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991.
Nicola Raffone Brieuc Le Fèvre Luisa Ottolini Riccardo Vannucci Alberto Zanetti 《Mikrochimica acta》2006,155(1-2):251-255
The high sensitivity of Secondary-Ion Mass Spectrometry (SIMS) in determining very low trace-element concentrations (down
to few ppb wt) has been used to address the important issue of the Light-Lithophile Element (LLE) signatures of mantle peridotites
and their potential utility as tracers of transfer of subducted material into the overlying mantle wedge operated either by
slab-related fluids or melts. The effects of such metasomatic agents have been described and interpreted on the basis of geochemical
and isotopic characteristics of peridotites. However, direct observation of metasomatic processes occurring in the mantle
is limited because the most highly metasomatised peridotites are usually found as xenoliths which do not allow large-scale
chemical information. In this context, the Finero phlogopite-peridotite massif (Ivrea-Verbano Zone, western Italian Alps)
offers a unique opportunity because it contains hydrous mineral assemblages (amphibole + phlogopite ± apatite) and trace element
enrichments, supposed to be related to the pervasive migration of slab-derived melts. In this study we report the results
of texture-related SIMS investigations performed on a wide range of trace elements such as Li, B, Large-Ion Lithophile Elements
(LILE), Rare Earth Elements (REE), Nb, Zr, Ti on clinopyroxenes from the Finero peridotite. SIMS analyses revealed unusual
LLE signatures that highlight the role of crust-derived components and open new perspectives on the timing of metasomatic
processes. 相似文献
992.
The three lowest (1(2)A', 2(2)A', and 1(2)A") potential-energy surfaces of the C2Cl radical, correlating at linear geometries with 2Sigma+ and 2Pi states, have been studied ab initio using a large basis set and multireference configuration-interaction techniques. The electronic ground state is confirmed to be bent with a very low barrier to linearity, due to the strong nonadiabatic electronic interactions taking place in this system. The rovibronic energy levels of the 12C12C35Cl isotopomer and the absolute absorption intensities at a temperature of 5 K have been calculated, to an upper limit of 2000 cm(-1), using diabatic potential-energy and dipole moment surfaces and a recently developed variational method. The resulting vibronic states arise from a strong mixture of all the three electronic components and their assignments are intrinsically ambiguous. 相似文献
993.
Lipid-modified membrane-binding proteins are essential in signal transduction events of the cell, a typical example being the GTPase ras. Recently, membrane binding of a doubly lipid-modified heptapeptide from the C-terminus of the human N-ras protein was studied by spectroscopic techniques. It was found that membrane binding is mainly due to lipid chain insertion, but it is also favored by interactions between apolar side chains and the hydrophobic region of the membrane. Here, 10 explicit solvent molecular dynamics simulations for a total time of about 150 ns are used to investigate the atomic details of the peptide-membrane association. The 16:0 peptide lipid chains are more mobile than the 14:0 phospholipid chains, which is in agreement with (2)H NMR experiments. Peptide-lipid and peptide-solvent interactions, backbone and side-chain distributions, as well as the effects of lipidated peptide insertion onto the structure, and dynamics of a 1,2-dimyristoylglycero-3-phosphocholine bilayer are described. The simulation results validate the structural model proposed by the analysis of spectroscopic data and highlight the main aspects of the insertion mechanism. The peptide in the membrane is rather rigid over the simulation time scale of about 10 ns, but different partially extended conformations devoid of backbone hydrogen bonds are observed in different trajectories. 相似文献
994.
Sampedro D Migani A Pepi A Busi E Basosi R Latterini L Elisei F Fusi S Ponticelli F Zanirato V Olivucci M 《Journal of the American Chemical Society》2004,126(30):9349-9359
Protonated Schiff bases (PSBs) of polyenals constitute a class of light-driven switchers selected by biological evolution that provide model compounds for the development of artificial light-driven molecular devices or motors. In the present paper, our primary target is to show, through combined computational and experimental studies, that it is possible to approach the design of artificial PSBs suitable for such applications. Below, we use the methods of computational photochemistry to design and characterize the prototype biomimetic molecular switchers 4-cyclopenten-2'-enylidene-3,4-dihydro-2H-pyrrolinium and its 5,5'-dimethyl derivative both containing the penta-2,4-dieniminium chromophore. To find support for the predicted behavior, we also report the photochemical reaction path of the synthetically accessible compound 4-benzylidene-3,4-dihydro-2H-pyrrolinium. We show that the preparation and photochemical characterization of this compound (together with three different N-methyl derivatives) provide both support for the predicted photoisomerization mechanism and information on its sensitivity to the molecular environment. 相似文献
995.
Raffaella Soave Riccardo Destro 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(8):o507-o509
The asymmetric unit of the title compound, C22H31N3O4·H2O, incorporates one water molecule, which is hydrogen bonded to the 3‐oxo O atom of the indolizidinone system. The two rings of the peptidomimetic molecule are trans‐fused, with the six‐membered ring having a slightly distorted half‐chair conformation and the five‐membered ring having a perfect envelope conformation. The structure is stabilized by intermolecular O—H?O interactions between the water and adjacent peptide molecules, and by N—H?O interactions between the peptide molecules, which link the molecules into infinite chains. 相似文献
996.
