Determination of chlorinated paraffins by GC-MS

Summary Although chlorinated paraffins are widely used and therefore produced in large amounts (about 250 kt/a) — with well known problems —, there is a lack of a selective, highly sensitive and reproducible analytical method for the determination of these substances. Such a method is presented using GC/MS with electron impact ionization for their quantitative determination. The samples, pretreated with conc. sulphuric acid, were cleaned up by solid-phase extraction on alumina, and the chlorinated paraffins were determined by GC/MS using highly selective ion clusters.By this method, determination limits of 3 ng (corresponding to about 1.5 ppb) were routinely obtained. In contrast to the general methods of maximum signal selection or the selection of molecule ions in mass spectroscopy, the presented approach leads to higher selectivity, less discrimination between different types of chlorinated paraffins and allows to obtain further information on the degree of chlorination.     

Electronic energy inequalities for isoelectronic molecular systems

Within the Born-Oppenheimer approximation an inequality relation is derived between points of electronic energy hypersurfaces of pairs of isoelectronic molecules. The inequality is directly applicable to point pairs fulfilling a symmetry criterion for the nuclear frameworks and it may be extended to coordinate domains on both hypersurfaces. The result is applied to special examples of conformational problems, dissociation reactions and impurity —vacancy centres in solid clusters.     

Functional Polyoxometalate Thin Films via Electrostatic Layer-by-Layer Self-Assembly

Polyoxometalates (POMs) comprise a structurally diverse class of inorganic transition metal oxygen clusters which—owing to their unique electronic properties—hold promise for a host of technological applications such as electrochromic windows, sensors, or heterogeneous catalysts, prototypic examples of which will be briefly exemplified. The integration of POMs into functional architectures and devices, however, necessitates the development of general methods that allow positioning these clusters in well-defined supramolecular architectures, thin films, or mesophases. This short review highlights recent advances in the preparation of composite multilayers fabricated by electrostatic layer-by-layer self-assembly (ELSA) of POMs and a variety of water-soluble cationic species, including transition metal complexes, cationic surfactants, polycations and bipolar pyridine.     

Continuous symmetry measures for complex symmetry group

Symmetry is a fundamental property of nature, used extensively in physics, chemistry, and biology. The Continuous symmetry measures (CSM) is a method for estimating the deviation of a given system from having a certain perfect symmetry, which enables us to formulate quantitative relation between symmetry and other physical properties. Analytical procedures for calculating the CSM of all simple cyclic point groups are available for several years. Here, we present a methodology for calculating the CSM of any complex point group, including the dihedral, tetrahedral, octahedral, and icosahedral symmetry groups. We present the method and analyze its performances and errors. We also introduce an analytical method for calculating the CSM of the linear symmetry groups. As an example, we apply these methods for examining the symmetry of water, the symmetry maps of AB₄ complexes, and the symmetry of several Lennard‐Jones clusters. © 2014 Wiley Periodicals, Inc.     

Regularities of thermal decay of carbonyl chalcogenide metal clusters

The thermal decay of 19 individual carbonyl homo- and heterochalcogenide clusters with different M/X ratios (M = Fe, Mn, Pt, Cr, W, Mo, Re, Ru; X = S, Se, Te) was studied by differential scanning calorimetry and thermogravimetry. The process is stepwise and occurs at relatively low temperatures (100—350 °C). The general fact of incomplete removal of carbon monoxide (due to the formation of carbide and oxide impurities) during thermolysis of narbonyl chalcogenide clusters with the M : X ratio greater than 1 was elucidated. Conversely, when M : X 1 (or at any M/X ratio for clusters containing methylcyclopentadienyl groups), pure metal chalcogenides are formed.     

A Perspective on the Science of Clusters

In this article, the interdisciplinary science of clusters is discussed in general terms. Different types of clusters across vast scales of matter, energy, space, and time in the physical world are discussed. Specific examples of clusters in chemistry and physics are used to illustrate various principles or models of clustering processes of atoms and molecules as well as to demonstrate the exquisite beauty and pattern of clusters and the clustering phenomena so ubiquitous in nature. Nowadays, “designer clusters” can be made with tailorable properties and used as “building blocks” to form supermolecules, or to construct large cluster-based hierarchical materials with tunable properties, or to fabricate cluster-based devices with specific functions, etc., thereby providing a materials base for nanotechnology. Clustering is a spontaneous self-assembly process and the similarity across scales reflects the intrinsic self-organization and self-similarity principle of the physical world. Geometry and symmetry transcend all clustering processes, in ordered as well as in disordered systems.     

