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51.
García-Fandiño R Gulías M Castedo L Granja JR Mascareñas JL Cárdenas DJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(1):272-281
The mechanism of the palladium-catalysed [3+2] intramolecular cycloaddition of alkylidenecyclopropanes to alkynes has been computationally explored at DFT level. The energies of the reaction intermediates and transition states for different possible pathways have been calculated in a model system that involves the use of PH3 as a ligand. The results obtained suggest that the most favourable reaction pathway involves the initial C--C oxidative addition of the cyclopropane to a Pd0 complex to give an alkylidenepalladacyclobutane, which isomerises to a methylenepalladacyclobutane intermediate. Subsequent cyclisation by alkyne carbometallation, followed by reductive elimination affords the final product. An alternative mechanism consisting of a palladaene-type rearrangement is less probable in terms of Gibbs energy, but cannot be fully discarded because it is competitive if one considers electronic energies. For substrates that present an ester group at the terminal position of the triple bond we have found an alternative, more favourable mechanistic route that explains why the [3+2] cycloaddition of these types of systems does not lead to the expected cycloadducts. 相似文献
52.
We give a tauberian theorem for boundary values of analytic functions. We prove that if is the distributional limit of the analytic function F defined in a region of the form (a, b) × (0, R), if F (x
0 + iy)→ γ as y → 0+, and if f is distributionally bounded at x = x
0, then f (x
0) = γ distributionally. As a consequence of our tauberian theorem, we obtain a new proof of a tauberian theorem of Hardy and
Littlewood.
Received: 10 December 2007 相似文献
53.
Dr. Rebeca Lara Gonzalo Millán Prof. Dr. M. Teresa Moreno Prof. Dr. Elena Lalinde Elvira Alfaro-Arnedo Dr. Icíar P. López Dr. Ignacio M. Larráyoz Dr. José G. Pichel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(63):15757-15772
The optical and biological properties of 2-(4-dimethylaminophenyl)benzothiazole cycloplatinated complexes featuring bioactive ligands ([{Pt(Me2N-pbt)(C6F5)}L] [L=Me2N-pbtH 1 , p-dpbH (4-(diphenylphosphino)benzoic acid) 2 , o-dpbH (2-(diphenylphosphino)benzoic acid) 3 ), [Pt(Me2N-pbt)(o-dpb)] 4 , [{Pt(Me2N-pbt)(C6F5)}2(μ-PRnP)] [PR4P=O(CH2CH2OC(O)C6H4PPh2)2 5 , PR12P=O{(CH2CH2O)3C(O)C6H4PPh2}2 6 ] are presented. Complexes 1 – 6 display 1ILCT and metal-perturbed 3ILCT dual emissions. The ratio between both bands is excitation dependent, accomplishing warm-white emissions for 2 , 5 and 6 . The phosphorescent emission is lost in aerated solutions owing to photoinduced electron transfer to 3O2 and the formation of 1O2, as confirmed in complexes 2 and 4 . They also exhibit photoinduced phosphorescence enhancement in non-degassed DMSO due to local oxidation of DMSO by sensitized 1O2, which causes a local degassing. Me2N-pbtH and the complexes specifically accumulate in the Golgi apparatus, although only 2 , 3 and 6 were active against A549 and HeLa cancer cell lines, 6 being highly selective in respect to nontumoral cells. The potential photodynamic property of these complexes was demonstrated with complex 4 . 相似文献
54.
Sonia Amaya-González Laura López-López Rebeca Miranda-Castro Noemí de-los-Santos-Álvarez Arturo José Miranda-Ordieres María Jesús Lobo-Castañón 《Analytica chimica acta》2015
Aptamers are starting to increase the reagents tool box to develop more sensitive and reliable methods for food allergens. In most of these assays, aptamers have to be modified for detection and/or immobilization purposes. To take full advantage of their affinity, which decisively influence the detectability, these modifications must be faced rationally. In this work, a recently developed aptamer for an immunotoxic peptide of gliadin associated to celiac disease is used in different configurations and modified with various markers and anchored groups to evaluate the influence of such modifications on the real affinity. The interaction in solution with the peptide is strong for a relatively small molecule (Kd = 45 ± 10 nM, 17 °C) and slightly stronger than that for the immobilized intact protein due to a cooperative binding effect. Comparatively, while only minor differences were found when the peptide or the aptamer were immobilized, labeling with a biotin resulted preferable over fluorescein (Kd = 102 ± 11 vs 208 ± 54 nM, 25 °C). These findings are of prime importance for the design of an aptamer-based analytical method for gluten quantification. 相似文献
55.
A highly efficient enantioselective aryl addition to aldehydes using boroxins as aryl source and conformationally restricted perhydro-1,3-benzoxazines as ligands is reported. Both enantiomeric forms of chiral arylphenylmethanols and 1,1'-disubstituted diarylmethanols are afforded with excellent yields and enantioselectivities using the same ligand by means of an appropriate combination of boroxin and aromatic aldehyde. The enantiocontrol is not significantly influenced by electronic effects or steric hindrance, even with substituted boroxins. Very homogeneous ee's are reached when substituted arylboroxins are employed, without the use of any class of additive or pre-treatment. 相似文献
56.
