Understanding the mechanism of molecular self-assembly to form well-organized nanostructures is essential in the field of supramolecular chemistry. Particularly, amphiphilic copolymers incorporated with polyhedral oligomeric silsesquioxanes (POSSs) have been one of the most promising materials in material science, engineering, and biomedical fields. In this review, new ideas and research works which have been carried out over the last several years in this relatively new area with a main focus on their mechanism in self-assembly and applications are discussed. In addition, insights into the unique role of POSSs in synthesis, microphase separation, and confined size were encompassed. Finally, perspectives and challenges related to the further advancement of POSS-based amphiphilics are discussed, followed by the proposed design considerations to address the challenges that we may face in the future.
A facile and sustainable electrochemical umpolung of bromide ion protocol was developed under mild reaction conditions. Transition metal catalysts and exogenous chemical oxidants were obviated for the bromination of C–H bond. Notably, graphite rod, which is commercially available at supermarkets and is inexpensive, was employed as the electrode material. This operationally easy and environmentally friendly approach accomplished the synthesis of 3-bromoindole in excellent yield and regioselectivity.
Solvents
for spherical agglomerates preparation are usually selected
according to the Lifshitz–van der Waals acid–base theory
with negative adhesion free energies. However, some solvents with
positive adhesion free energies in which spherical agglomerates can
be obtained are easily ignored. This work proposes that solvents should
be screened comprehensively by theoretical calculation combined with
experiments using m-aminobenzoic acid (m-ABA) as a model compound. According to the Lifshitz–van der
Waals acid–base theory, water, isopropyl alcohol, and ethylene
glycol with negative adhesion free energies were screened out as the
possible solvents for the preparation of m-ABA spherical
agglomerates. Crystallization experiments showed that in addition
to the three solvents, methanol and ethanol with positive adhesion
free energies were also appropriate for spherical crystallization
of m-ABA. A common feature of the five solvents which
can form spherical agglomerates is that they have both hydrogen-bond-donating
and hydrogen-bond-accepting capabilities. The single-factor analysis
method was used to systematically investigate the effects of stirring
speed, terminal temperature, and supersaturation on spherical agglomerates
of m-ABA. The formation mechanism of m-ABA spherical agglomerates was elucidated with the help of the in
situ Pixact Crystallization Monitoring system. Comparative experiments
proved that the obtained spherical agglomerates exhibit better chemical
stabilities and crystal form stability than needle-like crystals.
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