Self-assembly of anisotropic tethered nanoparticle shape amphiphiles

The varied and exotic shapes of new nanoscale organic and inorganic building blocks provide new opportunities to engineer materials possessing specific functionality and physical properties dictated by the unique packings of these particles. We briefly review some of the current strategies for inducing the self-assembly of these building blocks focusing on one strategy in particular—the attachment of tethers to the building blocks at precise locations to create tethered nanoparticle “shape amphiphiles”. We use computer simulation to demonstrate that the resulting anisotropy imparted to nanocrystals or nanocolloids by the tethers can be used to encode simple design rules into the building blocks that ultimately result in a unique self-assembled structure. We present a general classification scheme for tethered nanoparticles wherein the anisotropy of a shape amphiphile is described by a vector comprised of one or more axes each describing a measure of anisotropy.     

Exploring the electronic structure of elemental lithium: from small molecules to nanoclusters, bulk metal, and surfaces

Clusters of lithium atoms ranging in size from Li4 to Li40 and bulk metallic solids, including surfaces, are investigated through first principles electronic structure calculations, which are based upon density functional theory and the electron localization function (ELF). It is found that large lithium ppi-type contributions in the electronic wavefunction cause the electrons to localize in interstitial regions, which leads to multicenter bonding for both the clusters and the solids, including their surfaces. For the smaller clusters these stabilizing ppi interactions also lead to short Li-Li interatomic distances, which in conjunction with the longer bonds induces "distance alternation" in the range from 2.45 A to 3.15 A. This consequence of the additional ppi interactions is absent in simple solids due to symmetry. The electronic structure of the clusters is topologically insensitive to deformations that do not affect their general shape, but changes significantly upon isomerization. The ramifications upon dynamic properties is that the clusters are quasi-rigid at low temperatures and retain their shape though the distance alternation pattern is suppressed. The picture which emerges for bonding in the bulk solid is that the metallic state arises from the presence of a large number of partially occupied multicenter bonds. For nanoscale clusters only the surface of these clusters exhibits strong localization, whereas their interiors display localization properties similar to the bulk metallic solid. On the other hand, localized states similar to those of the clusters ("dangling bonds") are found on the (001) surface of body-centered cubic (bcc) and face-centered cubic (fcc) lithium solids.     

Solution of the patterson function (vector system) from its strong (multiple) peaks

Summary A method of solving the Patterson function is given which is based on the use of information found in the strong peaks.Two (and even one) strong peaks are sufficient for the successful use of this simple method. These strong peaks in Patterson space normally arise from crystals of low symmetry which contain large numbers of atoms in the unit cell (i.e. in those cases when other methods of solution are very difficult). It does not matter what kinds of atoms there are in the unit cell, because in the process of solution, we nowhere refer to their essential nature (in any case, no further than a rough estimate of the strength, or height, of the peaks).The normal final result of the analysis (several independent solutions) — the images of the main system of points — is not a disadvantage of the method, but conversely is an advantage because it makes internal control possible and gives an independent check on the correctness of the solution chosen.The method should give best results for crystals of low symmetry.N. I. Lobachevskii Gorkii State University. Institute of Crystallography, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 9, No. 5, pp. 820–829, September–October, 1968.     

A unification of chirality measures

A general classification of chirality measures is suggested, based on a new unifying scheme. Two classes of measures - congruity and resolution type — are defined All chirality measures so far reported in the literature are found to belong to one of these two classes. At a higher level of unification, a more general construction is suggested that includes congruity and resolution measures as limiting cases. It is shown that congruity measures are nested in clusters of eight, generated by 2³ combinations of their possible choice of a reference object (chiral vs. achiral), representation form (optimized vs. factorized) and type of chiral object under consideration (discrete vs. continuous). Each of the eight cases can have an infinite number of variations depending on the choice of averaging scheme. The problem of dimensionality is discussed for congruity measures and is shown to be unresolvable only for the case of chirality measures based on the discrete metric (e.g. overlap measures).     

