Palladium-catalyzed, stereoselective rearrangement of a tetracyclic allyl cyclopropane under arylation

The first example of a pi,sigma domino-Heck reaction under concomitant rearrangement of the tetracyclic allylcyclopropane endo,exo-bishomobarrelene (5) is reported; the stereoselective reaction proceeds via an intramolecular insertion of a primarily-formed carbopalladation intermediate into a strained cyclopropane C-C sigma-bond, giving 9.     

Core level photoemission study of Au deposited on Pt(111) in the submonolayer range

A photoemission study, using a synchrotron source, on the deposition of submonolayer amounts of Au on Pt(111) has been performed. The Au 4f emission shifts continuously to higher binding energies for increasing Au coverages. A good fit to the experimental spectra has been obtained by only one Doniac-Sunjic function. We discuss the initial versus final state effects in photoemission experiments on small supported particles.     

Growth atomic mechanisms of pulsed laser deposited La modified- $\mathsf{PbTiO_3}$ perovskites

The microstructure and morphology of 100/001-oriented La modified-PbTiO₃ (PLT) films grown by pulsed laser deposition have been analyzed and elucidated within the framework of morphology evolution models, such as the Dynamic Scaling Theory and Structure Zone Model. The experimental results were obtained from X-ray diffraction, atomic force microscopy and cross-section scanning electron microscopy. PLT grows with a compact columnar microstructure. The columns are formed by coherently grouped grains and show oblique walls and rounded tops. Connecting the experimental results with the morphology evolution models, the growth mechanisms involved in the deposition process were identified. While inside each column, the existing Pb vacancies govern the coarsening and coalescence of the grains, a non-local effect of geometric shadowing of the incident particle flux during growth controls competition between columns and their coarsening.Received: 18 June 2003, Published online: 22 September 2003PACS: 68.55.-a Thin film structure and morphology - 81.15.Fg Laser deposition - 77.84.Dy Niobates, titanates, tantalates, PZT ceramics, etc.E. Vasco: Current address: Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich, GermanyC. Polop: Current address: I. Physikalisches Institut, RWTH-Aachen, 52056 Aachen, Germany     

Strong water-mediated friction asymmetry and surface dynamics of zwitterionic solids at ambient conditions: L-alanine as a case study

Water molecules strongly interact with freshly cleaved (011) surfaces of L-alanine single crystals at low relative humidity (below 10%) promoting diffusion of L-alanine molecules. Species mobility is enhanced above ~40% leading to the formation of two-dimensional islands with long-range order through Ostwald ripening. Scanning force microscopy experiments reveal that both, islands and terraces, are identical in nature (composition and crystallographic structure) but a relevant friction asymmetry appearing upon water-surface interaction evidences that orientation dependent properties exist between them at the molecular level. We interpret this observation as due to water incorporation in the topmost surface crystal structure. Eventually, for high humidity values, surface dissolution and roughening occur.     

Real time scanning force microscopy observation of a structural phase transition in self-assembled alkanethiols

We present here a new approach based on high resolution scanning force microscopy that permits molecular determination and frictional discrimination between coexisting molecular configurations of alkanethiols on Au(111). The method has allowed visualizing in real time a phase transition between two differently ordered self-assembled configurations, which spontaneously takes place with time at constant coverage and under ambient conditions. Frictional force measurements indicate that the molecular rearrangement observed occurs via an order-disorder-order process.     

New insights in the c(4 x 2) reconstruction of hexadecanethiol on Au(111) revealed by grazing incidence X-ray diffraction

The c(4 x 2) structure of C16H33SH alkanethiol monolayers self-assembled on Au(111) has been studied by grazing incidence X-ray diffraction. This structure coexists on the surface with the (radical3x radical3)R30 degrees phase. The structural refinement of the c(4 x 2) phase has been accomplished by omitting the fractional order reflections common to both structures. The surface unit cell consists of four symmetry-independent molecules with atomic displacements related by couples, such that only two nonequivalent chains are present in the surface cell. The stability between neighbor chains is due to van der Waals interactions. The substrate plays an important and non-negligible role in the c(4 x 2) reconstruction. The lateral and normal substrate relaxations to the surface plane are small, and gold atom displacements are lower than 0.25 angstroms but contribute very strongly to the fractional order intensities. The molecular chains form a close packed structure tilted by 37 degrees from the surface normal with no indications of dimer formation between closest S atoms.     

Study of nanoconductive and magnetic properties of nanostructured iron films prepared by sputtering at very low temperatures

A combined study of the surface nanostructure and electrical characteristics of iron thin films prepared on naturally passivated silicon wafers is presented. By means of conductive-scanning force microscopy, the influence of the substrate temperature during film preparation on both surface morphology and conductivity response is investigated. In addition, magnetic properties of these films are reported and correlated with the nanostructural properties. Films prepared at 200 K show granular core–shell magnetic behaviour exhibiting exchange bias. Both conductive and magnetic data indicate that samples prepared at low temperature behave as a percolated network of nanometric metallic iron clusters (with typical sizes of 20 nm) interconnected by oxidized chains (of 10 nm in diameter), showing an excellent system for nanotechnological exchange bias applications.     

Synthesis,Spectroscopic, and Dyeing Properties of New Azo and Bisazo Dyes Derived from 5‐Pyrazolones

This study is in continuation of our work related to 5‐pyrazolones aimed at synthesizing new heterocycles with dyeing and anticipated biological properties. Compounds 1 and 2 ; 1‐methyl‐ or 1‐(2,4‐dimethylphenyl)‐3‐phenyl‐1H‐pyrazol‐5(4H)‐one, 3 ; 1‐methyl‐5‐oxo‐3‐phenyl‐4,5‐dihydro‐1H‐pyrazole‐4‐carbaldehyde and 4 ; 2‐(1‐methyl‐5‐oxo‐3‐phenyl‐1H‐pyrazol‐4(5H)‐ylidene)‐3‐phenylthiazolidin‐5‐one were prepared and subjected to diazotation with aromatic amines and diamines. New azo ( 1a – c , 2a, b , 3a , b , 4a , c ) and bisazo dyes ( 2c , d , 4b ) were obtained, and their structures were confirmed by spectroscopic and analytical methods. In addition, UV–vis measurements, dyeing performance, and fastness tests were carried out for all compounds.     

Synthesis of new aryl(hetaryl)-substituted tandospirone analogues with potential anxiolytic activity via reductive Heck type hydroarylations

Tandospirone (I), developed as an anxiolytic drug, is an aryl-piperazine compound that binds to both 5-HT_1A and dopamine D4 receptors. Palladium-catalysed hydroarylation reactions of tandospirone analogues containing an oxygen bridge and 3-(trifluoromethyl)phenyl or 2,3-dichlorophenyl groups were studied in order to find a new stereoselective access to a series of new exo-aryl(hetaryl)-substituted derivatives with potential biological activity.