共查询到20条相似文献,搜索用时 385 毫秒
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用量子化学从头算法,在RHF/6-31G(d,p)水平上优化了八种不对称方酸染料的分子构型,并对它们的分子内电荷转移程度与暗衰值,光敏值和最大吸收波长的定量关系进行研究,发现不对称方酸染料的分子内电荷转移性质,是影响不对称方酸染料光导性和最大吸收波长的重要因素。 相似文献
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《Tetrahedron letters》2014,55(52):7156-7166
Acyclic nucleosides and their phosphonates possess significantly antiviral and cytostatic activities. For acyclic nucleosides and their phosphonates, the introduction of a chiral group to their side chain or the absolute configuration of the chiral atom could affect their biological activities obviously. Thus, the asymmetric synthesis of chiral acyclic nucleosides and their phosphonates has received continuous attention. The previous reports mainly focus on employing the chiral pool and chiral auxiliary methods for the synthesis of chiral acyclic nucleosides and their phosphonates. In contrast, the asymmetric catalysis methods for the synthesis of acyclic nucleosides and their phosphonates are still in the beginning. This digest paper will serve to highlight the significant progress that has been made in these areas. 相似文献
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Karel Dušek 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(9):843-863
Polymer networks challenge a theorist to develop methods of their generation, describe their topology, and understand critical phenomena (gelation) during their formation. They challenge a technologist because of their unique properties based on their large-scale three-dimensional connectivity and their easy transformation of relatively low-viscosity liquids into crosslinked solids. Polymer networks challenge both, in that they are structurally very complex for the technologist who needs the theorist for understanding and controlling their structure and properties. Also, the theorist is challenged by problems appearing in technology which may initiate a basic reconsideration of the theories' assumptions. In this contribution, methods for modeling polymer network structures and their recent applications to relatively complex systems of technological importance are briefly discussed. 相似文献
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食品添加剂可以改善食品的品质,延长食品的保存期,增加食品的营养成分。本文介绍了生活中常见的食品添加剂:食品色素、食用香料、甜味剂、鲜味剂、防腐剂和抗氧化剂的性能、使用范围和化学结构。以便于在化学教学中开阔学生的知识视野,提高学生的学习兴趣,全面培养学生的科学素质。 相似文献
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Absalon C Fabre S Tarascou I Fouquet E Pianet I 《Analytical and bioanalytical chemistry》2011,401(5):1489-1499
Tannins represent a key element in red wine flavors, so researchers have made a lot of effort to try to understand the role
of their structure in wine taste in recent decades. We report some new routes to achieve a true structure–taste relationship
for the major tannins found in wine, which are procyanidins in their monomeric or oligomeric state. All these routes use synthetic
standards. New advances in their synthesis and their analyses using chromatographic methods, NMR spectroscopy, and mass spectrometry
to obtain more precise information about their chemical structure, including their stereochemistry and their precise degree
of polymerization and galloylation, are described. 相似文献
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There is considerable interest in the analysis of phenolic compounds due to their involvement in the organoleptic characteristics of foods and drinks, and their contribution to protection against cardiovascular diseases and cancers through their antioxidant activity. This article describes studies of the polyphenol content, both total (by means of the Folin-Ciocalteu method) and individual (by means of HPLC, LC-MS and LC-MS-MS) and the antioxidant power, of six varieties of grape over the course of their maturation. A good correlation is found to exist between the total polyphenol content of the samples and their antioxidant power, and both seem diminish along the maturation. 相似文献
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This short review concentrates on important aspects of fluoroarylphosphines, in particular their synthesis, ligand properties and chemical and catalytic properties of their complexes. Although the electronic, steric and chemical properties of fluoroarylphosphines have been known for 30 years, their use as ligands for homogeneous catalysis and in the synthesis of elaborate multidentate ligands has occurred more recently. The number of recent reports suggests that their importance is growing. 相似文献
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Pasqualina Liana Scognamiglio Chiara Platella Ettore Napolitano Domenica Musumeci Giovanni Nicola Roviello 《Molecules (Basel, Switzerland)》2021,26(12)
Peptides and their synthetic analogs are a class of molecules with enormous relevance as therapeutics for their ability to interact with biomacromolecules like nucleic acids and proteins, potentially interfering with biological pathways often involved in the onset and progression of pathologies of high social impact. Nucleobase-bearing peptides (nucleopeptides) and pseudopeptides (PNAs) offer further interesting possibilities related to their nucleobase-decorated nature for diagnostic and therapeutic applications, thanks to their reported ability to target complementary DNA and RNA strands. In addition, these chimeric compounds are endowed with intriguing self-assembling properties, which are at the heart of their investigation as self-replicating materials in prebiotic chemistry, as well as their application as constituents of innovative drug delivery systems and, more generally, as novel nanomaterials to be employed in biomedicine. Herein we describe the properties of nucleopeptides, PNAs and related supramolecular systems, and summarize some of the most relevant applications of these systems. 相似文献
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聚乙二醇及其单醚在咪唑N-烷基化反应中的应用 总被引:4,自引:1,他引:4
本文报道了在咪唑N-烷基化反应中以聚乙二醇(PEG)及其单醚作为相转移催化剂合成C_4-C_(16) N-烷基咪唑及咪唑N-烷基衍生物的新方法。该法反应条件温和,操作简便,收率可达70%左右。测定了N-烷基咪唑化合物的物理性能,~1H NMR和红外光谱,并讨论了反应条件和烷基化试剂的碳链结构对反应的影响。 相似文献
