Photomodulated molecular recognition of the guanidinium cation

Azobenzene moieties were incorporated into a synthetic receptor allowing its affinity for the guanidinium cation to be modulated ten-fold by photoirradiation and/or heating.     

Room temperature migration of boron in crystalline silicon

We demonstrate that substitutional B in silicon can migrate even at room temperature and below, stimulated by a high interstitial flux. Once mobile B is formed, it migrates for long distances with a diffusivity >5 x 10(-13) cm(2)/s, until it assumes an immobile configuration with a migration length independent of the temperature. This phenomenon is present during secondary ion mass spectrometry (SIMS) analyses of B profiles, altering the profile during the analysis itself. These results shed new light on all the data based on SIMS analyses and reported in literature in the last decades.     

The role of intermolecular and molecule-substrate interactions in the stability of alkanethiol nonsaturated phases on Au(111)

The structure and stability of alkanethiols self-assembled on Au(111) have been studied as a function of the molecular chain length by means of atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXD). Below saturation, phases consisting of molecules with different tilt angles and periodicities are formed. Differences in the mechanical stability of these phases are revealed by AFM experiments and discussed in terms of the competition between intermolecular and molecule-substrate interactions as a function of chain length. For long molecules, intermolecular interactions play a dominant role which stabilizes the formation of closed packed 30 degrees tilted ( radical 3x radical 3)R30 degrees structures. For short molecules, the van der Waals interaction with the gold substrate favors the formation of a 50 degrees tilted phase in which the molecules are arranged in a rectangular configuration.     

Excitable optical waves in semiconductor microcavities

We demonstrate experimentally and theoretically the existence of excitable optical waves in semiconductor microcavities. Although similar to those observed in biological and chemical systems, these excitable optical waves are self-confined. This is due to a new dynamical scenario, where a stationary Turning pattern controls the propagation of waves in an excitable medium, thus bringing together the two paradigms of dynamical behavior (waves and patterns) in active media.     

Unexpected coupling between an eta5-indenyl ligand and alkenyl-vinylidene fragments: synthesis of unprecedented (eta6-indene)ruthenium(II) metallacycles

Vinylidene complexes [Ru[=C=C(H)CR1R2CH2C(Me)=CH2](eta5-C9H7)(PPh3)2][BF4] undergo an intramolecular coupling between the alkenyl-vinylidene fragment and the eta5-indenyl ligand to afford indene-metallacyclic compounds (6a,b) in which the resulting functionalised indene group is eta6-coordinated to the metal.     

New building blocks for the assembly of sequence selective molecular zippers

Synthetic H-bonded molecular zippers contain no sequence information that can be used to engineer the selective binding interactions characteristic of biopolymers; reversing the sense of the amide bonds in the two binding partners generates a new orthogonal recognition motif and the mutually complementary binding partners form complexes an order of magnitude more stable than the corresponding mismatch complexes.     

Use of combinatorial chemistry to develop photocurable thermoplastic polyurethane elastomers (TPUs)

Combinatorial chemistry was used to develop photocurable thermoplastic polyurethane elastomers through the incorporation of photoreactive diacetylene diols as chain extenders. The methodology applied allowed, in 36 experiments, the choice of the best compromise between mechanical properties and lack of colour. The combinations chosen were scaled up and their properties were evaluated in terms of mechanical properties. The combinatorial approach reduced the estimated time tenfold in developing such type of materials.     

Microwave muffle furnace assisted decomposition of vegetable samples for flame atomic spectrometric determination of Ca, Mg, K, Fe, Mn and Zn

Summary Calcium, magnesium, potassium, iron, manganese and zinc can be accurately determined in vegetable samples by flame atomic absorption and flame emission spectrophotometry after a previous dry ashing of the sample in a microwave muffle furnace. This treatment is carried out in 45 min using a new accessory developed by us to obtain high temperatures on a domestic microwave oven. Sample ashes, obtained in the muffle, are diluted with nitric acid and the obtained slurry is introduced directly into an air-C₂H₂ flame for the analysis of Fe, Mn, and Zn, or injected into a double-channel FIA manifold to determine Ca, Mg and K. The obtained results agree with those certified and also with those obtained by a previous dry ashing in a conventional muffle furnace and they are more precise for all the determined elements.Presented at the XXVII CSI in Bergen (Norway), June 1991