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941.
作为膜的功能性砌块的磷脂酰胆碱及其类似物, 近年来被发现参与多种重要的生理过程和病理过程, 除了用作磷脂酶抑制剂和血小板活化因子, 还具有抗肿瘤的细胞毒性、潜在的抗AIDS剂以及抗真菌活性等, 这些活性与其结构密切相关, 而且通过膜的介入实现, 代表了一类新型的具有广阔医药学前景的强生理活性化合物。 相似文献
942.
943.
Shell thickness determination of polymer-shelled microbubbles using transmission electron microscopy
Intravenously injected microbubbles (MBs) can be utilized as ultrasound contrast agent (CA) resulting in enhanced image quality. A novel CA, consisting of air filled MBs stabilized with a shell of polyvinyl alcohol (PVA) has been developed. These spherical MBs have been decorated with superparamagnetic iron oxide nanoparticles (SPIONs) in order to serve as both ultrasound and magnetic resonance imaging (MRI) CA. In this study, a mathematical model was introduced that determined the shell thickness of two types of SPIONs decorated MBs (Type A and Type B). The shell thickness of MBs is important to determine, as it affects the acoustical properties. In order to investigate the shell thickness, thin sections of plastic embedded MBs were prepared and imaged using transmission electron microscopy (TEM). However, the sections were cut at random distances from the MB center, which affected the observed shell thickness. Hence, the model determined the average shell thickness of the MBs from corrected mean values of the outer and inner radii observed in the TEM sections. The model was validated using simulated slices of MBs with known shell thickness and radius. The average shell thickness of Type A and Type B MBs were 651 nm and 637 nm, respectively. 相似文献
944.
The world runs on networks over which signals communicate sequences of symbols, e.g. numerals. Examining both engineered and natural communications networks reveals an unsuspected order that depends on contact with an unpredictable entity. This order has three roots. The first is a proof within quantum theory that no evidence can ever determine its explanation, so that an agent choosing an explanation must do so unpredictably. The second root is the showing that clocks that step computers do not “tell time” but serve as self-adjusting symbol-handling agents that regulate “logically synchronized” motion in response to unpredictable disturbances. Such a clock-agent has a certain independence as well as the capacity to communicate via unpredictable symbols with other clock-agents and to adjust its own tick rate in response to that communication. The third root is the noticing of unpredictable symbol exchange in natural systems, including the transmission of symbols found in molecular biology. We introduce a symbol-handling agent as a role played in some cases by a person, for example a physicist who chooses an explanation of given experimental outcomes, and in other cases by some other biological entity, and in still other cases by an inanimate device, such as a computer-based detector used in physical measurements. While we forbear to try to explain the propensity of agents at all levels from cells to civilizations to form and operate networks of logically synchronized symbol-handling agents, we point to this propensity as an overlooked cosmic order, an order structured by the unpredictability ensuing from the proof. Appreciating the cosmic order leads to a conception of agency that replaces volition by unpredictability and reconceives the notion of objectivity in a way that makes a place for agency in the world as described by physics. Some specific implications for physics are outlined. 相似文献
945.
An Organometallic Compound which Exhibits a DNA Topology‐Dependent One‐Stranded Intercalation Mode 下载免费PDF全文
Dr. Zhujun Ma Dr. Giulia Palermo Dr. Zenita Adhireksan Dr. Benjamin S. Murray Thibaud von Erlach Prof. Paul J. Dyson Prof. Ursula Rothlisberger Prof. Curt A. Davey 《Angewandte Chemie (International ed. in English)》2016,55(26):7441-7444
Understanding how small molecules interact with DNA is essential since it underlies a multitude of pathological conditions and therapeutic interventions. Many different intercalator compounds have been studied because of their activity as mutagens or drugs, but little is known regarding their interaction with nucleosomes, the protein‐packaged form of DNA in cells. Here, using crystallographic methods and molecular dynamics simulations, we discovered that adducts formed by [(η6‐THA)Ru(ethylenediamine)Cl][PF6] (THA=5,8,9,10‐tetrahydroanthracene; RAED‐THA‐Cl[PF6]) in the nucleosome comprise a novel one‐stranded intercalation and DNA distortion mode. Conversely, the THA group in fact remains solvent exposed and does not disrupt base stacking in RAED‐THA adducts on B‐form DNA. This newly observed DNA binding mode and topology dependence may actually be prevalent and should be considered when studying covalently binding intercalating compounds. 相似文献
946.