Photometric extraction method for determination of cephalexin

Summary A photometric extraction method is developed for determination of cephalexin. Cephalexin is hydrolysed for 5 min in sulphuric acid medium on a steam-bath, the hydrolytic product forming a coloured compound with ninhydrin in 25% H₂SO₄. This compound is extracted with CHCl₃ and its absorbance measured at 520 nm. The reaction is selective — it is negative for the initial reagents in the cephalexin synthesis and for most other antibiotics. The only two antibiotics giving a similar reaction — ampicillin and cephalotin — do not interfere in the determination of cephalexin. The method is rather simple and permits rapid determination of cephalexin with satisfactory precision and accuracy — coefficient of variation 0.91–1,36%, relative error of the determination 0.66–1,19% (95% confidence limits).

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Zusammenfassung Eine extraktions-photometrische Bestimmungsmethode für Cephalexin wurde ausgearbeitet. Die Substanz wird 5 min auf dem Wasserbad in schwefelsaurem Milieu hydrolysiert. Das hydrolysierte Produkt bildet mit Ninhydrin in 25%iger Schwefelsäure eine gefärbte Verbindung. Diese wird mit Chloroform extrahiert und bei 520 nm gemessen. Die Reaktion ist selektiv; sie verläuft negativ bei den Ausgangsprodukten der CephalexinSynthese und bei den meisten anderen Antibioticis. Die einzigen beiden Antibiotika, die eine ähnliche Reaktion geben — Ampicillin und Cephalotin — stören die Bestimmung von Cephalexin nicht. Die Methode ist ziemlich einfach und ermöglicht die rasche Bestimmung von Cephalexin mit hinreichender Genauigkeit: der Variationskoeffizient beträgt 0,91–1,36%, der relative Fehler 0,66—1,19% (bei einer Vertrauensgrenze von 95%).

     

Structural chemistry of complexes with an encapsulated metal ion. α-Dioximate,oximehydrazonate, and dihydrazonate clathrochelates

The review surveys the main trends in the structural chemistry of clathrochelates: the determination of the crystal and molecular structures of various types of new complexes, their symmetry and functionality; the supramolecular organization and phase transitions of clathrochelate crystals; the structure—spectral parameter relationships and the deduction of the molecular structures; the use of X-ray diffraction data for explanation of the kinetic and thermodynamic parameters of the synthesis and decomposition of clathrochelates.Hereinafter, the papers marked with an asterisk ✾ are dedicated to Academician Yurii Nikolaevich Bubnov on the occasion of his 70th birthday.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2009–2020, October, 2004.     

A recycling technique for the chromatographic separation of enantiomers and diastereomers on triacetylcellulose

A simple and inexpensive equipment for the optical resolution of enantiomers (and separation of diastereomers) on triacetylcellulose in ethanol at elevated pressure is described. It involves a closed circuit of solvent (pump—column—detector—pump) allowing a continuous chromatography up to 16 cycles without stopping the flow or handling fractions.This useful and versatile method permitting also the determination of enantiomeric purities is illustrated by several examples of centro-, axial- and planarchiral arenes and metallocenes.Herrn Prof. Dr.U. Schmidt, Stuttgart, zum 60. Geburtstag gewidmet.     

DFT calculations of vibrational spectra and nonlinear optical properties for MgO nanotube clusters

The IR and Raman spectra, nonlinear optical properties of MgO nanotube clusters are studied by density-functional theory at B3LYP/6-31G(d) level. The IR spectra are match closely to those in the corresponding MgO cluster and bulk materials. The strongest peaks of the IR spectra are located in the range from 650 to 750 cm⁻¹. The Raman spectra are very sensitive to structural variations in MgO clusters, and redshift of vibrational frequency is observed in Raman spectra as increasing cluster length. The motion of the strongest peaks in spectra is discussed. The total dipole moment and the first hyperpolarizabilities oscillate between zero and a constant when the layer is grown for the layer dependence of symmetry in MgO nanotube clusters.     

A kinetic-catalytic method with repeated addition of one reactant — the determination of manganese, iodide, urease and cadmium

The use of a new kinetic-catalytic method with repeated addition of one reactant in the same system is described. The determination of manganese (periodate—malachite green; photometric observation), iodide (cerium(IV)—arsenic(III); potentiometric observation) and urease (hydrolytic splitting of urea; potentiometric observation) serves to illustrate the procedure.     

