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91.
Annibale Giuliano Brandolisio Matilde Bugarcic Zivadin Cattalini Lucio 《Transition Metal Chemistry》1998,23(6):715-719
The nucleophilicity of the undissociated thiols is compared to that of thioethers in the displacement of chloride ion from the PtII complexes [Pt(bipy)(NO2)Cl] (bipy=2,2-bipyridine) and [Pt(terpy)Cl]+(terpy= 2,2-6,2- terpyridine). As far as the neutral substrate is concerned the second order rate constants for RSH and RSR nucleophiles are equally related to the inductive and steric effects of the groups linked to the sulphur donor atom. By contrast, only thiols are reactive (under standard experimental conditions) towards the cationic substrate, and the difference can be explained, in this case, by the immediate deprotonation of the substituted product forcing the reaction to completion. The reverse reaction has been examined in one case (PhSH) and the complete protonation of the coordinated thiolate species requires [H+]>2 mol·dm–3. In both series of reactions, thiol molecules also containing a second acidic group (–OH, –CO2H, –NH3+) capable of facile interaction via hydrogen bonding with the developing chloride in the transition state, exhibit a reactivity larger than that expected on the basis of electronic and steric effects alone. 相似文献
92.
The cationic polymerization of N-vinyl carbazole, initiated by Ph3C+ AsF6? and Ph3C+ PF6? in methylene dichloride at 20 and 0°, has been studied in some detail. Reactions were very fast and rates of monomer consumption were measured using an adiabatic calorimetric technique. Initiation was relatively “slow” but complete, and termination was deduced to be insignificant during kinetic lifetimes. Values for kp were found to vary with the initial initiator concentration; this dependence is discussed in terms of current theories regarding equilibria between ion pairs and free ions in non-aqueous solvents. kp+ values estimated from two methods of extrapolation are 9.5 · 105 M?1 sec?1 at 20° and 4.8 · 105 M?1 sec?1 at 0°. Finally, it has been found that ion pairs are much less reactive than free ions in this system. 相似文献
93.
94.
Fondo M García-Deibe AM Ocampo N Sanmartín J Bermejo MR 《Dalton transactions (Cambridge, England : 2003)》2007,(4):414-416
Formation in basic solution of an asymmetric pentanuclear carbonate Ni(II) complex with a compartmental ligand involves atmospheric CO(2) uptake, either by reaction of two slightly different dinuclear precursors that yield its di- and trinuclear "building blocks", or directly, by spontaneous self-organization of metal and ligand starting reactants. 相似文献
95.
Abstract Multicolor fluorescence induced by UV light is a sensitive and specific tool that may be used to provide information about the primary and secondary metabolism of plants by monitoring signals of the chlorophyll fluorescence (Chl-F) and blue-green fluorescence (BGF), respectively. We have followed the systemic infection of Nicotiana benthamiana plants with the Pepper mild mottle virus (PMMoV) by means of a multicolor fluorescence-imaging system, to detect differences between two strains of PMMoV during the infection process and to establish a correlation between the virulence and changes induced in the host plant. Changes in both BGF and Chl-F were monitored. BGF increased mainly in the abaxial side of the leaf during pathogenesis and the corresponding images showed a clear vein-associated pattern in leaves of infected plants. HPLC analysis of leaf extracts was carried out to identify compounds emitting BGF, and determined that chlorogenic acid was one of the main contributors. BGF imaging was able to detect viral-induced changes in asymptomatic (AS) leaves before detection of the virus itself. Chl-F images confirmed our previous results of alterations in the photosynthetic apparatus of AS leaves from infected plants that were detected with other imaging techniques. Fluorescence ratios F440/F690 and F440/F740, which increase during pathogenesis, were excellent indicators of biotic stress. 相似文献
96.
The methanolic extract of Verbascum thapsus was evaluated for its antiviral activity against the pseudorabies virus strain RC/79 (PrV), and also for its cytotoxic activity on Vero cells. The extract showed CC?? values of 1100?μg?mL?1 and 1426?μg?mL?1 by NRU and MTT assays, respectively. The 50% inhibitory concentration of the extract for PrV plaque formation was determined at 35?μg?mL?1, and selectivity indices were 31.4 (NRU) and 40.7 (MTT). When cells were pre-treated with the extract prior to virus infection, the inhibition in plaque formation was 70%. PrV was highly inhibited when it was incubated with plant extract or when the extract was added during the adsorption phase (99%). However, no inhibitory effect was observed when the extract was added to the cells after the adsorption period. Thus, these results suggest that the methanolic extract of Verbascum thapsus may contain bioactive compound(s) that affect PrV mostly in the adsorption phase. 相似文献
97.
