Antibacterial behaviour of quaternized poly(vinyl chloride)-g-poly(4-vinyl pyridine) graft copolymers

Amphiphilic graft copolymers consisting of poly(vinyl chloride)(PVC) main chains and poly(4-vinyl pyridine)(P4VP) side chains were synthesized via atom transfer radical polymerization(ATRP) using direct initiation of chlorine atoms. The successful synthesis of PVC-g-P4 VP graft copolymers was confirmed by Fourier transform infrared spectroscopy(FTIR) and proton nuclear magnetic resonance(1H-NMR). Transmission electron microscope(TEM) and small angle X-ray scattering(SAXS) analysis showed that PVC-g-P4 VP exhibited microphase-separated, ordered structure with 37.6 nm of domain spacing, which was not observed in neat PVC. For antibacterial applications, the tertiary nitrogen atoms of PVC-gP4 VP was quaternized using 1-bromohexane, as confirmed by FTIR measurements. Bacteria including Escherichia coli(E. coli), Staphylococcus aureus(S. aureus), Bacillus cereus(B. cereus), and Pseudomonas aeruginosa(P. aeruginosa) were completely killed in 24 h on the quaternized PVC-g-P4VP(46% grafting) surface, indicating its excellent antibacterial behavior while it showed to be cytotoxic to mammalian cell.     

Synthesis of a PEG-PNIPAm thermosensitive dendritic copolymer and investigation of its self-association

A Novel thermosensitive dendritic copolymer based on polyethylene glycol(PEG) and poly(Nisopropylacrylamide)(PNIPAm) with a cloud point(CP) around 36 ?C was successfully synthesized by preparation of a dendritic polyol and followed by atom transfer radical polymerization(ATRP) of N-isopropylacrylamide. The dendritic copolymer was characterized using gel-permeation chromatography(GPC), FTIR and 1H-NMR spectroscopy. The selfassociation behavior of the copolymer in aqueous medium was investigated by dynamic light scattering(DLS) and transmission electron microscopy(TEM). These investigations confirmed that the dendritic copolymer showed different association behaviors at various temperatures.     

Dioxygen‐Mediated Decarbonylative CH Alkylation of Heteroaromatic Bases with Aldehydes

An operationally simple and economical method for the direct alkylation of heteroaromatic bases employing readily available aldehydes as alkyl radical precursors and molecular oxygen as a reagent is presented. This simple transformation demonstrates a broad substrate scope with respect to aldehydes and nitrogen heterocycles, enabling the introduction of several medicinally important yet challenging alkyl moieties, such as ethyl, isopropyl, tert‐butyl, and cyclohexyl to the different classes of heterocyclic bases in good to excellent yields.     

一种温敏型超大孔生物分离介质的制备及表征

采用改性琼脂糖对超大孔聚苯乙烯微球进行亲水化修饰(Agap-PS),通过酰基化反应在微球表面引入溴乙酰基(Agap-PS-Br),然后利用原子转移自由基聚合(ATRP)反应在Agap-PS-Br表面接枝温敏聚合物刷,得到一种温敏型超大孔生物分离介质(Agap-PS-PNIPAM).考察了配体、催化剂、溶剂和温度对N-异丙基丙烯酰胺ATRP反应的影响,在优化条件下PNIPAM的接枝量达到了15.07 mg/m2.采用红外光谱(FTIR)、扫描电镜(SEM)、压汞分析、激光共聚焦和蛋白吸附等手段对温敏型超大孔生物分离介质进行一系列表征,结果表明接枝温敏聚合物刷后Agap-PS-PNIPAM具有良好的温敏性,没有堵塞微球的超大孔,微球对蛋白的非特异性吸附大大降低.由于温敏聚合物刷发生了从亲水到疏水构象的转变,40℃时Agap-PS-PNIPAM对蛋白的吸附量是25℃时的2.69倍.压力流速实验表明Agap-PS-PNIPAM柱具有背压低、渗透性和机械稳定性好的优点,同样地由于PNIPAM链在40℃时收缩,此时Agap-PS-PNIPAM柱的床层渗透系数比25℃时提高了15.7％.     

