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81.
王少阶 《核技术(英文版)》1990,(Z1)
The principles of positron annihilation and four positron experimental techniques are described. The application of positron annihilation technique in material science. atomic physics and other related fields are discussed. 相似文献
82.
主要研究了喷射成形镍基高温合金的微观组织特征和时效硬化行为。合金经1140 ℃,8 h固溶处理,然后在780 ℃,2~12 h时效处理。分别测试了合金显微硬度、析出相大小及形态、电导率和正电子湮没寿命与时效时间的关系。结果表明,在时效8 h时,显微硬度达到最大值,此时γ'' 长大到临界尺寸56 nm。然而,时效时间超过8 h,合金显微硬度降低,这是由于γ'' 长大超过了其临界尺寸。随着时效时间延长至6 h,电导率快速增加到其最大值32%IACS,但是正电子湮没寿命则降低到最小值149 ps,在时效时间为10 h时,正电子湮没寿命达到最大值297 ps。这是由在时效过程中γ'' 尺寸的变化以及缺陷浓度的变化引起的 相似文献
83.
Comparative Assessment of Complex Stabilities of Radiocopper Chelating Agents by a Combination of Complex Challenge and in vivo Experiments 下载免费PDF全文
Shanna Litau Dr. Uwe Seibold Alicia Vall‐Sagarra Prof. Dr. Gert Fricker Prof. Dr. Björn Wängler Priv.‐Doz. Dr. Carmen Wängler 《ChemMedChem》2015,10(7):1200-1208
For 64Cu radiolabeling of biomolecules to be used as in vivo positron emission tomography (PET) imaging agents, various chelators are commonly applied. It has not yet been determined which of the most potent chelators—NODA‐GA ((1,4,7‐triazacyclononane‐4,7‐diyl)diacetic acid‐1‐glutaric acid), CB‐TE2A (2,2′‐(1,4,8,11‐tetraazabicyclo[6.6.2]hexadecane‐4,11‐diyl)diacetic acid), or CB‐TE1A‐GA (1,4,8,11‐tetraazabicyclo[6.6.2]hexadecane‐4,11‐diyl‐8‐acetic acid‐1‐glutaric acid)—forms the most stable complexes resulting in PET images of highest quality. We determined the 64Cu complex stabilities for these three chelators by a combination of complex challenge and an in vivo approach. For this purpose, bioconjugates of the chelating agents with the gastrin‐releasing peptide receptor (GRPR)‐affine peptide PESIN and an integrin αvβ3‐affine c(RGDfC) tetramer were synthesized and radiolabeled with 64Cu in excellent yields and specific activities. The 64Cu‐labeled biomolecules were evaluated for their complex stabilities in vitro by conducting a challenge experiment with the respective other chelators as challengers. The in vivo stabilities of the complexes were also determined, showing the highest stability for the 64Cu–CB‐TE1A‐GA complex in both experimental setups. Therefore, CB‐TE1A‐GA is the most appropriate chelating agent for *Cu‐labeled radiotracers and in vivo imaging applications. 相似文献
84.
Hans‐Jörg Breyholz Dr. Stefan Wagner Dr. Andreas Faust Dr. Burkhard Riemann Prof. Dr. Carsten Höltke Dr. Sven Hermann Dr. Otmar Schober Prof. Dr. Michael Schäfers Prof. Dr. Klaus Kopka Priv.‐Doz. Dr. 《ChemMedChem》2010,5(5):777-789
Matrix metalloproteinases (MMPs) are zinc‐ and calcium‐dependent endopeptidases. Representing a subfamily of the metzincin superfamily, MMPs are involved in the proteolytic degradation of components of the extracellular matrix. Unregulated MMP expression, MMP dysregulation and locally increased MMP activity are common features of various diseases, such as cancer, atherosclerosis, stroke, arthritis, and others. Therefore, activated MMPs are suitable biological targets for the specific visualization of such pathologies, in particular by using radiolabeled MMP inhibitors (MMPIs). The aim of this work was to develop a radiofluorinated molecular probe for noninvasive in vivo imaging for the detection of up‐regulated levels of activated MMPs in the living organism. Fluorinated MMPIs ( 26 , 31 and 38 ) based on the pyrimidine‐2,4,6‐trione lead structure RO 28‐2653 ( 1 ) were synthesized, and their MMP inhibition potency was evaluated in vitro. The radiosynthesis and the in vivo biodistribution of the first 18F‐labeled prototype, MMP‐targeted tracer [18F] 26 , suitable for molecular imaging by means of positron emission tomography (PET) were realized. 相似文献
85.
