Size Determination of Porosity Inclusions in an Organic Solid Material by (1)H NMR Diffusion and SEM-FIB Experiments: The TATB Case.

An original approach has been presented to characterize the local geometry of pores containing protonated small molecule impurities in organic materials. It was here applied in TATB (1,3,5-triamino-2,4,6-trinitrobenzene) powder material to investigate the porosity able to enclose water molecules. The presence of such defects may have a significant impact on TATB-based compositions mechanical properties, efficiency, and shock sensitivity.

Electrochemical detection of nitromethane vapors combined with a solubilization device.

During the past decade, the number of terrorism acts has increased and the need for efficient explosive detectors has become an urgent worldwide necessity. A prototype, Nebulex™, was recently developed in our laboratory. Basically, it couples the solubilization of an analyte from the atmosphere by a nebulization process and in-situ detection.

Olfactory foraging in temperate waters: sensitivity to dimethylsulphide of shearwaters in the Atlantic Ocean and Mediterranean Sea.

Many procellariiforms use olfactory cues to locate food patches over the seemingly featureless ocean surface. In particular, some of them are able to detect and are attracted by dimethylsulphide (DMS), a volatile compound naturally occurring over worldwide oceans in correspondence with productive feeding areas. However, current knowledge is restricted to sub-Antarctic species and to only one study realized under natural conditions at sea.

A simple thermodynamic approach to predict responses from polymer-coated quartz crystal microbalance sensors exposed to organic vapors.

As of lately, the demand for developing artificial sensors with improved capabilities for the detection of explosives, toxics or drugs has increased. Ideally, sensor devices should provide high sensitivity and give a response that is specific to a given target molecule without being influenced by possible interfering molecules in the atmosphere. These properties strongly depend on the structure of the chemical compound used as a sensitive material.

Sensitivity improvement of 1H-15N cross-polarization at high MAS frequency applied to NMR structural characterization of organic solids.

(15)N CP/MAS solid state NMR should be a method of choice to obtain essential structural information on organic materials containing nitrogen atoms. However, the technique is generally not selected for the characterization of non-labelled chemical compounds, which represents the most common situation encountered by chemists. Actually, due to the poor sensitivity of (15)N the method is time-consuming and a very fine calibration is often a prerequisite to reach a sufficient signal/noise.

Weak molecular associations investigated by 1H-NMR spectroscopy on a neat organosiloxane-solvent mixture.

The rational design of new sensitive materials for chemical sensors relies on the knowledge of molecular interactions between the chemical species in question with compounds that may potentially be present in the gas phase. In this context, the intermolecular interactions between a family of functionalized polysiloxanes and a series of organic compounds have been investigated. This work addresses the problem of determining the association constant or energy by studying neat liquid mixtures without solvents.

Chemical kin label in seabirds.

Chemical signals yield critical socio-ecological information in many animals, such as species, identity, social status or sex, but have been poorly investigated in birds. Recent results showed that chemical signals are used to recognize their nest and partner by some petrel seabirds whose olfactory anatomy is well developed and which possess a life-history propitious to olfactory-mediated behaviours. Here, we investigate whether blue petrels (Halobaena caerulea) produce some chemical labels potentially involved in kin recognition and inbreeding avoidance.

Design of interpenetrated networks of mesostructured hybrid silica and nonconductive poly(vinylidene fluoride)-cohexafluoropropylene (PVdF-HFP) polymer for proton exchange membrane fuel cell applications.

Organic-inorganic hybrid membranes of poly(vinylidene fluoride)-cohexafluoropropylene (PVdF-HFP) and mesostructured silica containing sulfonic acid groups were synthesized by using the sol-gel process. These hybrid membranes were prepared by in situ co-condensation of tetraethoxysilane and an organically modified silane (ormosil) by a self-assembly route using organic surfactants as templates for tuning the architecture of the hybrid organosilica component. In this paper, we describe the elaboration and characterization of hybrid membranes all the way from the precursor solution to the evaluation of the fuel cell performances.

(1)H, (13)C and (15)N NMR spectral assignments for new triazapentalene derivatives.

Mesomeric heteropentalene betaines are conjugated fused polyheterocyclic structures that represent interesting intermediates for organic synthesis. Five such structures, containing at least four nitrogen atoms and various substituents, have been characterized by (1)H, (13)C and (15)N NMR. We report, apparently for the first time, nitrogen NMR data and coupling information on such systems.

Restricted diffusion and exchange of water in porous media: average structure determination and size distribution resolved from the effect of local field gradients on the proton NMR spectrum.

NMR Pulsed field gradient measurements of the restrained diffusion of confined fluids constitute an efficient method to probe the local geometry in porous media. In most practical cases, the diffusion decay, when limited to its principal part, can be considered as Gaussian leading to an apparent diffusion coefficient. The evolution of the latter as a function of the diffusion interval yields average information on the surface/volume ratio of porosities and on the tortuosity of the network.

Diffusive diffraction measurements in porous media: effect of structural disorder and internal magnetic field gradients.

