Non-uniformly sampled Maximum Quantum spectroscopy

Maximum-Quantum (MaxQ) NMR is an approach that exploits the simple lineshape (a singlet) of the highest possible coherence quantum order for a given spin system to help resolving the interpretation of the spectrum of complex mixtures. In this setup, resolution in the indirect, multiple-quantum, dimension is crucial, and it may be linked to a long duration of the signal acquired along this axis. We explored if this boundary on the length of the indirect dimension could not necessarily translate into extended experimental times by applying Non-Uniform Sampling (NUS) schemes in conjunction with Recursive Multi-Dimensional Decomposition (R-MDD) data processing. The actual value of the MaxQ order depends on the size of the spin system, so that for a mixture several MQ correlation spectra must be recorded to detect all possible molecular fragments. As the sparseness of the MQ datasets vary dramatically in going from higher (sparser) to lower (denser) coherence orders, the optimal compressing conditions and the fidelity of NUS/R-MDD scheme may vary along the series of MQ spectra. The NUS-MaxQ approach is demonstrated on the aromatic region of the 1H spectrum of a mixture of 10 simple aromatic molecules.     

Ultrasonic scanning of straight micro tools in soft biological tissues: Methodology and implementation

The acoustical behaviour of straight micro tools (SMT), such as sub-millimetre needles or electrodes, is delicate and their automated maintaining in the image plane displayed to the practitioner must handle the extremely varying signal they backscatter. Because of the complex nature of the scattering by a narrow rod target, the localization process has to face two main tasks before being able to conduct 3D location: the reduction of the apparent diameter when this latter is visible, and the detection of the instrument and its real depth of penetration. In this paper, a methodology based on these steps is proposed, along with preliminary implementations of each of the steps. This methodology exploit the acoustic duality of those SMT and treat different acoustic aspects separately: first the apparent diameter is reduced through a deconvolution process, associating the backscattering to a purely linear acoustic process without attenuation; second, the imaging is treated as a pure attenuation process, and the signal is summed post-ROI to achieve the detection. Finally, the complete localisation is achieved by combining the two first steps with a previously tested global 3D straight line location technique: the Parallel Integral Projection. Experiments are conducted in vitro with 700 μm graphite rods and 150 μm in diameter tungsten electrode crossing gelatine and cryogel phantoms, and ex vivo on a porcine liver to assess the efficiency of the proposed implementations and of the whole methodology. The volumes were acquired with a Kretztechnic 530D scanner customized so as to provide the raw RF data. Results show that the combination of the different step-methods reduces progressively the apparent diameter, and that the detection step is essential to the proper localization of the micro tool. The final resolution improvement is at least of 3 and estimated to be typically of 12, for a final estimated apparent diameter reaching the average 400 μm resolution cell in the porcine liver.     

Direct amplification of ultrashort pulses in μ-pulling-down Yb:YAG single crystal fibers

We demonstrated that Yb:YAG single crystal fibers have a strong potential for the amplification of femtosecond pulses. Seeded by 230?fs pulses with an average power of 400?mW at 30?MHz delivered by a passively mode-locked Yb:KYW oscillator, the system produced 330?fs pulses with an average power of 12?W. This is the shortest pulse duration ever produced by an Yb:YAG amplifier. The gain in the single crystal fiber reached a value as high as 30 in a simple double-pass configuration.     

Adiabatic versus nonadiabatic photoisomerization in photochromic ruthenium sulfoxide complexes: a mechanistic picture from density functional theory calculations

Polypyridine ruthenium sulfoxide complexes are intriguing compounds which can display both photochromic and electrochromic properties. These properties are based on the Ru-S → Ru-O linkage isomerization capability of the sulfoxide group. The photoisomerization mechanism is of particular importance in order to understand the photophysical properties of such molecules. Density functional theory calculations demonstrate that the main photoisomerization mechanism is nonadiabatic for the system under study in agreement with the experimental observations. Indeed, funnels for efficient radiationless decay back to the ground state are shown to be easily accessible compared to transition states on the adiabatic triplet potential energy surface. However, we highlight for the first time that triplet metal-centered states play a central role in the photoisomerization mechanism of these compounds.     

