Simultaneous analysis of esters and acylglycerols in biodiesel by high-performance liquid chromatography with refractive index detection

Currently, gas chromatography (GC) is the most widely used analytical technique to verify the quality of biodiesel in relation to its glyceride and fatty acid methyl ester (FAME) contents, even though its use has some disadvantages, such as damage to the injector and column caused by the presence of trace levels of triacylglycerols in biodiesel, which means the column has to be replaced every 3 months; the need for the sample to be derivatized, which, while improving chromatographic separation, also increases analysis time; and the use of several imported standard solutions. The main aim of this work was to use high-performance liquid chromatography with refractive index detection (HPLC-RI) to simultaneously quantify the glyceride (mono, di, and triacylglycerol) and FAME contents of biodiesel. The proposed method showed satisfactory results when compared with those obtained by the reference method (GC), particularly when these results were within the working ranges of the reference method. The proposed method using HPLC-RI is therefore promising and could potentially be used instead of the reference method, since the results it yielded were statistically equivalent, with 95% confidence, to the results obtained by the reference method (GC) for the nine samples of commercial biodiesel analyzed in this study.     

Strong perturbation effects in heavy ion induced electronic sputtering of lithium fluoride

Electronic sputtering of lithium fluoride by swift heavy ions was studied as a function of electronic energy loss (dE/dx) _e . The single crystal targets were irradiated with swift heavy ion beams (166Z _P 692; 46E _P /M _P (MeV/u) 611). This allowed varying the deposited energy by a factor of 20 (1.86dE/dx (keV/nm) 632). The sputtered secondary ions were measured from well controlled LiF targets without surface contaminations, by means of the time-of-flight technique (TOF-SIMS). The mass spectrum reveals an important contribution of clusters (over single ions), which increases with (dE/dx) _e . Another observation for the strongest perturbation at high dE/dx (>8 keV/nm) is that the secondary ion yields saturate: Y(dE/dx) = constant. In contrast, at lower dE/dx (<8 keV/nm) for weaker perturbation, the yield Y scales with (dE/dx)². This quadratic increase would rather point towards a thermal evaporation-like mechanism leading to electronic sputtering, however, the origin of the yield saturation remains an open finding.     

Improvement of piezoelectric transformer performances using SSHI and SSHI-max methods

The piezoelectric transformers reach densities of power more significant than their magnetic counterparts. However, one of the principal factors limiting the density of power is the acceptable maximum deformation by material constituting the transformer. The heating of the piezoelectric transformers is mainly of mechanical origin. This heating generates a degradation of the characteristics which in its turn generates an additional heating being able to lead to a phenomenon of thermal avalanche. In this work, two nonlinear methods [synchronized switch harvesting on inductor (SSHI) and SSHI-max] have been explored to improve the performance of the Rosen transformer basing on the tension generated by the secondary so as to increase the capacity of mechanic-electric conversion. The simulation results show that SSHI and SSHI-max techniques significantly increase the capacity of mechanic-electric conversion of inserts stuck on a vibrating structure and consequently, the power recovered in electric form. The comparative results of voltage gain, efficiency and the transmitted power of the transformer, before and after SSHI-max and SSHI control are given. These ones indicated that the two nonlinear techniques are promising as applications to improve the performances of the piezo-transformers.     

Fourier transform infrared and Raman spectra. Semi empirical AM1 and PM3; MP2/DZV and DFT/B3LYP-6-31G(d) ab initio calculations for dimethylterephthalate (DMT)

Fourier transform infrared and Raman spectra of dimethylterephthalate (DMT), as microcrystalline powder, have been investigated. The vibrational spectra were calculated using the AM1 and PM3 semi empirical procedures, and the M?ller-Plesset (MP2/DZV), and the Becke-Lee, Yang and Parr gradient-corrected correlation functional: B3LYP/6-31G(d) ab initio calculations. On this basis, and assisted with the FT-IR and Raman spectra of the terephthalic acid, an assignment of the vibrational spectra of dimethylterephthalate was proposed. In the calculations, remarkable differences concerning the assignments of the vibrational spectra were noted between the AM1 and PM3 methods. Also, the ab initio procedure shows differences in interpreting the spectra compared with the semi empiric procedures, and among themselves. Calculated geometrical parameters were compared with the experimental values of dimethylterephthalate, diethylterephthalate and terephthalic acid.     

