Exploring acetylene chemistry in superbasic media: A theoretical study of the effect of water on vinylation and ethynylation reactions with acetylene in KOH/DMSO and NaOH/DMSO systems

A rapidly developing approach adding new dimensions to acetylene chemistry relying on employment of high basicity media such as alkali metal hydroxide suspensions in dimethyl sulfoxide (DMSO) has been, for the first time, investigated theoretically using ab initio models. Extending our recently introduced model of superbase catalysis with a nondissociated KOH (or NaOH) participation, we present here a model for a superbasic reaction center with the first solvation shell explicitly included. The alkali metal hydroxides in a DMSO solution were found to form KOH·5DMSO and NaOH·4DMSO complexes that are stabilized due to the interligand interaction. Our present MP2/6‐311++G**//B3LYP/6‐31+G* computations show that 1 and 2 water molecules can build themselves into the MOH close surrounding without substantially perturbing the DMSO ligands and easily travel between different insertion positions. Our results predict that the activation energies in the series of reactions of nucleophilic addition to a triple bond with water, methanol, methanethiol, sodium hydrosulfide, and acetone in the presence of dihydrated complexes should be larger than those obtained with the participation of monohydrated ones, which is in fair agreement with the experimental findings. The present model also explains an increase in the ethynylation reaction yield in the presence of water by suppression of the competitive enolization reaction.     

A study on the phase transformation behaviour of Cu-20wt.Sn alloy produced using powder metallurgy method: Experimental and molecular dynamics modelling

In this study, Cu-20wt.Sn alloy was produced by powder metallurgy (PM) method by using high purity element powders. The phases in the microstructure of the produced alloy were determined by XRD study. The phase transformation behaviour of the alloy was investigated by DSC and modelling method. Moreover, the Cu-20wt.Sn alloy system was modelled with molecular dynamics (MD) simulation based on modified Embedded Atom Method (MEAM). The radial distribution function (RDF) was calculated to determine the structural properties of system during the phase transformations. The experimental results showed that the transformation ($\alpha +\delta$) → ($\alpha +\gamma$) occur at temperature above 500°C. The simulation results showed that the phase transformation $\alpha +\delta \to \alpha +\gamma$ occurs at 550°C temperature. Our simulation results are in reasonable agreement with the experimental data.     

Micro‐Raman and stratigraphic studies of the paintings on the ‘Cembalo’ model musical instrument (A.D. 1650) and laser‐induced degradation of the detected pigments

Micro‐fragments of the painted part of the ‘Cembalo’ model by Michele Todini (1625–1689) are investigated. The technique used for painting the terracotta base was studied via the stratigraphic analyses. No background layer of inorganic materials, e.g. gypsum, was found. To prevent absorption effects due to the terracotta porosity, a very thin layer of proteinaceous material was probably used. The micro‐Raman analyses have revealed the use of pigments currently used in the post‐Renaissance period (lead white, indigo, yellow of iron hydroxide, gypsum, hematite and carbon black) mixed with a pigment, the Prussian blue, discovered in A.D . 1704. This raises the authenticity problem of the work of art, a problem analysed and discussed in presenting the history of the work of art, and after the pigment study. The presence of degraded lead white is recognized via the laser‐induced degradation of the irradiated material. The possibility of a restoring action of the painted parts, as opposite to the non‐originality of the work, is considered and discussed. Since most part of the investigated pigments shows laser‐induced effects, a careful study of this phenomenon is performed by using the modern counterparts of the ancient pigments. For different laser powers, the temperatures of the investigated zones have been obtained via the detailed balance principle and connected to the laser‐induced degradation effects. Copyright © 2007 John Wiley & Sons, Ltd.     

The effect of benzo‐annelation on intermolecular hydrogen bond and proton transfer of 2‐methyl‐3‐hydroxy‐4(1H)‐quinolone in methanol: A TD‐DFT study

Excited‐state intermolecular or intramolecular proton transfer (ESIPT) reaction has important potential applications in biological probes. In this paper, the effect of benzo‐annelation on intermolecular hydrogen bond and proton transfer reaction of the 2‐methyl‐3‐hydroxy‐4(1H)‐quinolone (MQ) dye in methanol solvent is investigated by the density functional theory and time‐dependent density functional theory approaches. Both the primary structure parameters and infrared vibrational spectra analysis of MQ and its benzo‐analogue 2‐methyl‐3‐hydroxy‐4(1H)‐benzo‐quinolone (MBQ) show that the intermolecular hydrogen bond O₁―H₂?O₃ significantly strengthens in the excited state, whereas another intermolecular hydrogen bond O₃―H₄?O₅ weakens slightly. Simulated electron absorption and fluorescence spectra are agreement with the experimental data. The noncovalent interaction analysis displays that the intermolecular hydrogen bonds of MQ are obviously stronger than that of MBQ. Additionally, the energy profile analysis via the proton transfer reaction pathway illustrates that the ESIPT reaction of MBQ is relatively harder than that of MQ. Therefore, the effect of benzo‐annelation of the MQ dye weakens the intermolecular hydrogen bond and relatively inhibits the proton transfer reaction.     

The effect of the pH on the interaction of L‐arginine with colloidal silver nanoparticles. A Raman and SERS study

Raman and surface enhanced Raman scattering (SERS) spectroscopies were used to study the pH effect (7 to 9) on the interaction of arginine (Arg) with colloidal Ag nanoparticles (AgNps). A new methodology was implemented in order to obtain reproducible SERS spectra in solution. The dependence of the Arg concentration on the stability of the AgNps is discussed. A pH increasing of the colloidal solution to the limits of the Arg pKa₂ value induces a preferential and stable Arg–metal interaction. ξ potential measurements of the Arg–AgNps system at different pH conditions studied provide information about the Arg–AgNps interaction; the pH increasing favors the interaction. SERS spectra at pH 7 indicate that the molecule interacts with the Ag surface only through the guanidinium fragment. By increasing the pH to 9, the molecule adopts a new conformation on the surface; the metal–analyte interaction is verified through the guanidinium, carboxylate and the aliphatic moieties. In addition, theoretical calculations performed by using the extended Hückel method for a model of Arg interacting with an Ag surface support the observed SERS results. Copyright © 2013 John Wiley & Sons, Ltd.