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991.
Vecchi A Melai B Marra A Chiappe C Dondoni A 《The Journal of organic chemistry》2008,73(16):6437-6440
A tetra-azido calix[4]arene derivative was allowed to react with ethynyl tetra- O-benzyl- C-galactoside in the presence of CuI and i-Pr 2EtN in three different ionic liquids, that is, [C 8dabco][N(CN) 2], [C 8dabco][Br], and Ammoeng 110. Reactions were performed at 80 degrees C by thermal and MW dielectric heating. In all cases, multiple cycloadditions took place to give a triazole-linked tetra- C-galactosyl-calix[4]arene in up to 90% yield. The [C 8dabco][N(CN) 2] ionic liquid was also used to perform the multiclick reactions with propargyl O-lactoside and S-sialoside. 相似文献
992.
The mechanism of the cascade oxidative dearomatization-transannular Diels-Alder was investigated in the context of an asymmetric route to (−)-11-O-debenzoyltashironin. Although the oxidative dearomatization provides two acetal intermediates, the transannular Diels-Alder proceeds spontaneously from only one of the acetal isomers. Access to enantioenriched tetracyclic adduct was gained through the use of optically active allene. 相似文献
993.
Sara Bonacchi Luisa Stella Dolci Claudio Lo Sterzo Alessandra Micozzi Marco Montalti Luca Prodi Antonella Ricci Nelsi Zaccheroni 《Journal of photochemistry and photobiology. A, Chemistry》2008,198(2-3):237-241
The metal ion binding properties of three photoactive poly-(arylene ethynylene) co-polymers with potentially complexing units have been described. Upon protonation or complexation, the intensity of the luminescence typical of these conjugated polymers is completely quenched, due to the extended electronic conjugation of the polymer backbones. In the case of the formation of complexes with Yb3+ and Er3+, one of the studied polymers gives rise to an efficient sensitization of their typical metal centred NIR emission. This feature is of particular interest for the preparation of new materials that are the subject of active research for their possible applications in optical imaging and in optical amplification for telecommunication purposes. 相似文献
994.
A combined gas chromatography-electron ionization (GC-EI), atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) and MS/MS approach has been used for characterizing organic residues of ceramic vessels of different forms and dimensions recovered from a vault of the apse of the 13th century church of Sant'Antimo in Piombino (Central Italy). The artifacts studied in this investigation are pots, jugs, colanders and pans probably used for cooking meals or as food containers. GC-MS has shown the presence of different fatty acids and other nonpolar markers, while APCI ionization proved to be particularly useful in the detection of diterpenoids and diacylglycerols. The data show that some organic markers may be of animal origin, while others are typical constituents or biodegradation products of vegetables. This allows one to propose the main use of these articles as vessels for cooking meat and maybe vegetable broths and soups. As there is no strict correlation between organic markers and shape, form and dimension of the ceramic vessel, it appears that the different objects probably served the same function. Chemical characterization of the organic residues of ceramic vessels, together with all the other archaeological data, contributes to a better understanding of their uses and the customs of people in the Middle Ages in Central Italy. 相似文献
995.
Luca Dieci M. Grazia Gasparo Alessandra Papini 《Mediterranean Journal of Mathematics》2008,5(1):21-31
Our purpose in this work is to explore smoothness properties of transformations of a matrix valued function A to Hessenberg and bidiagonal form. The interplay with the rank of associated Krylov functions is exploited to clarify what
one should expect for smooth functions A satisfying generic properties.
This work was supported in part under INDAM-GNCS and MIUR Rome-Italy. 相似文献
996.
Dr. Monica Fiorenza Boselli Dr. Niccolò Intini Prof. Dr. Alessandra Puglisi Prof. Dr. Laura Raimondi Dr. Sergio Rossi Prof. Dr. Maurizio Benaglia 《European journal of organic chemistry》2023,26(9):e202201309
The organophotoredox catalytic enantioselective addition of N-acyl radicals to aldehydes, to afford enantioenriched N-acyl 1,2 aminoalcohols was studied. Under the best conditions, in batch, the product was isolated in up to 52 % yield and 85 % e.e., using a low cost and commercially available chiral imidazolidinone as organocatalyst. The reaction was then studied in flow, exploring different experimental setups and photoreactors. Although modest yields were obtained, the in-flow process afforded the product in higher productivities (up to 60 times higher) and improved space time yields (increased up to 113 times) compared to the batch reaction, with no loss of stereoselectivity. 相似文献
997.
