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排序方式: 共有181条查询结果,搜索用时 15 毫秒
111.
Emiliano Manzo Maria Letizia Ciavatta Margherita Gavagnin Chandrakant Govind Naik 《Tetrahedron letters》2007,48(14):2569-2571
Chemical analysis of the secondary metabolite pattern of the gorgonian Echinogorgia complexa, collected along South Indian coasts, showed the presence of two new tricyclic guaiane furanosesquiterpenes, iso-echinofuran (3) and 8,9-dihydro-linderazulene (4), co-occurring with the known echinofuran (5) and structurally related to the pigment linderazulene (1). The unprecedented molecules 3 and 4 were characterized by spectral methods, mainly by NMR techniques. Compounds 3-5 displayed moderate activity in the mitochondrial respiratory chain inhibition assay. 相似文献
112.
Vattuone L Savio L Gerbi A Okada M Moritani K Rocca M 《The journal of physical chemistry. B》2007,111(7):1679-1683
We have investigated oxygen adsorption on Cu(410) by high-resolution electron energy loss spectroscopy, dosing O2 with a supersonic molecular beam at different surface temperatures and for different angles of incidence and beam energies or by backfilling. In the investigated crystal temperature range (127 < T < 570 K), adsorption is always dissociative. Depending on T, impact energy, and angle of incidence, the oxygen atoms end up in different adsorption configurations, characterized by different vibrational signatures. In particular, at grazing incidence when only the step edge is exposed to O2, the adatoms end up initially preferentially at the step edge. An ordered overlayer forms at half monolayer coverage when the adsorbate is mobile. Oxide patches develop eventually for large exposures performed by backfilling and at high crystal temperature. 相似文献
113.
114.
Silvia Ghirga Letizia Chiodo Riccardo Marrocchio Javier G. Orlandi Alessandro Loppini 《Entropy (Basel, Switzerland)》2021,23(9)
The comprehension of neuronal network functioning, from most basic mechanisms of signal transmission to complex patterns of memory and decision making, is at the basis of the modern research in experimental and computational neurophysiology. While mechanistic knowledge of neurons and synapses structure increased, the study of functional and effective networks is more complex, involving emergent phenomena, nonlinear responses, collective waves, correlation and causal interactions. Refined data analysis may help in inferring functional/effective interactions and connectivity from neuronal activity. The Transfer Entropy (TE) technique is, among other things, well suited to predict structural interactions between neurons, and to infer both effective and structural connectivity in small- and large-scale networks. To efficiently disentangle the excitatory and inhibitory neural activities, in the article we present a revised version of TE, split in two contributions and characterized by a suited delay time. The method is tested on in silico small neuronal networks, built to simulate the calcium activity as measured via calcium imaging in two-dimensional neuronal cultures. The inhibitory connections are well characterized, still preserving a high accuracy for excitatory connections prediction. The method could be applied to study effective and structural interactions in systems of excitable cells, both in physiological and in pathological conditions. 相似文献
115.
Alessio Cesaretti Letizia Mencaroni Carmela Bonaccorso Valentina Botti Eleonora Calzoni Benedetta Carlotti Cosimo Gianluca Fortuna Nicol Montegiove Anna Spalletti Fausto Elisei 《Molecules (Basel, Switzerland)》2022,27(12)
Small organic molecules arouse lively interest for their plethora of possible biological applications, such as anticancer therapy, for their ability to interact with nucleic acids, or bioimaging, thanks to their fluorescence emission. Here, a panchromatic series of styryl-azinium bicationic dyes, which have already proved to exhibit high water-solubility and significant red fluorescence in water, were investigated through spectrofluorimetric titrations to assess the extent of their association constants with DNA and RNA. Femtosecond-resolved transient absorption spectroscopy was also employed to characterize the changes in the photophysical properties of these fluorophores upon interaction with their biological targets. Finally, in vitro experiments conducted on tumor cell lines revealed that some of the bicationic fluorophores had a peculiar localization within cell nuclei exerting important antiproliferative effects, others were instead found to localize in the cytoplasm without leading to cell death, being useful to mark specific organelles in light of live cell bioimaging. Interestingly, this molecule-dependent behavior matched the different amphiphilicity featured by these bioactive compounds, which are thus expected to be caught in a tug-of-war between lipophilicity, ensured by the presence of aromatic rings and needed to pass cell membranes, and hydrophilicity, granted by charged groups and necessary for stability in aqueous media. 相似文献
116.
