Nano-reactors for controlling the selectivity of the free radical grafting of maleic anhydride onto polypropylene in the melt

This paper reports on a successful application of the concept of nanoreactors to effectively controlling the selectivity of the free radical grafting of maleic anhydride (MAH) onto polypropylene (PP) in the melt, an industrially relevant process. More specifically, a free radical initiator of type ROOR was first confined into (or encapsulated by) the galleries of an organically modified montmorillonite (o-MMT) whose interdistance was 2.4 nm. Primary free radicals (RO center dot) formed inside the o-MMT galleries had to diffuse out before they could react with the PP backbone. The controlled release of the primary free radicals significantly increased the grafting degree of MAH onto PP and greatly reduced the level of the chain scission of the latter. Those results were better understood by electron spin resonance studies on model systems and by Monte Carlo simulations.

Neodymium oxide-assisted melt free-radical grafting of maleic anhydride on isotactic-polypropylene by reactive extrusion

Rare earth oxide, neodymium oxide (Nd2O3), -assisted melt free-radical grafting of maleic anhydride (MAH) on isotactic-polypropylene (i-PP) was carried out by reactive extrusion. The experimental results reveal that the addition of Nd2O3 into reactive system leads to an enhancement of the grafting degree of MAH, along with an elevated degradation of i-PP matrix. When Nd2O3 content is 4.5 mmol %, the increment of the grafting degree of MAH (maximally) is up to about 30% compared with that of the related system without adding Nd2O3, while the severest degradation of i-PP matrix simultaneously occurs. On the basis of the reaction mechanism of PP-g-MAH proposed before, the sequence of beta-scission and grafting reaction is discussed in detail. It is found that, for the reactive system studied, most tertiary macroradicals first undergo beta-scission, and then, grafting reaction with MAH takes place at the new radical chain ends. The imported Nd2O3 has no effect on the aforementioned reaction mechanism, whereas it enhances the initiating efficiency of the initiator, dicumyl peroxide (DCP).

Synthesis and free-radical ring opening polymerization of macrocyclic aryl thioether ether ketone (sulfone) oligomers

Two kinds of novel macrocyclic aryl thioether ether oligomers were synthesized by nucleophilic condensation reaction in high yields under pseudo-high-dilution condition. A combination of H-1 NMR, GPC and MALDI-TOF MS analyses unambiguously confirmed the cyclic nature and their distributions, Macrocyclic thioether ether ketone oligomers can undergo facile melt ring opening polymerization(ROP) initiated by thiyl radical to give a high molecular weight polymer.

Novel macrocyclic aryl thioether ester oligomers: structure characterization and free-radical ring opening polymerization

Novel macrocyclic aryl thioether ester oligomers have been synthesized in high yield from phthaloyl dichloride and 4,4'-thiodiphenol under pseudo high dilution conditions. The cyclic nature was unambiguously confirmed by a combination of MALDI-TOF MS, gel permeation chromatography and NMR analyses. Single-crystal X-ray diffraction of cyclic ester dimer reveals no severe strain on the cyclic structure. The free-radical ring opening polymerization (ROP) of the macrocyclic oligomers was achieved to give high molecular weight polymers via a transthioetherification reaction. The molecular weight of the polymer resulting from ROP decreases as the conversion of cyclic oligomers increases after a polymerization period of 30 min.

海洋红藻多管藻和松节藻的化学成分及抗氧化活性研究

海洋生物具有产生丰富多样的次生代谢产物的能力，其中红藻门松节藻科海藻卤代次生代谢产物以其结构新颖、生物活性独特引起了天然产物化学家的重视。 本论文对海洋红藻多管藻和松节藻进行了化学成分研究，综合利用各种色谱学方法 (硅胶柱层析、反相硅胶柱层析、凝胶Sephadex LH-20柱层析、半制备高效液相色谱以及重结晶等) 和现代波谱学技术 (IR、UV、EI-MS、FAB-MS、HR-ESI-MS、CD、1H-NMR、13C-NMR、DEPT、1H-1H COSY、HSQC、HMBC等)，共分离鉴定了100个化合物，发现25个新化合物。 从多管藻中分离鉴定38个化合物 (24个溴酚化合物)，其中7个新化合物 (均为溴酚化合物)，包括1个菲并呋喃结构溴酚 (P1), 2个二氢菲结构溴酚 (P2, P3)，1个含 5,7-dihydrodibenzo[c,e]oxepine 结构溴酚 (P4)和3个简单溴酚 (P5, P6, P7)。P1 (urceolatin) 属首例报道的具有菲并呋喃结构的天然产物，从该种中分离的化合物P12 和 P13 可能是其生源合成的前体。P2和P3为第二例报道的具有二氢菲结构的溴酚化合物。 从松节藻中分离并鉴定了62 个化合物，其中18 个为溴酚类新化合物，44 个为已知化合物。化合物具有多变的取代基团，包括2 个脲基吡咯烷酮溴酚化合物 (R1, R2), 4 个γ-脲基丁酸溴酚化合物 (R3-R6)，5 个酰胺溴酚化合物 (R7, R8, R9, R13, R14)，1 个溴酚砜化合物 (R12), 1 个Xanthene 溴酚化合物 (R10)和5 个简单溴酚化合物 (R11, R15, R16, R17, R18)。R1、R2 是首例报道的含有脲基吡咯烷酮片段的天然产物，R10 为首次报道的溴代Xanthene 类天然产物。 对分离到的化合物进行了清除DPPH 和ABTS两种自由基活性的筛选。结果发现溴酚类天然产物具有显著的DPPH自由基清除活性，其中R3 的IC50 仅为3.3 μM, 其活性强度约为阳性对照BHT (IC50 为82.1 μM) 的24倍。另外，溴酚类天然产物对ABTS自由基有较强的清除活性，R2 的TEAC（Trolox efficency activity capacity）值为5.2 mM，约为阳性对照 (ascorbic acid, 1.02 mM) 的 5 倍。初步的构效关系研究发现，稠环分子、多羟基和邻位甲氧基等结构特点能有效增强DPPH 自由基清除活性；特殊取代基如脲基、吡咯烷酮等含有氮原子的基团，能有效增强ABTS 自由基清除活性，多羟基、溴代等结构特点也使其活性有所增强。 本研究结果丰富了海藻卤代化合物的结构类型，为多管藻和松节藻的合理利用提供了一定的科学依据。

