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171.
Virgil Percec Bogdan Barboiu Tushar K. Bera Marcel Van Der Sluis Robert B. Grubbs Jean M. J. Frchet 《Journal of polymer science. Part A, Polymer chemistry》2000,38(Z1):4776-4791
The similarities and differences between sulfonyl chloride and alkyl halide initiators for metal‐catalyzed living radical polymerizations are discussed. The differences in the rates of formation, reactivities, and reactions of primary radicals derived from sulfonyl halides and alkyl halides demonstrated the design principles for monosulfonyl and multisulfonyl chlorides that provided quantitative initiation and higher rates of initiation than of propagation. Multifunctional initiators with two, three, four, six, and eight sulfonyl chloride groups that produced perfect star polymers in 95% conversions were designed and synthesized on the basis of these principles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4776–4791, 2000 相似文献
172.
Virgil Barboiu Emilia Streba Cornelia Luca Ionela Radu George Ervant Grigoriu 《Journal of polymer science. Part A, Polymer chemistry》1998,36(10):1615-1623
Unsaturated macromolecular carboxybetaines were obtained by reaction of poly(4-vinylpyridine) and poly(N-vinylimidazole) with propiolic acid. A kinetic model was presented for 4-methylpyridine. It consists of three coupled reactions: neutralization, addition which involves two molecules of acid and leads to a cation–anion pair structure, where the cation results from the addition of the amine nitrogen to the triple bond of acid, and an equilibrium reaction between the ion-pair structure and the betaine structure. The addition rate was found to be higher for poly(4-vinylpyridine) than for poly(N-vinylimidazole); it was also higher in water than in a water–methanol mixture. The reaction with acetylenedicarboxylic acid was carried out on poly(N-vinylimidazole), but the transformed units showed the structure that results from propiolic acid. The betaine products from 4-methylpyridine did not polymerize by radical initiation. The polymeric products show characteristics of photocrosslinking polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1615–1623, 1998 相似文献
173.
gota Simon Tatiana Tozar Adriana Smarandache Mihai Boni Alexandru Stoicu Alan Dowson Jack J. W. A. van Loon Mihail Lucian Pascu 《Molecules (Basel, Switzerland)》2022,27(5)
Pharmaceuticals carried into space are subjected to different gravitational conditions. Hypergravity is encountered in the first stage, during spacecraft launching. The stability of medicines represents a critical element of space missions, especially long-duration ones. Therefore, stability studies should be envisaged before the implementation of drugs for future deep space travel, where the available pharmaceuticals would be limited and restocking from Earth would be impossible. Multipurpose drugs should be proposed for this reason, such as phenothiazine derivatives that can be transformed by optical methods into antimicrobial agents. Within this preliminary study, promethazine and thioridazine aqueous solutions were exposed to UV laser radiation that modified their structures and generated a mixture of photoproducts efficient against particular bacteria. Subsequently, they were subjected to 20 g in the European Space Agency’s Large Diameter Centrifuge. The aim was to evaluate the impact of hypergravity on the physico-chemical and spectral properties of unirradiated and laser-irradiated medicine solutions through pH assay, UV-Vis/FTIR absorption spectroscopy, and thin-layer chromatography. The results revealed no substantial alterations in centrifuged samples when compared to uncentrifuged ones. Due to their stability after high-g episodes, laser-exposed phenothiazines could be considered for future space missions. 相似文献
174.
Dr. Yan Zhang Ye Zhang Han Cui Dr. Mihail Barboiu Prof. Jinghua Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(71):16994-16999
The fabrication of biocompatible adaptive materials with high stiffness and self-healing properties for medical applications is a challenging endeavor. Collagen is a major extracellular matrix component acting as a substrate for cell adhesion and migration. Dynamers are constitutional polymers whose monomeric components are linked through reversible bonds, able to modify their constitution through reversible exchange of their components. In the current work, we demonstrate that the rational combination of collagen and dynameric networks connected with reversible covalent imine bonds is a very important and previously unreported strategy to provide biocompatible membranes with self-healing ability and excellent mechanical strength. The key challenge in the construction of such membranes is the required adaptive interaction between collagen chains and the dynamic cross-linkers, preventing the formation of defects. For example, by varying structure and molecular lengths of the dynamers, the tensile strength of the dynameric membranes reach over 80 MPa, more than 400 % higher than that observed for the reference collagen membrane, and the highest value for break strain found, was 19 %. The self-healing properties were observed when reconnecting two membrane pieces or even from crushed status of the membranes. Moreover, both MTT assay and confocal laser scanning microscopy method demonstrated the good biocompatibility of the collagen membranes, leaving more than 90 % viability for NIH 3T3 cells after 24 h co-culture. 相似文献
175.