Quantitative determination of several mono- and oligosaccarides in food products by means of high-pressure liquid chromatography replacement of the toxic eluent 'acetonitrile/water' by a mixture of harmless solvents

Summary The toxic eluent mixture acetonitrile/water frequently used for separation of mono- and oligosaccarides is replaced by the harmless temary mixture acetone/ethyl acetate/water. By various techniques — degassing of the eluent, parallel connection of two columns and temperature control of the columns, of the eluate and RI-detector — the method is made suitable for the determination of lower saccharide concentrations than usual. Methods for rational preparation of samples — extraction of the saccarides, deionizing of the sample solution — are suggested. Based on examples, the efficiency of the method is demonstrated.     

Verfahren zur Bestimmung des Fungicids Dithianon auf ?pfeln

Zusammenfassung Es werden spezifische Verfahren zur Aufreinigung und Bestimmung von Dithianon auf der OberflÄche bzw. im Homogenisat von Äpfeln beschrieben. Der Wirkstoff wird mit Dichlormethan oder Chloroform extrahiert, von pflanzlichen Begleitstoffen durch Verteilung in einem zweiphasigen Lösungsmittelsystem und — bei der Untersuchung des Homogenisats — durch prÄparative Schicht-Chromatographie an Kieselgel abgetrennt und nach Farbreaktion mit Morpholin bei 510 nm colorimetriert. Die in Zusatzversuchen ermittelte Standardabweichung betrÄgt für OberflÄchenrückstÄnde 5,1% (8,7% für RückstÄnde im Homogenisat), die untere Bestimmungsgrenze 0,06 ppm (0,05 ppm), die Wiederfindung 95% (61%). Eine selektive Identifizierung und halbquantitative Bestimmung des Wirkstoffes gelingt nach dünnschicht-chromatographischer Trennung durch eine empfindliche Farbreaktion mit, o-Aminothiophenol. — An Äpfeln und Sauerkirschen erstellte Abbaukurven werden diskutiert.

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Procedures for the determination of the fungicide dithianon on apples

Specific methods are described for clean-up and determination of dithianon on the surface and in the fruit pulp of apples. The compound is extracted with dichloromethane or chloroform and separated from interfering vegetable substances by distribution in a two-phase solvent system and—for the fruit pulp—by chromatography on silica gel. Determination is carried out photometrically at a wavelength of 510 nm after colour reaction with morpholin. The relative standard deviation is 5.1% for surface residues (8.7% for the fruit pulp), the limit of determination is 0.06 ppm (0.05 ppm) and the recovery is 95% (61%). A selective identification and half quantitative determination can be performed by thin-layer chromatography combined with a sensitive colour reaction with o-aminothiophenol.—Degradation curves on apples and cherries are discussed.

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Herrn Prof. Dr. K. G. Krebs zum 60. Geburtstag gewidmet.

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Die experimentellen Arbeiten wurden von Frl. G. Kissel und Herrn K. Hallstein durchgeführt.     

Polynuclear manganese grids and clusters—A magnetic perspective

High nuclearity paramagnetic, spin-coupled transition metal clusters and grids are fascinating chemists and physicists partly because of their structural beauty, and the challenge of creating them, but also because of their novel physical properties. Magnetic interactions between the spin centers are a primary focus. This review will examine a selection of Mn(II) polynuclear grids and clusters, with nuclearities in the range Mn₄ to Mn₉. Theoretical treatments of the magnetic properties are discussed, and approaches to solving the exchange problem for ‘large’ spin systems related to computational difficulties. A freely available software package (MAGMUN4.1) is presented as a means of dealing simply with spin-coupled clusters in general, and symmetry reduction methods are discussed briefly as a means of dealing with ‘large’ spin systems.     

Preparation of halogen-modified titanium(II) arene complexes and their electronic spectra

Summary Complexes of overall formula TiAl₂X₈ · Ar (X = Cl, Br or I, Ar = benzene or hexamethylbenzene) and the complexes containing various amounts of Br or I in addition to Cl were prepared both by a direct synthesis — the reduction of titanium tetrahalide by aluminium in the aromatic solvent and in excess of the corresponding aluminium halide — and by halogen exchange between the complexes and aluminium halides. The interpretation of the electronic spectra of the complexes is given on the assumption of pseudooctahedral symmetry of the ligand field. The values of 10 Dq and B obtained are compatible with the assignment.