两株海藻内生真菌次生代谢产物及其生物活性研究

海洋微生物拥有丰富多样的次生代谢途径，其中海洋生物内生真菌次生代谢产物研究日益受到天然产物化学界的重视。本论文以菌丝体生物量、发酵产物重量、抗菌与细胞毒活性、薄层色谱分析结果以及高效液相色谱分析结果等为评价依据对采自青岛沿海的13株海藻内生真菌在四种液体培养基上的静置发酵产物进行了综合评价，并从中选择了黑曲霉Aspergillus niger EN-13（分离自褐藻囊藻Colpomenia sinuosa）和杂色曲霉A. versicolor EN-7（分离自褐藻鼠尾藻Sargassum thunbergii）两株真菌进行了30升规模发酵（分别采用GPYM培养基和PDB培养）和化学成分的研究，对分离得到的大部分化合物进行了初步的生物活性筛选。 发酵提取物采用常规的硅胶柱层析、反相硅胶柱层析，凝胶Sephadex LH-20柱层析、制备薄层层析、半制备高效液相色谱以及重结晶等分离手段，得到单体化合物。利用各种现代波谱技术(IR、UV、EI-MS、FAB-MS、HR-ESI-MS、1H-NMR、13C-NMR、DEPT、1H-1H COSY、HSQC、HMBC等)并结合化学方法从两种菌株发酵提取物中鉴定了55个化合物的结构。其中从菌株A. niger EN-13分离鉴定了31个化合物，发现9个新化合物，包括2个鞘酯类化合物（AN-1~2）、3个萘并-γ-吡喃酮类化合物（AN-3~5）、3个苯乙基取代的α-吡喃酮类化合物（AN-17, AN-19~20）和1个甾体Diels-Alder加成产物（AN-21），另有1个新的天然环二肽（AN-27）被分离鉴定；从菌株A. versicolor EN-7分离鉴定了24个化合物，发现2个新化合物，为蒽醌AV-12与AV-17，另外，从前一菌株（A. niger EN-13）中鉴定的2个新鞘酯类化合物（AN-1~2）在A. versicolor EN-7中也被再次分离到。 对大部分单体化合物进行了抗菌活性、DPPH自由基清除活性和细胞毒活性测试。结果显示新化合物AN-1、AN-5和AN-20具有弱或中等强度的抑制白色念珠菌生长的活性，AN-4、AN-5、AN-21显示了弱或中等强度的抑制黑曲霉生长的活性，AV-12、AV-17显示了弱的抑制大肠杆菌生长的活性。在DPPH自由基清除活性筛选中，AN-5显示了中等强度的活性，其EC50为109.3 mM，与阳性对照BHT相近（EC50为81.8 mM）。其它部分已知化合物在抗菌和DPPH自由基清除活性的筛选中也显示了弱或中等强度的活性。在针对人肝癌细胞株SMMC-7721和人肺腺癌细胞株A549的体外细胞毒活性筛选中，所测样品均未显示显著活性。

Synthesized oversulphated, acetylated and benzoylated derivatives of fucoidan extracted from Laminaria japonica and their potential antioxidant activity in vitro

Three sulphated polysaccharide derivatives (oversulphated, acetylated and benzoylated fucoidan) were successfully synthesized, and their antioxidant activities were investigated employing various established in vitro systems. A novel catalyst N-bromosuccinimide (NBS) was used in acetylation and benzoylation reaction, and the degree of acetylation was evaluated using IR and NMR spectra. Both fucoidan derivatives possessed considerable antioxidant activity, and had stronger antioxidant ability than fucoidan in certain tests. The benzoylated fucoidan showed strongest superoxide and hydroxyl radical scavenging activity, however, the acetylated fucoidan exhibited strongest activity on scavenging DPPH radical and reducing power. Available data obtained with in vitro models suggested that substituted groups of fucoidan played an important role on antioxidant activity. The mechanism on the antioxidant activity of sulphonyl, acetyl and benzoyl group is different. (C) 2008 Elsevier Ltd. All rights reserved.

