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1.
树枝状过渡金属催化剂是在树枝状大分子上负载上过渡金属活性中心,因此,此类催化剂既具有树枝状大分子特有的艺术结构,同时还具有过渡金属配合物的功能化性能,使其两者能够协同发挥作用,兼具均相和非均相催化体系的特点,在催化烯烃聚合方面具有较高的催化活性和良好的催化稳定性,近年来备受关注,催化乙烯聚合就是其中的研究热点之一。本文按其过渡金属活性中心进行分类,综述了近年来国内外树枝状过渡金属催化剂在这乙烯聚合方面的进展,阐述了多种树枝状效应产生的原因,并且对乙烯聚合用树枝状过渡金属催化剂的发展前景进行了展望。  相似文献   
2.
为开发具有高效过滤性能的膜材料,以超支化季铵盐(HBP-HTC)为枝化促进剂,利用静电纺丝技术一步法制备了聚偏氟乙烯(PVDF)树枝状纳米纤维膜,探讨了纺丝工艺对纤维膜成形结构的影响,分析了树枝状纳米纤维膜的力学性能及其空气过滤性能。结果表明:由于HBP-HTC表面丰富的季铵基团具有对电荷的稳定富集作用,可获得比用小分子季铵盐制成膜更多的树枝状纳米纤维结构,当PVDF质量分数为12%,季铵基团添加量为 0.10 mol/L, 纺丝电压为25 kV时,制得的纤维膜树枝状覆盖率高达78.32%,且具有较好的力学性能;所制备的纳米纤维膜厚度为40 μm时,其过滤效率高达99.995%,而压降为122.4 Pa。  相似文献   
3.
Numerous brain diseases are associated with abnormalities in morphology and density of dendritic spines, small membranous protrusions whose structural geometry correlates with the strength of synaptic connections. Thus, the quantitative analysis of dendritic spines remodeling in microscopic images is one of the key elements towards understanding mechanisms of structural neuronal plasticity and bases of brain pathology. In the following article, we review experimental approaches designed to assess quantitative features of dendritic spines under physiological stimuli and in pathological conditions. We compare various methodological pipelines of biological models, sample preparation, data analysis, image acquisition, sample size, and statistical analysis. The methodology and results of relevant experiments are systematically summarized in a tabular form. In particular, we focus on quantitative data regarding the number of animals, cells, dendritic spines, types of studied parameters, size of observed changes, and their statistical significance.  相似文献   
4.
Neoantigen vaccines and adoptive dendritic cell (DC) transfer are major clinical approaches to initiate personalized immunity in cancer patients. However, the immunization efficacy is largely limited by the in vivo trajectory including neoantigens’ access to resident DCs and DCs’ access to lymph nodes (LNs). Herein, an innovative strategy is proposed to improve personalized immunization through neoantigen-loaded nanovaccines synergized with adoptive DC transfer. It is found that it enables selective delivery of neoantigens to resident DCs and macrophages by coating cancer cell membranes onto neoantigen-loaded nanoparticles. In addition, the nanovaccines promote the secretion of chemokine C-C motif ligand 2 (CCL2), CCL3, and C-X-C motif ligand 10 from macrophages, thus potentiating the access of transferred DCs to LNs. This immunization strategy enables coordinated delivery of identified neoantigens and autologous tumor lysate-derived undefined antigens, leading to initiation of antitumor T cell immunity in a personalized manner. It significantly inhibits tumor growth in prophylactic and established mouse tumor models. The findings provide a new vision for potentiating adoptive cell transfer by nanovaccines, which may open the door to a transformative possibility for improving personalized immunization.  相似文献   
5.
Horizontal directional solidification experiments were carried out with a monophasic Sn-2%Sb (mass fraction) alloy to analyze the influence of solidification thermal parameters on the morphology and length scale of the microstructure. Continuous temperature measurements were made during solidification at different positions along the length of the casting and these temperature data were used to determine solidification thermal parameters, including the growth rate (VL) and the cooling rate (TR). High cooling rate cells and dendrites are shown to characterize the microstructure in different regions of the casting, with a reverse dendrite-to-cell transition occurring for TR>5.0 K/s. Cellular (lc) and primary dendrite arm spacings (l1) are determined along the length of the directionally-solidified casting. Experimental growth laws relating lc and l1 to VL and TR are proposed, and a comparative analysis with results from a vertical upward directional solidification experiment is carried out. The influence of morphology and length scale of the microstructure on microhardness is also analyzed.  相似文献   
6.
Experience‐dependent synapse remodeling is associated with information storage in the nervous system. Neuronal synapses show alteration in various neurological and cognitive disorders in their structure and function. At the ultrastructural level, parallel fiber boutons contacting multiple spines of Purkinje cells in the cerebellar cortex are commonly observed in physiologically enriched animals as well as pathological ataxic mutants. However, the dendritic origin of those spines on parallel fiber multiple‐synapse boutons (MSBs) has been poorly understood. Here, we investigated this issue by 3‐dimensional ultrastructural analysis to determine synaptic connectivity of MSBs in both mice housed in physically enriched environment and cerebellar ataxic mutants. Our results demonstrated that environmental enrichment selectively induced MSBs to contact spines from the same parent dendrite, indicating focal strengthening of synapse through the simultaneous activation of two adjacent spines. In contrast, ataxic mutants displaying impaired motor coordination had significantly more MSBs involving spines originating from different neighboring dendrites compared to both wild‐type and environmentally enriched animals, suggesting that compromising multiple synapse formation may lead to abnormal motor behavior in the mutant mice. These findings propose that environmental stimulation in normal animals mainly involves the refinement of preexisting synaptic networks, whereas pathological ataxic conditions may results from less‐selective but compromising multiple synaptic formation. This study underscores that different types of multiple synapse boutons may have disparate effects on cerebellar synaptic transmission.  相似文献   
7.