Balasingham RG Thorp-Greenwood FL Williams CF Coogan MP Pope SJ 《Inorganic chemistry》2012,51(3):1419-1426
A range of luminescent, dimetallic complexes based upon the rhenium fac-tricarbonyl diimine core, linked by aliphatic chains of varying lengths and functionality, have been synthesized and their photophysical properties examined. Each complex displays characteristic (3)M(Re)L(diimine)CT emission in aerated acetonitrile solution, with long lifetimes in the range of 129-248 ns and corresponding quantum yields in the range 3.2-8.0%. In aqueous solution, as opposed to acetonitrile, the complexes generally show a small hypsochromic shift in λ(em) and an extension of the (3)MLCT lifetime, attributed to a hydrophobically driven association of the alkyl chains with the rhenium-bound diimine units. In live cell imaging experiments using MCF7 cells the complexes all show good uptake by non-energy dependent mechanisms without endosomal entrainment, and with varying propensity to localize in organelles. The degrees of uptake and localization properties are discussed in terms of the length and chemical nature of the linkers, and in terms of the likely interactions between these and the various cellular components encountered. 相似文献
57.
Beccia MR Biver T García B Leal JM Secco F Ruiz R Venturini M 《Dalton transactions (Cambridge, England : 2003)》2012,41(24):7372-7381
The equilibria and kinetics (stopped-flow) of the binding of Ni(II) to salicylhydroxamic acid (SHA) and phenylbenzohydroxamic acid (PBHA) have been investigated in aqueous solutions containing SDS micelles. The two ligands are fairly distributed between the two pseudophases present, so the binding reaction occurs in both phases. The contributions to the total reaction from each phase has been evaluated, following a procedure where use is made of the experimentally determined partition coefficients of the reactants involved. The mechanism of the reaction occurring on the micelle surface has been derived and comparison with the mechanism in water shows that the step Ni(2+) + HL ? NiHL(2+) is operative in both pseudophases, whereas the step Ni(2+) + L(-)? NiL(+), which is operative in water, is replaced in SDS by the step NiOH(+) + HL ? NiL(+). The analysis of the equilibrium and of the kinetic data enabled the evaluation of the equilibrium and the rate constants of the individual steps taking part in the binding process over the micelle surface. Interestingly, the first hydrolysis constant of the Ni(H(2)O)(6)(2+) ion in SDS is more than two orders of magnitude higher than in water. The agreement between the equilibrium constants derived from kinetics and those obtained by static measurements confirms the validity of the proposed mechanism. 相似文献
58.
Mikel Sanz Rebeca de Nalda José F. Marco Jesús G. Izquierdo Marta Castillejo 《Applied Surface Science》2009,255(10):5206-5210
Nanostructured deposits of TiO2 were grown on Si (1 0 0) substrates by laser ablating a TiO2 sintered target in vacuum or in oxygen using a Ti:sapphire laser delivering 80 fs pulses. The effect of the laser irradiation wavelength on the obtained nanostructures, was investigated using 800, 400 and 266 nm at different substrate temperatures and pressures of oxygen. The composition of the deposits was characterized using X-ray photoelectron spectroscopy (XPS) and the surface morphology was studied by environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM). Deposits are absent of microscopic droplets in all conditions explored. The best deposits, constituted by nanoparticles of an average diameter of 30 nm with a narrow size distribution, were obtained at the shorter laser wavelength of 266 nm under vacuum at substrate room temperature. 相似文献
59.
Rebeca Ruiz Begoa García Giuseppe Ruisi Arturo Silvestri Giampaolo Barone 《Journal of Molecular Structure》2009,915(1-3):86-92
The interaction of proflavine (PR) with two B-DNA decamers of alternating AT and GC sequence, called [deca(dG-dC)]2 and [deca(dA-dT)]2, respectively, was computationally investigated by the ONIOM method, exploiting a three-layer QM/QM/MM hybrid approach. The highest level QM method was applied to the model system, which comprises the intercalation site (5th and 6th base pairs) and the inserted PR molecule. The connecting sugar phosphate backbone was added in the medium layer region. Both higher and medium level layers, differing in the size of the basis set used, were treated by the DFT MPWB1K functional. The full system in the lower layer was described by the empirical AMBER force field. The calculated values of the interaction energy of PR with [deca(dG-dC)]2 and [deca(dA-dT)]2, as well as with the dinucleotides d(GpC)2, and d(ApT)2, the latter considered either in vacuo and in the mimicked water solvent, support for a static higher affinity toward G-C compared to the A-T DNA base sequences, in agreement with structural results from crystallographic studies. Furthermore, the different structural characteristics of the [deca(dG-dC)]2/PR complex compared to those of the [deca(dA-dT)]2/PR, furnish a possible interpretation of apparently controversial experimental thermodynamic data, explained in terms of two possible modes of non-covalent binding of ligands with DNA, namely intercalation and external binding, respectively. 相似文献
60.
Marcela Hurtado Dr. Manuel Yánez Prof. Dr. Rebeca Herrero Andrés Guerrero Juan Z. Dávalos Dr. José‐Luis M. Abboud Prof. Dr. Brahim Khater Dr. Jean‐Claude Guillemin Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(18):4622-4629
The acidity‐enhancing effect of BH3 in gas‐phase phosphine ? boranes compared to the corresponding free phosphines is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. Thus, the enhancement of the acidity of protic acids by Lewis acids usually observed in solution is also observed in the gas phase. For example, the gas‐phase acidities (GA) of MePH2 and MePH2 ? BH3 differ by about 118 kJ mol?1 (see picture).