纤维素及其衍生物的高压静电纺丝

高压静电纺丝作为一种制备纳米纤维的先进技术,近年来受到普遍关注。而纤维素和纤维素衍生物由于其优越的性质已应用于各个领域。运用高压静电纺丝技术对纤维素及其衍生物进行研究,开拓了新的研究领域和发展方向。本文介绍了高压静电纺丝技术的研究背景和原理,总结了近几年研究者们在纤维素以及纤维素衍生物高压静电纺丝方面的工作进展,尤其对不同溶剂体系溶解纤维素用于静电纺丝的优缺点进行了比较,评述了这方面的前沿性探索研究,并对未来的发展进行了展望。     

静电纺丝纳米纤维膜固定化酶及其应用*

静电纺丝是一种简单有效的制备聚合物纳米纤维的技术,在组织工程、药物控释和传感器等方面具有广泛的应用。采用静电纺丝技术制备得到的纳米纤维膜具有比表面积大、孔隙率高和易于分离回收等优点,可以作为一种优良的酶固定化载体,目前在酶固定化领域受到了广泛的关注。本文综述了近年来静电纺丝纳米纤维膜固定化酶的研究进展,在阐述静电纺丝纳米纤维膜制备技术的基础上,详细介绍了纳米纤维膜表面担载法和包埋法固定化酶的原理和方法,分析了不同固定化方法的优缺点,并讨论了静电纺丝纳米纤维膜固定化酶的应用前景,对静电纺丝纳米纤维膜固定化酶的发展方向进行了展望。     

静电纺丝制备杯芳烃功能化纳米纤维的应用

静电纺丝技术是制备连续微纳米纤维的一种简单易行且高效的方法,所制备的纳米纤维因其独特的结构尺寸和广泛的应用领域而备受材料科学界的青睐。 作为第三代超分子主体化合物的杯芳烃及其衍生物因其独特的分子结构、优异的离子选择识别性和吸附性能而显示出广阔的应用前景。 本文简述了静电纺丝制备杯芳烃功能化纳米纤维的原理,系统地探讨了其作为吸附剂和催化剂载体的应用以及静电纺丝与杯芳烃相结合的优势。 讨论了目前静电纺丝制备杯芳烃功能化纳米纤维存在的问题,对未来的发展方向进行展望。     

静电纺丝制备醋酸纤维素复合纳米纤维的研究进展

静电纺丝技术就是通过带电聚合物溶液或熔体的喷射来制备纳米纤维,是一种制备纳米纤维材料简单有效的技术。醋酸纤维素(CA)易溶于有机溶剂,常作为纤维素的替代材料应用于静电纺丝领域。本文总结了近年来国内外采用静电纺丝技术制备CA复合纳米纤维的研究新进展,重点介绍了CA/CNTs复合纳米纤维、CA/金属粒子复合纳米纤维、CA/金属氧化物复合纳米纤维、CA基载药复合纳米纤维、CA/PAN复合纳米纤维、CA/PVA复合纳米纤维、CA/CS复合纳米纤维等CA复合纳米纤维的研究进展以及潜在的应用领域。     

聚合物的静电纺丝

静电纺丝法是聚合物溶液或熔体在静电作用下进行喷射拉伸而获得纳米级纤维的纺丝方法.由纳米纤维制得的无纺布,具有孔隙率高、比表面积大、纤维精细程度与均一性高、长径比大等优点,从而赋予了静电纺丝纤维广泛的应用前景,它已在国内外引起了广泛的关注.本文介绍了静电纺丝的装置、基本原理及静电纺丝制备纳米纤维的研究进展,同时也叙述了其在各个领域的应用,最后展望了静电纺丝制备纳米纤维的发展方向及前景.     