Effect of supercritical CO2 plasticization on the degradation and residual crystallinity of melt‐extruded spironolactone

Immediate‐release solid dispersions of a slowly dissolving active pharmaceutical ingredient, spironolactone, were prepared by supercritical‐CO₂‐assisted melt extrusion (a solvent‐free and continuous manufacturing technology) using Eudragit E as matrix. Through optimizing process parameters (i.e. temperature, melt throughput, pressure and CO₂ flow), stable foams with high porosity, homogeneous structure and thin (even submicronic) walls could be prepared, as revealed by scanning electron microscopy. The samples were found to be rigid enough to mill, enabling further processing, as is necessary to formulate tablets. The influence of extrusion temperature and melt throughput on residual drug crystallinity was measured using non‐invasive confocal Raman mapping coupled with chemometric analysis, while the influence on the degree of drug degradation was determined using high performance liquid chromatography. The plasticizing effect of supercritical CO₂ was shown to reasonably improve the purity of the prepared solid dispersions by enabling high‐yield production at lower temperature ranges. At the same time, shorter residence time and lower temperature slightly increased residual drug crystallinity. The obtained foamy structures ensured immediate drug dissolution in an acidic medium. Copyright © 2014 John Wiley & Sons, Ltd.     

Paramagnetic pyrrole-based semiconductor molecular material

The electrochemical oxidation of hexa-N-pyrrolylbenzene in organic media leads, via intramolecular coupling of the pyrrole residues, to the deposition of a molecular semiconductor film on an electrode surface. In situ electron spin resonance–electrochemical experiments reveal that the semiconductor is endowed with both properties of conducting polymers (i.e., reversible oxidation) and polyaromatic molecular materials (i.e., highly paramagnetic). The material, which is easy to process as soft homogeneous thin film, shows a tunable 0 to 1 spin concentration per molecule at room temperature by controlling the electrochemical potential. Contribution to the Fall Meeting of the European Materials Research Society, Symposium D: 9th International Symposium on the Electrochemical–Chemical Reactivity of Metastable Materials, Warsaw, 17th–21st September, 2007. An erratum to this article can be found at     

Stability in solution of indolium heptamethine cyanines and related pH‐sensitive systems

Relative stabilities of methanolic solutions of dyes that are potentially important for labeling of biological macromolecules with a visible‐red or near‐infrared fluorophore were evaluated in the presence of molecular oxygen under dark and light conditions.     

Carbon isotopic ratio analysis by gas chromatography/combustion/isotope ratio mass spectrometry for the detection of gamma-hydroxybutyric acid (GHB) administration to humans

Since GHB (gamma-hydroxybutyric acid) is naturally produced in the human body, clinical and forensic toxicologists must be able to discriminate between endogenous levels and a concentration resulting from exposure. To suggest an alternative to the use of interpretative concentration cut-offs, the detection of exogenous GHB in urine specimens was investigated by means of gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). GHB was isolated from urinary matrix by successive purification on Oasis MCX and Bond Elute SAX solid-phase extraction (SPE) cartridges prior to high-performance liquid chromatography (HPLC) fractioning using an Atlantis dC18 column eluted with a mixture of formic acid and methanol. Subsequent intramolecular esterification of GHB leading to the formation of gamma-butyrolactone (GBL) was carried out to avoid introduction of additional carbon atoms for carbon isotopic ratio analysis. A precision of 0.3 per thousand was determined using this IRMS method for samples at GHB concentrations of 10 mg/L. The (13)C/(12)C ratios of GHB in samples of subjects exposed to the drug ranged from -32.1 to -42.1 per thousand, whereas the results obtained for samples containing GHB of endogenous origin at concentration levels less than 10 mg/L were in the range -23.5 to -27.0 per thousand. Therefore, these preliminary results show that a possible discrimination between endogenous and exogenous GHB can be made using carbon isotopic ratio analyses.     

A novel low-E field coil to minimize heating of biological samples in solid-state multinuclear NMR experiments

A novel coil, called Z coil, is presented. Its function is to reduce the strong thermal effects produced by rf heating at high frequencies. The results obtained at 500MHz in a 50 microl sample prove that the Z coil can cope with salt concentrations that are one order of magnitude higher than in traditional solenoidal coils. The evaluation of the rf field is performed by numerical analysis based on first principles and by carrying out rf field measurements. Reduction of rf heating is probed with a DMPC/DHPC membrane prepared in buffers of increasing salt concentrations. The intricate correlation that exists between the magnetic and electric field is presented. It is demonstrated that, in a multiply tuned traditional MAS coil, the rf electric field E(1) cannot be reduced without altering the rf magnetic field. Since the detailed distribution differs when changing the coil geometry, a comparison involving the following three distinct designs is discussed: (1) a regular coil of 5.5 turns, (2) a variable pitch coil with the same number of turns, (3) the new Z coil structure. For each of these coils loaded with samples of different salt concentrations, the nutation fields obtained at a certain power level provide a basis to discuss the impact of the dielectric and conductive losses on the rf efficiency.