The impact of polystyrene resins in solid-phase organic synthesis

Summary A major objective of the DIVERSOMER^® technology is to provide pure and characterized compounds for biological testing in order to prevent false negatives in our libraries. On several occasions, analysis of the final products by¹H-NMR and MS, has revealed by-products from the polystyrene solid support. Subsequently, three alternative methods were studied to remove polystyrene by-products; (i) prewashing of the resin prior to execution of the synthesis; (ii) pretreatment of the resin with the cleavage conditions consistent with the solid-phase synthesis reaction scheme; and (iii) parallel purification.     

Abelian Ward identity from the background field dependence of the effective action

The dependence of the effective action for gauge theories on the background field obeys an exact identity. We show that for Abelian theories the Ward identity follows from the more general background field identity. This observation is relevant for the formulation of effective actions with an infrared cutoff since the solution of exact flow equations must obey an anomalous Ward identity.     

Nanoscale interaction mechanism between a solid tip and a layered material while in relative motion: the boric acid case

The interaction occurring between a layered material (boric acid) and an atomic force microscope tip is discussed. It is shown that images containing the periodicity of a boric acid crystal, and the low friction occurring between the tip and the crystal surface, are caused by an effective tip composed of boric acid molecules. The friction at the sliding system decreases with an increase of the scanning velocity, suggesting that the dependence of friction on the velocity can be caused by a change of the energy dissipation regime from the nonlinear dynamics of a sliding system to phonon excitation.     

Persistence of the Feigenbaum Attractor in One-Parameter Families

Consider a map ψ₀ of class C ^r for large r of a manifold of dimension n greater than or equal to 2 having a Feigenbaum attractor. We prove that any such ψ₀ is a point of a local codimension-one manifold of C ^r transformations also exhibiting Feigenbaum attractors. In particular, the attractor persists when perturbing a one-parameter family transversal to that manifold at ψ₀. We also construct such a transversal family for any given ψ₀, and apply this construction to prove a conjecture by J. Palis stating that a map exhibiting a Feigenbaum attractor can be perturbed to obtain homoclinic tangencies. Received: 4 August 1998 / Accepted: 11 May 1999     

Raman spectroscopic characterization of a thiophene‐based active material for resistive organic nonvolatile memories

A combined theoretical and experimental Raman study is presented on a diphenyl bithiophene molecule known as a good candidate for the development of organic nonvolatile memory devices. Spectroscopic markers suitable to distinguish the different stable conformers of the molecule have been predicted and detected. The combined analysis of theoretical and experimental Raman spectra recorded in solution indicates that at room temperature a dynamical equilibrium, characterized by interconversion between the two more stable conformers (namely trans and cis), takes place and that the more populated species is the cis form. Referring to the solid phase instead, Raman spectra of single‐crystal samples show the presence of the only trans conformer, as confirmed by X‐ray measurements. Finally, Raman spectra of thin films, as those used for the memory device, were collected; samples just deposited from solution and after few hours from the deposition were analyzed. Following the evolution of selective spectroscopic Raman markers, an isomerization process from the abundant cis (as‐deposited) to the totally trans (after few hours) conformer in the solid phase was detected. These results open the way to the identification of the molecular isomers present in the thin film of the memory cell and finally of the active molecular species involved in the switching mechanism of the operating device. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of Al(III) complexes with hematein in artistic alum logwood inks

The complexes between Al(III) and hematein, the main coloring matter in alum logwood inks, were characterized by Raman and ²⁷Al NMR (nuclear magnetic resonance) spectroscopies. Raman spectra of the crystallized complexes and of the compounds applied on a paper substrate are presented and assigned based on published data for the parent compounds. These Raman spectra show that the coordination of the hematein to the Al(III) ions takes place in both cases through the carbonyl and hydroxyl groups in the molecule, and that the aromatic rings are also involved in the interaction. The Raman spectra of the pure hematein–Al(III) complexes were found to be consistent with those recorded for a logwood ink prepared following a late 19th century recipe, using logwood chips instead of pure hematein, and applied on a paper substrate. These spectra can be used as references for the noninvasive identification of the compounds in works of art. ²⁷Al solid‐state NMR showed that the coordination of the Al(III) atoms in the crystallized powder is predominantly octahedral, while when applied on a paper substrate the colorant is present mainly as a tetrahedral complex, with an octahedral coordination also present in a smaller proportion. The fact that the predominant coordinations for the complexes in the crystallized material and for the ones present on the paper substrate are different is relevant for the study of the lightfastness and thermal stability of works of art bearing these media. Copyright © 2009 John Wiley & Sons, Ltd.     