Synthesized phosphorylated and aminated derivatives of fucoidan and their potential antioxidant activity in vitro

Three sulfated polysaccharide derivatives (phosphorylated and aminated fucoidan) were synthesized, and their potential antioxidant activities were investigated employing various established in vitro systems. Two methods were used in phosphorylation fucoidan: polyphosphoric acid and POCl3 method. Aminated fucoidan was prepared using the epichlorohydrin and ammonia water. All fucoidan derivatives possessed considerable antioxidant activity, and exhibited stronger antioxidant ability than fucoidan in certain tests. The phosphorylated fucoidan showed stronger hydroxyl radical and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and reducing power. The mechanism on influence the antioxidant activity of samples of phosphate and amino group was indicated. (C) 2008 Elsevier B.V. All rights reserved.

Synthesis and hydroxyl radicals scavenging activity of quaternized carboxymethyl chitosan

In order to determine the effect of the forms of the amido groups of chitosan on antioxidant activity, quaternized carboxymethyl chitosan (QCMC) derivatives were prepared with a degree of quaternization ranging from 34.3% to 59.5%. The antioxidant activity of QCMCs against hydroxyl radicals was assessed. The results indicated that QCMCs have better hydroxyl radicals scavenging activity than that of carboxymethyl chitosan, as a result of the positive charge of the quaternized chitosan. (C) 2007 Elsevier Ltd. All rights reserved.

Antioxidant activity of sulfated polysaccharide fractions extracted from Laminaria japonica

Fucoidan, a group of sulfated heteropolysaccharide, was extracted from Laminaria japonica, an important economic alga species in China. Three sulfated polysaccharide fractions (F1, F2, and F3) were successfully isolated through anion-exchange column chromatography and had their antioxidant activities investigated employing various established in vitro systems, including superoxide and hydroxyl radical scavenging activity, chelating ability, and reducing power. Chemical analysis suggested that F1 and F3 were heteropolysaccharide in which galactose was the major component, while F2 was a typical fucoidan. All fractions possessed considerable antioxidant activity, and F1, F2 and F3 had stronger antioxidant ability than fucoidan in certain tests. The correlation between the sulfate content and scavenging superoxide radical ability was positive. Available data obtained with in vitro models suggested that the ratio of sulfate content/fucose was an effective indicator to antioxidant activity of the samples. (C) 2007 Elsevier B.V. All rights reserved.

Hydroxyl radicals scavenging activity of N-substituted chitosan and quaternized chitosan

N-substituted chitosan and quaternized chitosan were synthesized and their antioxidant activity against hydroxyl radicals was assessed, respectively. Compared with the antioxidant activity of chitosan, the results indicated that the two kinds of chitosan derivatives had different scavenging ability on hydroxyl radicals, which should be related to the form of amido in the two kinds of chitosan derivatives. (c) 2006 Elsevier Ltd. All rights reserved.

Interaction of glucose and long chain fatty acids (C18) on antioxidant defences and free radical damage in porcine vascular smooth muscle cells in vitro.

Aims/hypothesis: Abnormalities of glucose and fatty acid metabolism in diabetes are believed to contribute to the development of oxidative stress and the long term vascular complications of the disease therefore the interactions of glucose and long chain fatty acids on free radical damage and endogenous antioxidant defences were investigated in vascular smooth muscle cells. Methods: Porcine vascular smooth muscle cells were cultured in 5 mmol/l or 25 mmol/l glucose for ten days. Fatty acids, stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2) and gamma-linolenic acid (18:3) were added with defatted bovine serum albumin as a carrier for the final three days. Results. Glucose (25 mmol/l) alone caused oxidative stress in the cells as evidenced by free radical-mediated damage to DNA, lipids, and proteins. The addition of fatty acids (0.2 mmol/l) altered the profile of free radical damage; the response was J-shaped with respect to the degree of unsaturation of each acid, and oleic acid was associated with least damage. The more physiological concentration (0.01 mmol/l) of gamma-linolenic acids was markedly different in that, when added to 25 mmol/l glucose it resulted in a decrease in free radical damage to DNA, lipids and proteins. This was due to a marked increase in levels of the antioxidant, glutathione, and increased gene expression of the rate-limiting enzyme in glutathione synthesis, gamma-glutamylcysteine synthetase. Conclusion/Interpretation: The results clearly show that glucose and fatty acids interact in the production of oxidative stress in vascular smooth muscle cells.