Laser ultrasonic receivers based on organic photorefractive polymer composites

We present two laser ultrasonic receivers based on organic photorefractive polymer composites with 2-[4-bis(2-methoxyethyl)aminobenzylidene]malononitrile (AODCST) or 2-dicyanomethylen-3-cyano-5,5-dimethyl-4-(4′-dihexylaminophenyl)-2,5-dihydrofuran nonlinear optical chromophores. Experimental results show sensitivities of the ultrasonic receivers of ~9.5 × 10^?8 nm (W/Hz)^0.5 for both composites, and a faster response time (~60 ms) for the AODCST-based laser ultrasonic receiver. We show that such LUS detectors are highly suitable for contactless thickness measurements of aluminum, steel sheets and defect detection with an accuracy of 100 μm.     

Application of MRI to monitor the process of ripening and decay in citrus treated with chitosan solutions

Chitosan is a biopolymer, which has numerous applications in agriculture and agroindustries. Coating fruit and vegetables with chitosan has some positive advantages for the long-term storage of foods, because the film of chitosan provides a kind of an active package, which allows a gradual release of preservatives, thus inhibiting fungal growth and maintaining the external appearance of the fruit for a longer time In this study, two varieties of citrus, Fortune mandarins and Valencia oranges were coated with Biorend(R) (IDEBIO S.L., Salamanca, Spain) (a compound whose active molecule is chitosan), to investigate its effect on maturity, decay, and damage, and therefore, to find a better method for the long term storage of fruit. The effect of chitosan as a fungistatic was also studied. To that end, the fruit was maintained in a damp storage room, ideal conditions for the growth of fungi. The magnetic resonance imaging (MRI) technique was used to monitor the process of ripening and decay in the citrus fruit that had been coated with chitosan. The dissolution of the chitosan on the mandarins and oranges produced excellent results in terms of percentage of weight loss, MRI, and visual appearance.     

Computer reconstruction of pine growth rings using MRI

This work explores the use of magnetic resonance imaging (MRI) for nondestructive determination of wood characteristics and for 3D wood modeling. In this context, one of the applications under development is the automatic recognition and reconstruction of rings from transversal images obtained from MRI scanners. The algorithm analyzes a set of transversal MRI images, detecting and reconstructing growth ring edges. The information generated is then interpolated in order to obtain an accurate 3D picture of the log and its fundamental constituents (individual rings, knots, defects, etc). Results also show that the technique has potential for defect recognition, providing a powerful tool for future developments in wood analysis. The results are encouraging and further research is needed to develop automatic detection not only of rings, but also of different types of defects that are of paramount importance in the sawmill and plywood industries.     

Experimental and theoretical vibrational study of 2,2,2-trifluoroethyl trifluoromethanesulfonate, CF3SO2OCH2CF3

The infrared spectra of 2,2,2-trifluoroethyl trifluoromethanesulfonate (CF3SO2OCH2CF3) were obtained in the gaseous, liquid and solid states as well as the Raman spectrum of the liquid. Quantum chemistry calculations using the density functional theory were used to predict the most stable geometry and conformation of the studied molecule. Subsequently, the harmonic vibrational frequencies and force field were calculated. An assignment of the observed spectral features made after comparison with the related molecules and with the predicted frequencies was used as the basis of a scaling of the original force field in order to reproduce as well as possible the experimental frequencies. With this purpose a set of scale factors was calculated by a least square procedure, leading to a final root mean square deviation (RMSD) of 9.7 cm(-1).     

Pt(hkl) surface charge and reactivity

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Peptide sequencing using a patchwork approach and surface-induced dissociation in sector-TOF and dual quadrupole mass spectrometers

Surface-induced ion activation in combination with a database search strategy based on the Patchwork concept is applied to the determination of peptide sequences. Surface-induced dissociation (SID) is performed in a tandem quadrupole mass spectrometer and in a hybrid sector/time-of-flight mass spectrometer in order to evaluate the importance of accurate mass analysis of the SID fragment ions for peptide identification. The modified Patchwork approach is based on piecing together the peptide blocks in a bidirectional way, simultaneously using low-mass fragments originating from the C-terminus and N-terminus of the molecule, and relying on the measurement of the peptide's molecular weight with moderate mass accuracy. The results from this analysis are used as search filters in MASCOT's (http://www.matrixscience.com) Sequence Query search engine, with the simultaneous addition of the full MS/MS peak list. SID is performed with collision targets coated with pure and mixed composition self-assembled monolayers produced by fluorocarbon and hydrocarbon alkanethiolate solutions of varying chemical composition. The resulting MS/MS spectra produced on pure and mixed hydrocarbon SAMs are submitted to the modified version of Patchwork sequencing. It is found that hydrocarbon surfaces improve the relative abundance of larger fragments. Under the moderate mass accuracy conditions (±0.3 u) offered by our linear-TOF-SID instrument, it is found that increasing the abundance of larger fragments dramatically improves the sequencing scores.     

Aryne insertion into I-I σ-bonds

A new protocol for the efficient synthesis of o-diiodoarenes has been developed. This method allows the synthesis of substituted and polycyclic o-diiodoarenes, which are difficult to obtain by classical methods. This diiodination process involves the formal insertion of arynes into the I-I σ-bond.     

Gold-catalyzed 1,2-/1,2-bis-acetoxy migration of 1,4-bis-propargyl acetates: a mechanistic study

The late transition metal catalyzed rearrangement of propargyl acetates offers an interesting platform for the development of synthetically useful transformations. We have recently shown that gold complexes can catalyze a highly selective tandem 1,2-/1,2-bis-acetoxy migration in 1,4-bis-propargyl acetates to form 2,3-bis-acetoxy-1,3-dienes. In this way, (1Z,3Z)- or (1Z,3E)- and (1E,3Z)-1,3-dienes could be obtained in a stereocontrolled manner depending on the electronic and steric features of the ancillary ligand bound to gold and the substituents at the propargylic positions. In this work, we report an experimental study on the scope of this transformation, plus a detailed theoretical examination of the reaction mechanism, which has revealed the key features responsible for the reaction stereoselectivity. Synthetic applications towards the one-pot synthesis of quinoxaline heterocycles and tandem Diels-Alder processes have also been devised.     

1H,89Y HMQC and further NMR spectroscopic and X-ray diffraction investigations on yttrium-containing complexes exhibiting various nuclearities

2D (1)H,(89)Y heteronuclear shift correlation through scalar coupling has been applied to the chemical-shift determination of a set of yttrium complexes with various nuclearities. This method allowed the determination of (89)Y NMR data in a short period of time. Multinuclear NMR spectroscopy as function of temperature, PGSE NMR-diffusion experiments, heteronuclear NOE measurements, and X-ray crystallography were applied to determine the structures of [Y(5)(OH)(5)(L-Val)(4)(Ph(2)acac)(6)] (1) (Ph(2)acac=dibenzoylmethanide, L-Val=L-valine), [Y(2)(OTf)(3)] (3), and [Y(2)(4)(OTf)(5)] (5) (2: [(S)P{N(Me)N=C(H)Py}(3)], 4: [B{N(Me)N=C(H)Py}(4)](-)) in solution and in the solid state. The structures found in the solid state are retained in solution, where averaged structures were observed. NMR diffusion measurements helped us to understand the nuclearity of compounds 3 and 5 in solution. (1)H,(19)F HOESY and (19)F,(19)F EXSY data revealed that the anions are specifically located in particular regions of space, which nicely correlated with the geometries found in the X-ray structures.