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31.
D'Amelio N Gaggelli E Gaggelli N Molteni E Baratto MC Valensin G Jezowska-Bojczuk M Szczepanik W 《Dalton transactions (Cambridge, England : 2003)》2004,(3):363-368
The complexes formed by kanamycin A at three different pH values (5.5, 7.4 and 12.0) were investigated by NMR and EPR spectroscopy. Paramagnetic relaxation contributions to proton relaxation rates were measured using a combination of the TOCSY sequence with the inversion recovery experiment in order to gain signal resolution in the bulk region. Measured contributions were converted into distances and used for structural determination by restrained simulated annealing where all possible chair and boat conformations of the rings were taken into account. The interaction of the Cu(II) ion with the nitrogen of the C ring is apparent at all pH values. At higher pH also the amino group of ring A starts to be involved in the metal coordination sphere. This is accompanied by a switch in conformation of ring C. Structures are consistent with the involvement in the coordination sphere either of the 2' or 4' hydroxyl oxygens at pH 5.5 and the 5 and the 6' hydroxyl oxygens (or the ring oxygen) at pH 12.0. 相似文献
32.
We recall Newtons iteration for computing the inverse or Moore–Penrose generalized inverse of a matrix. Then we specialize this approach to the case of structured matrices where all input, output and intermediate auxiliary matrices are represented in a compressed form, via their short displacement generators. We design a new Newton-like iteration based on a cubic polynomial and show its effectiveness by some numerical experiments for matrices from the Toeplitz-like class and the Cauchy-like class. 相似文献
33.
We compute the -limit of a sequence obstacle functionals in the case of periodic obstacles. 相似文献
34.
Gianni Bosi Juan Carlos Candeal Esteban Induráin Esteban Oloriz Margarita Zudaire 《Order》2001,18(2):171-190
In the framework of the analysis of orderings whose associated indifference relation is not necessarily transitive, we study the structure of an interval order and its representability through a pair of real-valued functions. We obtain a list of characterizations of the existence of a representation, showing that the three main techniques that have been used in the literature to achieve numerical representations of interval orders are indeed equivalent. 相似文献
35.
Roberto Gianni Paola Mannucci 《NoDEA : Nonlinear Differential Equations and Applications》2001,8(2):219-235
We prove a well posedness result for a free boundary problem describing the filtration of an incompressible viscous fluid
in a porous medium containing water absorbing granules.?The location of the wetting front (the free boundary) is described
by a Stefan like problem for a parabolic equation which is coupled with an hyperbolic equation describing the absorption kinetic
of the granules.
Received December 1999 相似文献
36.
We modelled the adsorption of tetra-pyridyl-porphyrin (TPyP) and Fe(II)-tetra-pyridyl- porphyrin (Fe-TPyP) molecules on Ag(1 1 1). TPyP adsorbs in a flat geometry at a distance of 5.6 Å from the surface. The dihedral angle of the pyridyl rings is found to be 70°. The molecular structure remains largely unaffected by the adsorption. The structure of the molecular adlayer should thus be determined mainly by lateral intermolecular interactions. These conclusions are confirmed by scanning tunnelling microscopy observations. Upon metalation spin-polarized states with strong Fe d-character appear in Fe-TPyP near the centre of the gap between the highest occupied and the lowest unoccupied states of a TPyP molecule. We find also that the gap is widened in the presence of Fe. This implies a shift of 0.3 eV of unoccupied states as identified by scanning tunnelling spectroscopy simulations and confirmed by experimental data. 相似文献
37.
Cristina Cimarelli Davide Fratoni Andrea Mazzanti Gianni Palmieri 《Tetrahedron: Asymmetry》2011,22(5):2991-596
A novel synthesis of useful enantiomerically pure arylglycinates via spontaneous reaction between phenol or naphthol derivatives and enantiopure α-imino glyoxylate in the absence of an acid catalyst is reported. A library of enantiopure substituted phenol or naphthol glycinates was obtained in good yields and high diastereoselectivities. Diastereoisomerically pure aryl glycinates were obtained by direct flash chromatography separation of the crude reaction mixture. The free OH moiety of the phenols or naphthols contributed to the activation of the imino group to form an intermolecular hydrogen bond and promoted the reaction in the absence of an acid catalyst, as shown in the transition state reported. The diastereoselectivity is due to thermodynamic control in the addition step. 相似文献
38.
Gianni Pavan 《Applied Acoustics》2010,71(11):991-993
39.
Gradient bounds for minimizers of free discontinuity problems related to cohesive zone models in fracture mechanics 总被引:2,自引:0,他引:2
Gianni Dal Maso Adriana Garroni 《Calculus of Variations and Partial Differential Equations》2008,31(2):137-145
In this note we consider a free discontinuity problem for a scalar function, whose energy depends also on the size of the
jump. We prove that the gradient of every smooth local minimizer never exceeds a constant, determined only by the data of
the problem. 相似文献
40.
Daniele Balducci Simone Contaldi Ilaria Lazzari Gianni Porzi 《Tetrahedron: Asymmetry》2009,20(12):1398-1401
A new, practical and very convenient stereocontrolled synthesis of (S)-2′,6′-dimethyltyrosine [(S)-Dmt] 4 was accomplished in a good yield, starting from the chiral synthon 1,4-N,N-[(S)-phenylethyl]-piperazine-2,5-dione 1. The procedure, which is an extension of our original strategy and occurs with a high level of stereoselectivity (>98%), is simple and inexpensive allowing us to prepare the unnatural α-aminoacid (S)-Dmt also on a multi-gram scale. 相似文献