Joël Mercier Laurence Archen Véronique Bollu Stéphane Carré Yves Evrard Dr. Eric Jnoff Dr. Benoît Kenda Bénédicte Lallemand Dr. Philippe Michel Dr. Florian Montel Dr. Florence Moureau Nathalie Price Dr. Yannick Quesnel Dr. Xavier Sauvage Dr. Anne Valade Dr. Laurent Provins 《ChemMedChem》2014,9(4):693-698
The role of the synaptic vesicle protein 2A (SV2A) protein, target of the antiepileptic drug levetiracetam, is still mostly unknown. Considering its potential to provide in vivo functional insights into the role of SV2A in epileptic patients, the development of an SV2A positron emission tomography (PET) tracer has been undertaken. Using a 3D pharmacophore model based on close analogues of levetiracetam, we report the rationale design of three heterocyclic non‐acetamide lead compounds, UCB‐A, UCB‐H and UCB‐J, the first single‐digit nanomolar SV2A ligands with suitable properties for development as PET tracers. 相似文献
86.
Chenfei Shi Yuling Su Jinjin Guo Jiangying Zhang Gaoshang Gong Huiyun Hu Yongqiang Wang 《Ceramics International》2021,47(8):10887-10892
In this paper, the crystal structure, vacancy defect, local electron density and magnetic properties of Gd1-xCaxCrO3 (0 ≤ x ≤ 0.3) polycrystalline samples were investigated systematically. The crystal structural analyses show that all the samples are orthorhombic phase and a structural distortion happens around x = 0.3. Due to the formation of Cr4+ ions, both the lattice constant and the Cr–O bond length decrease. The results of positron annihilation spectrum reveals that the vacancy defect concentration increases and the local electron structure changes with the introduction of Ca2+ ions. The field-cooled (FC) and zero-field cooled (ZFC) curves of Gd1-xCaxCrO3 samples measured under H = 100 Oe exhibits negative magnetization characteristics due to the interaction between Gd3+ and Cr3+ ions, and the magnetism can be affected by the structural distortion. 相似文献
87.
Christian Gentzsch Dr. Matthias Hoffmann Dr. Yasuhiro Ohshima Naoko Nose Dr. Xinyu Chen Prof. Dr. Takahiro Higuchi Prof. Dr. Michael Decker 《ChemMedChem》2021,16(9):1427-1437
The enzyme butyrylcholinesterase (BChE) represents a promising target for imaging probes to potentially enable early diagnosis of neurodegenerative diseases like Alzheimer's disease (AD) and to monitor disease progression in some forms of cancer. In this study, we present the design, facile synthesis, in vitro and preliminary ex vivo and in vivo evaluation of a morpholine-based, selective inhibitor of human BChE as a positron emission tomography (PET) tracer with a pseudo-irreversible binding mode. We demonstrate a novel protecting group strategy for 18F radiolabeling of carbamate precursors and show that the inhibitory potency as well as kinetic properties of our unlabeled reference compound were retained in comparison to the parent compound. In particular, the prolonged duration of enzyme inhibition of such a morpholinocarbamate motivated us to design a PET tracer, possibly enabling a precise mapping of BChE distribution. 相似文献
88.
