Determination of total,and bound Se in sera by INAA

In this study we report on the comparison between the total selenium in serum (total Se) with that which is apparently bound to high molecular weight (>12,000 D) species, presumably proteins (bound Se). Nine hundred seventy seven (977) serum samples arising out of a population-based epidemiological study were prepared in duplicate for the determination of total Se by pipeting directly into irradiation vials; and separate duplicate aliquots were dialyzed against DI water for the determination of bound Se. All samples were analyzed by neutron activation analysis via^77mSe (17.4 s). A small dialyzable Se component (6%) (free Se), defined as the difference between the total Se minus the bound Se, was identified.     

Tautomerism and stereochemistry of isohypericin,bromohypericines, and gymnochromes: Force field investigations

Summary Using an MM2 derived force field the stereochemistry and tautomerism of isohypericin and several bromohypericines, including gymnochrome D and isogymnochrome D, were investigated. The geometries of the propeller and double butterfly conformers of isohypericin were similar to those of hypericin. However, an interconversion barrier between the enantiomeric propeller conformers was found, which was 53 kJ/mol lower in isohypericin. From the ten tautomers of isohypericin the 7,14-dioxo tautomer was calculated to be the most stable one by about 50 kJ/mol. In the bromo derivatives and the gymnochromes the bromine substituents caused a ruffling of the biaryl fragments. The buttressing effect of the bromine led to an enhancement of the interconversion barriers between enantiomeric conformers. The double butterfly conformer was found to be more stable than the propeller conformer for tetrabromohypericin and the gymnochromes.

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Tautomerie und Stereochemie von Isohypericin und Bromhypericinen: Untersuchungen mit Hilfe der Kraftfeld-Methodik

Zusammenfassung Die Stereochemie von Isohypericin und einiger Bromhypericine sowie von Gymnochrom D und Isogymnochrom D wurden mit Hilfe eines von MM2 abgeleiteten Kraftfeldes untersucht. Die Geometrien der Propeller- und Doppelschmetterlings-Konformeren sind vergleichbar mit jenen des Hypericins. Die Interkonversionsbarriere zwischen den enantiomeren Propeller-Konformeren ist jedoch um etwa 53 kJ/mol niederer als im Hypericin. Von den zehn Isohypericin-Tautomeren ist das 7,14-Dioxotautomere das um etwa 50kJ/mol stabilste. In den Bromderivaten und den Gymnochromen bewirken die Bromsubstituenten eine Wellung der Biarylfragmente, wobei der Buttressing-Effekt der Bromsubstituenten zu einer Erhöhung der Interkonversionsbarrieren zwischen enantiomeren Konformeren führt. Das Doppelschmetterlings-Konformere ist beim Tetrabromhypericin und bei den Gymnochromen stabiler als das Propeller-Konformere.

     

The time evolution of the pair distribution function of polymeric systems

Summary The stress tensor of a polymeric system, solution or melt, is the sum of single molecule terms which may be expressed as integrals involving the distribution function in the phase space of a single molecule and intermolecular terms which involve the distribution function in the configuration space of pairs of molecules. The evaluation of the single molecule terms is usually based on the solution of the diffusion equation in the configuration space of a single molecule. In the present development, an analogous diffusion equation in the configuration space of a pair of molecules is developed. The development is based on a generalization of the time-smoothing ideas introduced by Kirkwood. Expressions are obtained for the various friction coefficients as time correlation functions.     

Identification of the plant source of the Chinese crude drug „Dan-zhu-ye“ using the low-temperature plasma ashing technique

Summary A microchemical approach for the identification of plant source of Chinese diuretic crude drug Dan-zhu-ye using low-temperature plasma ashing is reported. The specimen was ashed on a microscope slide and the remaining ashed tissue was microscopically compared with other specimens of bamboo and bamboo grasses. Characteristic distribution patterns of silicon bodies and their shape in Dan-zhu-ye have suggested that the plant source of the crude drug isLophatherum sinense Rendle or at least its very close relative.

