Comprehensive two-dimensional liquid chromatography×gas chromatography: evaluation of the applicability for the analysis of edible oils and fats

Edible fats and oils are complex mixtures containing a wide range of (classes of) compounds. The most important group of compounds are the triglycerides (triacylglycerides, TAGs). Because of the large number of possible fatty acid combinations, an enormous number of TAGs is possible. In the present feasibility study, the applicability of different modes of comprehensive two-dimensional LC×GC for detailed oil and fat analysis is evaluated. Comprehensive LC×GC was found to be an extremely powerful analytical method for the analysis of complex TAG samples. Using the new comprehensive set-ups, TAGs can be separated according to two independent parameters: carbon number vs. number of double bonds, or fatty acid composition vs. number of double bonds. The information content of comprehensive separations by far exceeds that of the current generation of analytical methods. The quantitative results of the separations show a good agreement with data obtained from standard analytical methods. The comprehensive methods studied can also be used for fingerprinting of oil samples, as well as for the analysis of target compounds or compound groups. Highly detailed separations of olive oil samples were obtained. Zooming in on one region of the chromatogram allowed reliable analysis of wax esters without interferences of sterol esters.     

Lithiumhydridosiloxysilylamide – Reaktionen in n-Octan und Tetrahydrofuran in Gegenwart von Chlortrimethylsilan

Lithium Hydridosiloxysilylamides – Reactions in n-Octane and Tetrahydrofuran in Presence of Chlorotrimethylsilane The hydrido-siloxy-silylamino-silanes (Me₃SiO)HSiMe(NHSiMe₃) 1 , (Me₃SiO)HSi(NHSiMe₃)₂ 2 and (Me₃SiO)₂HSi(NHSiMe₃) 3 were prepared by coammonolysis of the chlorosiloxysilanes (Me₃SiO)HSiMeCl and (Me₃SiO)_3–nHSiCl_n (n = 1, 2) with chlorotrimethylsilane. The reaction behaviour of lithiated compounds 1 , 2 and 3 has been investigated in n-octane and tetrahydrofuran (THF) in presence of chlorotrimethylsilane.     

Trinuclear nickel complexes with triplesalen ligands: simultaneous occurrence of mixed valence and valence tautomerism in the oxidized species

The coordination chemistries of the triple tetradentate triplesalen ligands H(6)talen, H(6)talen(t)(-)(Bu)(2), and H(6)talen(NO)(2) have been investigated with nickel(II). These triplesalen ligands provide three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone. The structures of the complexes [(talen)Ni(II)(3)], [(talen(t)(-)(Bu)(2)Ni(II)(3)], and [(talen(NO)(2)Ni(II)(3)] have been determined by single-crystal X-ray diffraction. All three compounds are composed of neutral trinuclear complexes with square-planar coordinated Ni(II) ions in a salen-like coordination environment. Whereas the overall molecular structure of [(talen(NO)(2)Ni(II)(3)] is nearly planar, the structures of [(talen)Ni(II)(3)] and [(talen(t)(-)(Bu)(2)Ni(II)(3)] are bowl-shaped as a result of ligand folding. The strongest ligand folding occurs at the central nickel-phenolate bond of [(talen(t)(-)(Bu)(2)Ni(II)(3)], resulting in the formation of a chiral hemispherical pocket. The dependence of the physical properties by the substituents on the terminal phenolates has been studied by FTIR, resonance Raman, UV-vis-NIR absorption, and electrochemistry. The three nickel-salen subunits are electronically interacting via the pi system of the bridging phloroglucinol backbone. The strength of this interaction is mediated by two opposing effects: the electron density at the terminal phenolates and the folding of the ligand at the central phenolates. The parent complex [(talen)Ni(II)(3)] is irreversibly oxidized at 0.32 V versus ferrocenium/ferrocene (Fc(+)/Fc), whereas [(talen(t)(-)(Bu)2)Ni(II)(3)] and [(talen(NO)(2)Ni(II)(3)] exhibit reversible oxidations at 0.22 V versus Fc(+)/Fc and 0.52 V versus Fc(+)/Fc, respectively. The oxidized species [(talen(t)(-)(Bu)(2)Ni(3)](+) and [(talen(NO)(2)Ni(3)](+) undergo a valence-tautomeric transformation involving a Ni(III) and a phenoxyl radical species, as observed by EPR spectroscopy. Thus, these oxidized forms exhibit the phenomena of valence tautomerism and mixed valence simultaneously. The extent of delocalization of the radical species and of the Ni(III) species is discussed.     