Xudong An Te Zhu Mingpan Wan Yuanhui Li Qianqian Wang Peng Zhang Jinyang Liu Yamin Song Zhaokuan Zhang Baoyi Wang Xingzhong Cao 《International Journal of Hydrogen Energy》2021,46(24):13162-13170
The formation of mono-vacancy, vacancy clusters and hydrogen-vacancy complexes with 30 keV H ion-irradiated pure titanium at different doses and temperatures was measured using by Positron annihilation spectroscopy (PAS). Results show a large number of HmVn clusters and vacancy-like defects in the samples irradiated at for room temperature, and that the formation of HmVn (m > n) at the sample irradiated at a high dose inhibits the increase of the S parameter. At increased irradiation temperature, the shrinkage of vacancy clusters and the effective open volume of defects decrease the S parameters. The high-temperature irradiation results in decreased vacancy-type defect concentration, and some hydrogen atoms diffuse from the cascade region to the track region, forming a large number of hydrogen-vacancy complexes in the track region. The coincidence Doppler broadening spectroscopy, an element analysis method, used to detect hydrogen in the ion-irradiated pure titanium sample, and results show hydrogen-related peaks in the high-momentum region, which may be due to the information of positron annihilation in the covalent bond formed by the H and the Ti elements. The increased radiation dose and temperature contribute to the formation of the hydrogen vacancy-complex, and the positron annihilation in high-momentum regions easily obtain hydrogen-related information. 相似文献
89.
Rinat Meir Tal Hirschhorn Sungsoo Kim Kealan J. Fallon Emily M. Churchill Dino Wu Hee Won Yang Brent R. Stockwell Luis M. Campos 《Advanced functional materials》2021,31(31):2010907
The ability to optically induce biological responses in 3D has been dwarfed by the physical limitations of visible light penetration to trigger photochemical processes. However, many biological systems are relatively transparent to low-energy light, which does not provide sufficient energy to induce photochemistry in 3D. To overcome this challenge, hydrogels that are capable of converting red or near-IR (NIR) light into blue light within the cell-laden 3D scaffolds are developed. The upconverted light can then excite optically active proteins in cells to trigger a photochemical response. The hydrogels operate by triplet–triplet annihilation upconversion. As proof-of-principle, it is found that the hydrogels trigger an optogenetic response by red/NIR irradiation of HeLa cells that have been engineered to express the blue-light sensitive protein Cry2olig. While it is remarkable to photoinduce the clustering of Cry2olig with blanket NIR irradiation in 3D, it is also demonstrated how the hydrogels trigger clustering within a single cell with great specificity and spatiotemporal control. In principle, these hydrogels may allow for photochemical control of cell function within 3D scaffolds, which can lead to a wealth of fundamental studies and biochemical applications. 相似文献
90.
Lili Hou Axel Olesund Shameel Thurakkal Xiaoyan Zhang Bo Albinsson 《Advanced functional materials》2021,31(47):2106198
Developing high-performance visible-to-UV photon upconversion systems based on triplet–triplet annihilation photon upconversion (TTA-UC) is highly desired, as it provides a potential approach for UV light-induced photosynthesis and photocatalysis. However, the quantum yield and spectral range of visible-to-UV TTA-UC based on nanocrystals (NCs) are still far from satisfactory. Here, three different sized CdS NCs are systematically investigated with triplet energy transfer to four mediators and four annihilators, thus substantially expanding the available materials for visible-to-UV TTA-UC. By improving the quality of CdS NCs, introducing the mediator via a direct mixing fashion, and matching the energy levels, a high TTA-UC quantum yield of 10.4% (out of a 50% maximum) is achieved in one case, which represents a record performance in TTA-UC based on NCs without doping. In another case, TTA-UC photons approaching 4 eV are observed, which is on par with the highest energies observed in optimized organic systems. Importantly, the in-depth investigation reveals that the direct mixing approach to introduce the mediator is a key factor that leads to close to unity efficiencies of triplet energy transfer, which ultimately governs the performance of NC-based TTA-UC systems. These findings provide guidelines for the design of high-performance TTA-UC systems toward solar energy harvesting. 相似文献