystallography.
Dynamic hydrogels with thermosensitive
cross-links are highly promising
platforms for “on-demand” drug delivery
systems. However, there is a problem with triggering a response in
their whole volume, which reduces their efficiency. To achieve better
thermoresponsiveness, a graphene oxide-filled composite hydrogel based
on boronic ester cross-links, composed of hyperbranched polyglycidol,
HbPGL, and poly(acrylamide-ran-2-acrylamidephenylboronic acid), poly(AM-ran-2-AAPBA),
has been constructed. The homogeneous embedment of graphene oxide
(GO) in the network assured near-infrared (NIR)-photothermal response
in its bulk due to the rapid light-to-heat conversion. The rate and
amplitude of materials response increase with graphene oxide concentration.
The temperature of the hydrogel containing graphene oxide at a concentration
of 13.2 mg/mL increased from 36.6 to 41 °C in 29 s upon NIR irradiation.
The network diffusivity and the extent of its change with temperature
can be regulated by the length of the applied boronic acid-based cross-linking
agent. The hydrogel constructed on the shorter copolymer (M
n = 23 000 g/mol) displayed a significant
increase in diffusivity with temperature. A diffusion ordered NMR
study revealed that the diffusion coefficient determined for niacin,
a model drug encapsulated in the hydrogel, increased from 6.09 ×
10–10 at 25 °C to 1.28 × 10–9 m2/s at 41 °C. In the case of the hydrogel constructed
on the longer acrylamide copolymer (M
n = 43 000 g/mol), in which physical entanglements stabilize
the network, the change of encapsulated niacin diffusion coefficient
was significantly smaller, i.e., from 3.83 × 10–10 at 25 °C to 6.63 × 10–10 m2/s at 41 °C. The possibility of on-demand NIR-regulated diffusivity
of the reported boronic ester-based hydrogels makes them promising
candidates for controlled drug delivery platforms.
We present an unexpected self-assembly of a glycoluril clip-poly(ε-caprolactone) conjugate in chloroform. The conjugate forms homodimer aggregates due to supramolecular interactions between glycoluril moieties, which was confirmed with MALDI-TOF-ms and 1H NMR. TEM revealed the formation of multilayered nanosized prism-shaped objects resembling tree bark in nature.
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