Spectrophotometric determination of organic nitrogen by a modified Lassaigne method and its application to meat products and baby food

A modified Lassaigne method was developed for N determination based on fusion of the organic substance with metallic Na, conversion of the cyanide in the aqueous leachate to thiocyanate by ammonium polysulfide treatment, and colorimetric measurement of the thiocyanate formed by the addition of excessive ferric ions in acidic medium. The mean molar absorptivity of the Fe(NCS)2+ complex at 480 nm is 2.96 x 10(3) L/mol x cm, enabling quantitation of 0.25-7.72 ppm N (linear range) in the final solution. The relative amounts of Na, (NH4)2S2, and Fe(III) with respect to nitrogen in the analyte were optimized. The developed method was successfully applied to the determination of N in various brands of baby food, and it was compared statistically with the conventional Kjeldahl and elemental analysis methods. Protein nitrogen in a number of meat products was also precisely determined by the developed method. Thus, the total digestion time of the conventional Kjeldahl method was reduced considerably (e.g., to approximately 15 min for a dried sample) with a relatively simple spectrophotometric method requiring no sophisticated instrumentation.     

A process control method for the electric current-activated/assisted sintering system based on the container-consumed power and temperature estimation

Journal of Thermal Analysis and Calorimetry - In this paper, the current, voltage and temperature of the container of an electric current-activated/assisted sintering (ECAS) system are measured and...     

A new reagent for the synthesis of [26]hexaphyrin: N-sulfonyl aldimine

The selective synthesis of [26]hexaphyrin(1.1.1.1.1.1) has been achieved by the reaction of meso-substituted tripyrrane and N-sulfonyl aldimine. The protocol is simple and requires only a catalytic amount of copper(II) triflate under mild reaction conditions.     

Determination of Total Antioxidant Capacity by a New Spectrofluorometric Method Based on Ce(IV) Reduction: Ce(III) Fluorescence Probe for CERAC Assay

A Ce(IV)-based reducing capacity (CERAC) assay was developed to measure the total antioxidant capacity (TAC) of foods, in which Ce(IV) would selectively oxidize antioxidant compounds but not citric acid and reducing sugars which are not classified as antioxidants. The method is based on the electron-transfer (ET) reaction between Ce(IV) ion and antioxidants in optimized acidic sulphate medium (i.e., 0.3 M H₂SO₄ and 0.7 M Na₂SO₄) and subsequent determination of the produced Ce(III) ions by a fluorometric method. The fluorescent product, Ce(III), exhibited strong fluorescence at 360 nm with an excitation wavelength of 256 nm, the fluorescence intensity being correlated to antioxidant power of the original sample. The linear concentration range for most antioxidants was quite wide, e.g., 5.0 × 10⁻⁷–1.0 × 10⁻⁵ M for quercetin. The developed procedure was successfully applied to the TAC assay of antioxidant compounds such as trolox, quercetin, gallic acid, ascorbic acid, catechin, naringin, naringenin, caffeic acid, ferulic acid, glutathione, and cysteine. The proposed method was reproducible, additive in terms of TAC values of constituents of complex mixtures, and the trolox equivalent antioxidant capacities (TEAC coefficients) of the tested antioxidant compounds gave good correlations with those found by reference methods such as ABTS and CUPRAC.     

Stress distribution caused by two neighboring out-of-plane locally cophasally curved fibers in a composite material

In the present paper, within the framework of a piecewise homogenous body model, with the use of the exact three-dimensional equations of elasticity theory, a method proposed earlier is developed for investigating the stress distribution caused by two neighboring out-of-plane locally cophasally curved fibers located along two parallel planes in an infinite elastic body. The body is loaded at infinity by uniformly distributed normal forces in the direction of fiber location. The self-equilibrated normal and shear stresses caused by the curved fibers are analyzed, and the influences of interaction between the fibers and of the geometric nonlinearity on the distribution of these stresses are studied. Numerical results for this interaction are obtained.     

Synthesis,molecular conformation,vibrational, electronic transition,and chemical shift assignments of 4-(thiophene-3-ylmethoxy)phthalonitrile: a combined experimental and theoretical analysis

This work presents the synthesis and characterization of a novel compound, 4-(thiophene-3-ylmethoxy)phthalonitrile (TMP). The spectroscopic properties of the compound were examined by FT-IR, FT-Raman, NMR, and UV techniques. FT-IR and FT-Raman spectra in solid state were observed in the region 4000–400 cm⁻¹ and 3500–50 cm⁻¹, respectively. The ¹H and ¹³C NMR spectra were recorded in CDCl₃ solution. The UV absorption spectrum of the compound that dissolved in THF was recorded in the range of 200–800 nm. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational wavenumbers were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts (¹³C NMR and ¹H NMR) were calculated using the gauge-invariant atomic orbital (GIAO) method. A study on the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The HOMO and LUMO analyses have been used to elucidate information regarding charge transfer within the molecule. Comparison of the calculated frequencies, NMR chemical shifts, absorption wavelengths with the experimental values revealed that DFT method produces good results.     

Experimental vibrational spectra (Raman,infrared) and DFT calculations on monomeric and dimeric structures of 2‐ and 6‐bromonicotinic acid

In this work, the Fourier transform infrared and Raman spectra of 2‐bromonicotinic acid and 6‐bromonicotinic acid (abbreviated as 2‐BrNA and 6‐BrNA, C₆H₄BrNO₂) have been recorded in the region 4000–400 and 3500–50 cm⁻¹. The optimum molecular geometry, normal mode wavenumbers, infrared intensities and Raman scattering activities, corresponding vibrational assignments and intermolecular hydrogen bonds were investigated with the help of B3LYP density functional theory (DFT) method using 6‐311++G(d,p) basis set. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. From the calculations, the molecules are predicted to exist predominantly as the C1 conformer. Copyright © 2009 John Wiley & Sons, Ltd.     

The effect of temperature on urea–urea interactions in water: a molecular dynamics simulation

We investigate the temperature effect on the structural and dynamical properties (translation, rotation) of an urea/water system at 0.20 mole fraction of urea. We report the radial distribution functions of like and unlike molecules and conclude that, even at large distances, these molecules are spatially correlated (with respect to their centers of mass). This behavior is interpreted as an indication that urea molecules are not uniformly distributed at a microscopic level. However, the orientational distribution shows that, at long distances, the urea molecules are not orientationally correlated. A strong correlation between urea molecules is observed within the first-shells of neighboring molecules. In view of these results, it is postulated that urea behaves slightly like a nonpolar molecule. The dynamical properties were analyzed using the velocity (translation) and angular velocity (rotation) time autocorrelation functions, as well as their Fourier transforms. The results indicate a significant hydrogen bonding between urea and other molecules in the solution.