5 research outputs found
Chiral Microspheres Consisting Purely of Optically Active Helical Substituted Polyacetylene: The First Preparation via Precipitation Polymerization and Application in Enantioselective Crystallization
This article reports on a novel type of microspheres
(∼720 nm in diameter) prepared via precipitation polymerization
and constructed by optically active helical substituted polyacetylene
(PSA). The microspheres were obtained in high yield (>80%), with
regular morphology and narrow size distribution. PSA forming the microspheres
was found to adopt helices with predominant one-handed screw sense,
according to circular dichroism and UV–vis absorption spectroscopies
and specific optical rotation measurements. The helical conformations
of PSA endowed the microspheres thereof with considerable optical
activity. The chiral microspheres feature in combining in one entity
the advantages of both chiral polymers and the micrometer-sized particles
in scale and spherical morphology and thus are expected to find some
significant applications. This is well exemplified by successful induction
of enantioselective crystallization with the chiral microspheres.
Such chiral microspheres efficiently induced enantioselective crystallization
of alanine enantiomers: (<i>S</i>)-PSA preferably induced l-alanine to form octahedral crystals while (<i>R</i>)-PSA toward d-alanine forming needle-like crystals, with
a remarkably high ee (85%). This is the first precipitation polymerization
of substituted acetylenes for preparing chiral polymeric microspheres.
The present chiral microspheres represent a new type of advanced functional
chiral materials
Lithium-Assisted Copolymerization of CO<sub>2</sub>/Cyclohexene Oxide: A Novel and Straightforward Route to Polycarbonates and Related Block Copolymers
A facile
route toward alternating polycarbonates by anionic copolymerization
of carbon dioxide (CO<sub>2</sub>) and cyclohexene oxide (CHO), using
lithium halide or alkoxide as initiators and triisobutylaluminum
(TiBA) as activator, is reported. α,ω-Heterobifunctional
and α,ω-dihydroxypoly(cyclohexene carbonate)s (PCHC)
as well as poly(CHC-<i>co</i>-CHO) copolymers with different
carbonate composition could also be easily synthesized by adjusting
the amount of TiBA or by adding inert lithium salts. The value of
this initiating system also resides in the easy access to PSt-<i>b</i>-PCHC (PSt: polystyrene) and PI-<i>b</i>-PCHC
(PI: polyisoprene) block copolymers which can be derived by mere one-pot
sequential addition of styrene or dienes first and then of CO<sub>2</sub> and CHO under the same experimental conditions
Thermostable Microspheres Consisting of Poly(<i>N</i>‑phenylmaleimide-<i>co</i>-α-methyl styrene) Prepared by Precipitation Polymerization
General polymeric microspheres are
not satisfactorily thermostable.
This article reports on an unprecedented type of poly(<i>N</i>-phenylmaleimide-<i>co</i>-α-methyl styrene) [denoted
as poly(<i>N</i>-PMI-<i>co</i>-AMS)] microspheres
showing remarkable thermal stability. The microspheres were prepared
by free-radical precipitation polymerization in a solvent mixture
consisting of methyl ethyl ketone (favorable solvent) and heptane
(unfavorable solvent). Microspheres of good morphology and narrow
size distribution were obtained in high yield (>85%) under appropriate
conditions. Growth of poly(<i>N</i>-PMI-<i>co</i>-AMS) microspheres was characterized by scanning electron microscopy.
The microspheres, although without cross-linking, exhibited excellent
thermal stability, and their decomposition temperature was up to about
370 °C. This feature cannot be achieved in typical polymeric
microspheres. Also, notably, this is the first precipitation polymerization
of maleimide and AMS and their derivatives for preparing microspheres.
The present novel microspheres are expected to find practical applications
as novel heat-resistant additives, solid carriers for catalysts, and
so on
Multifunctional Biomaterial Coating Based on Bio-Inspired Polyphosphate and Lysozyme Supramolecular Nanofilm
Current implant materials have widespread
clinical applications
together with some disadvantages, the majority of which are the ease
with which infections are induced and difficulty in exhibiting biocompatibility.
For the efficient improvement of their properties, the development
of interface multifunctional modification in a simple, universal,
and environmently benign approach becomes a critical challenge and
has acquired the attention of numerous scientists. In this study,
a lysozyme-polyphosphate composite coating was fabricated for titanium(Ti)-based
biomaterial to obtain a multifunctional surface. This coating was
easily formed by sequentially soaking the substrate in reduced-lysozyme
and polyphosphate solution. Such a composite coating has shown predominant
antibacterial activity against Gram-negative bacteria (<i>E.
coli</i>) and improved cell adhesion, proliferation, and differentiation,
which are much better than those of the pure substrate. This facile
modification endows the biomaterial with anti-infective and potential
bone-regenerative performance for clinical applications of biomaterial
implants
Bioinspired Peptide-Decorated Tannic Acid for in Situ Remineralization of Tooth Enamel: In Vitro and in Vivo Evaluation
Tooth enamel can be eroded by the
local cariogenic bacteria in
plaque or nonbacterial factors in the oral environment. The damage
is irreversible in most situations. For the etched human tooth enamel
to be restored in situ, a salivary-acquired pellicle (SAP) bioinspired
tannic acid (SAP-TA) is synthesized. Statherin is one of the SAP proteins
that can selectively adsorb onto enamel surface. Peptide sequence
DDDEEKC is a bioinspired sequence of statherin and has the adsorption
capacity of hydroxyapatite (HAP). TA has abundant polyphenol groups
that can grasp Ca<sup>2+</sup> in saliva to induce the regeneration
of HAP crystal. Hence, SAP-TA not only enhances the binding force
at the interface of remineralization but also mimics the biomineralization
process of tooth enamel. Moreover, ferric ion can coordinate with
SAP-TA to form a compact coating that increases the adsorbed amounts
of SAP-TA on tooth enamel. Compared with SAP-TA alone, the etched
enamels treated with SAP-TA/Fe(III) have a better remineralization
effect and mechanical properties (surface microhardness recovery >80%
and binding force of 64.85 N) when being incubated in artificial saliva
for 2 weeks. In vivo remineralization performance is evaluated in
a classical rat caries model. The polarizing microscope and micro-CT
results show that SAP-TA/Fe(III) has a good effect on the remineralization
process in a real oral environment, indicating that it is a promising
repair material for in situ remineralization of enamel