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Satinder K. Brar 《Trends in analytical chemistry : TRAC》2011,30(1):4-17
Nanoparticles (NPs), due to their unique physical and chemical properties, especially their minute particle size (?100 nm), find applications in numerous industrial, commercial and consumer products. After their end-user applications, these NPs find their way into the environment and food products. The NPs so discharged need to be quantified accurately to determine their toxicity and exposure levels.At this time, there is a need to develop a unified method for their determination. There are plenty of techniques available in the market that were initially used for colloidal particles (e.g., microscopy, spectroscopy and the recent addition of magnetic resonance), but each of these techniques has a certain degree of uncertainty.Further, sample homogeneity, sample preparation, instrument-operating procedures, and statistical practices are likely to add to the complexity of the problem. In this context, this review attempts to understand the widely-used light-scattering techniques, including their theory, practice and real-world use in determination of NPs in environmental and food applications. 相似文献
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Biological applications of carbon dots 总被引:1,自引:0,他引:1
Carbon dots (C-dots), since their first discovery in 2004 by Scrivens et al. during purification of single-walled carbon nanotubes, have gradually become a rising star in the fluorescent nanoparticles family, due to their strong fluorescence, resistance to photobleaching, low toxicity, along with their abundant and inexpensive nature. In the past decade, the procedures for preparing C-dots have become increasingly versatile and facile, and their applications are being extended to a growing number of fields. In this review, we focused on introducing the biological applications of C-dots, hoping to expedite their translation to the clinic. 相似文献
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Maria Ochsenkühn-Petropoulou Angeliki Lampropoulou Hansjürgen Becker Wolfgang Spyra 《Mikrochimica acta》2001,136(3-4):185-191
An analytical technique for the simultaneous determination of PAHs (polycyclic aromatic hydrocarbons) in wooden railway beams,
impregnated with coal tar for their protection, has been developed, based on the effective extraction of the PAHs and their
determination by GC-MS. Two extraction techniques, the Soxhlet and the ultrasonic one, using two different solvents, hexane
and toluene have been compared for their efficiency for PAHs which can be determined in ppb-ppt range after optimised clean
up and enrichment. Several parameters, such as the degree of impregnation of the wooden beams, the effect of sun radiation
on the degradation of the PAHs and their migration to the soil have been investigated by following the concentration of the
PAHs and that of their methylated products found at various sampling positions. The results are useful for the decision about
recycling procedure or their further disposal. 相似文献
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《高分子科学杂志,C辑:聚合物评论》2013,53(3):323-383
Abstract Even though the history and chemistry of polyperoxides is long known, they need further investigation with respect to their reactivity and applications to understand their real potential. For instance, unlike in acid polyperoxides, only scanty reports have been made on the initiating behavior of vinyl polyperoxides inspite of their well-known synthetic chemistry. Hence, it appears that there remains a significant gap between the discovery of vinyl polyperoxides and in our understanding of their role as radical initiator. This article is intended to fill this gap by ventilating the significant developments on polyperoxides, which are finding an increasing role both in fundamental and applied polymer science. However, the scope of this article is restricted to their synthetic methodologies, degradation and applications as initiators/curatives. The kinetics and mechanism of their formation and degradation have been dealt with briefly. The characteristic and notable features of the kinetics and mechanism on polyperoxide initiated polymerizations are also discussed, and some of their applications are highlighted. Emphasis has also been laid on the futuristic research trends on polyperoxides. 相似文献
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He F Liang NN Mu L Pan QH Wang J Reeves MJ Duan CQ 《Molecules (Basel, Switzerland)》2012,17(2):1571-1601
Originating in the grapes, monomeric anthocyanins in young red wines contribute the majority of color and the supposed beneficial health effects related to their consumption, and as such they are recognized as one of the most important groups of phenolic metabolites in red wines. In recent years, our increasing knowledge of the chemical complexity of the monomeric anthocyanins, their stability, together with the phenomena such as self-association and copigmentation that can stabilize and enhance their color has helped to explain their color representation in red wine making and aging. A series of new enological practices were developed to improve the anthocyanin extraction, as well as their color expression and maintenance. This paper summarizes the most recent advances in the studies of the monomeric anthocyanins in red wines, emphasizing their origin, occurrence, color enhancing effects, their degradation and the effect of various enological practices on them. 相似文献
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Manfred Dunky 《Macromolecular Symposia》2004,217(1):417-430
Formaldehyde based resins are by far the most important adhesives for the production of wood based panels. This paper reviews in compact form the main application near features of these products including their composition, their molar mass distribution as well as their hardening behaviour, which all three parameters have decisive influence on the properties of the resins themselves and their performance as wood adhesives. 相似文献