Emiliano Manzo Dario Pagano Genoveffa Nuzzo Margherita Gavagnin Maria Letizia Ciavatta 《Tetrahedron letters》2012,53(52):7083-7084
Parazoanthine A (7.0% overall yield) and its O-methyl derivative (6.2% overall yield) were prepared by a concise biomimetic synthesis based on the coupling reaction of l-arginine methyl ester dihydrochloride with isocyanate derivatives of p-coumaric acid and 4-methoxy-cinnamic acid, respectively. The synthetic approach is designed to obtain a wider class of parazoanthine analogs. 相似文献
117.
Manzo E Carbone M Mollo E Irace C Di Pascale A Li Y Ciavatta ML Cimino G Guo YW Gavagnin M 《Organic letters》2011,13(8):1897-1899
The first chemical study of an Actinocyclidae nudibranch, Actinocyclus papillatus, resulted in the isolation of (-)-actisonitrile (1), a lipid based on a 1,3-propanediol ether skeleton. The structure was established by spectroscopic methods, whereas the absolute configuration of the chiral center was determined by comparing the optical properties of natural actisonitrile with those of (+)- and (-)-synthetic enantiomers, opportunely prepared. Both (-)- and (+)-actisonitrile were tested in preliminary in vitro cytotoxicity bioassays on tumor and nontumor mammalian cells. 相似文献
118.
Patrizia Galzerano Dario Agostino Giorgio Bencivenni Dr. Letizia Sambri Dr. Giuseppe Bartoli Prof. Paolo Melchiorre Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(20):6069-6076
A simple and convenient method for the direct, aminocatalytic, and highly enantioselective Mannich reactions of aldehydes with in situ generated N‐carbamoyl imines has been developed. Both α‐imino esters and aromatic imines serve as suitable electrophilic components. Moreover, the judicious selection of commercially available secondary amine catalysts allows selective access to the desired stereoisomer of the N‐tert‐butoxycarbonyl (Boc) or N‐carbobenzyloxy (Cbz) Mannich adducts, with high control over the syn or anti relative configuration and almost perfect enantioselectivity. Besides the possibility to fully control the stereochemistry of the Mannich reaction, the main advantage of this method lies in the operational simplicity; the highly reactive N‐carbamate‐protected imines are generated in situ from stable and easily handled α‐amido sulfones. 相似文献
119.
Maria Letizia De Marco Dr. Sanaa Semlali Prof. Brian A. Korgel Dr. Philippe Barois Dr. Glenna L. Drisko Dr. Cyril Aymonier 《Angewandte Chemie (International ed. in English)》2018,57(17):4478-4498
Metamaterials have optical properties that are unprecedented in nature. They have opened new horizons in light manipulation, with the ability to bend, focus, completely reflect, transmit, or absorb an incident wave front. Optically active metamaterials in particular could be used for applications ranging from 3D information storage to photovoltaic cells. Silicon (Si) particles are some of the most promising building blocks for optically active metamaterials, with high scattering efficiency coupled to low light absorption for visible frequencies. However, to date ideal Si building blocks cannot be produced by bulk synthesis techniques. The key is to find a synthetic route to produce Si building blocks between 75–200 nm in diameter of uniform size and shape, that are crystalline, have few impurities, and little to no porosity. This Review provides a theoretical background on Si optical properties for metamaterials, an overview of current synthetic methods and gives direction towards the most promising routes to ideal Si particles for metamaterials. 相似文献
120.
Ignazio Blanco Lorenzo Abate Marta Letizia Antonelli Francesco Agatino Bottino 《Polymer Degradation and Stability》2013
The kinetics of the isothermal degradation in static air atmosphere of four well known polymers, polyethylene (PE), polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA) was studied by both a long-term (more than three years) experiment at relatively low temperature (423 K) and a set of short-term experiments at higher temperatures. The activation energy (Ea) values of degradation were determined by both the MacCallum and Wilkinson literature methods, and were compared with those obtained through a new very simple method we set up, based on the direct regression of TG mass loss data. About two years ago we published the results concerning PE and PS because their mass losses during long-term experiments were sufficiently high. The long-term degradation experiments were continued until now and in this second part we report the results concerning PC and PMMA. The degradation Ea values calculated from short-term experimental data through the three different methods were in good agreement with each other for both PC and PMMA, thus confirming the general applicability of our simple method for the determination of Ea. The experimental data at lower temperature of PC were not in agreement with those at higher temperatures, thus confirming the low reliability of the kinetic parameters (and then of lifetime predictions) at low temperature determined by experiments at higher temperatures. Partially disagreeing results were obtained for PMMA, which were discussed and interpreted. 相似文献