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排序方式: 共有1221条查询结果,搜索用时 921 毫秒
61.
Benjamin Brocart Christian Hurtevent 《Journal of Dispersion Science and Technology》2013,34(10):1496-1504
Naphthenic oil production is known to be made difficult by stable emulsion formation and possible scaling of calcium naphthenates. From a flow assurance point of view, it is of major importance to foresee these two possible issues at the earliest stage of the project development especially for deep-offshore fields. In this article, a classification of crude oils based on density, acidity and acid types is proposed. Process schemes adapted to the different oil types are also described. 相似文献
62.
Oil refinery is one of the fast growing industries across the globe and it is expected to progress in the near future. The worldwide increase in the generation of refinery wastewater along with strict environmental regulations in the discharge of industrial effluent, persistent efforts have been devoted to recycle and reuse the treated water. The wastewater from the refining operation leads to serious environmental threat to the ecosystem. Therefore, this study aimed to synthesize silica (SiO2) and calcium carbonate nanoparticles (CaCO3) in the reduction of organics from refinery wastewater. The synthesized nanoparticles were employed in the reduction of chemical oxygen demand (COD) from refinery wastewater by studying the influence of solution pH, contact time, dosage of nanoparticles and stirring speed on adsorption performance. From the batch experimental studies, the optimized processing conditions for the reduction of COD using SiO2 nanoparticles are pH 4.0, dosage 0.5 g, stirring speed 125 rpm and 90 min stirring time, and the corresponding values for CaCO3 nanoparticles are pH 8.0, dosage 0.4 g, stirring speed 100 rpm and 90 min stirring time. The study demonstrates that SiO2 and CaCO3 nanoparticles have a promising future in the reduction organics from refinery wastewater in different pH regimes. 相似文献
63.
Here, agar hydrogel was selected as diffusion medium and template to control the biomimetic mineralization of calcium carbonate (CaCO3). Due to three dimensional network structures and abundant functional groups (such as, hydroxyl groups), Ca2+ ions were uniformly distributed in the network and electrostatically attracted. The diffusion speed and range of CO32? ions were mediated by the concentration of hydrogel medium. Under the synergistic effect of Mg2+ ions, the crystal CaCO3 was induced by gas phase diffusion method in the hydrogel system. The results showed that the concentrations of Mg2+ ions and agar hydrogel had no obvious effect on the calcite phase of CaCO3, but the morphologies and sizes changed with concentrations of medium and Mg2+ ions. Attribute to template effect, the crystallization behavior and growth rate of CaCO3 crystals were regulated. Since Mg2+ ions were easily adsorbed on the surfaces of unit cell, the unique structure of CaCO3 was precisely controlled. This study provides a useful reference and inspiration for the understandings of the contributions of ion supply rate in bio-mineralization and hydrogel medium in biomimetic mineralization. 相似文献
64.
《Arabian Journal of Chemistry》2022,15(3):103647
An optical biosensor for urea based on urease enzyme immobilised on functionalised calcium carbonate nanoparticles (CaCO3-NPs) was successfully developed in this study. CaCO3-NPs were synthesised from discarded cockle shells via a simple and eco-friendly approach, followed by surface functionalisation with succinimide ester groups. The fabricated biosensor is comprised of two layers. The first (bottom layer) contained functionalised NPs covalently immobilised to urease, and the second (uppermost layer) was alginate hydrogel physically immobilised to the pH indicator phenolphthalein. The biosensor provided a colorimetric indication of increasing urea concentrations by changing from colourless to pink. Quantitative urea analysis was performed by measuring the reflectance intensity of the colour change at a wavelength of 633.16 nm. The determination of urea concentration using this biosensor yielded a linear response range of 30–1000 mM (R2 = 0.9901) with a detection limit of 17.74 mM at pH 7.5. The relative standard deviation of reproducibility was 1.14%, with no signs of interference by major cations, such as K+, Na+, NH?+, and Mg2+. The fabricated biosensor showed no significant difference with the standard method for the determination of urea in urine samples. 相似文献
65.