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Zusammenfassung Über die Ergebnisse der Tieftemperatur-Veraschung der chinesischen Rohdroge Dan-zhu-ye zwecks pflanzlicher Zuordnung dieses Diureticums wurde berichtet. Das Untersuchungsobjekt wurde auf einem Objektträger verascht und der Geweberückstand unter dem Mikroskop mit anderen Proben von Bambus und Bambusgräsern verglichen. Charakteristische Verteilungsmuster von Siliziumkörperchen und deren Form in Dan-zhu-ye legen die Annahme nahe, daß die Droge von Lophatherum sinense Rendle stammt oder ihm wenigstens sehr nahe steht.

     

Thermal analysis of macromolecules

This review traces the development of thermal analysis over the last 40 years as it was experienced and contributed to by the author. The article touches upon the beginning of calorimetry and thermal analysis of polymers, the development of differential scanning calorimetry (DSC), single run DSC and other special instrumentations, up to the recent addition of modulation to calorimetry. Many new words and phrases have been introduced to the field by the author and his students, leaving a trail of the varied interests one can have over 40 years. It began with cold crystallization and most recently the term oriented, intermediate phase was coined, creating in-between: extended chain crystals, the irreversible thermodynamics of melting of polymer crystals, dynamic differential thermal analysis (DDTA), the rule of constant increase ofC _p per mobile bead within a molecule at the glass transition temperature, superheating of polymer crystals, melting kinetics, crystallization during polymerization, the chain-folding principle, molecular nucleation, rigid amorphous phase, a system of classifying molecules, macroconformations, amorphous defects, rules for the entropy of fusion based on molecular shape and flexibility, single-molecule single-crystals, a system of classifying phases and mesophases, and condis phase.First and foremost I would like to acknowledge the unwavering support through my wife, Heidel, without whom many of the projects simply could not have been completed. Similarly, our children had to grow up knowing that often research and teaching had to take precedence. Without coworkers, little could have been accomplished. Of the about 120 postdoctoral fellows, graduate students, and technicians, most of whom contributed to the listed references, and many have participated on their own in this issue, goes my thanks for the bulk of the scientific work. Many friends and colleagues contributed with discussion and constructive criticism, some of them have also contributed in this collection of papers related to thermal analysis. Little work can be done without this interplay of ideas. The limited space has not permitted to give a full appreciation of the importance of the ideas drawn from the literature. These thousands of additional references can be found in the initial papers and reviews of the subjects treated.Material support was received from the three major instrument companies for thermal analysis equipment: TA Instruments, Inc.; Perkin-Elmer Corp.; and Mettler-Toledo, Inc. Without this help we would not always have been able to be at the forefront of instrumentation. Major financial support for the research came from outside the universities. I estimate that over the 40 years about 4 Megadollars were spent by government agencies, companies, and private foundations to support coworkers, myself during the summers, research equipment, expenses, and travel. A large amount of money, but not too much if one compares it to typical expenditures in the field of athletics (about 10 k$ per paper). Major sustained funding came from the Advanced Projects Agency (ARPA), the Office of Naval Research (ONR), the National Aeronautics and Space Agency (NASA), the Department of Energy (DOE), and, most prominently, the National Science Foundation (NSF). At present our work is supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 90-00520 and the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract DE-AC05-84OR21400 with Lockheed Martin Energy Systems, Inc. Industrial support is presently given by TA Instruments, Inc; ICI Paints; Exxon Res. and Eng. Co.; Shell Development Co.; Toray Research Center; and Mettler-Toledo, Inc.Last, but by no means least, I would like to thank Dr. E. Turi for the invitation to write this paper and for her untiring effort to entice so many of my students and friends to contribute to this issue of the Journal of Thermal Analysis.     

Meeting the need for reference measurements

Summary Reference materials do fulfil a very useful function in that they provide means to check, verify and calibrate measurement procedures and instrumentation. However, the material is often idealized compared to real life samples: it is either (very) pure or does not correspond in concentration level or matrix to the real life case. It is shown how this situation could be remedied if real life samples with carefully assessed reference values could be made available regularly as unknowns to measurement laboratories. Comparison of the latter's measurements with the reference values then would provide a picture of the real performance of the particular measurement community in general and of each participating laboratory in particular. The opinion is expressed that isotope-specific methods have now matured to the stage that, if they are correctly applied under rigorous control and based on highly skilled expertise, they can provide such reference values against which laboratories can then evaluate their routine performance in regular Interlaboratory Measurement Evaluation Programmes (IMEPs).

