Polyoxometalates (POMs) have a broad
array of applied platforms
with well-characterized catalysis including photocatalysis to achieve
aliphatic C(sp3)–H bond functionalization. However,
the reaction mechanism of POMs in organic transformation remains unknown
due to the complexity of POM structures. Here, a challenging [W10O32]4–/Ni metallaphotoredox-catalyzed
C(sp3)–H arylation of alkane has been investigated
by density functional theory (DFT) calculations. The calculation revealed
that the superficial active center located in bridged oxygen of *[W10O32]4– is responsible for the
abstraction of a foreign hydrogen atom and the activation of a C(sp3)–H bond. Furthermore, we discussed this activated
process using the direct activation model of the C(sp3)–H
σ-bond to deepen our mechanistic understanding of POM mediated
C–H bond activation via the hydrogen atom transfer (HAT) pathway.
Specifically, comparing three common mechanisms for nickel catalysis
inducing by Ni0, NiI, and NiII to
construct a C–C bond, the nickel catalytic cycle induced by
the NiI active catalyst is profitable in kinetics and thermodynamics.
Finally, a radical mechanism merging the ([W10O32]4––*[W10O32]4––[HW10O32]4––[W10O32]4–) decatungstate
reductive quenching cycle, ([HW10O32]4––[H2W10O32]4––[HW10O32]4–) electron
relay, and (NiI–NiII–NiI–NiIII–NiI) nickel catalytic
cycle is proposed to be favorable. We hope that this work would provide
a better understanding of the unique catalytic activity of decatungstate
anions for the direct functionalization of the C(sp3)–H
bond.
The liquid molding used was a straightforward and simple method to produce drug releasing highly mucoadhesive films, which could be utilized in treating local oral diseases, such as periodontitis. All materials used were natural biodegradable polymers from renewable sources, which are generally regarded as safe.
Herein,
a simple hierarchical surface patterning method is presented
by effectively combining buckling instability and azopolymer-based
surface relief grating inscription. In this technique, submicron patterns
are achieved using azopolymers, whereas the microscale patterns are
fabricated by subsequent thermal shrinkage. The wetting characterization
of various topographically patterned surfaces confirms that the method
permits tuning of contact angles and choosing between isotropic and
anisotropic wetting. Altogether, this method allows efficient fabrication
of hierarchical surfaces over several length scales in relatively
large areas, overcoming some limitations of fabricating multiscale
roughness in lithography and also methods of creating merely random
patterns, such as black silicon processing or wet etching of metals.
The demonstrated fine-tuning of the surface patterns may be useful
in optimizing surface-related material properties, such as wetting
and adhesion, producing substrates that are of potential interest
in mechanobiology and tissue engineering.
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