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

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    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

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    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

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    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

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    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

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    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
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