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Wie der Notwendigkeit von Referenzmessungen entsprochen werden kann

     

Zero-Dimensional Nanodots on One-Dimensional Nanowires: Reductive Deposition of Metal Nanoparticles on Silicon Nanowires

We review herein the surface chemical properties of silicon nanowires (SiNWs) and show how SiNWs can be used as platforms in doing chemistry in the nanorealm. In particular, the surfaces of HF-treated SiNWs (which are H-terminated) exhibit interesting chemical reactivities towards reductive deposition of metal ions such as silver, copper, palladium, etc., giving rise to metal particles or aggregates on the SiNW surfaces. By varying the concentration of the metal ions in solution, nanostructures of these metals of different shapes, sizes, and morphologies can be fabricated. The reductive growth of ligated Au–Ag clusters of single size, shape, composition, and structure, on the SiNWs was also investigated. Two interesting phenomena, the sinking cluster and the cluster fusion processes, were observed by TEM. These assemblies of metal nanoparticles on silicon nanowires may be considered as zero-dimensional nanodots, on one-dimensional nanowires. It is hoped that fabrication of these metallic nanodots on silicon nanowires will lead to new and novel composite materials of importance in nanotechnology.     

Multivariate Statistical Assessment of Air Quality: A Case Study

The present paper deals with the application of several chemometrical methods (cluster and principal components analysis, source apportioning on absolute principal components scores) to an aerosol data collection from Unterloibach, Austria. It is shown that seven latent factors explaining almost 80% of the total variance are responsible for the data structure and are conditionally identified as secondary aerosol, mineral dust, oil burning, lead smelter, coal burning, salt and fertilizer emission sources. Furthermore, the contribution of each identified source to the formation of the particle total mass and chemical compounds total concentration is calculated. Thus, a reliable assessment of the air quality in the region is performed. The requirements of the sustainability concept for ecological indicators in this case is easily transformed into a multivariate statistical problem taking into account not separate indicators but the specific multivariate nature of aerosol pollution.     

An augmented ribbon model of protein structure

In this paper, work on a new model,an augmented ribbon model, for describing a number of features of primary, secondary, and super-secondary protein structure in a qualitative but mathematically rigorous way is discussed. The structural features that can be treated by the model include connectivity, directionality, chirality, orientation, and proximity which, in many cases, are difficult to deal with using more traditional structural representations (e.g. wireframe, ball-and-stick, or space-filling CPK). In practice, the information encoded in the augmented ribbon model is represented by a labelled, directed graph (digraph) which provides an efficient means for storing and analyzing the information on computers. This opens the way to computer-based analyses of proteins and for the application of similarity methods that have been shown to be quite useful in treating small molecules.     

Preparation of La(OH)3 colloids and tactoid structures

Summary Lanthanum(III) hydroxide colloids have been prepared by in situ and repeptization method. The in situ colloids were aggregated in schiller layers. The formation of the sol is a relatively slow process which accounts for a good uniformity of the particles size. The characteristic lateral array of the colloidal particles in Schiller layers could be destroyed by simple shaking the sample. Lanthanum(III)hydroxide sols prepared by the repeptization method were needle-shaped and not tactoidally orientated.

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Zusammenfassung Lanthan(III)hydroxid-Kolloide wurden in situ und durch Repeptisation hergestellt. Eine regelmäßige Aggregation der Kolloidteilchen wurde nur bei in situ bereiteten Solen beobachtet (SchillerSchichten). Die Bildung der Sole ist ein verhältnismäßig langsamer Prozeß, was mit der ziemlich engen Verteilung der Teilchengr6ßen zusammenhängen k6nnte. Die Schiller-Schichten werden durch Schütteln zerstört. Ein durch Repeptisation gebildetes Lanthan (III)hydroxid war nadelförmig ausgebildet und nicht taktoidal aggregiert.

