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151.
A complete tree with roots, trunk and crown remains an appropriate model to represent all steps of life's development, from the emergence of a unique genetic code up to the last universal common ancestor and its further radiation. Catalytic closure of a mixture of prebiotic polymers is a heuristic alternative to the RNA world. Conjectures about emergence of life in an infinite multiverse should not confuse probability with possibility. 相似文献
152.
F. Marques L. Gano M. K. S. Batista C. A. R. Gomes P. Gomes I. Santos 《Journal of labelled compounds & radiopharmaceuticals》2009,52(3):79-83
153Sm/166Ho‐chitosan complexes have been considered promising agents for internal radiation therapy. By direct administration, complexes solution converts into a gel, at physiological pH, allowing its retention for a long time. Herein, we report on the synthesis of 153Sm/166Ho complexes with the novel amino acid–chitosan polymers, N‐(γ‐propanoyl‐valin)–chitosan (CHICO‐val) and N‐(γ‐propanoyl‐aspartic acid)–chitosan (CHICO‐asp). The main goal of this study was to obtain data on the radiochemical and biological behaviour of these complexes and information regarding their therapeutic potential when compared to 153Sm/166Ho‐chitosan. Radiolabelling yield of 153Sm/166Ho‐amino acid–chitosan complexes was dependent on polymer concentration but less dependent on pH. Radiochemical stability was shown to be higher for amino acid–chitosans than for chitosan, with 153Sm/166Ho‐CHICO‐val being stable up to 3 h, while 153Sm/166Ho‐CHICO‐asp is stable up to 24 h. In the presence of ascorbic acid radiochemical stability of 153Sm/166Ho‐CHICO‐val and 153Sm/166Ho‐CHICO was improved, decreasing for 153Sm/166Ho‐CHICO‐asp. In vivo behaviour of 153Sm complexes was studied in mice. The radioactive amino acid–chitosans can be directly injected into blood stream without significant retention on injection site, being trapped by liver. Biodistribution studies suggest that the radioactive amino acid–chitosans, due to its water solubility and stability may be considered potential candidates to be further explored for liver targeted nuclear therapy. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
153.
V. V. Burunova Yu. G. Suzdaltseva A. V. Voronov I. B. Cheglakov I. V. Vakhrushev K. N. Yarygin V. N. Yarygin 《Bulletin of experimental biology and medicine》2008,145(4):526-530
We proposed a new model of DNA structure, which allows rearrangement of monomers in the polymer chain backbone according to
mathematical laws. On the basis of the analysis of structural organization of DNA we concluded that rearrangements of monomers
should also occur during the formation of the molecular structure of other polymers (RNA and proteins).
Translated from Kletochnye Tehnologii v Biologii i Medicine, No. 4, pp. 211–215, November, 2008 相似文献
154.
155.
Comparative Study of Distribution of Active Sites According to Their Stereospecificity in Propylene Polymerization over the Traditional TiCl3 and Supported Titanium–Magnesium Catalysts with Different Composition 下载免费PDF全文
Marina Nikolaeva Mikhail Matsko Vladimir Zakharov 《Macromolecular chemistry and physics.》2018,219(5)
The preparative‐temperature rising elution fractionation method is used to obtain comparative data on contents of fractions with different microtacticities for polypropylene (PP) samples prepared using three catalytic systems: the traditional Ziegler–Natta (Z–N) catalyst δ‐TiCl3 and two types of supported titanium–magnesium catalysts: the “donor‐free” TiCl4/MgCl2 catalyst and TiCl4/MgCl2·nDBP catalyst (DBP – dibutylphthalate used as an internal donor) at polymerization with the same cocatalyst (AlEt3) in the absence and presence of an external donor (propyltrimetoxy silane). The separated individual PP fractions are also studied by gel permeation chromatography (molecular weight and molecular weight distribution) and differential scanning calorimetry. The results demonstrate general regularities and differences in the formation of active sites having different isospecificities for the traditional TiCl3‐based Z–N catalyst and highly active supported titanium–magnesium catalysts. 相似文献
156.
Base Catalyzed Thiol–Ene Click Chemistry toward Inner ?CHCF? Bonds for Controlled Functionalization of Poly(vinylidene fluoride) 下载免费PDF全文
《Macromolecular chemistry and physics.》2018,219(11)
A facile and controlled base catalyzed thiol–ene click chemistry toward electron‐deficient ? CH?CF? double bonds in poly(vinylidene fluoride) PVDF (P(VDF‐DB)) is reported in present contribution for the first time. The addition reaction is carefully conducted under varied conditions including at the elevated temperature, in the different solvents, and with the altered catalysts and thiols. The addition reaction is well confirmed to follow the base catalyzed route and exhibits close dependence onto the reaction conditions. Besides the addition reaction, the other two side reactions catalyzed by alkylamines, including the further main chain degradation of P(VDF‐DB) substrates together with the nucleophilic substitution of thiols to ? CH?CF? units, can be completely avoided by choosing a catalyst with a proper pKa value. With respect to the universality and well controlled feature of the reaction, the low cost and readily prepared P(VDF‐DB) substrate and the mild reaction conditions, this strategy may offer a robust tool for attaching various functional groups into PVDF side chain. 相似文献
157.
