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.     

Kernel Theorems for Modulation Spaces

Journal of Fourier Analysis and Applications - We deal with kernel theorems for modulation spaces. We completely characterize the continuity of a linear operator on the modulation spaces $$M^p$$...     

Gadolinium(III)-Based Dual 1H/19F Magnetic Resonance Imaging Probes

We present two novel octadentate cyclen-based ligands bearing one (L¹) or two (L²) phenylacetamide pendants with two CF₃ groups either at positions 3 and 5 (L¹) or 4 (L²). The corresponding Gd³⁺ complexes possess one coordinated water molecule, as confirmed by luminescence lifetime measurements on the Eu^III and Tb^III analogues. A detailed ¹H and ¹⁷O relaxometric characterization has revealed the parameters that govern the relaxivities of these complexes. The water-exchange rate of the mono-amide derivative GdL¹ (k_ex²⁹⁸=1.52×10⁶ s⁻¹) is faster than that determined for the bis-amide complex GdL² (k_ex²⁹⁸=0.73×10⁶ s⁻¹). ¹H and ¹⁹F NMR studies have indicated that the complexes are present in solution almost exclusively as the square-antiprismatic (SAP) isomers. ¹⁹F NMR relaxation studies indicated Gd ⋅⋅⋅ F distances of 7.4±0.1 and 9.1±0.1 Å for GdL¹ and GdL², respectively. Phantom MRI studies revealed the favorable properties of GdL² as a dual ¹H/¹⁹F magnetic resonance imaging (MRI) probe, whereas the shorter Gd ⋅⋅⋅ F distance of GdL¹ reduces the signal-to-noise ratio due to the very short transverse relaxation time of the ¹⁹F NMR signal.     

On general infinite dimensional complementarity problems

The aim of this paper is to present a way to study directly generalized complementarity problems in normed spaces. By means of new results on infinite dimensional Lagrange theory we show some optimality conditions which reduce the study of the problems to the one of suitable systems of equalities and inequalities.     

Synthesis of highly regioregular poly[3‐(4‐alkoxyphenyl)‐thiophene]s by oxidative catalysis using copper complexes

A novel, easy, and cost‐effective synthetic procedure is reported for the production of very highly regioregular poly[3‐(4‐alkoxyphenyl)thiophene]s by means of oxidative coupling. Four copper complexes were synthesized and used as catalysts to obtain polymers with higher regioregularity compared to the previous oxidative coupling methodologies reported in the literature and similar to that obtained by McCullough and Rieke methods in the synthesis of poly‐3‐alkylthiophenes. The regioregularity of the synthesized polymers was investigated by UV–Visible characterization on polymer thin films and ¹H NMR analysis. The remarkable potentialities of these polymers have emerged from field‐effect transistor mobility measurements operated on devices with bottom‐contact configuration and hexamethyldisilazane‐treated SiO₂ gate dielectric, showing a well‐defined p‐type field‐effect response and maximum mobility values in air higher than 10^?4 cm² V^?1 s^?1. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4351–4360