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With 5 figures

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*) Our thanks are due to Dr. N. LjubeN for the electron microscopy work.     

Chromium (III) trihalide complexes of 4-aminobenzophenone

Summary The following chromium(III) complexes of 4-aminobenzophenone have been prepared and investigated by infrared and electronic spectra and magnetic susceptibility measurements: CrCl₃L, CrCl₃L₂ (pink and brown), CrCl₃L₃, CrCl₃L₆, CrBr₃L₂, CrBr₃L₃, CrBr₃L₄, CrBr₃L₆, CrBr₃L₇ and CrBr₃L₈. The CrBr₃ complexes were each isolated in a yellow and a red form. In the red CrBr₃ and in the yellow CrBr₃L₂ the ligand is bonded through the amine nitrogen. The CrCl₃ complexes are probably molecular complexes.     

Similarity and dissimilarity in posets

The relevance of partially ordered sets (or posets) in a wide diversity of contexts in chemistry is emphasized, and the utility of distance functions (or metrics) on such posets is noted. First a notion of scale similarity is introduced to make comparisons within certain so-called scaled posets, for which there is formulated natural comparators, which in turn lead to associated distance functions. Beyond taking note of several chemically relevant examples of these scaled posets and their consequent associated similarity measures, a second chemically relevant class of so-called shifted posets is similarly developed, with examples. Even further extension of some aspects of the current approach is indicated, and finally the multi-posetic character of chemical periodic law is suggested.     

The influence of substituted alcohols on the temperature of maximum density of water

The influence of various substituted (including halogenated) alcohols on the temperature of maximum density (TMD) of water has been investigated. Evaluation of the structural contribution to the shift in the TMD demonstrates that trifluoroethanol, hexafluoroisopropanol, and neopentyl alcohol are structure makers, whereas trichloroethanol and tribromoethanol are structure breakers. The results are discussed in terms of an excluded volume model.     

Natural flavours of wine: correlation between instrumental analysis and sensory perception

Summary The aroma of wine consists of 600 to 800 aroma compounds from which especially those, typical for the variety, are already present in the grapes. The aroma extracts — received by extraction with trichlorofluoromethane — are separated by gas chromatography. There are significant varietal differences between the aromagrams (fingerprint pattern). Thus the amount of some flavour compounds (key substances) shows typical dependence on the variety. Especially monoterpene compounds play an important role in the differentiation of wine varieties.The German white wines can be differentiated into three groups only by quantitative determination of 12 monoterpenes (terpene profile). These groups are: Riesling type, Muscat type and Silvaner-Weißburgunder type. Such terpene profiles are also useful for the separation of real Riesling wines from others called Riesling (e.g. Welschriesling, Kap Riesling, Emerald Riesling) but not produced from grapes of the variety Riesling. Including further components and by means of statistical methods as for example linear discriminant analysis even the different varieties within the mentioned groups (for instance the Riesling-group: Riesling, Kerner, Ehrenfelser, Bacchus, Müller-Thurgau) can be separated from each other.To identify compounds causing off-flavours the sniffing technique is the method of choice. The off-flavour is pinpointed during gas chromatography separation of the complex aroma mixture by effluent sniffing. Once allocated, the chemical nature of the off-flavours is elucidated by spectroscopic methods. Substances contributing to the green pepper taint, the strawberry note, mousiness, corkiness etc. in wine could be found in this way.     

Interpretation of electronic spectra of aromatic hydrocarbons by the “molecules in molecules” method

The molecules in molecules method has been applied to five groups of hydrocarbon molecules or ions. Energy, polarisation and intensity of electronic transitions have been compared with experimental data and previous theoretical results. The results show that the method is applicable even when there is relevant conjugation between the fragments.

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Zusammenfassung Die molecules in molecules-Methode wurde auf fünf Gruppen von Kohlenwasserstoff-Molekülen angewandt. Energie, Polarisation und Intensität von elektronischen Übergängen wurden mit experimentellen und theoretischen Resultaten verglichen. Die Resultate beweisen, daß die Methode anwendbar ist, auch wenn eine wesentliche Konjugation zwischen den Fragmenten besteht.

