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41.
Marco Brunella 《Bulletin of the Brazilian Mathematical Society》1995,26(2):117-128
We prove that a holomorphic foliation on a Stein surface transverse to the boundary of a 4-ball is conjugated inside the ball to the foliation generated by the holomorphic vector field
, provided that the transversely holomorphic flow induced by on the boundary of the ball has a parabolic closed orbit. The proof contains a classification of transversely holomorphic flows on 3-manifolds with a parabolic closed orbit. 相似文献
42.
Andreina Ricci Brunella Di Rienzo Federico Pepi Anna Troiani Stefania Garzoli Pierluigi Giacomello 《Journal of mass spectrometry : JMS》2015,50(1):228-234
Understanding on a molecular level the acid‐catalysed decomposition of the sugar monomers from hemicellulose and cellulose (e.g. glucose, xylose), the main constituent of lignocellulosic biomass is very important to increase selectivity and reaction yields in solution, key steps for the development of a sustainable renewable industry. In this work we reported a gas‐phase study performed by electrospray triple quadrupole mass spectrometry on the dehydration mechanism of d ‐glucose. In the gas phase, reactant ions corresponding to protonated d ‐glucose were obtained in the ESI source and were allowed to undergo collisionally activated decomposition (CAD) into the quadrupole collision cell. The CAD mass spectrum of protonated d ‐glucose is characterized by the presence of ionic dehydrated daughter ion (ionic intermediates and products), which were structurally characterized by their fragmentation patterns. In the gas phase d ‐glucose dehydration does not lead to the formation of protonated 5‐hydroxymethyl‐2‐furaldehyde, but to a mixed population of m/z 127 isomeric ions. To elucidate the d ‐glucose dehydration mechanism, 3‐O‐methyl‐d ‐glucose was also submitted to the mass spectrometric study; the results suggest that the C3 hydroxyl group plays a key role in the reaction mechanism. Furthermore, protonated levulinic acid was found to be formed from the monodehydrated d ‐glucose ionic intermediate, an alternative pathway other than the known route consisting of 5‐hydroxymethyl‐2‐furaldehyde double hydration. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
43.
Riccardo Ferrero Stefano Pantaleone Massimo Delle Piane Fabrizio Caldera Marta Corno Francesco Trotta Valentina Brunella 《Molecules (Basel, Switzerland)》2021,26(19)
Melatonin (MT) is a molecule of paramount importance in all living organisms, due to its presence in many biological activities, such as circadian (sleep–wake cycle) and seasonal rhythms (reproduction, fattening, molting, etc.). Unfortunately, it suffers from poor solubility and, to be used as a drug, an appropriate transport vehicle has to be developed, in order to optimize its release in the human tissues. As a possible drug-delivery system, β-cyclodextrin (βCD) represents a promising scaffold which can encapsulate the melatonin, releasing when needed. In this work, we present a computational study supported by experimental IR spectra on inclusion MT/βCD complexes. The aim is to provide a robust, accurate and, at the same time, low-cost methodology to investigate these inclusion complexes both with static and dynamic simulations, in order to study the main actors that drive the interactions of melatonin with β-cyclodextrin and, therefore, to understand its release mechanism. 相似文献
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45.
Maria Cristina Paganini Valentina Brunella Mario Chiesa 《Magnetic resonance in chemistry : MRC》2012,50(9):615-619
Ultra high molecular weight polyethylene (UHMWPE) has been studied with different magnetic resonance techniques to elicit information on the nature and the location of radicals generated during high energy irradiation. Field swept electron paramagnetic resonance, pulsed Davies electron nuclear double resonance and hyperfine sublevel correlation spectroscopic measurements allowed extracting for the first time the full 1H hyperfine coupling tensors of the most abundant radical, i.e. a secondary alkyl radical and to ascertain the formation of allyl radicals in the first stages of the irradiation process. The 1H hyperfine coupling tensors are analogous to those reported for single crystal irradiated polyethylene, suggesting that radicals generated in UHMWPE are located in the crystalline region of the polymer. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
46.
Vitamin C: an experimental and theoretical study on the gas‐phase structure and ion energetics of protonated ascorbic acid 下载免费PDF全文
Andreina Ricci Federico Pepi Paola Cimino Anna Troiani Stefania Garzoli Chiara Salvitti Brunella Di Rienzo Vincenzo Barone 《Journal of mass spectrometry : JMS》2016,51(12):1146-1151
In order to investigate the gas‐phase mechanisms of the acid catalyzed degradation of ascorbic acid (AA) to furan, we undertook a mass spectrometric (ESI/TQ/MS) and theoretical investigation at the B3LYP/6‐31 + G(d,p) level of theory. The gaseous reactant species, the protonated AA, [C6H8O6]H+, were generated by electrospray ionization of a 10?3 M H2O/CH3OH (1 : 1) AA solution. In order to structurally characterize the gaseous [C6H8O6]H+ ionic reactants, we estimated the proton affinity and the gas‐phase basicity of AA by the extended Cooks's kinetic method and by computational methods at the B3LYP/6‐31 + G(d,p) level of theory. As expected, computational results identify the carbonyl oxygen atom (O2) of AA as the preferred protonation site. From the experimental proton affinity of 875.0 ± 12 kJ mol?1 and protonation entropy ΔSp 108.9 ± 2 J mol?1 K?1, a gas‐phase basicity value of AA of 842.5 ± 12 kJ mol?1 at 298 K was obtained, which is in agreement with the value issuing from quantum mechanical computations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
47.
V. Brunella 《Polymer Degradation and Stability》2007,92(8):1498-1503
The interaction of UHMWPE with an electron beam in vacuum and in the presence of oxygen has been investigated. UHMWPE irradiated to various doses was examined with Electron Paramagnetic Resonance (EPR) and Fourier Transform infra-red (FTIR) spectroscopies. EPR was used to explore the nature of radicals produced in UHMWPE upon irradiation and to follow their decay as a function of time. Hydroperoxides formation and distribution throughout the samples were studied with FTIR spectroscopy.A correlation between the rate of decay of macroradicals and that of hydroperoxide formation has been proposed. Accordingly, the lifetime of secondary alkyl macroradicals in the amorphous phase of the polymer was found to range approximately from 3 to 10 h. 相似文献
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49.
Turillazzi S Mastrobuoni G Dani FR Moneti G Pieraccini G la Marca G Bartolucci G Perito B Lambardi D Cavallini V Dapporto L 《Journal of the American Society for Mass Spectrometry》2006,17(3):376-383
Two new antibacterial peptides, denominated as Dominulin A and B, have been found on the cuticle and in the venom of females of the social paper wasp Polistes dominulus. The amino acidic sequence of the two peptides, determined by mass spectrometry, is INWKKIAE VGGKIL SSL for Dominulin A (MW = 1854 Da) and INWKKIAEIGKQVL SAL (MW = 1909 Da) for Dominulin B. Their presence on the cuticle was confirmed using MALDI-TOF by means of micro-extractions and direct analyses on body parts. The presence in the venom and the primary structure of the dominulins suggest their classification in the mastoparans, a class of peptides found in the venom of other Aculeate hymenoptera. Their antimicrobial action against Gram+ and Gram- bacteria fits in the range of the best natural antimicrobial peptides. Dominulins can represent an important defense of the colony of Polistes dominulus against microbial pathogens. 相似文献