Pulsed Field Gradient NMR (PFG-NMR) method used to measure the self-diffusion coefficient of liquids can also be exploited to probe the local geometry of porous media. In most practical cases, the measured diffusion attenuation is generally Gaussian and can be interpreted in terms of an apparent diffusion coefficient. Using well chosen experimental conditions, a so called "diffusive diffraction" phenomenon can be observed in the diffusion curve with a specific shape and maxima location characteristic of the system local dimensions.

Diffusive diffraction phenomenon in a porous polymer material observed by NMR using radio-frequency field gradients.

Pulsed field gradient NMR diffusion experiments can, in principle, lead to the "diffusive diffraction" phenomenon. In practice, its observation by gradients of the static magnetic field is difficult in real systems because they involve internal gradients due to the static magnetic field (necessary for polarizing nuclear spins). This latter drawback can be circumvented by using gradients of the radio-frequency (rf) field (the other magnetic field used in any NMR experiment).

Spectral assignments for 1H, 13C and 15N solution and solid-state NMR spectra of s-tetrazine and dihydro-s-tetrazine derivatives.

Tetrazine-based organic species are interesting intermediates for organic synthesis and represent a source of new materials bearing specific properties with potential applications in biology and material science. 1H, 13C, 15N NMR measurements carried out in solution and in the solid-state have been used to characterize a series of 3,6-disubstituted 1,2,4,5-tetrazine/dihydrotetrazine new derivatives. Experimental results presented here provide data for the assignment of 15N chemical shifts including new organic small molecules; two polymers having the tetrazine ring in the main chain and several previously published compounds.

Management of duodenal ulcer disease in the era of H. pylori.

Background: Today it is expected that the great majority of patients with duodenal ulcer (DU) respond to H. pylori eradication treatment without DU recurrence. The aim of the research is to identify patients who need a different therapeutic approach and the best management of their disease.

Tautomerism and 1H, 13C and 15N NMR spectral assignments of some nitro derivatives of malonic acid diamide.

Because of its reactivity, malonic acid diamide (1) was initially identified as an alternative precursor for the development of a new class of high-density insensitive energetic materials possessing low sensitivity to thermal decomposition and detonation by impact. Nitration of 1 was studied under different conditions and led to three different tautomeric forms (2-4) of nitromalonic acid diamine. Using stronger oxidation conditions the oxadiazole 5 was generated in one step.

Sexual transmission of hepatitis C virus: the Turin study.

Background: Hepatitis C virus infection (HCV) is a major cause of chronic liver disease with the risk of evolution towards hepatic cirrhosis and hepatocellular carcinoma. Numerous studies have documented the possibility of HCV transmission through blood transfusions during surgery or during intravenous drug use. The percentage of the risk of sexual transmission, in the general population not presenting the aforesaid risks is still very controversial.

Magnitudes and mutual orientations of dipolar and shielding interaction tensors determined from the orientation dependence of spinning sidebands of slowly rotating powder samples.

It is shown that the orientation dependence of spinning sidebands of slowly rotating solids can be exploited to determine with good precision the heteronuclear bond distances and mutual orientation of dipolar and shielding tensors from a single dipolar modulated chemical shift anisotropy spectrum. The method is based on the dynamics of polarization transfer in the initial period of tens of microseconds, and may be useful in solids with relatively isolated groups of spins.

Mapping the active site of factor Xa by selective inhibitors: an NMR and MD study.

The structure of two selective inhibitors, Ac-Tyr-Ile-Arg-Ile-Pro-NH2 and Ac-(4-Amino-Phe)-(Cyclohexyl-Gly)-Arg-NH2, in the active site of the blood clotting enzyme factor Xa was determined by using transferred nuclear Overhauser effect nuclear magnetic resonance (NMR) spectroscopy. They represent a family of peptidic inhibitors obtained by the screening of a vast combinatorial library. Each structure was first calculated by using standard computational procedures (distance geometry, simulated annealing, energy minimization) and then further refined by systematic search of the conformation of the inhibitor docked in the active site and repeating the simulated annealing and energy minimization.

Influence of proton chemical-shift anisotropy on magic-angle spinning spectra of hydrate crystals.

It is shown that the proton chemical-shift anisotropy of hydrate crystals affect dipolar powder pattern at 7.0 T. This may be clearly observed via an asymmetric envelope of dipolar spinning sidebands in magic-angle spinning proton spectra.

Measurement of Hartmann-Hahn cross-polarization dynamics with quenching of proton T1 rho relaxation dependence.

A simple modification of the standard cross-polarization method designed for quenching the proton T1 rho dependence when studying polarization transfer is presented. It is demonstrated that by using this simple procedure, new and subtle details of cross-polarization dynamics, previously hidden by the T1 rho(1H) effect, can be observed in dipolar-coupled spin systems.

Dipolar local field measurements from indirect observation of 1H nuclei via cross-polarization 13C nuclear magnetic resonance spectroscopy.

An extension of the exploitation of a simple pulse sequence designed for indirect observation of 1H nuclei through 13C resonances is presented. It is shown that by using this pulse sequence under conditions of rapid magic-angle rotation and coherent energy transfer between directly bonded protons and carbons, an insight into the local dipolar interactions is available in typical organic solids.