A new process for the electrochemical preparation of the fluorinating agent MoF6 is described. Solutions fo MoF4 in anhydrous HF are electrolyzed in a multielectrode cell at 20°C, 5.4÷5.7V cell voltage and 50÷100 A/m2 current density, using nickel anodes and cathodes. A new modified Simons cell has been designed, equipped with a stirring system for the efficient recirculation of the electrolyte and with a condenser held at ?15°C.The reaction product MoF6 (b.p. 35°C) dissolves in the electrolyte, contributing to its conductivity and in part is volatilized together with HF and some byproduct fluorine.Gaseous MoF6 passing beyond the condenser can be easily collected and separated in a nickel trap held at low temperature.The process presents substantial advantages in comparison with known alternatives, such as the synthesis of MoF6 from the elements Mo and F2 at 250°C or the dismutation reaction: 2MoCl5 + 10HF → MoF4 + MoF6 + 10 HClPreparation of the starting material MoF4, operating conditions and experimental results are illustrated. 相似文献
997.
Amorati R Lucarini M Mugnaini V Pedulli GF Roberti M Pizzirani D 《The Journal of organic chemistry》2004,69(21):7101-7107
The antioxidant activity of the cis and trans isomers of several analogues of resveratrol and pterostilbene has been investigated, especially with regard to the effect of the stereochemistry about the olefinic double bond. The antioxidant power of these compounds was estimated by measuring the rate constants for their reactions with peroxyl radicals and, with two of them, the bond dissociation enthalpy (BDE) of the phenolic O-H bond which is cleaved in the inhibition reaction. The present data show that in homogeneous solution the various hydroxystilbenes investigated behave as mild antioxidants with the notable exceptions of the trans isomer of 4 and 6, whose activities are only slightly lower than that of alpha-tocopherol (vitamin E). The rate constants of the inhibition reaction show that the antioxidant activity of the cis-hydroxystilbene is in all the examined cases worse, by a factor ranging between 2 and 6, than that of the corresponding trans isomers. This lower reactivity depends on enthalpy factors as it can be inferred by the experimental values of the O-H bond dissociation enthalpy in the two geometric isomers of 3',5'-di-tert-butyl-4'-hydroxy-3,5-dimethoxystilbene showing that the strength of the O-H bond in the cis isomer is larger by 1.8 kcal/mol. DFT calculations provide a rationalization of this result, indicating that, although the cis geometry implies a destabilization with respect to the trans species of both phenoxyl radical and parent hydroxystilbene, the destabilization of the radical is larger because the folding of the structure strongly reduces the delocalization of the unpaired electron on the styryl group. A comparison of these results with previously reported data on the proapoptotic activity of these stilbenoids suggests that these two properties are not correlated. 相似文献
998.
Roberta Biolo Giulio Jori Marina Soncin Riccardo Pratesi Umberto Vanni Boris Rihter Malcom E. Kenney Michael A. J. Rodgers 《Photochemistry and photobiology》1994,59(3):362-365
The possibility of extending photodynamic therapy to the treatment of highly pigmented neoplastic lesions was tested by using Si(IV)-naphthalocyanine (SiNc) as a tumor-localizing agent. Si(IV)-naphthalocyanine displays intense absorbance at 776 nm (ɛ= 5 × 105 M−1 cm−1 ), where melanin absorption becomes weaker. As an experimental model we selected B16 pigmented melanoma subcutaneously transplanted to C57BL mice. Upon injection of 0.5 or 1 mg kg−1 of liposome-incorporated SiNc, maximal accumulation of the photosensitizer in the tumor was observed at 24 h with recoveries of 0.35 and 0.57 μg g−1 , respectively. However, the tumor targeting by SiNc shows essentially no selectivity, since the photosensitizer concentrations in the skin (peritumoral tissue) were very similar to those found in the tumor at all postinjection times examined by us. Irradiation of SiNc-loaded melanoma with 776 nm light from a diode laser at 24 h postinjection induces tumor necrosis and delay of tumor growth. The effect appears to be of purely photochemical nature at dose rates up to 260 mW cm−2 ; at higher dose rates, thermal effects are likely to become important. 相似文献
999.
Riccardo Giachetti Emanuele Sorace Riccardo Ricci 《Letters in Mathematical Physics》1980,4(4):297-300
The geometrical and mechanical aspects of a particle interacting with a Poincaré gauge field are considered and the relation with a gravitational interaction is studied. 相似文献
1000.
A promising elimination treatment of non-biodegradable organic pollutants is the direct electro-oxidation. In this work has been proposed the electrochemical elimination of polyacrylates by using boron-doped diamond (BDD) as anodic material. The complete elimination of organic contaminants has been obtained and this is the first case of successful electrochemical treatment of polymeric and bio-refractory species. The tests of the electrochemical oxidation have been conducted at constant current conditions and a complete elimination of organic species has been reached. The decrease of the COD value with time follows the behaviour of an ideal anode as in the case of low molecular organic compounds. 相似文献