Convenient preparation of (η-alkadiene)dichloroplatinum(II) complexes from [PtCl6] anions and their reduction to platinum(0) alkene complexes under phase-transfer catalysis conditions

Convenient one-pot reduction-complexation reactions of hexachloroplatinato(IV) anions to (η⁴-alkadiene)dichloroplatinum(II) complexes (η⁴-alkadiene = COD, DAE, DCPD, NBD) under suitable phase-transfer catalysis conditions are reported. Reduction to zerovalent platinum alkene complexes has been obtained in the presence of an excess of alkene, potassium formate and 18-crown-6 as phase-transfer catalyst (alkene = COD, NB, dba). The crystal and molecular structure of [Pt_1.03(dba)₃]·CH₂Cl₂ has been studied by X-ray diffraction methods: it can be described as a solid solution of Pt(dba)₃ and Pt₂(dba)₃, the mononuclear complex being largely prevailing.     

Host–guest interactions and their role in enantioselective hydrogenation of α-keto esters: An analysis of model systems

The interaction between cinchonidine and methyl pyruvate has been proposed as the key step leading to enantiodifferentiation in the enantioselective hydrogenation of α-ketoesters. In the present work, we employ ab initio MP2/6-31G(d) and MP2/6-31G(d,p) methods to carry out an analysis of the most relevant kind of interactions operating in representative model systems. These interactions are discussed in terms of orbital superposition and dipolar interaction. When approaching H₂CO to NH₃ at distances lower than 3.4 Å, orbital superposition is the predominant interaction, while at distances above 3.4 Å, both orbital superposition and dipolar interactions may contribute to stabilization, with a small prevalence of dipolar interactions. The stabilization energy at large distances (above 4.5 Å) is very small (about 0.5 kcal mol⁻¹), probably not enough to be responsible for the enantiodifferentiation process. Semiempirical calculations on the parent systems were also unable to reveal any special interaction which could be attributed to the enantiodifferentiation process.     

A mathematical model of “Gone with the Wind”

We develop a mathematical model for mimicking the love story between Scarlett and Rhett described in “Gone with the Wind”. In line with tradition in classical physics, the model is composed of two Ordinary Differential Equations, one for Scarlett and one for Rhett, which encapsulate their main psycho-physical characteristics. The two lovers are described as so-called insecure individuals because they respond very strongly to small involvements of the partner but then attenuate their reaction when the pressure exerted by the partner becomes too high. These characteristics of Scarlett and Rhett clearly emerge during the first part of the film and are sufficient to develop a model that perfectly predicts the complex evolution and the dramatic end of the love story. Since the predicted evolution of the romantic relationship is a direct consequence of the characters of the two individuals, the agreement between the model and the film supports the high credibility of the story. Although credibility of a fictitious story is not necessary from a purely artistic point of view, in most cases it is very appreciated, at the point of being essential in making the film popular. In conclusion, we can say that we have explained with a scientific approach why “Gone with the Wind” has become one of the most successful films of all times.     

Solvent suppression in solid-state DNP NMR using Electronic Mixing-Mediated Annihilation (EMMA)

We show here that the Electronic Mixing-Mediated Annihilation (EMMA) method, previously reported for the suppression of background signals in solid-state nuclear magnetic resonance spectra, can be successfully applied to remove the solvent signals observed in the case of nuclear magnetic resonance spectra obtained with dynamic nuclear polarization. The methodology presented here is applied to two standard sample preparation methods for dynamic nuclear polarization, namely, glass forming and incipient wetness impregnation. It is demonstrated that the Electronic Mixing-Mediated Annihilation method is complementary to the different methods for solvent suppression based on relaxation filters and that it can be used to preserve the quantitative information that might be present in the pristine spectra.     

A simple methodology for the determination of fatty acid composition in edible oils through 1H NMR spectroscopy

A simple methodology for the determination of the fatty acid composition of edible oils through ¹H NMR is proposed. The method is based on the fact that all fatty acid chains are esterified to a common moiety, glycerol, and the quantification is done directly in the ¹H NMR spectra through the relationship between the areas of a characteristic signal of each fatty acid and a signal of the glycerol moiety, without the use of mathematical equations. The methodology was successfully applied to determine the fatty acid composition of several edible oils, with equivalent results to those given by the AOAC Official method by gas chromatography. Its main advantages are simplicity and the lack of need for sample pre‐treatment such as derivatization or extraction. Copyright © 2010 John Wiley & Sons, Ltd.     

Composite PEDOT/Au Nanoparticles Modified Electrodes for Determination of Mercury at Trace Levels by Anodic Stripping Voltammetry

Electrode modifications consisting of poly(3,4‐ethylenedioxythiophene) (PEDOT), including gold nanoparticles according to simple though innovative procedure, are developed. The resulting nanocomposite shows interesting performances as electrode material for determination of mercury by anodic stripping technique, even down to concentration levels as low as 0.83 ng/mL. The analytical performance is evaluated by optimized experimental parameters such as the charge spent during the potentiostatic electrodeposition of PEDOT, the preconcentration time, and the waveform parameters for the differential pulse voltammetry (DPV) redissolution scan. No evidence of significant oxidative degradation of the polymer over repeated analysis cycles is evidenced.     

Stochastic Precedence and Minima Among Dependent Variables

Methodology and Computing in Applied Probability - The notion of stochastic precedence between two random variables emerges as a relevant concept in several fields of applied probability. When one...     

Metalinsulator transition induced by pressure in chemically bonded solids

Abstract

A review is given of metal-insulator transitions induced by pressure in chemically bonded solids.

After an introduction to energy band overlap mechanisms, which appear very useful to characterize the insulator-metal transitions in some solids (the rare gases He and Xe, the iso-electronic sequence of Xe, H₂ and I₂), some discussion is given of electron correlation in relation to molecular dissociation. However, it is to be emphasized that such dissociation is a sufficient, but not a necessary, condition for metallization in H. and I₂. For N₂, the above considerations, which focussed dominantly on ground-state properties as a function of pressure, need transcending because the observation of metallization in this system plainly involves thermal effects in an important way.

The final part of the review considers the way various low-dimensional solids (polyacetylene, TTF-TCNQ, and appropriate phases of H₂ and I₂) are altered by application of high pressures. Present understanding leads to the conclusion that there should be an interesting interplay between Hubbard on-site electron correlation, bond-charge repulsion and near-neighbour interaction, as a function of thermodynamic state.