Translations of fields represented by spherical-harmonic expansions for molecular calculations

In quantum chemistry one needs expansions of Orbitals and operators, defined with respect to one origin, about another origin. Because there is no straightforward method of obtaining such expansions, it is helpful to interpret them as translations of fields. The connection between translations and rotations of fields with the transformations of functions is considered. Of special physical interest are expansions in spherical harmonics, which have the form of an addition theorem. General properties of such expansions and possible methods to derive them are discussed.     

Functional group analysis on oxidized surfaces of synthetic textile polymers

A comprehensive collection of wet-chemical analyses of functional groups on oxidatively treated surfaces of hydrophobic polymers like poly(ethylene terephthalate) or polyolefine is presented. New methods are introduced. Textiles and foils have been subjected to advanced oxidation processes and the different oxygen functions have been quantified. Analysis of surface functional groups includes radical site determination with radical scavengers like diphenylpicrylhydrazyl, reduction of peroxides determined iodometrically, cationic dyestuff adsorption, carbonyl binding to Girard reagent P and surface hydroxyl group determination by surface nitrosation and subsequent azo-dye formation photometrically determinable. Use of potential surface swelling agents has been excluded except for addition of wetting agent. Wet-chemical analyses on textile surfaces bear the benefit of integrating over (relatively) large sample areas, a point which is interesting when regarding inhomogenities of textile or other surface constructions. In addition examples for visualisation for the existence of surface groups are described.     

Mass spectra of polymeric thioformaldehydes (CH2S)3, (CH2S)4, (CH2S)5 and (CH2S)x

The mass spectral fragmentations of various thioformaldehydes, 1,3,5-trithiacyclohexane, 1,3,5,7-tetrathiacyclooctane, 1,3,5,7,9-pentathiacyclodecane and a polymeric form (CH₂S)_x have been examined. The principal features of the spectra are reported. The fragmentation occurred by fracture of the ring in the cyclic compounds with or without rearrangement.     

Octahedral non-heme non-oxo Fe(IV) species stabilized by a redox-innocent N-methylated cyclam-acetate ligand

The ligand 1,4,8-tri-N-methyl-1,4,8,11-tetraazacyclotetradecane-11-acetic acid (Me3cyclam-acetic acid) has been synthesized by Eschweiler-Clarke methylation of cyclam-acetic acid, and the iron(III) complex [(Me3cyclam-acetate)FeN3]PF6, 1, has been synthesized, which has been found to have significantly different properties than its unmethylated analogue, [(cyclam-acetate)FeN3]PF6, 2. Whereas the iron ion in 2 is low spin with S = 1/2, 1 is found to be high spin at temperatures above 100 K, though low-spin species are observed at lower temperatures, indicating a spin crossover phenomenon. The iron(II) species 1red is electrochemically more accessible than 2red since the Fe2+/3+ redox wave in 1 appears approximately 350 mV more positive than the corresponding wave in 2. Also, 1 displays a reversible Fe3+/4+ redox wave, which is irreversible in 2, denoting that the Fe(IV) species 1ox is kinetically stable. 1red and 1ox have been generated electrochemically in solution and studied spectroscopically. M?ssbauer spectroscopy has confirmed that, in both reduction and oxidation, iron is the redox center, that 1red is high spin (S = 2), and that 1ox is low spin (S = 1), in contrast to 2red which is low spin and 2ox which could not be isolated.     

