Spectroscopic studies of folic acid adsorbed on various metal substrates: does the type of substrate play an essential role in temperature dependence of spectral features?

Folic acid is an essential nutrient involved in biosynthetic processes and cell growth. From an analytical point of view, folic acid can be used as an active part of sensors for substances with affinity to folic acid molecules. In biological environment, sensors can be exposed to temperatures that differ from room temperature. Thus, it is important to describe the influence of temperature on adsorbed molecules, especially on orientation of molecules towards the metal surface and on stability of adsorbed layer. Surface‐enhanced Raman scattering spectroscopy is a useful tool for investigation of architecture of molecular layers adsorbed on metal surfaces because the spectral features change with varying orientation of molecules towards the surface, as well as with changes in interactions among adsorbed molecules. In this study, folic acid was adsorbed on electrochemically prepared Au and Ag substrates, and both these substrates were exposed to temperature changes according to the temperature program consisting of stabilization, the substrate temperature at 10°C, at 50°C and back at 10°C. Decomposition of adsorbed folic acid at 50°C can be excluded on both metals, though the metal (Ag or Au) influences the arrangement of adsorbed molecules and its temperature‐induced changes. In the case of Ag substrate, significant and irreversible increase of certain Stokes band intensities is observed, whereas in the case of Au substrate, the band intensity increase is negligible. Experimental spectra were analyzed using principal component analysis and supplemented with calculated data for folic acid molecule adsorbed on small metal cluster using density functional theory. Moreover, it was proved that changes of surface plasmon resonance and collision frequency of Ag substrate are negligible in the studied temperature interval. Slight re‐orientation of adsorbed folic acid molecules was identified as the main source of band intensity variation in the spectra of folic acid adsorbed on Ag. Copyright © 2014 John Wiley & Sons, Ltd.     

Artificial amino acids in nickel(II) and nickel(II)/lanthanide(III) chemistry

The synthesis and magnetic properties of five new homo- and heterometallic nickel(II) complexes containing artificial amino acids are reported: [Ni(4)(aib)(3)(aibH)(3)(NO(3))](NO(3))(4)·3.05MeOH (1·3.05MeOH), [Ni(6)La(aib)(12)](NO(3))(3)·5.5H(2)O (2·5.5H(2)O), [Ni(6)Pr(aib)(12)](NO(3))(3)·5.5H(2)O (3·5.5H(2)O), [Ni(5)(OH)(2)(l-aba)(4)(OAc)(4)]·0.4EtOH·0.3H(2)O 6(4·0.4EtOH·0.3H(2)O), and [Ni(6)La(l-aba)(12)][La(2)(NO(3))(9)] (5; aibH = 2-aminoisobutyric acid; l-abaH = l-2-aminobutyric acid). Complexes 1 and 4 describe trigonal-pyramidal and square-based pyramidal metallic clusters, respectively, while complexes 2, 3, and 5 can be considered to be metallocryptand-encapsulated lanthanides. Complexes 4 and 5 are chiral and crystallize in the space groups I222 and P2(1)3, respectively. Direct-current magnetic susceptibility studies in the 2-300 K range for all complexes reveal the presence of dominant antiferromagnetic exchange interactions, leading to small or diamagnetic ground states.     

Provenance study of volcanic glass using 266–1064 nm orthogonal double pulse laser induced breakdown spectroscopy

