Cell-penetrating γ-peptide/antimicrobial undecapeptide conjugates with anticancer activity

In this study, we combined a cell-penetrating γ-peptide, PEG-1, with antimicrobial undecapeptides in order to provide compounds with anticancer properties against MDA-MB-231 human breast cancer cells. We demonstrated that the conjugates were more cytotoxic than Ac-PEG-1 and the parent undecapeptides. We also evaluated the toxicity of the conjugates against non-malignant cells. The peptide conjugate with the best biological profile was BP77-PEG-1, which, at 10 μM, showed a 71% growth inhibition in MDA-MB-231 cells and only a 17% inhibition in non-malignant cells. Therefore, this study suggests that PEG-1 mediated the undecapeptide delivery into cancer cells and that these conjugates are the proof-of-concept of this strategy to generate improved anticancer drugs based on peptides.     

Temperature effects on platinum single-crystal electrodes

This work reviews three different approaches for the study of temperature effects on the platinum single-crystal | solution interphase. First, the method of analysis of temperature-dependent voltammetric data with the help of a generalized isotherm is described and illustrated for the case of adsorbed hydrogen and OH species on Pt(111) in 0.1 M HClO₄. This method of analysis allows a detailed evaluation of the thermodynamic data of charge-transfer adsorbed species, namely, the standard molar Gibbs energy, enthalpy and entropy of adsorption and the magnitude of the lateral interaction between adsorbed species. However, a number of assumptions are involved in the application of a generalized isotherm, namely, the assumption of a Langmuirian configurational term and an arbitrary separation of capacitive and faradaic processes. The second approach described here overcomes these assumptions, since it employs Gibbs thermodynamic equations for interphaces to describe temperature effects on electrosorption processes including those in which charge-transfer is allowed. This approach allows evaluation of the entropy of formation of the interphase, being defined as the difference in entropy of the components of the interphase when they are forming it and when they are in the bulk phases. This method of analysis is illustrated through the evaluation of the entropy of formation of the interphase for Pt(111) in 0.1 M HClO₄. Finally, it is shown that temperature effects on interfacial processes can also be studied by means of the application of a fast temperature perturbation. This approach opens the possibility to separate the effect of temperature on the different components of the interphase. The fast temperature perturbation is usually achieved with short laser pulses, and hence the method is called the laser-induced temperature jump method. This approach is illustrated here for the case of Pt(111) in 1 mM HClO₄ + 0.1 M KClO₄, and it is shown that the corresponding laser-induced transients provide direct evidence on the reorientation of the interfacial water network.     

Highly Modular P?OP Ligands for Asymmetric Hydrogenation: Synthesis,Catalytic Activity,and Mechanism

A library of enantiomerically pure P? OP ligands (phosphine–phosphite), straightforwardly available in two synthetic steps from enantiopure Sharpless epoxy ethers is reported. Both the alkyloxy and phosphite groups can be optimized for maximum enantioselectivity and catalytic activity. Their excellent performance in the Rh‐catalyzed asymmetric hydrogenation of a wide variety of functionalized alkenes (26 examples) and modular design makes them attractive for future applications. The lead catalyst incorporates an (S)‐BINOL‐derived (BINOL=1,1′‐bi‐2‐naphthol) phosphite group with computational studies revealing that this moiety has a dual effect on the behavior of our P? OP ligands. On one hand, the electronic properties of phosphite hinder the binding and reaction of the substrate in two out of the four possible manifolds. On the other hand, the steric effects of the BINOL allow for discrimination between the two remaining manifolds, thereby elucidating the high efficiency of these catalysts.     

Proton abstraction mechanism for the palladium-catalyzed intramolecular arylation

Under the usual conditions, the Pd-catalyzed arylation does not involve an electrophilic aromatic substitution reaction. On the basis of DFT calculations, we propose a mechanism for the Pd-catalyzed arylation that involves a proton abstraction by a carbonate or related ligand and that provides a satisfactory explanation for the experimental data.     

Influence of alloying elements and etching treatment on the passivating films formed on aluminium alloys

This paper studies the characteristics of aluminium oxide layers present on the surface of commercial aluminium specimens after thermomechanical processing and after subsequent etching in an alkaline solution, highlighting the main differences observed. An attempt is made to establish possible relationships between alloying elements and the characteristics of these layers. Copyright © 2006 John Wiley & Sons, Ltd.     