Agkisacutacin isolated from the venom of Agkistrodon acutus is a coagulation factor IX / coagulation factor X-binding protein with marked anticoagulant- and platelet-modulating activities.
Ca2+ ion-induced stabilization and refolding of Agkisacutacin have been studied by following fluorescent measurements. Ca2+ ions not only increase the structural stability of agkisacutacin against GdnHCl denaturation, but also induce its refolding.
The GdnHCl-induced unfolding of the apo-agkisacutacin and the purified agkisacutacin is a single-step process with no detectable
intermediate state. Ca2+ ions play an important role in the stabilization of the structure of agkisacutacin. Ca2+-stabilized agkisacutacin exhibits higher resistance to GdnHCl denaturation than the apo-agkisacutacin. It is possible to
induce refolding of the unfolded apo-agkisacutacin merely by adding 1 mM Ca2+ ions without changing the concentration of the denaturant. The kinetic result of Ca2+-induced refolding provides evidences for that agkisacutacin consists of at least two refolding phases and the first phase
of Ca2+-induced refolding should involve the formation of the compact Ca2+-binding site regions, and subsequently, the protein undergoes further conformational rearrangements to form the native structure. 相似文献
66.
Currently nanosystems composed of polynucleotides and lipid vesicles (nanolipoplexes) are considered to be promising tools for gene therapeutics. Successful in vivo application of these vectors depends on their physicochemical, technological and biological characteristics including morphology, size distribution, molecular interactions and stability. Anionic nanoliposomes (DPPC:DCP:CHOL) were prepared by two different techniques, namely the conventional thin-film hydration method followed by extrusion, and the heating method (HM), in which no volatile solvent or detergent is used. A non-viral and non-cationic gene transfer vector was constructed by incorporating plasmid DNA (pcDNA3.1/His B/lacZ) to the HM-nanoliposomes by the electrostatic mediation of Ca2+ ions. Transfection efficiency of the nanolipoplexes was evaluated using a human bronchial epithelial cell line (16HBE14o-) in the presence of serum. Particle characterisation, stability of the formulations and lipid–DNA interaction studies were performed using transmission electron microscopy (TEM) and light scattering. TEM pictures of nanolipoplexes showed presence of two to four closely packed vesicles with signs of fusion. Efficient delivery of plasmid DNA and subsequent β-galactosidase expression was achieved using the anionic nanolipoplexes. Transfection efficiency increased with lipid:DNA ratio up to 7:1 (w/w), where transfection efficiency was 12-fold higher than in untreated cells. Further increase in lipid ratio decreased transfection. These nanolipoplexes appear to be safe, stable and efficient in the protection and delivery of DNA to different cells and tissues. 相似文献
67.
《印度化学会志》2021,98(8):100097
Two rare hetero-metallic calcium(II)-zinc(II) complexes [CaZn4(OBz)10(μ2-hmt)2]n (1) and [Ca2Zn4(OBz)12(μ2-hmt)2]n (2) have been synthesized using basic zinc carbonate, benzoic acid (HOBz), hydrated calcium chloride and hexamethylenetetramine (hmt) by varying the molar ratio of the reactants. Both the complexes have been analyzed by elemental analysis, IR spectroscopy and X-ray crystallography. The complex 1 is a 1D polymer which contains one calcium ion and four zinc atoms in the asymmetric unit together with ten benzoates and two hmts. The polymer has been constructed by the alternate joining of paddle-wheel Zn2(OBz)4 units and Zn2Ca trinuclear species by μ2-hmt bridging molecules connecting Zn2+ ions. Zinc atoms have five coordinate square pyramidal geometries and four coordinate tetrahedral geometries in Zn2(OBz)4 and Zn2Ca moieties, respectively, whereas calcium atoms have six-coordinate distorted octahedral geometry. Complex 2 is also a 1D polymer but unlike complex 1, it contains four independent zinc and two independent calcium atoms in the asymmetric unit together with twelve benzoates and two hmts. By contrast, the polymeric structure of complex 2 has been formed by the connection of Zn2Ca trinuclear species via μ2 hmt bridging molecules at Zn centers. Complex 2 is also a 1D polymer but unlike complex 1, it contains four independent zinc and three independent calcium atoms in the asymmetric unit together with twelve benzoates and two hmts. All four zinc atoms are four coordinate with tetrahedral environments and the calcium atoms are six coordinated (two are located on a center of symmetry) exhibiting a distorted octahedral geometry. 相似文献
68.