A uniform dendritic NiCo2S4@NiCo2S4 hierarchical nanostructure of width ≈100 nm is successfully designed and synthesized. From kinetic analysis of the electrochemical reactions, those electrodes function in rechargeable alkaline batteries (RABs). The dendritic structure exhibited by the electrodes has a high discharge‐specific capacity of 4.43 mAh cm?2 at a high current density of 240 mA cm?2 with a good rate capability of 70.1% after increasing the current densities from 40 to 240 mA cm?2. At low scan rate of 0.5 mV s?1 in cyclic voltammetry test, the semidiffusion controlled electrochemical reaction contributes ≈92% of the total capacity, this value decreases to ≈43% at a high scan rate of 20 mV s?1. These results enable a detailed analysis of the reaction mechanism for RABs and suggest design concepts for new electrode materials.  相似文献   
8.
Synthetic vaccines, based on antigenic peptides that comprise MHC−I and MHC-II T-cell epitopes expressed by tumors, show great promise for the immunotherapy of cancer. For optimal immunogenicity, the synthetic peptides (SPs) should be adjuvanted with suitable immunostimulatory additives. Previously, we have shown that improved immunogenicity in vivo is obtained with vaccine modalities in which an SP is covalently connected to an adjuvanting moiety, typically a ligand to Toll-like receptor 2 (TLR2). SPs were covalently attached to UPam, which is a derivative of the classic TLR2 ligand Pam3CysSK4. A disadvantage of the triply palmitoylated UPam is its high lipophilicity, which precludes universal adoption of this adjuvant for covalent modification of various antigenic peptides as it renders the synthetic vaccine insoluble in several cases. Here, we report a novel conjugatable TLR2 ligand, mini-UPam, which contains only one palmitoyl chain, rather than three, and therefore has less impact on the solubility and other physicochemical properties of a synthetic peptide. In this study, we used SPs that contain the clinically relevant neoepitopes identified in a melanoma patient who completely recovered after T-cell therapy. Homogeneous mini-UPam-SP conjugates have been prepared in good yields by stepwise solid-phase synthesis that employed a mini-UPam building block pre-prepared in solution and the standard set of Fmoc-amino acids. The immunogenicity of the novel mini-UPam-SP conjugates was demonstrated by using the cancer patient's T-cells.  相似文献   
9.
Loss of tolerance of the adaptive immune system towards indigenous flora contributes to the development of inflammatory bowel diseases (IBD). Defects in dendritic cell (DC)-mediated innate and adoptive immune responses are conceivable. The aim of this study was to investigate the expression of the inhibitory molecules CD200R1 and their ligand CD200 on DCs, to clarify the role of the DCs in the pathogenesis of IBD. Thirty-seven pediatric IBD patients (23 with Crohn’s disease (CD) and 14 with ulcerative colitis (UC)) with mean age 13.25 ± 2.9 years were included. Fourteen age-matched healthy pediatric volunteers (five males and nine females) served as a control group (HC). The percentage of CD11c+ myeloid dendritic cells (mDCs) and CD123+ plasmacytoid DCs (pDCs) expressing CD200R1 and CD200 were evaluated in peripheral blood using flow cytometry and were correlated with routine biochemical, serological markers, serum levels of cytokines and with the percentages of circulating regulatory T cells (Treg) and CD4+ producing IL-17 (Th17). IBD patients showed a significant decrease in the percentage of pDCs and mDCs expressing CD200R1 compared to that of HC. Patients with UC showed increased expressions of the CD200 molecule on pDCs as compared to HC. DCs expressing CD200R1 were found to be correlated positively with Treg and negatively with TH17 and erythrocyte sedimentation rate (ESR). Our findings suggest that IBD is associated with dysregulation in the CD200R1/CD200 axis and that the decrease in DCs expressing CD200R1 may contribute to the imbalance of Th17 and Treg cells and in the pathogenesis of IBD.  相似文献   
10.
Au基树枝状杂聚体纳米结构形成机理研究   总被引:2,自引:2,他引:0  
以油胺为还原剂和稳定剂,通过晶种生长法顺序还原HAuCl4·xH2O和H2PtCl6·6H2O,成功制备了Au-Pt树枝状杂聚体纳米颗粒。通过对Pt在Au颗粒表面沉积过程的研究,探讨了杂聚体结构的形成机理。研究发现油胺还原得到的Au纳米颗粒表面是由不同晶面组成的,随后还原的Pt会选择性地沉积到Au{111}表面处成核生长,形成Pt的纳米岛结构,当有足量的Pt前体时,Pt会在纳米岛的表面继续生长形成附着于Au颗粒表面的树枝状结构,研究表明树枝状Pt形貌的形成与油胺的使用有着重要关系。  相似文献   
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