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1.
L. Cianchi F. Del Giallo F. Pieralli M. Mancini S. Sciortino G. Spina 《Hyperfine Interactions》1991,66(1-4):387-391
Mössbauer parameters of151Eu in Eu1+x Ba2?x Cu3O7+δ have been studied as a function of temperature, forx=0.15 andx=0.25. The areas of the absorption spectra for the two samples are almost equal. This could mean that thef-Mössbauer factor for151Eu at the barium sites is much smaller than that for151Eu at the rare earth sites, i.e. we only observe the spectra of the latter sites. According to this, the fits of the spectra with a single quadrupolar pattern and with two quadrupolar patterns have given equivalent χ2 values. 相似文献
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Pablo Ríos Javier Borge Francisco Fernndez de Crdova Giuseppe Sciortino Agustí Lleds Amor Rodríguez 《Chemical science》2021,12(7):2540
The concept of metal–ligand cooperation opens new avenues for the design of catalytic systems that may offer alternative reactivity patterns to the existing ones. Investigations of this concept with ligands bearing a boron center in their skeleton established mechanistic pathways for the activation of small molecules in which the boron atom usually performs as an electrophile. Here, we show how this electrophilic behavior can be modified by the ligand trans to the boron center, evincing its ambiphilic nature. Treatment of diphosphinoboryl (PBP) nickel–methyl complex 1 with bis(catecholato)diboron (B2Cat2) allows for the synthesis of nickel(ii) bis-boryl complex 3 that promotes the clean and reversible heterolytic cleavage of dihydrogen leading to the formation of dihydroborate nickel complex 4. Density functional theory analysis of this reaction revealed that the heterolytic activation of H2 is facilitated by the cooperation of both boryl moieties and the metal atom in a concerted mechanism that involves a Ni(ii)/Ni(0)/Ni(ii) process. Contrary to 1, the boron atom from the PBP ligand in 3 behaves as a nucleophile, accepting a formally protic hydrogen, whereas the catecholboryl moiety acts as an electrophile, receiving the attack from the hydride-like fragment. This manifests the dramatic change in the electronic properties of a ligand by tuning the substituent trans to it and constitutes an unprecedented cooperative mechanism that involves two boryl ligands in the same molecule operating differently, one as a Lewis acid and the other one as a Lewis base, in cooperation with the metal. In addition, reactivity towards different nucleophiles such as amines or ammonia confirmed the electrophilic nature of the Bcat moiety, allowing the formation of aminoboranes.A bis(boryl)nickel complex promotes the facile and reversible activation of H2 through a cooperative mechanism that involves the metal and both boryl moieties in a concerted five-center process. 相似文献
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The three-component ionic microemulsion system consisting of AOT/water/decane shows an unusual phase behavior in the vicinity
of room temperature. The phase diagram in the temperature-volume fraction (of the dispersed phase) plane exhibits a lower
consolute critical point at about 40 degrees centigrades and 10% volume fraction. A percolation line, starting from the vicinity
of the critical point, cuts across the plane, extending to high volume fraction side at progressively lower temperatures.
In this paper we review the evidence that allows to interpret the phase behavior of our system in terms of interacting spherical
droplets. We also investigate the dynamics of droplets, below and approaching the critical point by dynamic light scattering.
The first cumulant and time evolution of the droplet density correlation function can be quantitatively calculated by assuming
the existence of polydispersed fractal clusters formed by the microemulsion droplets due to attraction. The relaxation phenomena
observed in an extensive set of measurements of electrical conductivity and permittivity close to percolation is also reviewed
and interpreted through the same cluster-forming mechanism, which reproduces the most relevant features of the frequency-dependent
complex dielectric constant of this system.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
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Stanley HE Buldyrev SV Goldberger AL Hausdorff JM Havlin S Mietus J Peng C-K Sciortino F Simons M 《Physica A》1992,191(1-4):1-12
Here we discuss recent advances in applying ideas of fractals and disordered systems to two topics of biological interest, both topics having common the appearance of scale-free phenomena, i.e., correlations that have no characteristic length scale, typically exhibited by physical systems near a critical point and dynamical systems far from equilibrium. (i) DNA nucleotide sequences have traditionally been analyzed using models which incorporate the possibility of short-range nucleotide correlations. We found, instead, a remarkably long-range power law correlation. We found such long-range correlations in intron-containing genes and in non-transcribed regulatory DNA sequences as well as intragenomic DNA, but not in cDNA sequences or intron-less genes. We also found that the myosin heavy chain family gene evolution increases the fractal complexity of the DNA landscapes, consistent with the intron-late hypothesis of gene evolution. (ii) The healthy heartbeat is traditionally thought to be regulated according to the classical principle of homeostasis, whereby physiologic systems operate to reduce variability and achieve an equilibrium-like state. We found, however, that under normal conditions, beat-to-beat fluctuations in heart rate display long-range power law correlations. 相似文献
10.
Akhil Kumar Singh Dr. Mohammad Usman Dr. Giuseppe Sciortino Prof. Dr. Eugenio Garribba Prof. Dr. Sankar Prasad Rath 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(43):10098-10110
Metallophilic interactions between closed-shell metal ions are becoming a popular tool for a variety of applications related to high-end materials. Heavier d8 transition-metal ions are also considered to have a closed shell and can be involved in such interactions. There is no systematic investigation so far to estimate the structure and energy characteristics of metallophilic interactions in AgII/AgII (d9/d9), AgIII/AgIII (d8/d8), and mixed-valent AgII/AgIII (d9/d8) complexes, which have been demonstrated in the present study. Both interporphyrinic and intermetallic interactions were investigated on stepwise oxidation by using a rigid ethene-bridged cis silver(II) porphyrin dimer and the results compared with those for highly flexible ethane-bridged analogues. By controlling the nature of chemical oxidants and their stoichiometry, both 1e and 2e oxidations were done stepwise to generate AgII/AgIII mixed-valent and AgIII/AgIII porphyrin dimers, respectively. Unlike all other ethene-bridged metalloporphyrin dimers reported earlier, in which 2e oxidation stabilizes only the trans form, such an oxidation of silver(II) porphyrin dimer stabilizes only the cis form because of the metallophilic interaction. Besides silver(II) ⋅⋅⋅ silver(II) interactions in cis silver(II) porphyrin dimer, stepwise oxidations also enabled us to achieve various hitherto-unknown silver(II) ⋅⋅⋅ silver(III) and silver(III) ⋅⋅⋅ silver(III) interactions, which thereby allow significant modulation of their structure and properties. The strength of Ag ⋅⋅⋅ Ag interaction follows the order AgII/AgII (d9/d9)<AgII/AgIII (d9/d8)<AgIII/AgIII (d8/d8). Single-crystal XRD, X-ray photoelectron spectroscopy (XPS), 1H NMR and EPR spectroscopy, and variable-temperature magnetic investigations revealed various oxidation states of silver and metallophilic interactions, which are also well supported by computational analysis. 相似文献