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91.
Mantsinen MJ Ingesson LC Johnson T Kiptily VG Mayoral ML Sharapov SE Alper B Bertalot L Conroy S Eriksson LG Hellsten T Noterdaeme JM Popovichev S Righi E Tuccillo AA 《Physical review letters》2002,89(11):115004
Experiments on the JET tokamak show that the wave-induced pinch in the presence of toroidally asymmetric waves can provide a tool for controlling the profile of ion-cyclotron-resonant 3He ions. Direct evidence for the wave-induced pinch has been obtained from the measured gamma-ray emission profiles. Concurrent differences in the excitation of Alfvén eigenmodes (AEs), sawtooth stabilization, electron temperatures, and fast-ion stored energies are observed. The measured location of the AEs and gamma-ray emission profiles are consistent with the fast-ion radial gradient providing the drive for AEs. 相似文献
92.
93.
In this Letter we show that friction of anticorrugating systems can be dramatically decreased by applying an external load. The counterintuitive behavior that deviates from the macroscopic Amonton law is dictated by quantum mechanical effects that induce a transformation from anticorrugation to corrugation in the near-surface region. We describe the load-driven modifications occurring in the potential energy surface of different rare gas-metal adsorbate systems, namely, Ar, Kr, Xe on Cu(111), and Xe on Ag(111), and we calculate the consequent friction drop for the commensurate Xe/Cu system by means of combined ab initio and classical molecular dynamics simulations. 相似文献
94.
95.
A facile synthetic approach to the direct preparation of various novel unnatural boronated protected tryptophans using a regio- and chemoselective electrophilic substitution of 4- and 5-boronated indoles with N-protected dehydroalanine is described. The gram-scale synthesis of two free tryptophan boronic acids is also reported. 相似文献
96.
K. Ramalingam R. Thiruneelakandan G. Bocelli L. Righi 《Transition Metal Chemistry》2012,37(3):265-270
The complexes trans-[Ni(4-MP)2(NCS)2]·MeCN (1) and trans-[Ni(3-MP)2(NCS)2] (2) (4-MP = tri(4-methylphenyl)phosphine, 3-MP = tri(3-methylphenyl)phosphine) were prepared and characterized by IR, UV–visible,
NMR spectra, CV, TGA and single crystal X-ray crystallography. Both the complexes have planar geometry and are diamagnetic.
The Ni–P distances in both complexes are relatively short as a result of strong back donation from nickel to phosphorus. The
phenyl rings in the 3-MP analogue (2) show increased pitching with reference to the plane formed by the ipso carbons due to increased steric effects. For complex
(2), the N–Ni–N and P–Ni–P angles are significantly lower than the almost linear N–Ni–N and N–Ni–P angles observed for both
complex (1) and trans-[Ni(PPh3)2(NCS)2]. This observation indicates that the 3-methylphosphine ligand forces complex (2) to distort towards a tetrahedral geometry. IR spectra of both complexes show strong bands around 2,090 cm−1 due to N-coordinated thiocyanate, while the electronic spectra contain d–d transitions around 452 nm. Cyclic voltammograms
show that the irreversible one-electron reduction potentials increase in the following order: trans- [Ni(PPh3)2(NCS)2] < trans- [Ni(3-MP)2(NCS)2] < trans-[Ni(4-MP)2(NCS)2], revealing the electron releasing effect of the methyl groups. The planar complexes exhibit interallogony in coordinating
solvents. 相似文献
97.
Summary: Results of electrospinning of gelatin/PEO blends from aqueous solutions are presented. The effects of applied electric field (15–25 kV), flow rate (0.25–0.75 mL/h) and gelatin concentration in the final fiber diameter were studied. It was observed that the resulting fiber system presented high polydispersity, where fiber diameters ranged from 150 nm to 1.3 µm. In some cases an adequate fibrous system were not obtained. It was observed that the average diameter decreased mainly when the flow rate and gelatin concentration decreased. 相似文献
98.
Kuppukkannu Ramalingam Raghavan Thiruneelakandan Gabriele Bocelli Lara Righi 《Central European Journal of Chemistry》2012,10(4):1199-1207
Trans influence of triphenylphosphines and pseudohalogens on Ni-S bonds of NiS2PN and NiS2PC chromophores has been investigated by synthesizing and characterizing them. The complexes show the characteristic thioureide IR band at ∼ 1530 cm−1. Electronic spectrum of the cyanide analogue shows a strong blue shift relative to others. X-ray structures of [Ni(pipdtc)(4-MP)(NCS)] (1), [Ni(pipdtc)(PPh3)(NCS)] (2) and [Ni(pipdtc)(PPh3)(CN)] (3) (pipdtc = piperidinecarbodithioate anion, 4-MP = tri(4-methylphenyl)phopshine) are reported. Ni-S bond distance trans to 4-MP(1) is longer than the distances in (2) and (3) and Ni-S bond distances trans to Ni-NCS/CN decrease as follows: (3) > (2) > (1). Particularly, 4-MP shows a highly significant trans influence than triphenylphosphine on Ni-S bond. Similarly, CN− exerts a marginally significant trans influence compared to NCS-. Thioureide C-N distances are relatively very short due to the drift of electron density towards the metal. The Ni-N-C angle (163.5(2)°) observed in (2) indicates deviation from linearity to a larger extent compared to that in (1) (176.3(3)°) due to the steric effect of the 4-methyl group. The reduction potentials (CV) for the mixed ligand complexes are much less compared to that of the parent NiS4 chromophore due to the π-acidic phosphines. 相似文献
99.
The Lewis acid-catalysed regioselective azidolysis of 2,3-epoxy amines has been investigated. The results obtained demonstrated that using TMSN3 as a source of azide, the appropriate choice of Lewis acid allowed to direct the regiochemistry of the ring opening. The present methodologies provide a powerful tool in organic synthesis for the preparation of diaminoalcohol moieties. 相似文献
100.
Giovanni Centonze Chiara Portolani Prof. Paolo Righi Prof. Giorgio Bencivenni 《Angewandte Chemie (International ed. in English)》2023,62(31):e202303966
Axially chiral compounds have been always considered a laboratory curiosity with rare prospects of being applied in asymmetric synthesis. Things have changed very quickly in the last twenty years when it was understood the important role and the enormous impact that these compounds have in medicinal, biological and material chemistry. The asymmetric synthesis of atropisomers became a rapidly expanding field and recent reports on the development of N−N atropisomers strongly prove how this research field is a hot topic open to new challenges and frontiers of asymmetric synthesis. This review focuses on the recent advances in the enantioselective synthesis of N−N atropisomers highlighting the strategies and breakthroughs to obtain this novel and stimulating atropisomeric framework. 相似文献