Application of copper(i) iodide/diorganoyl dichalcogenides to the synthesis of 4-organochalcogen isoquinolines by regioselective cn and cchalcogen bond formation

A copper-catalyzed cyclization of (ortho-alkynyl)benzaldimines with diorganoyl dichalcogenides allowed the synthesis of 4-organochalcogen isoquinolines, whereas the presence of base in the reaction medium inhibited the product formation producing the undesirable isoquinoline without the organochalcogen atom at the 4-position. The cyclization reaction was carried out by using CuI (20?%) as a catalyst with diorganoyl dichalcogenides (1.5?equiv) in the presence of DMF at 100?°C. Furthermore, the reaction did not require an argon atmosphere and was carried out in an open flask. The cyclization reaction tolerated a variety of functional groups both in ortho-alkynylbenzaldimines and diorganoyl dichalcogenides, such as trifluoromethyl, chloro, fluorine, and methoxyl, to give the six-membered heterocyclic ring exclusively through a 6-endo-dig cyclization process. The organochalcogen group present at the 4-position of the isoquinoline ring was further subjected to a selective chalcogen-lithium exchange reaction followed by the addition of aldehydes to afford the desired secondary alcohols in good yields. The obtained isoquinolines also proved to be suitable substrates for the Suzuki and Sonogashira coupling conditions affording the corresponding products through C?C bond formation.     

Mapping of surface-enhanced fluorescence on metal nanoparticles using super-resolution photoactivation localization microscopy

Photoactivation localization microscopy (PALM) was applied to study surface-enhanced fluorescence (SEF) on metal nanostructures (SEF-PALM). The detection of fluorescence from individual single molecules can be used to image the point-spread-function and spatial distribution of the fluorescence emitted in the vicinity of a metal surface. Due to the strong scattering effect, the angular distribution of the fluorescence is altered by metals, resulting in a spatial shift of fluorescence spots with respect to the metal nanostructures, and has to be taken into account in the analysis. SEF-PALM can be used to discriminate effects of labelling density when estimating the enhancement factor in SEF. Furthermore, nanostructures with sizes below the diffraction limit can be resolved using this technique. SEF-PALM is established as a powerful tool to study plasmon-mediated phenomena on metal nanostructures.     

Can Aromaticity Coexist with Diradical Character? An Ab Initio Valence Bond Study of S2N2 and Related 6π‐Electron Four‐Membered Rings E2N2 and E42+ (E=S,Se, Te)

A series of 6π‐electron 4‐center species, E₂N₂ and E₄²⁺ (E=S, Se, Te) is studied by means of ab initio valence bond methods with the aims of settling some controversies on 1) the diradical character of these molecules and 2) the radical sites, E or N, of the preferred diradical structure. It was found that for all molecules, the cumulated weights of the two possible diradical structures are always important and close to 50 %, making these molecules comparable to ozone in terms of diradical character. While the two diradical structures are degenerate in the E₄²⁺ dications, they have on the contrary strongly unequal weights in the E₂N₂ neutral molecules. In these three molecules, the electronic structure is dominated by one diradical structure, in which the radical sites are the two nitrogen atoms, while the other diradical structure is much less important. The ordering of the various VB structures in terms of their calculated weights is confirmed by the relative energies of individual VB structures. In all cases, the major diradical structure (or both diradical structures when they are degenerate) is (are) the lowest one(s), while the covalent VB structures lie higher in energy. The vertical resonance energies are considerable in S₂N₂ and S₄²⁺, about 80 % of the estimated value for benzene, and diminish as one goes down the periodic table (S→Se→Te). This confirms the aromatic character of these species, as already demonstrated for S₂N₂ on the basis of magnetic criteria. This and the high weights and stabilities of one or both diradical structures in all systems indicates that aromaticity and diradical character do not exclude each other, contrary to what is usually claimed. Furthermore, it is shown that the diradical structures find their place in a collective electron flow responsible for the ring currents in the π system of these species.