Sonia DeAngelis Mario Franco Alessandra Triminì Ana Gonzlez Raquel Sainz Leonardo Degennaro Giuseppe Romanazzi Claudia Carlucci Valentina Petrelli Alejandro delaEsperanza Asier Goi Rafael Ferritto Jos Luis Acea Renzo Luisi M. Beln Cid 《化学:亚洲杂志》2019,14(17):3011-3018
The use of graphene derivatives as supports improves the properties of heterogeneous catalysts, with graphene oxide (GO) being the most frequently employed. To explore greener possibilities as well as to get some insights into the role of the different graphenic supports (GO, rGO, carbon black, and graphite nanoplatelets), we prepared, under the same standard conditions, a variety of heterogeneous Cu catalysts and systematically evaluated their composition and catalytic activity in azide–alkyne cycloadditions as a model reaction. The use of sustainable graphite nanoplatelets (GNPs) afforded a stable CuI catalyst with good recyclability properties, which are compatible with flow conditions, and able to catalyze other reactions such as the regio‐ and stereoselective sulfonylation of alkynes (addition reaction) and the Meerwein arylation (single electron transfer process). 相似文献
998.
Andrea Fiorani Juan Pedro Merino Alessandra Zanut Alejandro Criado Giovanni Valenti Maurizio Prato Francesco Paolucci 《Current Opinion in Electrochemistry》2019
Electrochemiluminescent biosensors are nowadays an established technology in the field of immunosensors and diagnostics. Along with the advent of nanotechnology, the marriage between electrochemiluminescence and nanomaterials results in promising enhancing strategies in many biosensor applications. Among nanomaterials, carbon-based ones are the most used, as (i) scaffolds, (ii) luminophores and (iii) electrode materials of the sensor. In this review, we describe the importance of a rational modification and functionalization of carbon nanomaterials to optimize electrochemiluminescence signal, and we also resume the latest and most relevant applications of electrochemiluminescent biosensors based on carbon nanomaterials. 相似文献
999.
Alessandra Silveira Machado Ramon Silva Santos Amanda Goulart Rodrigues Leonardo Borghi Davi Ferreira de Oliveira Marcelino José dos Anjos Ricardo Tadeu Lopes 《X射线光谱测定》2019,48(5):543-552
Carbonate rocks play an important role in petroleum geology by acting as reservoir rocks, generators, and even hydrocarbon sealants, accounting for about half of the oil and gas reserves known in the world. The study of these carbonate rocks have become very important in the hydrocarbon exploration scene in Brazil because of they consist in analogous for reservoir rocks of the presalt interval. Thus, the objective of this research was to use X-ray microfluorescence (micro-XRF) and X-ray microtomography analysis, as complementary techniques, in order to characterize samples of carbonate rocks in respect to their structures, textures, mineralogy, and pores. The microtomographic analyses allowed the identification of the horizontal structures as parallel lamination, horizontal, and vertical fractures filled by calcite and biotic constituents (gastropods bioclasts). Different composition of minerals were also identified, as calcite, quartz, feldspars, iron sulfides, and oxides. The porosity (ranges <1 to17%), and the high-density elements could also be quantified, as well as their distribution in each sample. The micro-XRF analysis present a direct relationship with the distribution of minerals that compound carbonate rocks, highlighting some structures, as well as helping to identify trace and minor elements in the carbonates (Mn, Sr, and Mg). 相似文献
1000.
Effects of soft X‐ray radiation damage on paraffin‐embedded rat tissues supported on ultralene: a chemical perspective
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Diana E. Bedolla Andrea Mantuano Arissa Pickler Carla Lemos Mota Delson Braz Camila Salata Carlos Eduardo Almeida Giovanni Birarda Lisa Vaccari Regina Cély Barroso Alessandra Gianoncelli 《Journal of synchrotron radiation》2018,25(3):848-856
Radiation damage is an important aspect to be considered when analysing biological samples with X‐ray techniques as it can induce chemical and structural changes in the specimens. This work aims to provide new insights into the soft X‐ray induced radiation damage of the complete sample, including not only the biological tissue itself but also the substrate and embedding medium, and the tissue fixation procedure. Sample preparation and handling involves an unavoidable interaction with the sample matrix and could play an important role in the radiation‐damage mechanism. To understand the influence of sample preparation and handling on radiation damage, the effects of soft X‐ray exposure at different doses on ultralene, paraffin and on paraffin‐embedded rat tissues were studied using Fourier‐transform infrared (FTIR) microspectroscopy and X‐ray microscopy. Tissues were preserved with three different commonly used fixatives: formalin, glutaraldehyde and Karnovsky. FTIR results showed that ultralene and paraffin undergo a dose‐dependent degradation of their vibrational profiles, consistent with radiation‐induced oxidative damage. In addition, formalin fixative has been shown to improve the preservation of the secondary structure of proteins in tissues compared with both glutaraldehyde and Karnovsky fixation. However, conclusive considerations cannot be drawn on the optimal fixation protocol because of the interference introduced by both substrate and embedding medium in the spectral regions specific to tissue lipids, nucleic acids and carbohydrates. Notably, despite the detected alterations affecting the chemical architecture of the sample as a whole, composed of tissue, substrate and embedding medium, the structural morphology of the tissues at the micrometre scale is essentially preserved even at the highest exposure dose. 相似文献