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801.
Reactions of KPPh2 with the dimeric cyclopalladated complex {Pd(N∩C)(μ-Cl)}21 derived from N,N-dimethylbenzylamine were studied using different reagent ratios, temperature, reaction time, concentrations and solvents. Complex 3, the μ-Cl-μ-PPh2 analog of 1, was obtained in 76% yield in the one-hour reaction using the 1:1 ratio of dimer 1 and KPPh2 in THF at rt. ortho-(Diphenylphosphino)benzylamine 4 was synthesized in 58% yield by reacting complex 1 with 4.5 equiv. of KPPh2 in THF at rt. A possible mechanism of the aminophosphine formation is proposed on the basis of the experimental data including 31P{1H} NMR spectra of reaction mixtures. 相似文献
802.
Albahily K Fomitcheva V Gambarotta S Korobkov I Murugesu M Gorelsky SI 《Journal of the American Chemical Society》2011,133(16):6380-6387
Reaction of the divalent [(t-Bu)NP(Ph)(2)N(t-Bu)]CrCl(2)Li(THF)(2) (1) with 1 equiv of vinyl Grignard (CH(2)=CH)MgCl reproducibly afforded the triangulo {π-[(t-Bu)N-P(Ph)(2)-N(t-Bu)]Cr}(2)(μ,μ',η(4),η(4)'-C(4)H(4)){σ-[(t-Bu)N-P(Ph)(2)-N(t-Bu)]Cr} (2) containing a σ-/π-bonded butadiene-diyl unit. The diene-diyl moiety was generated by an oxidative coupling and deprotonation of two vinyl anions. The crystal structure revealed that of the three chromium atoms, each bearing one NPN ligand, two are perpendicularly bonded to the two sides of the π-system of the butadiene-diyl residue in a sort of inverted sandwich type of structure. The third is instead coplanar with the doubly deprotonated C(4) unit and σ-bonded to the two terminal carbon atoms. Despite the appearance as a Cr(II)/Cr(I) mixed valence species, DFT calculations have revealed that the structure of 2 consists of three divalent chromium atoms, while the additional electron resides on the π-system of the bridging organic residue. Complex 2 behaves as a single component selective catalyst for ethylene trimerization. 相似文献
803.
Cucurbit[6]uril nanocavity as an enhanced spectrofluorimetric method for the determination of pyrene
The effect of the addition of macrocyclic host cucurbit[6]uril (CB6) on the photophysical properties of polycyclic aromatic hydrocarbon pyrene (PYR) was analyzed. The fluorescence emission spectra of the aromatic compound were determined at 25.0 °C in different acidic media (HCl 18%, w/v, or HCOOH 55%, w/v) with and without CB6. A significant enhancement in the fluorescence signals in the presence of CB6 was observed. The average values of the association constant (KA) for the 1:1 stoichiometry complex and the relative fluorescence quantum yield ratio between the complexed and free PYR (?PYR–CB6/?PYR) in acidic media were (4.0 ± 0.5) × 102 M−1 and (5.7 ± 0.2), respectively.The analytical parameters improved in the presence of CB6. The relative decrease in the limit of detection was 92%. The matrix effect was evaluated in fortified samples of tap water and tea extracts. Apparent recoveries obtained by the proposed method in tap water and tea extracts were (82–103)% and (89–99)%, respectively. Selectivity studies with inorganic and organic species were performed. The method is rapid, direct, selective and simple. 相似文献
804.
Laurent Desvillettes François Golse Valeria Ricci 《Journal of statistical physics》2008,131(5):941-967
We propose a mathematical derivation of Brinkman’s force for a cloud of particles immersed in an incompressible viscous fluid.
Specifically, we consider the Stokes or steady Navier-Stokes equations in a bounded domain Ω⊂ℝ3 for the velocity field u of an incompressible fluid with kinematic viscosity ν and density 1. Brinkman’s force consists of a source term 6π
ν
j where j is the current density of the particles, and of a friction term 6π
ν
ρ
u where ρ is the number density of particles. These additional terms in the motion equation for the fluid are obtained from the Stokes
or steady Navier-Stokes equations set in Ω minus the disjoint union of N balls of radius ε=1/N in the large N limit with no-slip boundary condition. The number density ρ and current density j are obtained from the limiting phase space empirical measure
, where x
k
is the center of the k-th ball and v
k
its instantaneous velocity. This can be seen as a generalization of Allaire’s result in [Arch. Ration. Mech. Anal. 113:209–259,
[1991]] who considered the case of periodically distributed x
k
s with v
k
=0, and our proof is based on slightly simpler though similar homogenization arguments. Similar equations are used for describing
the fluid phase in various models for sprays. 相似文献
805.
Abdulkarim A. Amirov Yogesh A. Chaudhari Subhash T. Bendre Ksenia A. Chichay Valeria V. Rodionova Dibir M. Yusupov Zairbek M. Omarov 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(4):63
Multiferroic BiFe1?xZn x O3 ceramics were prepared by solution combustion method. Their structure, magnetoelectric, dielectric, magnetic, thermal characteristics were studied. The magnetic M(T) and heat capacity C p (T) measurements demonstrate an antiferromagnetic to paramagnetic phase transition (T N ) around 635 K. The anomaly on the temperature dependence of the dielectric constant near T N was observed, which could be induced by the magnetoelectric coupling between electric and magnetic ordering. The magnetoelectric behavior was also confirmed by the linear relation between Δε and M2, which is in the agreement of the Ginzburg-Landau theory for the second-order phase transition. 相似文献
806.