Tian Bai Kongyin Zhao Zijie Lu Xuefang Liu Ze Lin Mengmeng Cheng Ziyi Li Dunwan Zhu Linhua Zhang 《中国化学快报》2021,32(3):1051-1054
Herein,copper ion doped calcium alginate(Cu~(2+)/CaAlg) composite hydrogel filtration membranes were prepared by using natural polymer sodium alginate(NaAlg) as raw material.The thermal stability and structure of the composite membranes were characterized by thermogravimetric analysis and infrared spectroscopy.The mechanical strength,anti-fouling performance,hydrophilicity and filtration performance of the membrane were studied.The results show that Cu~(2+)/CaAlg hydrogel membrane has excelle nt mechanical properties and thermal stability.The anti-swelling ability of the membrane was greatly enhanced by doping Cu~(2+).After three alternate filtration cycles,the flux recovery rate of Cu~(2+)/CaAlg hydrogel membrane can still reach 85%,indicating that the membrane has good antipollution performance.When the operation pressure was 0.1 MPa,the rejection of coomassie brilliant blue G250 reached 99.8% with a flux of 46.3 L m ~2 h ~1,while the Na_2 SO_4 rejection was less than 10.0%.The Cu~(2+)/CaAlg membrane was recycled after 24 h in the filtration process,and its flux and rejection rate did not decrease significantly,indicating that the hydrogel membrane has long-term application potential.The Cu~(2+)/CaAlg membrane has a wide range of applications prospect in dye desalination,fine separation and biopharmaceutical technology fields. 相似文献
69.
ω-芋螺毒素属于海洋生物活性多肽,由24-31个氨基酸残基组成.特异性作用于电压敏感的钙离子通道(VGCCs),能够直接开发成药物或作为先导化合物进行新药开发.本文应用新型氨基酸残基结构描述符cscales和遗传偏最小二乘算法,对ω-芋螺毒素进行定量构效关系(QSAR)研究,并设计、构建了容量为2244个化合物的N-型和P/Q-型VGCC拮抗剂虚拟组合多肽库,然后分别采用QSAR模型预测和相似性搜索方法对组合多肽库进行了虚拟筛选.研究结果表明,建立的N-型和P/Q-型VGCC拮抗剂QSAR模型均具有较好的预测能力,交叉验证相关系数(CV-r2)均大于0.89.主成分分析和聚类分析结果表明,虚拟组合多肽库中化合物具有较好的结构多样性和差异性.通过虚拟筛选,得到了具有高预测活性的6个N-型和19个P/Q-型钙离子通道拮抗剂,为进一步的合成和活性评价奠定了理论基础.同时,本文建立的多肽QSAR预测模型和虚拟筛选策略,为其它多肽类化合物的定量构效关系研究和虚拟筛选提供了参考. 相似文献
70.
Laila SADALLAH Aicha BOUKHRIS Hassan HANNACHE Said GMOUH 《Turkish Journal of Chemistry》2020,44(1):142
Two organic fluorophores, fluorescein (F) and rhodamine B (Rd), were entrapped in calcium phosphate nanoparticles. The as-obtained nanoparticles can be used for biological release applications. For this aim, calcium phosphate nanoparticles were synthesized using the precipitation method. Structural analysis of these nanoparticles was performed using XRD, FTIR, and Raman spectroscopy, confirming that the synthesized nanoparticles were hydroxyapatite. TEM and SEM analyses demonstrated that these nanoparticles had a size of 20 nm and a well-defined morphology. F and Rd (about 0.5 wt.%) were entrapped in these nanoparticles and their release, as a function of time, was studied via UV-Vis spectroscopy. The obtained results showed that the release of both fluorophores was progressive over time. The trapping efficiencies of the fluorophores were 67.15% and 90.76% for F and Rd, respectively. 相似文献