Analysis of biodiesel and frying vegetable oils by means of FTIR photoacoustic spectroscopy

Fourier Transform Infrared Photoacoustic Spectroscopy was used to determine the mid-infrared vibrational modes of biodiesel and vegetable oils. Our results indicate that this method can contribute significantly to the biodiesel wash process during the sample preparation. Besides, by analyzing the spectra of vegetable oils used to fry snacks we could to monitor the degradation in function of the fried time.     

Stability of the Feasible Set Mapping of Linear Systems with an Exact Constraint Set

This paper deals with the stability of the feasible set mapping of linear systems of an arbitrary number (possibly infinite) of equations and inequalities such that the variable x ranges on a certain fixed constraint set X?? ⁿ (X could represent the solution set of a given constraint system, e.g., the positive cone of ? ⁿ in the case of sign constraints). More in detail, the paper provides necessary as well as sufficient conditions for the lower and upper semicontinuity (in Berge sense), and the closedness, of the set-valued mapping which associates, with any admissible perturbation of the given (nominal) system its feasible set. The parameter space is formed by all the systems having the same structure (i.e., the same number of variables, equations and inequalities) as the nominal one, and the perturbations are measured by means of the pseudometric of the uniform convergence.     

Use of multivariate analysis techniques for the characterization of analytical results for the determination of the mineral composition of kale

This paper describes the determination and evaluation of the mineral composition (calcium, magnesium, iron, manganese and zinc) of kale (Brassica oleracea L. var. acephala DC.) grown in soils within four cities in Bahia State, Brazil. The sampling process was performed during the summer and winter. Samples were digested with concentrated nitric acid and a digestion pump. Analyses were performed with inductively coupled plasma optical emission spectrometry (ICP OES) and the accuracy was confirmed with a certified reference material of apple leaves furnished by the National Institute of Standard and Technology. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) revealed different mineral compositions of the samples collected in the summer and winter. Samples collected in the winter have a higher concentration of micronutrients (iron, zinc and manganese) and macronutrients (calcium and magnesium). The average contents (wet weight and mg per 100 g) for the winter and summer were 551 and 535 for calcium; 117 and 106 for magnesium; 2.13 and 1.48 for iron; 2.63 and 1.95 for zinc and 2.05 and 1.34 for manganese, respectively. These results are in agreement with values previously reported in the literature.     

Hulls for Various Kinds of α-Completeness in Archimedean Lattice-Ordered Groups

Within Archimedean -groups, and with an infinite cardinal or , we consider X-hulls where X stands for any of the following classes of -groups: -projectable; laterally -complete; boundedly laterally -complete; conditionally -complete; combinations of the preceding, together with divisibility and/or relative uniform completeness. All these hulls exist, and may be obtained by iterated adjunction of the required extra elements, within the essential hull. When the -groups is relatively -complemented one step in the iteration suffices for several crucial properties. We derive from the above a considerable number of equations involving combinations of these hull operators.     

A hybrid model for the acoustic response of a two-dimensional rough surface to an impulse incident from a refracting medium

A numerical model to calculate the impulse response of a two-dimensional, impenetrable, rough surface directly in the time domain has been recently introduced [J. Acoust. Soc. Am. (2000) 107, 27]. This model is based on wedge diffraction theory and assumes that the half-space containing the source and receiver is homogeneous. In this work, the model is extended to handle media where the index of refraction varies with the distance to the surface by merging the scattering model with a ray-based propagation model. The resulting hybrid model is tested against a Finite-Difference Time-Domain (FDTD) method for the problem of backscattering from a corrugated surface in the presence of a refractive layer. This new model can be applied, for example, to calculate acoustic reverberation from the sea surface in cases where the water mass is inhomogeneous and in the presence of a subsurface bubble layer at low frequencies where dispersion is negligible. It can also be used for atmospheric propagation problems where there is a sound speed gradient overlying rough terrain.     

New silica-immobilized chiral amino alcohol for the enantioselective addition of diethylzinc to benzaldehyde

[reaction: see text] A readily available chiral amino alcohol has been immobilized on silica by sol-gel synthesis and grafting. The solid prepared according to the latter method led to the best enantioselectivity (77% ee) described for the asymmetric addition of diethylzinc to benzaldehyde using inorganic solids.     

A convergent synthetic approach to the nucleoside-type liposidomycin antibiotics

[reaction: see text] A synthetic approach toward the liposidomycins, a family of complex nucleoside-type antibiotics, is reported based on the synthesis of epoxy-amides derived from the reaction of sulfur ylides with the uridyl aldehyde derivative 6. To this end, the epoxy-amide derivative of indoline 14 was stereoselectively prepared and, after treatment with DDQ, transformed into the corresponding N-indole epoxyamide 15. The indole 15 provides ready access to a variety of structures related to the diazepanone core present in the liposidomycins by reaction with a variety of amines.     

On the origin of the optical activity in the d-d transition region of tris-bidentate Co(III) and Rh(III) complexes

Time-dependent density functional theory (TD-DFT) has been employed to calculate the rotatory strengths in the d-d transition region for various tris-bidentate Co(III) and Rh(III) complexes. Optimized structural parameters are also reported. Our results confirm a previously proposed relationship between the azimuthal distortion of a complex containing saturated tris(diamine) and its optical activity. Formally d-d transitions are forbidden and should not exhibit optical activity. However, it is shown here that the intensity of these bands originates from a coupling of even ligand combination (participating in the e(g) type LUMO) and an odd ligand combination (participating in the t(2)(g) HOMO). For complexes containing planar unsaturated ligands, the signs of the d-d bands observed from the single-crystal circular and linear dichroisms are in accordance with the TD-DFT predictions. It is shown that by using hypothetical Co(NH(3))(6)(3+) complexes it is possible to estimate the contribution from the azimuthal distortion to the total rotatory strengths of the saturated tris(diamine) complexes. A discussion is also provided of previous theoretical studies and the way in which these investigations rationalized the optical activity.     

Chiral pyrimidine metallacalixarenes: synthesis, structure and host-guest chemistry

A set of enantiomerically pure cyclic multinuclear complexes with the formula cis-[a(2)PdL](n) (n+) [a(2)=(R,R)-1,2-diaminocyclohexane (R,R-dach), (S,S)-1,2-diaminocyclohexane (S,S-dach); n=4, 6; LH=2-hydroxypyrimidine (2-Hpymo), 4,6-dimethyl-2-hydroxypyrimidine (2-Hdmpymo) and 4-hydroxypyrimidine (4-Hpymo)] were obtained by reaction of cis-[a(2)Pd(H(2)O)(2)](2+) and LH in aqueous media. The polynuclear complexes were studied by (1)H NMR spectroscopy and X-ray crystallography. These studies revealed that the N1,N3-bridging mode exhibited by the pyrimidine moieties is ideally suited for formation of inorganic analogues of calixarenes (metallacalixarenes) in a self-assembly process. The most stable species are the tetranuclear metallacalix[4]arenes, which are obtained in all cases. Hexanuclear species, namely, [a(2)Pd(2-dmpymo)](6) (6+), were also isolated and fully characterised. (1)H NMR experiments show conversion of [a(2)Pd(2-dmpymo)](6) (6+) to [a(2)Pd(2-dmpymo)](4) (4+) on heating. Analogously to organic calixarenes, these systems are also capable of incorporating hard metal ions at the oxo surface. Additionally, investigations on the receptor properties of these metallacalixarenes towards mononucleotides showed that enantioselective recognition processes occur in aqueous media.