Luisa Affatigato Alice Sciortino Giuseppe Sancataldo Alessio Incocciati Roberta Piacentini Alessandra Bonamore Marco Cannas Fabrizio Messina Mariano Licciardi Valeria Militello 《Photochemistry and photobiology》2023,99(5):1218-1224
Ferritin nanoparticles play many important roles in theranostic and bioengineering applications and have been successfully used as nanovectors for the targeted delivery of drugs due to their ability to specifically bind the transferrin receptor (TfR1, or CD71). They can be either genetically or chemically modified for encapsulating therapeutics or probes in their inner cavity. Here, we analyzed a new engineered ferritin nanoparticle, made of the H chain mouse ferritin (HFt) fused with a specific lanthanide binding tag (LBT). The HFt-LBT has one high affinity lanthanide binding site per each of the 24 subunits and a tryptophane residue within the tag that acts as an antenna able to transfer the energy to the lanthanide ions via a LRET process. In this study, among lanthanides, we selected europium for its red emission that allows to reduce overlap with tissue auto-fluorescence. Steady state emission measurements and time-resolved emission spectroscopy have been employed to investigate the interaction between the HFt-LBT and the Eu3+ ions. This allowed us to identify the Eu3+ energy states involved in the process and to pave the way for the future use of HFt-LBT Eu3+ complex in theranostics. 相似文献
807.
Jonas Žurauskas Dr. Soňa Boháčová Dr. Shangze Wu Dr. Valeria Butera Simon Schmid Michał Domański Dr. Tomáš Slanina Dr. Joshua P. Barham 《Angewandte Chemie (International ed. in English)》2023,62(44):e202307550
Electron-deficient acridones and in situ generated acridinium salts are reported as potent, closed-shell photooxidants that undergo surprising mechanisms. When bridging acyclic triarylamine catalysts with a carbonyl group (acridones), this completely diverts their behavior away from open-shell, radical cationic, ‘beyond diffusion’ photocatalysis to closed-shell, neutral, diffusion-controlled photocatalysis. Brønsted acid activation of acridones dramatically increases excited state oxidation power (by +0.8 V). Upon reduction of protonated acridones, they transform to electron-deficient acridinium salts as even more potent photooxidants (*E1/2=+2.56–3.05 V vs SCE). These oxidize even electron-deficient arenes where conventional acridinium salt photooxidants have thusfar been limited to electron-rich arenes. Surprisingly, upon photoexcitation these electron-deficient acridinium salts appear to undergo two electron reductive quenching to form acridinide anions, spectroscopically-detected as their protonated forms. This new behaviour is partly enabled by a catalyst preassembly with the arene, and contrasts to conventional SET reductive quenching of acridinium salts. Critically, this study illustrates how redox active chromophoric molecules initially considered photocatalysts can transform during the reaction to catalytically active species with completely different redox and spectroscopic properties. 相似文献
808.
Dr. Michele Porto Prof. Ruggero Angelico Dr. Pietro Calandra Dr. Valeria Loise Dr. Abraham A. Abe Prof. Cesare Oliviero Rossi Dr. Paolino Caputo 《Chemphyschem》2023,24(24):e202300217
In this investigation the dynamics of two types of bitumens with different penetration grade were tested by using dynamic shear rheometry (DSR) and Nuclear Magnetic Resonance (NMR) at unaged conditions, and upon both short- and long-term artificial aging. The gel-sol transition temperature was found to increase with increasing the time of aging treatment. Arrhenius parameters of the viscosity were found, unexpectedly, to be correlated with those of simple liquids, suggesting that the two kinds of systems, although chemically and physically quite different, share the same basic process at the molecular level. The molecular dynamics has been then investigated by NMR Pulsed Field Gradient Stimulated-Echo (PFGSE) and relaxometry (Carr-Purcell-Meiboom-Gill, CPMG, spin-echo pulse sequence) to capture the effect of aging upon dynamics variables such as self-diffusion coefficients D and transverse relaxation times T2. The translational diffusion at T> of the light molecular components of both types of bitumens was characterized by broad distributions of D which were found independent of the experimental time scale up to 0.2 s. Similarly, T2 data could be described as a continuous unimodal distributions of relaxation times determined both at T< and T> . 相似文献
809.
810.
Maria Carannante Valeria D'Amato Paola Fersini Salvatore Forte Giuseppe Melisi 《商业与工业应用随机模型》2023,39(4):549-566
Dependence among different cyber risk classes is a fundamentally underexplored topic in the literature. However, disregarding the dependence structure in cyber risk management leads to inconsistent estimates of potential unintended losses. To bridge this gap, this article adopts a regulatory perspective to develop vine copulas to capture dependence. In quantifying the solvency capital requirement gradient for cyber risk measurement according to Solvency II, a dangerous paradox emerges: an insurance company does not tend to provide cyber risk hedging products as they are excessively expensive and would require huge premiums that it would not be possible to find policyholders. 相似文献