Double pulse laser induced breakdown spectroscopy in orthogonal configuration was used for the analysis of twelve samples of volcanic glass. Raw material and artifact samples originated from Czech, Slovak, German, Hungarian, Greek, Turkish, and Ukrainian sites. The primary 266 nm laser beam was focused onto a sample area of about 0.1 mm in diameter at the optimised energy of 10 mJ resulting in only very slight sample damage, almost unrecognizable even by a microscope. The secondary 1064 nm laser beam, positioned parallel to the sample surface and focused onto the intersection with the primary beam, induced a spark with enhanced radiation at the optimised energy of 100 mJ. Measurement of emission lines selected on basis of chemical composition, signal intensity, signal-to-background ratio, and minimum interference from the surrounding spectra: Si(I) 288.16 nm, Mg(II) 279.55 nm, 280.27 nm, Mg(I) 285.21 nm, Ca(II) 317.93 nm, Na(I) 589.59 nm, Al(I) 308.22 nm, Fe(II) 259.94 nm, Ti(II) 334.94 nm, Sr(II) 407.77 nm, Ba(II) 455.40 nm, K(I) 769.90 nm, provided experimental data sufficiently sensitive to differentiate the properties of the studied samples. Rare earth elements were not detected even though the double pulse technique is more sensitive than the single pulse variant. Visualisation methods of multidimensional statistical analyses such as radar chart, Chernoff faces, scatterplots, and the Spearman correlation matrix provided successful differentiation of the sample groups and/or particular samples by their origin.     

Supercritical fluid chromatography as a tool for enantioselective separation; A review

Supercritical fluid chromatography (SFC) has become popular in the field of enantioselective separations. Many works have been reported during the last years. This review covers the period from 2000 till August 2013. The article is divided into three main chapters. The first one comprises a basic introduction to SFC. The authors provide a brief explanation of general principles and possibilities of this method. The advantages and drawbacks are also listed. Next part deals with chiral separation systems available in SFC, namely with the commonly used chiral stationary phases. Properties and interaction possibilities of the chiral separation systems are described. Recent theoretical papers are emphasized in this chapter. The last part of the paper gives an overview of applications of enantioselective SFC in analytical chemistry, in both analytical and preparative scales. Separation systems and conditions are summed up in tables so that they provide a helpful tool for analysts who search for a particular method of analysis.     

What about Dinner? Chemical and Microresidue Analysis Reveals the Function of Late Neolithic Ceramic Pans

The Late Neolithic palafitte site, Ustie na Drim, in the northern part of Lake Ohrid (North Macedonia), excavated in 1962, offered ceramic fragments of large, flat, elongated pans. These artifacts could be dated by relative chronology to roughly around 5200–5000 BC. According to their shape and technological traits, the ceramic pans were probably used for baking. The attached materials on the surface of studied pan fragments were sampled for consequent chemical and microscopical analyses (i.e., analyses of starch, phytoliths, and microscopic animal remains). An immunological method revealed the presence of pork proteins in samples. The presence of organic residues of animal origin was, moreover, confirmed by the detection of cholesterol using gas chromatography coupled to mass spectrometry. Analysis of detected microscopic botanical objects revealed starch grains of several plants (i.e., oak, cattail, and grasses). An interesting find was the hair of a beetle larva, which could be interpreted contextually as the khapra beetle, a pest of grain and flour. Based on our data, we suppose that the ceramic pans from Ustie na Drim were used for the preparation of meals containing meat from common livestock in combination with cereals and wild plants.     

Characterization of coal fly ash components by laser-induced breakdown spectroscopy

The high sensitivity of laser-induced breakdown spectroscopy (LIBS) for the detection of most of the fly ash components enables the analysis of these residues produced during the combustion of coal. Fly ash consists of oxides (SiO₂, Al₂O₃, Fe₂O₃, CaO…) and unburnt carbon which is the major determinant of combustion efficiency in coal fired boilers. For example, an excessive amount of residual carbon dispersed in the fly ash means a significant loss of energy (Styszko et al., 2004 [1]). Standard methods employed for the analysis of fly ash make not possible a control of boiler in real time. LIBS technique can significantly reduce the time of analysis, in some cases even an online detection can be performed. For this reason, some studies have been addressed in order to demonstrate the capability of the laser-induced breakdown spectroscopy technique for the detection of carbon content in high pressure conditions typical of thermal power plants (Noda et al., 2002 [2]) and for the monitoring of unburnt carbon for the boiler control in real time (Kurihara et al., 2003[3]).In particular, the content of unburnt carbon is a valuable indicator for the control of fly ash quality and for the boiler combustion. Depending on this unburnt carbon content, fly ash can be disposed as an industrial waste or as a raw material for the production of concrete in the construction sector. In this study, analyses were performed on specimens of various forms of preparation. Pressed pellets were prepared with two different binders. Presented results concern the nature and amount of the binder used to pelletize the powder, and the laser-induced breakdown spectroscopy parameters and procedure required to draw calibration curves of elements from the fly ash. Analysis “on tape” was performed in order to establish the experimental conditions for the future “online analysis”.     