Matilde S. Rodrigues Samira G. Ferreira Csar Quiroz Christopher J. Earley Diego García-Borreguero Rodrigo A. Cunha Francisco Ciruela Attila Kfalvi Sergi Ferr 《Molecules (Basel, Switzerland)》2022,27(5)
Brain iron deficiency (BID) constitutes a primary pathophysiological mechanism in restless legs syndrome (RLS). BID in rodents has been widely used as an animal model of RLS, since it recapitulates key neurochemical changes reported in RLS patients and shows an RLS-like behavioral phenotype. Previous studies with the BID-rodent model of RLS demonstrated increased sensitivity of cortical pyramidal cells to release glutamate from their striatal nerve terminals driving striatal circuits, a correlative finding of the cortical motor hyperexcitability of RLS patients. It was also found that BID in rodents leads to changes in the adenosinergic system, a downregulation of the inhibitory adenosine A1 receptors (A1Rs) and upregulation of the excitatory adenosine A2A receptors (A2ARs). It was then hypothesized, but not proven, that the BID-induced increased sensitivity of cortico-striatal glutamatergic terminals could be induced by a change in A1R/A2AR stoichiometry in favor of A2ARs. Here, we used a newly developed FACS-based synaptometric analysis to compare the relative abundance on A1Rs and A2ARs in cortico-striatal and thalamo-striatal glutamatergic terminals (labeled with vesicular glutamate transporters VGLUT1 and VGLUT2, respectively) of control and BID rats. It could be demonstrated that BID (determined by measuring transferrin receptor density in the brain) is associated with a selective decrease in the A1R/A2AR ratio in VGLUT1 positive-striatal terminals. 相似文献
98.
Giorgio De Luca Marlon Basantes Valverde Matilde Morrone Lorenzo S. Caputi 《International journal of quantum chemistry》2019,119(10):e25890
Multi-shell fullerenes are widely studied for their interesting properties although comparative studies on single- and multi-shell structures remain scarce. In this work, important electronic features of single- and double-shell icosahedral fullerenes as a function of their sizes were calculated in the framework of the density functional theory. Fully optimized structures were used to get the gap between the highest occupied molecular and the lowest unoccupied molecular orbital (H-L gap), electronegativity, softness and density of the electronic states. This work shows that the H-L gap of the single-shell fullerenes decreases nonlinearly as the nanoparticles size increases, whereas for the double-shell fullerenes an opposite trend is obtained. A decrease of the H-L gap is found going from single- to double-shell fullerenes with similar external sizes, up to a diameter of 3.13 nm. The electron density of states revealed that isolated peaks give way to more dense electronic states for nanoparticles with diameters above 2 nm. 相似文献
99.
This paper uses techniques in noncommutative geometry as developed by Alain Connes [Co2], in order to study the twisted higher
index theory of elliptic operators on orbifold covering spaces of compact good orbifolds, which are invariant under a projective
action of the orbifold fundamental group, continuing our earlier work [MM]. We also compute the range of the higher cyclic
traces on K-theory for cocompact Fuchsian groups, which is then applied to determine the range of values of the Connes–Kubo Hall conductance
in the discrete model of the quantum Hall effect on the hyperbolic plane, generalizing earlier results in [Bel+E+S], [CHMM].
The new phenomenon that we observe in our case is that the Connes–Kubo Hall conductance has plateaux at integral multiples
of a fractional valued topological invariant, namely the orbifold Euler characteristic. Moreover the set of possible fractions has been determined, and
is compared with recently available experimental data. It is plausible that this might shed some light on the mathematical
mechanism responsible for fractional quantum numbers.
Received: 4 November 1999 / Accepted: 22 September 2000 相似文献
100.
We consider q-deformations of Witt rings, based on geometric operations on zeta functions of motives over finite fields, and we use these deformations to construct q-analogs of the Bost-Connes quantum statistical mechanical system. We show that the q-deformations obtained in this way can be related to Habiro ring constructions of analytic functions over F1 and to categorifications of Bost-Connes systems. 相似文献