Role of the Platinum Nanoclusters in the Iodide/Triiodide Redox System of Dye Solar Cells

The publication covers materials and cluster science aspects of the platinum counter electrode (CE) in the “monolithic type” dye sensitized solar cell systems (DSSC). Nanocluster based catalytic platinum layers are utilized for the iodide/triiodide reduction in different electrolytes. Various preparative methods have been applied for the preparation of platinum nanoparticles for the CE. The structure, properties, and performance of the different nanoparticles obtained by thermal decomposition of H₂PtCl₆, triorganohydroborate reduction of a platinum salt, reductive stabilization of Pt(acac)₂ by trialkylaluminium, the “polyol method”, and the reduction of the H₂PtCl₆ by hydrogen are compared. The oxidation states of the platinum surface- and core-atoms were analyzed by X-Ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Near Edge Structure (XANES) respectively. Size and the crystalline structure of the particles were investigated by Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD). The charge transfer resistance of the different catalytic platinum layers resulted from the above mentioned preparative methods, was compared by electrochemical impedance spectroscopy (EIS). Dedicated to Prof. Günter Schmid on the occasion of 70th anniversary     

Single- and double-cubane clusters in the multiple oxidation states [VFe(3)S(4)](3+,2+,1+)

A new series of cubane-type [VFe(3)S(4)](z)() clusters (z = 1+, 2+, 3+) has been prepared as possible precursor species for clusters related to those present in vanadium-containing nitrogenase. Treatment of [(HBpz(3))VFe(3)S(4)Cl(3)](2)(-) (2, z = 2+), protected from further reaction at the vanadium site by the tris(pyrazolyl)hydroborate ligand, with ferrocenium ion affords the oxidized cluster [(HBpz(3))VFe(3)S(4)Cl(3)](1)(-) (3, z = 3+). Reaction of 2 with Et(3)P results in chloride substitution to give [(HBpz(3))VFe(3)S(4)(PEt(3))(3)](1+) (4, z = 2+). Reaction of 4 with cobaltocene reduced the cluster with formation of the edge-bridged double-cubane [(HBpz(3))(2)V(2)Fe(6)S(8)(PEt(3))(4)] (5, z = 1+, 1+), which with excess chloride underwent ligand substitution to afford [(HBpz(3))(2)V(2)Fe(6)S(8)Cl(4)](4)(-) (6, z = 1+, 1+). X-ray structures of (Me(4)N)[3], [4](PF(6)), 5, and (Et(4)N)(4)[6] x 2MeCN are described. Cluster 5 is isostructural with previously reported [(Cl(4)cat)(2)(Et(3)P)(2)Mo(2)Fe(6)S(8)(PEt(3))(4)] and contains two VFe(3)S(4) cubanes connected across edges by a Fe(2)S(2) rhomb in which the bridging Fe-S distances are shorter than intracubane Fe-S distances. M?ssbauer (2-5), magnetic (2-5), and EPR (2, 4) data are reported and demonstrate an S = 3/2 ground state for 2 and 4 and a diamagnetic ground state for 3. Analysis of (57)Fe isomer shifts based on an empirical correlation between shift and oxidation state and appropriate reference shifts results in two conclusions. (i) The oxidation 2 --> 3 + e(-) results in a change in electron density localized largely or completely on the Fe(3) subcluster and associated sulfur atoms. (ii) The most appropriate charge distributions are [V(3+)Fe(3+)Fe(2+)(2)S(4)](2+) (Fe(2.33+)) for 1, 2, and 4 and [V(3+)Fe(3+)(2)Fe(2+)S(4)](3+) (Fe(2.67+)) for 3 and [V(2)Fe(6)S(8)(SEt)(9)](3+). Conclusion i applies to every MFe(3)S(4) cubane-type cluster thus far examined in different redox states at parity of cluster ligation. The formalistic charge distributions are regarded as the best current approximations to electron distributions in these delocalized species. The isomer shifts require that iron atoms are mixed-valence in each cluster.