Spectroscopic Study of Egyptian Blue Mixed with Other Pigments

The Romans used a vast array of colors in their mural paints. The applied pigment mixtures containing Egyptian blue resulting in green, ochre, brown, gray, and white hues were studied. The chromatic characterization of wall paintings by electronic spectroscopy provided an easy and reliable procedure for the grouping of the samples to be studied (see Table). Subsequent use of other spectroscopic techniques such as Fourier‐transform (FT) IR and energy‐dispersive X‐ray spectroscopy (EDS), combined with X‐ray diffraction (XRD), led to convenient identification of the pictorial layer components that define and differentiate each chromatic group. Colors impossible to produce with only one pigment can be obtained by mixing Egyptian blue with other pigments. The dominant wavelength is displaced in such way that the artist obtains new tonalities.     

Reaction of Alkynes and Azides: Not Triazoles Through Copper–Acetylides but Oxazoles Through Copper–Nitrene Intermediates

Well‐defined copper(I) complexes of composition [Tpm*^,BrCu(NCMe)]BF₄ (Tpm*^,Br=tris(3,5‐dimethyl‐4‐bromo‐pyrazolyl)methane) or [Tpa^*Cu]PF₆ (Tpa^*=tris(3,5‐dimethyl‐pyrazolylmethyl)amine) catalyze the formation of 2,5‐disubstituted oxazoles from carbonyl azides and terminal alkynes in a direct manner. This process represents a novel procedure for the synthesis of this valuable heterocycle from readily available starting materials, leading exclusively to the 2,5‐isomer, attesting to a completely regioselective transformation. Experimental evidence and computational studies have allowed the proposal of a reaction mechanism based on the initial formation of a copper–acyl nitrene species, in contrast to the well‐known mechanism for the copper‐catalyzed alkyne and azide cycloaddition reactions (CuAAC) that is triggered by the formation of a copper–acetylide complex.     

An Unusual Example of Hypervalent Silicon: A Five‐Coordinate Silyl Group Bridging Two Palladium or Nickel Centers through a Nonsymmetrical Four‐Center Two‐Electron Bond

Pd and Ni dimers supported by PSiP ligands in which two hypervalent five‐coordinate Si atoms bridge the two metal centers are reported. Crystallographic characterization revealed a rare square‐pyramidal geometry at Si and an unusual asymmetric M₂Si₂ core (M=Pd or Ni). DFT calculations showed that the unusual structure of the core is also found in a model in which the phosphine and Si centers are not part of a pincer group, thus indicating that the observed geometry is not imposed by the PSiP ligand. NBO analysis showed that an asymmetric four‐center two‐electron (4c‐2e) bond stabilizes the hypervalent Si atoms in the M₂Si₂ core.     

State of the art in the electrochemical characterization of the surface structure of shape-controlled Pt,Au, and Pd nanoparticles

The application of shape-controlled metal nanoparticles in electrocatalysis has improved significantly the activity, selectivity, and even the stability of many relevant electrocatalytic reactions. It is well accepted that, by controlling the shape of the nanoparticles, it is possible to provide nanoparticles with a preferential surface structure. However, to fully understand the capabilities of these nanomaterials, it is extremely relevant to correlate shape, surface structure, and electrocatalytic reactivity. Particularly, establishing the correlations between surface structure and reactivity is the key point to be studied and understood. Consequently, having tools to characterize the surface structure of these nanoparticles is of critical importance. In this short review, we discuss about the progress in the in situ characterization of the surface structure of shaped Pt, Au, and Pd nanoparticles by electrochemical probes. The results here included clearly demonstrate the potentialities of the electrochemical tools to gain detailed information of the surface structure of these shaped nanomaterials.     

DFT characterization of the mechanism for Staudinger/aza-Wittig tandem organocatalysis

A computational simulation with DFT calculations and microkinetic modeling is carried out on a complete catalytic cycle, involving Staudinger ligation, aza-Wittig condensation and phosphine oxide recycle, for non-truncated substrates and catalyst. The Staudinger reaction produces phosphazenes (R₃P?=?NR), also known as iminophosphoranes, from phosphines and organic azides. Electrophilic carbonyl groups react with phospazenes to produce imines and phosphine oxides. Recently the Staudinger reaction and the aza-Wittig condensation have been combined to spawn intramolecular tandems producing cyclic molecules of great pharmaceutical interest (e.g. benzoxazoles). The release of diatomic nitrogen combined with the formation of phosphine oxide represents the driving force of the reaction. The implementation of in situ recycling of the exhausted phosphine oxide into the Staudinger/aza-Wittig tandem improves the scopes and the applicability of the reaction, transforming it into a powerful and versatile synthetic tool.