Ultrastructural analysis of midgut cells from Culex quinquefasciatus (Diptera: Culicidae) larvae resistant to Bacillus sphaericus

The larvicidal action of the entomopathogen Bacillus sphaericus towards Culex quinquefasciatus is due to the binary (Bin) toxin present in crystals, which are produced during bacterial sporulation. The Bin toxin needs to recognize and bind specifically to a single class of receptors, named Cqm1, which are 60-kDa α-glucosidases attached to the apical membrane of midgut cells by a glycosylphosphatidylinositol anchor. C. quinquefasciatus resistance to B. sphaericus has been often associated with the absence of the α-glucosidase Cqm1 in larvae midgut microvilli. In this work, we aimed to investigate, at the ultrastructural level, the midgut cells from C. quinquefasciatus larvae whose resistance relies on the lack of the Cqm1 receptor. The morphological analysis showed that midgut columnar cells from the resistant larvae are characterized by a pronounced production of lipid inclusions, throughout the 4th instar. At the end of this stage, resistant larvae had an increased size and number of these inclusions in the midgut cells, while only a small number were observed in the cells from susceptible larvae. The morphological differences in the midgut cells of resistant larvae found in this work suggested that the lack of the Cqm1 receptor, which also has a physiological role as being an α-glucosidase, can be related to changes in the cell metabolism. The ultrastructural effects of Bin toxin on midgut epithelial cells from susceptible and resistant larvae were also investigated. The cytopathological alterations observed in susceptible larvae treated with a lethal concentration of toxin included breakdown of the endoplasmic reticulum, mitochondrial swelling, microvillar disruption and vacuolization. Some effects were observed in cells from resistant larvae, although those alterations did not lead to larval death, indicating that the receptor Cqm1 is essential to mediate the larvicidal action of the toxin.This is the first ultrastructural study to show differences in the cell morphology of resistant larvae and further investigation is needed to understand the impact of the lack of expression of midgut enzymes on the physiology of resistant insects.     

The unbearable heaviness of colloids: facts, surprises, and puzzles in sedimentation

Sedimentation has played a key role in the development of colloid science. In fact, it is because of the celebrated experiments by Perrin, yielding a concrete demonstration of molecular reality and giving strong support to Einstein's theory of Brownian motion, that colloids enter the realm of basic physics. Subsequent investigations have shown that a lot more can be learnt both from sedimentation equilibrium and from particle settling dynamics. These advances, together with new experimental approaches, will be reviewed in this paper. Yet, we shall also show that inquiring about gravity settling is far from being a closed matter: for instance, the concept of buoyancy for a settling colloidal mixture is far from being obvious. Moreover, sedimentation holds novel surprises, such as colloidal inflations and settling disasters, showing that a simple external field like gravity may induce mind-boggling, and theoretically challenging effects.     

The Tausk Controversy on the Foundations of Quantum Mechanics: Physics, Philosophy, and Politics

In 1966 the Brazilian physicist Klaus Tausk (b. 1927) circulated a preprint from the International Centre for Theoretical Physics in Trieste, Italy, criticizing Adriana Daneri,Angelo Loinger,and Giovanni Maria Prosperi’s theory of 1962 on the measurement problem in quantum mechanics. A heated controversy ensued between two opposing camps within the orthodox interpretation of quantum theory, represented by Léon Rosenfeld and Eugene P.Wigner. The controversy went well beyond the strictly scientific issues, however, reflecting philosophical and political commitments within the context of the Cold War, the relationship between science in developed and Third World countries, the importance of social skills, and personal idiosyncrasies.