Interface effects on Gd induced disordering of Co films on Pt(111)

Amorphization of epitaxial Co thin films grown on top of a Pt(111) surface has been studied by surface X-ray diffraction after deposition of Gd overlayers. The results indicate strong differences of the disordering process depending on the thickness of the Co film. First basic difference is that thick Co films (15 atomic layers) are only partially amorphized by 4 atomic layers of Gd on top of them, whereas thinner Co films (5 atomic layers) are completely disordered by just 2 atomic layers of Gd. Moreover, amorphization by Gd overlayers induces different stress relaxation processes in both cases. For 15 atomic layers thick Co films a preferential amorphization of the more strained Co grains is observed, leading to an effective relaxation of about ? 0.5% of the in-plane lattice parameter during amorphization, approaching its relaxed value. On the contrary, for 5 atomic layers thick Co films, the initial steps of disordering are accompanied by a stronger increase of the in-plane lattice constant, by about 1.4%, typical of Co–Pt interface alloy formation, followed by a complete amorphization. Furthermore, the magnetic characterization, carried out by magneto-optical Kerr effect and resonant magnetic surface X-ray diffraction, strongly supports that the amorphization of thin Co films is changing the nature of the Co/Pt interface. In particular, as Gd overlayers are deposited, and the amorphization proceeds, the structural disordering of the Co/Pt interface flips its characteristic perpendicular magnetic anisotropy toward in-plane orientation before the complete magnetic depolarization of the interface Pt atoms is reached. All these results confirm a marked dependence of amorphization processes on film thickness, which can be related to the enhanced influence of the nearby film/substrate interface.     

Synthesis, characterization and electrochemical studies of the heterometallic diclusters [{Fe2(μ-CO)(CO)6(μ-PPh2)Au}2(diphosphine)] (diphosphine=dppm, dppip, dppe, dppp)

Treatment of [(ClAu)₂(diphosphine)] {diphosphine=bis(diphenylphosphino)methane (dppm), bis(diphenylphosphino)isopropane (dppip), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp)} with two equivalents of the anion [Fe₂(μ-CO)(CO)₆(μ-PPh₂)]⁻ in the presence of TlBF₄ gives the new heterometallic diclusters [{Fe₂(μ-CO)(CO)₆(μ-PPh₂)Au}₂(diphosphine)] that have been isolated and characterized. Their ³¹P-NMR spectra show different patterns as a function of the diphosphine ligand. The electrochemical behavior of these compounds has been investigated and compared with that of the mono- [Fe₂(μ-CO)(CO)₆(μ-PPh₂)(μ-AuPPh₃)] and tricluster [{Fe₂(μ-CO)(CO)₆(μ-PPh₂)Au}₃(triphos)] derivatives.     

Synthesis of New Brassinosteroid 24-Norcholane Type Analogs Conjugated in C-3 with Benzoate Groups

The metabolism of brassinosteroid leads to structural modifications in the ring skeleton or the side alkyl chain. The esterification and glycosylation at C-3 are the most common metabolic pathways, and it has been suggested that conjugate brassinosteroids are less active or inactive. In this way, plants regulate the content of active brassinosteroids. In this work, the synthesis of brassinosteroid 24-norcholane type analogs conjugated at C-3 with benzoate groups, carrying electron donor and electron attractant substituents on the aromatic ring, is described. Additionally, their growth-promoting activities were evaluated using the Rice Lamina Inclination Test (RLIT) and compared with that exhibited by brassinolide (used as positive control) and non-conjugated analogs. The results indicate that at the lowest tested concentrations (10⁻⁸–10⁻⁷ M), all analogs conjugated at C-3 exhibit similar or higher activities than brassinolide, and the diasteroisomers with S configuration at C-22 are the more active ones. Increasing concentration (10⁻⁶ M) reduces the biological activities of analogs as compared to brassinolide.     

Monte carlo estimates of domain-deformation sensitivities

It is shown that, when a Monte Carlo algorithm is used for estimation of any physical quantity A, a simple and fast additional procedure can be implemented that simultaneously estimates the sensitivity of A to any problem parameter. The proposed approach is general and systematic in the sense that: (i) it includes domain-deformation sensitivities, i.e., cases where a change in the parameter modifies the domain over which the sampled random variables are defined and (ii) a simple generic procedure is presented to address all remaining free choices in terms of variance minimization.     

Imaging the Magnetic Reversal of Isolated and Organized Molecular‐Based Nanoparticles using Magnetic Force Microscopy

In the race towards miniaturization in nanoelectronics, magnetic nanoparticles (MNPs) have emerged as potential candidates for their integration in ultrahigh‐density recording media. Molecular‐based materials open the possibility to design new tailor‐made MNPs with variable composition and sizes, which benefit from the intrinsic properties of these materials. Before their implementation in real devices is reached, a precise organization on surfaces and a reliable characterization and manipulation of their individual magnetic behavior are required. In this paper, it is demonstrated how molecular‐based MNPs are accurately organized on surfaces and how the magnetic properties of the individual MNPs are detected and tuned by means of low‐temperature magnetic force microscopy (LT‐MFM) with variable magnetic field. The magnetization reversal on isolated and organized MNPs is investigated; in addition, the temperature dependence of their magnetic response is evaluated.     

Synthesis and complete assignment of the 1H and 13C NMR signals of new acetamido and aminoflavonoid derivatives

The complete ¹H and ¹³C NMR assignment of 9 acetamidochalcones, 18 acetamidoflavones, 18 aminoflavones, 9 acetamidoflavonols and 9 aminoflavonols has been performed using one‐ and two‐dimensional NMR techniques including COSY, HMQC and HMBC experiments. Copyright © 2010 John Wiley & Sons, Ltd.     

Improving the efficiency of DC global optimization methods by improving the DC representation of the objective function

There are infinitely many ways of representing a d.c. function as a difference of convex functions. In this paper we analyze how the computational efficiency of a d.c.optimization algorithm depends on the representation we choose for the objective function, and we address the problem of characterizing and obtaining a computationally optimal representation. We introduce some theoretical concepts which are necessary for this analysis and report some numerical experiments.      

Palladium(0) pre‐catalysts with heteroditopic NHC–amine ligands by transmetallation from their silver(I) complexes

The synthesis of an air‐stable series of Pd⁰ complexes with dissymmetric bidentate N‐heterocyclic carbene–amine ligands has been performed. The key step is an unprecedented carbene transfer from Ag^I to obtain electron‐rich zero‐valent palladium precatalysts. The coordination behavior of the ligands was determined with X‐ray crystallography. Surprising results were obtained in the catalysis of transfer semi‐hydrogenation, where the addition of base appeared not to be necessary to obtain the desired product stereoselectively. Copyright © 2009 John Wiley & Sons, Ltd.