Mingran Si Weijia Zhu Prof. Yan Zhang Dr. Mihail Barboiu Prof. Jinghua Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(45):10191-10194
Dynamic covalent polymers—dynamers—are adaptive materials that offer timely variant adaptive macroscopic organization across extended scales. In the current study, imine exchange reactions and fluorescence transfer can occur at the interfaces between various solutions and solid state dynameric films. The fluorescence quenching upon imine formations for designed fluorogen was successfully demonstrated, and this tunable fluorescence was further used to study the re-composition of a solid film. Moreover, the dynamic covalent films also exhibited responsiveness to competing amines and acid/base conditions, both in solutions and solid film–solution interface. This work can provide more insights into interface dynamic chemistry and holds great potential for further applications in optical and biomedical materials. 相似文献
176.
177.
Squalyl Crown Ether Self‐Assembled Conjugates: An Example of Highly Selective Artificial K+ Channels
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Dr. Zhanhu Sun Dr. Arnaud Gilles Istvan Kocsis Dr. Yves‐Marie Legrand Eddy Petit Dr. Mihail Barboiu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(6):2158-2164
The natural KcsA K+ channel, one of the best‐characterized biological pore structures, conducts K+ cations at high rates while excluding Na+ cations. The KcsA K+ channel is of primordial inspiration for the design of artificial channels. Important progress in improving conduction activity and K+/Na+ selectivity has been achieved with artificial ion‐channel systems. However, simple artificial systems exhibiting K+/Na+ selectivity and mimicking the biofunctions of the KcsA K+ channel are unknown. Herein, an artificial ion channel formed by H‐bonded stacks of squalyl crown ethers, in which K+ conduction is highly preferred to Na+ conduction, is reported. The K+‐channel behavior is interpreted as arising from discreet stacks of dimers resulting in the formation of oligomeric channels, in which transport of cations occurs through macrocycles mixed with dimeric carriers undergoing dynamic exchange within the bilayer membrane. The present highly K+‐selective macrocyclic channel can be regarded as a biomimetic alternative to the KcsA channel. 相似文献
178.
Xuan Liu Pengzhu Zhang Xin Li Hsinchun Chen Yan Dang Catherine Larson Mihail C. Roco Xianwen Wang 《Journal of nanoparticle research》2009,11(8):1845-1866
China, Russia, and India are playing an increasingly important role in global nanotechnology research and development (R&D).
This paper comparatively inspects the paper and patent publications by these three countries in the Thomson Science Citation
Index Expanded (SCI) database and United States Patent and Trademark Office (USPTO) database (1976–2007). Bibliographic, content
map, and citation network analyses are used to evaluate country productivity, dominant research topics, and knowledge diffusion
patterns. Significant and consistent growth in nanotechnology papers are noted in the three countries. Between 2000 and 2007,
the average annual growth rate was 31.43% in China, 11.88% in Russia, and 33.51% in India. During the same time, the growth
patterns were less consistent in patent publications: the corresponding average rates are 31.13, 10.41, and 5.96%. The three
countries’ paper impact measured by the average number of citations has been lower than the world average. However, from 2000
to 2007, it experienced rapid increases of about 12.8 times in China, 8 times in India, and 1.6 times in Russia. The Chinese
Academy of Sciences (CAS), the Russian Academy of Sciences (RAS), and the Indian Institutes of Technology (IIT) were the most
productive institutions in paper publication, with 12,334, 6,773, and 1,831 papers, respectively. The three countries emphasized
some common research topics such as “Quantum dots,” “Carbon nanotubes,” “Atomic force microscopy,” and “Scanning electron
microscopy,” while Russia and India reported more research on nano-devices as compared with China. CAS, RAS, and IIT played
key roles in the respective domestic knowledge diffusion. 相似文献
179.
Arcady Zhukov Carlos Garcia Maxim Ilyn Rastislav Varga Juan Jose del Val Alexander Granovsky Valeria Rodionova Mihail Ipatov Valentina Zhukova 《Journal of magnetism and magnetic materials》2012
We studied magnetic and structural properties of granular CoxCu100−x (5<x<40 at%), Cu63Fe37 and Heusler-type Ni2MnGa glass-coated microwires. We found that the structure of Co–Cu microwires consists of two phases: fcc Cu for all the samples and fcc α-Co present for higher Co content. In the case of low Co content, Co atoms are distributed within the Cu matrix. The quantity and the size of grains strongly depend on the geometry of the microwire. Co–Cu and Fe–Cu microwires exhibited considerable magnetoresistance (MR). For CoxCu100−x microwires at x≥30 the anisotropic contribution to MR has been observed. Temperature dependences of magnetization measured without an external magnetic field (ZFC) and in the presence of a field (FC) show considerable difference below 20 K, indicating the presence of small α-Fe or Co grains embedded in the Cu matrix. Annealed Ni2MnGa microwires showed ferromagnetic behavior with Curie temperature about 330 K and polycrystalline structure with space group I4/mmm and lattice parameters a=3.75 Å and c=6.78 Å. 相似文献
180.
The imine-bond formation on chitosan backbones occurs with very low yields in aqueous solutions and is significantly improved in hydrogels or in solid state films. The dynamic exchanges of imino-R groups and colour transfer can occur at the interfaces between various hydrogels and solid state films. 相似文献