通过天门冬氨酸(Asp)、异亮氨酸(Ile)热缩聚反应,制备了天门冬氨酸-异亮氨酸共聚物(AI),通过乙二胺(EDA)胺化,并与1,4,7,10-四氮杂环十二烷-1,4,7,10-四羧酸(DOTA)连接,再与钆离子(Gd3+)络合,合成了生物相容性大分子磁共振成像(MRI)造影剂——AI-EDA-DOTA-Gd.运用红外光谱(IR)、核磁共振(NMR)、电感耦合等离子谱(ICP)等方法对其进行结构表征,并通过弛豫性能、溶血性质、急性毒性及动物体内成像对其进行综合评价.体外弛豫结果表明,AI-EDA-DOTA-Gd的纵向弛豫效率(r_1=12.6mmol~(–1)×L×s~(–1))是商用造影剂Gd-DOTA(r_1=5.8 mmol~(–1)×L×s~(–1))的2.2倍.动物组织生理切片和溶血性实验结果说明其具有良好的生物相容性和较低的毒性.动物体内成像结果显示,AI-EDA-DOTA-Gd的最佳成像时间为30~70 min,注射AI-EDA-DOTA-Gd后的肝脏组织信号相比于未注射造影剂时增强了约(55.1±5.7)%. 相似文献
947.
Chenglang Li 《Journal of Macromolecular Science: Physics》2016,55(2):128-137
The effect of the metallic salts of phenylmalonic acid (PMA), as novel nucleating agents, on the melt and crystallization behaviors, spherulitic morphologies, and crystal structures of poly(L-lactide) (PLLA) was studied by means of differential scanning calorimetry, polarized light microscopy, and wide angle X-ray diffraction (WAXD). The results showed that calcium and cadmium salts of PMA are good nucleating agents for PLLA. Lithium, sodium, magnesium, strontium, and zinc salts of PMA are moderate nucleating agents, barium and aluminum salts of PMA are weak nucleating agents, while potassium phenylmalonate is not a nucleating agent for PLLA. The presence of nucleating agents significantly increased the number and decreased the size of the spherulites, but the crystal structures of the nucleated PLLA samples were not changed. 相似文献
948.
949.
R. Fernández-Ruiz R. Costo M.P. Morales O. Bomatí-Miguel S. Veintemillas-Verdaguer 《Spectrochimica Acta Part B: Atomic Spectroscopy》2008
This work presents the first application of the total-reflection X-ray fluorescence (TXRF) to the compositional study of magnetic ferrofluids. With the aims of validating the best analytical conditions and also, limitations of the TXRF in the compositional study of these materials, an alternative empirical method, based in the use of angle-dependence TXRF (AD-TXRF) measurements, is proposed. Three kinds of ferromagnetic nanoparticles, with different morphologies, have been studied. The techniques of inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES) have been used to validate the TXRF results. In contrast with the plasma techniques, the developed TXRF procedure need not of previous chemical acid digestion. Additionally, two procedures of magnetic nanoparticles synthesis, co-precipitation and laser-pyrolysis, have been checked for the contaminants trace metals Zn, Mn and Cr. It has been found that the method of laser-pyrolysis produces nanoparticles of higher purity. 相似文献
950.
Phosphinodiselenoic acid esters are synthesized from the reaction of chlorodiphenylphosphine and aryl- or alkyl-magnesium bromide in the presence of selenium powder. They are employed as RAFT agents in thermally initiated, styrene polymerization. The phosphinodiselenoic acid esters 6a and 6b showed some degree of control over the radical polymerization of styrene. 相似文献