静电纺丝法在制备改性醋酸纤维素中的应用

纤维素是一种天然存在于有机物或植物中储量巨大的可再生资源。醋酸纤维素是在催化剂的作用下,将纤维素的羟基酯化而得到的一种热塑性树脂。由于其具有稳定,易于加工,不易燃烧,生物可降解性等特点,常用来替代天然纤维素作为静电纺丝的原料。静电纺丝技术作为目前制备纳米纤维材料的一种简单有效的方法,近些年来一直备受关注。本文系统介绍了以醋酸纤维素为静电纺丝的基体材料, 通过添加纳米粒子、聚合物溶液、表面改性、同轴电纺等物理改性方法以及再生纤维处理和硝化反应等化学改性方法制备改性醋酸纤维素纤维, 讨论了改性后的新材料结构和性能等多方面的变化。综述了近几年来国内外关于以静电纺丝法制备改性醋酸纤维素纤维的研究进展以及其在生物医药、组织工程支架、过滤膜以及功能性织物等方面的应用前景。     

定形相变复合材料的研究进展——静电纺丝法

静电纺丝是制备定形相变复合材料的重要方法之一,本文综述了静电纺丝法制备定形相变复合材料的研究进展,主要包括溶液静电纺丝、溶液-溶液同轴静电纺丝、熔融-溶液同轴静电纺丝和静电纺纳米纤维膜物理吸附等,总结了静电纺丝常用的固-液相变材料(如脂肪族长链烷烃、大豆蜡、脂肪酸及其二元低共熔物、脂肪酸酯和聚乙二醇等)和支撑材料(如醋酸纤维素、聚对苯二甲酸乙二醇酯、聚乙烯吡咯烷酮、聚偏氟乙烯、聚乳酸、聚氨酯、聚酰胺6、聚丙烯腈及其碳纳米纤维等)。     

静电纺丝法制备纳米抗菌纤维的研究进展

纳米抗菌材料是防止细菌等致病微生物对人们生产、生活的破坏而发展起来的一类新型材料.在纳米抗菌材料的众多制备方法中,静电纺丝是一种成本低,工艺可控的技术,制备的纳米纤维具有比表面积大、孔隙率高、纤维均匀等特点.本文作者首先简述了静电纺丝技术以及该技术制备纳米抗菌纤维材料的特点;接着按照菌剂种类不同,对静电纺丝技术制备的抗菌纤维材料进行归类,将其分为无机抗菌纤维材料、天然抗菌纤维材料和复合抗菌纤维材料3类,并对其研究进展进行了评述;最后对静电纺丝技术制备纳米抗菌纤维的研究现状进行了总结与展望.     

取向静电纺丝纳米纤维的制备及应用研究进展

简单描述了静电纺丝的基本装置、原理;为制得高性能的取向纳米纤维,对静电纺丝中出现的不稳定性进行了研究,介绍了三种不稳定状况,并分析了其产生原因.列举了通过改变接收装置、控制电场和附加磁场等方法,改进静电纺丝技术来制取连续取向的纳米纤维,并对各种方法进行了简单的评价,指出磁化静电纺丝(MES)是目前制备取向纳米纤维最具有发展前景的方法.简要介绍了取向纳米纤维在生物组织工程领域方面的应用,并对其未来作了展望.     

聚丙烯腈纳米纤维的高效制备及结晶取向性能

分别采用传统静电纺丝装置和自行搭建的离心-静电纺丝装置制备出聚丙烯腈(PAN)纳米初生纤维,并在热空气浴中和一定外力作用下进行牵伸,牵伸后使其伸长至原长的1倍到3倍.通过广角X射线衍射(WAXD)、扫描电子显微镜(SEM)等方法对2种纺丝方法制备的PAN纳米初生纤维及经过热空气浴牵伸后的PAN纳米纤维的晶态结构、取向及形貌等进行了表征.研究表明:(1)离心-静电纺丝效率远高于静电纺丝,可达静电纺丝的120倍(离心-静电纺丝纺丝液流速为2 m L/min,静电纺丝纺丝液流速1 m L/h);(2)无论是离心纺丝还是静电纺丝制得的纳米初生纤维结晶度均很低(离心纺丝为25%,静电纺丝为10.1%),但离心纺丝制得的纳米初生纤维有一定的取向(60.5%),而静电纺丝基本没有;(3)经过热空气浴牵伸后,2种纺丝方式制得的纳米纤维结晶度均有所提高(分别为45.8%和36.2%),取向度也有所提高(分别为72.5%和59.8%),随着牵伸温度的提高和牵伸应力的增大,纤维的平均直径不断减小(离心纺丝由675 nm降至510 nm,静电纺丝由460 nm降至355 nm).纳米纤维在制备过程晶态结构及取向的效果有限,但通过热空气浴牵伸可以使晶态结构及取向得到进一步完善.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.