目的探讨脂肪间充质干细胞(adipose tissue-derived mesenchymal stem cells,ADMSCs)移植治疗兔急性心肌梗死后心力衰竭的作用及其可能机制。方法 30只健康日本大耳白兔随机分为注射磷酸盐缓冲液的假手术组(n=10)、心肌梗死对照组(n=10)以及注射ADMSCs移植组(n=10)。结扎兔前室间支,建立急性心肌梗死动物模型,急性心肌梗死1h内将4',6-二脒-2-苯基吲哚(4',6-diamidio-2-phenylindole,DAPI)标记的第三代ADMSCs(5×106个,1mL)植入ADMSCs移植组梗死心肌,对照组及假手术组注射等量磷酸盐缓冲液液。术前及术后4周分别做超声心动图检查其心功能变化。取心肌梗死区组织作冰冻切片,荧光显微镜下验证移植后的ADMSCs是否向心肌细胞分化,苏木素-伊红染色和CD34免疫组化观察梗死区毛细血管新生情况。结果超声心动图检测证实移植后4周ADMSCs组左心室收缩末期直径、舒张末期直径与左心室重量指数均小于心肌梗死对照组[(0.72±0.04)cm vs.(0.88±0.07)cm,P0.05;(1.07±0.12)cm vs.(1.21±0.09)cm,P0.05;(1.176±0.057)g/kg vs.(1.361±0.095)g/kg,P0.05],而短轴缩短率、射血分数均大于心肌梗死对照组[31.87%±2.03%vs.28.00%±3.38%,P0.05;51.75%±3.37%vs.43.13%±3.72%,P0.05];ADMSCs移植组荧光显微镜下可以观察到DAPI标记细胞存在,并分化为心肌样细胞;CD34免疫组化染色显示ADMSCs组梗死局部毛细血管密度明显高于心肌梗死对照组[(20.00±2.65)个vs.(7.75±2.12)个,P0.05]。结论同种异体移植的ADMSCs能够在梗死心肌内存活并分化为心肌样细胞,增加梗死区血管新生,抑制心室重构、改善心肌梗死后心功能。 相似文献
158.
A novel platform system, comprising a mucoadhesive core and a rapid release carrier, was designed for targeted drug delivery to the colon. Prednisolone pellets containing different carbomers, including Carbopol 971P, Carbopol 974P and Polycarbophil AA-1, with or without organic acids, were produced by extrusion-spheronization. Mucoadhesive pellets were coated with a new enteric double-coating system, which dissolves at pH 7. This system comprises an inner layer of partially neutralized Eudragit® S and buffer salt and an outer coating of standard Eudragit® S. A single layer of standard Eudragit S was also applied for comparison purposes. Dissolution of the coated pellets was assessed in USP II apparatus in 0.1 N HCl followed by Krebs bicarbonate buffer pH 7.4. Visualization of the coating dissolution process was performed by confocal laser scanning microscopy using fluorescent markers in both layers. The mucoadhesive properties of uncoated, single-coated and-double coated pellets were evaluated ex vivo on porcine colonic mucosa. Mucoadhesive pellets coated with a single layer of Eudragit® S release its cargo after a lag time of 120 min in Krebs buffer. In contrast, drug release from the double-coated mucoadhesive pellets was significantly accelerated, starting at 75 min. In addition, the mucoadhesive properties of the core of the double coated pellets were higher than those from single-coated pellets after the core had been exposed to the buffer medium. This novel platform technology has the potential to target the colon and overcome the variability in transit and harmonize drug release and bioavailability. 相似文献
159.
Sheng‐Hsiung Yang Chun‐Hao Huang Chiu‐Hsiang Chen Chain‐Shu Hsu 《Macromolecular chemistry and physics.》2009,210(1):37-47
A new series of disubstituted polyacetylene derivatives that contain multi‐fluorine atoms on the pendent phenyl ring have been synthesized and characterized. The results reveal a greater red‐shift in UV‐vis absorption and PL emission upon incorporating more fluorine atoms on the pendent phenyl ring. Among them, disubstituted polyacetylene with a difluorophenyl group ( PDPA‐2F ) showed the highest luminescent efficiency. The device performance can be promoted by blending a hole‐transporting material TM‐TPD into PDPA‐2F as the active layer or by using a light‐emitting copolymer in which PDPA‐2F was copolymerized with a carbazole group ( PDPA‐2Fcab ). A light‐emitting diode of ITO/PEDOT/ PDPA‐2Fcab /Ca/Al revealed a maximum luminescence of 4230 cd · m?2 at 14 V and a maximum current efficiency of 3.37 cd · A?1 at 7 V.
160.
Yanhui Hou Min Yang Xiangjian Wan Jie Mao Yanfeng Ma Yi Huang Yongsheng Chen 《Macromolecular chemistry and physics.》2009,210(12):1044-1051
Two oligo‐(aryleneethynylene)s, with coplanarity of main chain and tetrathiafulvalene (TTF) side chains, have been prepared and characterized. The X‐ray diffractions (XRDs) show that their π‐extended coplanar backbones can form continuous π‐stacking. For the two oligomers, one stacks in the inter‐digitation packing mode; another stacks in the end‐to‐end packing mode. Cyclic voltammetries reveal that the two oligomers have almost the same reversible electroactive properties. The TTF units of the two oligomers can be oxidized to TTF . 1+ by Fe(bpy)3(PF6)3 (bpy = 2,2′‐bipyridine). The band gaps, deduced from UV‐Vis absorption spectra, are 1.92 and 2.03 eV, respectively. The conductivities of the two oligomers are 1 × 10?5 and 6 × 10?8 S · cm?1 at room temperature. The charge transfer (CT) complexes of the oligomers and tetracyanoquinodimethane (TCNQ) exhibit higher conductivity up to 0.2 S · cm?1.