Detection of irradiated fresh fruits treated by e-beam or gamma rays

Since about 1990, the amount of commercially irradiated food products available worldwide has increased. Commercial irradiation of foods has been allowed in Brazil since 1973 and now more than 20 different food products are approved. Among these products are a number of fresh fruits which may be irradiated for insect disinfestation, to delay ripening and to extend shelf-life. Today, there is a growing interest to apply radiation for the treatment of fruits instead of using fumigation or e.g. vapour-heat treatments, and an increased international trade in irradiated fruits is expected. To ensure free consumer choice, methods to identify irradiated foods are highly desirable. In this work, three detection methods for irradiated fruits have been employed: DNA Comet Assay, the half-embryo test and ESR. Both electron-beam (e-beam) and gamma rays were applied in order to compare the response with these two different kinds of radiation. Fresh fruits such as oranges, lemons, apples, watermelons and tomatoes were irradiated with doses in the range 0, 0.50, 0.75, 1.0, 2.0 and 4.0 kGy. For analysis, the seeds of the fruits were utilized. Both DNA Comet Assay and the half-embryo test enabled an easy identification of the radiation treatment. However, under our conditions, ESR measurements were not satisfactory.     

Continuum limits and exact finite-size-scaling functions for one-dimensionalO(N)-invariant spin models

We solve exactly the general one-dimensionalO(N)-invariant spin model taking values in the sphereS ^N–1, with nearest-neighbor interactions, in finite volume with periodic boundary conditions, by an expansion in hyperspherical harmonics. The possible continuum limits are discussed for a general one-parameter family of interactions and an infinite number of universality classes is found. For these classes we compute the finite-size-scaling functions and the leading corrections to finite-size scaling. A special two-parameter family of interactions (which includes the mixed isovector/isotensor model) is also treated and no additional universality classes appear. In the appendices we give new formulae for the Clebsch-Gordan coefficients and 6–j symbols of theO(N) group, and some new generalizations of the Poisson summation formula; these may be of independent interest.     

Effect of pressure on soot formation in the pyrolysis of <Emphasis Type="Italic">n</Emphasis>-hexane and the oxidation of fuel-rich mixtures of <Emphasis Type="Italic">n</Emphasis>-heptane behind reflected shock waves

The results of detailed kinetic simulations of the formation of soot particles in the pyrolysis of n-hexane–argon mixtures and in the oxidation of fuel-rich (φ = 5) n-heptane–oxygen–argon mixtures behind reflected shock waves at pressures of 20–100 bar and a constant concentration of carbon atoms or a constant fraction of argon in the initial mixture within the framework of a modified reaction mechanism are reported. The choice of n-hexane and n-heptane for examining the effect of pressure on the process of soot formation was motivated by the availability for these hydrocarbons of experimental measurements in reflected shock waves at high pressures (up to ~100 bar). The temperature dependences of the yield of soot particles formed in the pyrolysis of n-hexane are found to be very weakly dependent on pressure and slightly shifting to lower temperatures with increasing pressure. In general, pressure produces a very weak effect on the soot formation in the pyrolysis of n-hexane. The effect of pressure and concentration of carbon atoms in the initial mixture on the process of soot formation during the oxidation of fuel-rich n-heptane mixtures behind reflected shock waves is studied. The results of our kinetic simulations show that, for both the pyrolysis of n-hexane and the oxidation of fuel-rich n-heptane–oxygen mixtures, the influence of pressure on the process of soot formation is negligible. By contrast, the concentration of carbon atoms in the initial reaction mixture produces a much more pronounced effect.