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Resumé La méthode molecules in molecules a té appliquée à cinq groupes de molécules ou ions d'hydrocarbures. On a comparé les energies, la polarisation et l'intensité des transitions électroniques avec les données experimentales et les données théoriques qu'on avait précedemment calculées. Les résultats indiquent que la méthode est appliquable, même lorsqu'on a une conjugation assez importante entre les fragments.

     

Zur gas-chromatographischen Analyse strahlenchemischer Reaktionsprodukte

Zusammenfassung Strahlenschemische Reaktionsprodukte sind für die gaschromatographische Analyse als komplizierte Mischungen zu betrachten. Große Flüchtigkeits- und oft extreme Konzentrationsunterschiede zwischen den Komponenten erschweren die Analyse und erfordern die Anwendung spezieller Methoden und Techniken der Probenvorbereitung und-aufgabe sowie der Trennung und Bestimmung nur der wirklich interessanten Komponenten. Doppelsäulentechniken unter Einbeziehung von heartcutting, backflushing und trapping in geschlossenen, automatisch steuerbaren Apparaturen spielen dabei eine wichtige Rolle.

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Gas chromatographic analysis of reaction products from chemical irradiation

Summary The products of chemical irradiation can be regarded, from the gas chromatographic point of view, as being complex mixtures whose analyses are made difficult by the large differences in volatility and concentration of the various components. Special techniques must be used in the sample preparation and introduction as well as in the exclusive separation and determination of the components of particular interest. An important rôle in this process is played by double column techniques with heartcutting, backflushing and trapping in an automatically controlled closed system.

     

A new computational microscope for molecules: High resolution MEDLA images of taxol and HIV-1 protease,using additive electron density fragmentation principles and fuzzy set methods

Based on the molecular electron density lego assembler (MEDLA) method, a computational microscope was developed that generates accurate images of bodies of large molecules at a resolution far exceeding current experimental techniques. The MEDLA microscope can be tuned to display the high electron density regions of formal chemical bonds; or to show the low density regions of hydrogen bonds and secondary interactions, or to display local shape requirements important in molecular recognition. The power of the method is illustrated by examples of detailed images of taxol, an important anti-cancer agent, and HIV-1 protease, a protein of 1564 atoms. A mathematical framework of the approach, based on fuzzy sets, and the fundamentals of several additional applications of the additive, fuzzy fragmentation principle are presented.     

On the recognition of structural features: Some general problems illustrated by hamiltonian paths in polyhexes

Human and machine recognition skills are discussed, though not comprehensively reviewed, and some of the difficulties are illustrated by algorithms written to search for Hamiltonian paths in polyhexes. The most successful strategy for this is based upon the branching graph, a recently introduced graph-theoretical device which can aid the recognition of edges that arenot part of a Hamiltonian path. Another, more widely applicable approach that is interesting, although in this preliminary form only a little better than random methods, uses the metaphor of biological evolution, and tries to breed and grow paths subjected to natural selection.     

Trends and demands in and on trace element analysis in the biomedical and environmental field

Problems in trace element analysis in the biomedical and environmental field are discussed, especially for the most interesting elements, as well as adequate analytical techniques for their analysis. The state of the art for the relevant elements, the recommended methods as well as the new speciation analysis are briefly described. Besides these points, quality control, becoming more and more important to improve the reliability of analytical data, is discussed.     

Understanding the properties of isospectral points and pairs in graphs: The concept of orthogonal relation

The mathematical property orthogonal relationship is used in proving the fact that isospectrality, isocodality and isocoefficiency of vertices within a graph are all equivalent. The same is true for isospectrality, strict isocodality and strict isocoefficiency of pairs (including edges) within a graph, whereas the weak versions of the latter properties are necessary but not sufficient for isospectrality of pairs. Similarly, necessary and sufficient conditions for isospectrality of vertices and pairs in different graphs are derived. In all these proofs, the concept of orthogonal relation plays a major role in that it allows the use of tools of elementary linear algebra.