Metal‐Catalyzed β‐Functionalization of Michael Acceptors through Reductive Radical Addition Reactions

Transition‐metal‐catalyzed radical reactions are becoming increasingly important in modern organic chemistry. They offer fascinating and unconventional ways for connecting molecular fragments that are often complementary to traditional methods. In particular, reductive radical additions to α,β‐unsaturated compounds have recently gained substantial attention as a result of their broad applicability in organic synthesis. This Minireview critically discusses the recent landmark achievements in this field in context with earlier reports that laid the foundation for today′s developments.     

An Isolable Radical Anion of an Organosilicon Cluster Containing Only σ Bonds

The radical anion of octa‐tert‐butyloctasilacubane was generated and isolated. The EPR spectrum showed the satellites due to the tertiary ¹³C nuclei of the eight tert‐butyl groups. The X‐ray crystallographic analysis showed that the Si? Si bonds are shortened and the Si? C bonds are elongated compared with those of octa‐tert‐butyloctasilacubane. These results are well explained by the distribution of an unpaired electron in the singly occupied molecular orbital (SOMO).     

Substrate‐Tuned Catalysis of the Radical S‐Adenosyl‐L‐Methionine Enzyme NosL Involved in Nosiheptide Biosynthesis

NosL is a radical S‐adenosyl‐L ‐methionine (SAM) enzyme that converts L ‐Trp to 3‐methyl‐2‐indolic acid, a key intermediate in the biosynthesis of a thiopeptide antibiotic nosiheptide. In this work we investigated NosL catalysis by using a series of Trp analogues as the molecular probes. Using a benzofuran substrate 2‐amino‐3‐(benzofuran‐3‐yl)propanoic acid (ABPA), we clearly demonstrated that the 5′‐deoxyadenosyl (dAdo) radical‐mediated hydrogen abstraction in NosL catalysis is not from the indole nitrogen but likely from the amino group of L ‐Trp. Unexpectedly, the major product of ABPA is a decarboxylated compound, indicating that NosL was transformed to a novel decarboxylase by an unnatural substrate. Furthermore, we showed that, for the first time to our knowledge, the dAdo radical‐mediated hydrogen abstraction can occur from an alcohol hydroxy group. Our study demonstrates the intriguing promiscuity of NosL catalysis and highlights the potential of engineering radical SAM enzymes for novel activities.     

Controlled Light‐Mediated Preparation of Gold Nanoparticles by a Norrish Type I Reaction of Photoactive Polymers

Gold nanoparticles (AuNPs) are subjects of broad interest in scientific community due to their promising physicochemical properties. Herein we report the facile and controlled light‐mediated preparation of gold nanoparticles through a Norrish type I reaction of photoactive polymers. These carefully designed polymers act as reagents for the photochemical reduction of gold ions, as well as stabilizers for the in situ generated AuNPs. Manipulating the length and composition of the photoactive polymers allows for control of AuNP size. Nanoparticle diameter can be controlled from 1.5 nm to 9.6 nm.     

Directed meta‐Selective Bromination of Arenes with Ruthenium Catalysts

A Ru‐catalyzed direct C? H activation/meta‐bromination of arenes bearing pyridyl, pyrimidyl, and pyrazolyl directing groups has been developed. A series of bromo aryl pyridines and pyrimidines have been synthesized, and further coupling reactions have also been demonstrated for a number of representative functionalized arenes. Preliminary mechanistic studies have revealed that this reaction may proceed through radical‐mediated bromination when NBS is utilized as the bromine source. This type of transformation has opened up a new direction for the radical non‐ipso functionalization of metal with regard to future C? H activation development that would allow the remote functionalization of aromatic systems.