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.     

Computer-aided library search of combined LC-Retention and diode-array-UV-spectral data

An automated library search system for computer-aided identification of organic compounds using combined UV-spectral and LC-retention data, as acquired by HPLC with linear diodearray-UV-detection, is presented.The keystone of the system is a set of similarity indices which have been developed on the basis of mathematical-statistical models of the reproducibility of the spectral and retention data. The similarity indices have the form of a significance probability, a quantity originating from the general theory of hypothesis testing. The output of the LC-UV retrieval system is a compound identity or a list of identities (if any) for which the relevant similarity index has a value above a preset threshold. The data base used in this investigation contained 186 sets of UV-spectral and LC-retention data of 74 organophosphorus pesticides measured from standard solutions under various experimental conditions. A test set consisted of 186 alternative data sets of the same compounds as contained in the data base, however measured under different experimental conditions. The performance of the LC-UV reproducibility-based retrieval (LUVRR) system was evaluated using recall/reliability plots. The results appeared to be quite promising: for 95% of the unknowns, the target reference (correct positive) was on top of the hit list with a similarity index value being significantly higher than values found for false positives.The software is written in Pascal. The present (experimental) version of the system runs on a Data General Eclipse MV/4000 minicomputer.     

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.     

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.     

Philosophical aspects of chemometrical strategy in Analytical Chemistry

Summary This paper discusses the philosophical aspects of the three main chemometrical strategies in analytical chemistry: statistical data treatment, optimization and modelling, pattern recognition. It is possible by a more general consideration of these approaches to find a proper place of different philosophical categories such as form and content, induction and deduction, concrete and general in analytical chemistry. The philosophical aspect of the considerations allows a deeper penetration into the theoretical basis of chemical analysis.

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Philosophische Betrachtungen zu chemometrischen Strategien in der Analytischen Chemie

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Presented at the First International Symposium on History and Philosophy in Analytical Chemistry, Vienna, November 22–23, 1985     

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.     

Interplay of Thermochemistry and Structural Chemistry,the Journal (Volume 13, 2002) and the Discipline

As practiced disciplines, structural chemistry and thermochemistry need not be related. In the current study they are: the contents of the journal Structural Chemistry (Vol. 13) for the year 2002 have been reviewed and then most articles that appeared therein were given a thermochemical commentary, spin or slant.     

State-of-the-art in organic elemental micro and ultramicro analysis

Summary Nernst developed a quartz torsion microbalance in 1903. In consequence of this pioneering work, Emich in the Technical University of Graz, Austria, had systematized a series of chemical operations in microscale as well as a microchemical analysis. Further advances in technique and method of organic microanalysis had been accomplished by Pregl in Graz in 1912. His work had been strongly supported by a new microbalance which was known as Kuhlmann microbalance. Pregl's original methods of analysis were arranged and published in 1916 as Die quantitative organische Mikroanalyse. It is still noteable that the Nobel prize of 1933 had been presented to Dr. Pregl. In accordance with a combination of electronic microbalance and computer techniques, organic elemental microanalysis has grown to include advanced instrumentation and on-line computation. Successful adaptation of microchemical analysis has expanded today not only to pure organic compounds, but on industrial intermediates, polymers, food additives and many other compositions. The paper includes a discussion of the relative merits of traditional and modern analytical techniques together with the progression of microbalances. Recent developments in organic micro and ultramicro analysis in Japan are also described.     

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.     

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.     

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.

     

Interplay of Thermochemistry and Structural Chemistry, the Journal (Volume 11, 2000), and the Discipline

As practiced disciplines, structural chemistry and thermochemistry need not be related. In the current study they are: the entire contents of the journal Structural Chemistry (Vol. 11) for the year 2000 has been reviewed and then each and every article that appeared therein was given a thermochemical commentary, spin or slant.     

The measurement of “enhanced” L and M X-ray yields from charge-induced studies with protons and1H 2 + ion beams

Earlier work on Charge Induced X-rays (CHIX) was extended to include the X-ray energy region between 0.70 to 4.0 keV. Protons of 700 keV, and¹H ₂ ⁺ ion beams of equivalent proton energies in the range 350–450 keV were used to produce enhanced yields of L and MX-rays from a suitable selection of highly compacted non-conducting samples. Enhancement factors are given and possible applications are mentioned.     

Zur Frage des Einsatzes ionenspezifischer Elektroden in der Automation

Zusammenfassung Es wurden Untersuchungen mit anionenspezifischen Membranelektroden nach Pungor durchgeführt. Dazu werden Reproduzierbarkeit, Eichfunktion, Einstellzeiten bei auf- und absteigender Konzentration und Querempfindlichkeit im Hinblick auf den Einsatz in automatischen Systemen behandelt. Es wird vorgeschlagen, für die Angabe der Selektivität einen p-Sel analog zum pH zu verwenden, die Behandlung eines Analysensensorsystems wird vorgenommen.

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On the use of ion-specific electrodes in automation

Investigations on anion-specific membrane electrodes are described. Problems of reproducibility, calibration, time-response in respect of in- and decreasing concentrations and sensitivity to interfering ions are demonstrated and discussed with regard to automation. It is proposed to define a p-sel for the selectivity constant analogue to pH and a calculation method for an Analysis-Sensor-System is shown.

     

Aryloxydihydropyrans. XII. Configuration and conformations of 8-(3,4-dihydro-2-pyranyloxy)quinoline derivatives

The configuration and conformations of stereoisomeric 4R-8-(3,4-dihydro-2-pyranyloxy)quinolines were studied by means of their PMR spectra. It was established that the trans isomers of the investigated compounds have primarily a half-chair conformation and display an anomeric effect. A sofa conformation is proposed for the labile cis isomers.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 607–610, May, 1976.     

A possibility to study the properties of substances using positronium as the simplest "labeled" atom

A bound state of positron (e⁺) and electron (e^-) (positronium Ps) can be considered as a kind of hydrogen-like atom and the simplest free radical, which has a positron instead of a heavy nucleus. Annihilation g-radiation is in fact a label of this short-lived atom. Therefore, positronium chemistry is radiochemistry of the lightest short-lived labeled atom. Application of positronium chemistry to various chemical problems is essentially dependent on our knowledge of analogies and differences in the formation and chemical conversion of Ps, a atomic hydrogen, and other free radicals. In this review, experimental results of the authors and some other publications are briefly analyzed from this point of view.     

Isolation of a urease from watermelon seeds and the study of its properties

The enzyme urease has been isolated from the seeds of the watermelon of the Ogonek variety and has been characterized. The molecular weight of a rechromatographed sample of the enzyme has been determined as 480,000. The pH dependence of the activity of the urease and the kinetic parameters of the enzyme have been studied.All-Union Scientific-Research Institute of the Chemistry and Technology of Drugs, Khar'kov. Vitaminy Scientific-Production Amalgamation, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 624–628, September–October, 1983.     

Some effective solvents for rapid and reliable characterization of phenylthiohydantoin-amino acids

Summary One-dimensional chromatography with internal standards permits reliable identification of the phenylthiohydantoins from all the common amino acids with the following TLC systems: silica gel — chloroform/n-butyl acetate (9010), di-isopropylether/ethanol (955), dichloromethane/ethanol/acetic acid (9082) ortrans-dichloroethylene/ethanol/acetic acid (88102); and cellulose with 25% formic acid — heptane/isobutanol/75% fromic acid (40309) or silica gel — chloroform/ ethanol/acetic acid/water (50470.52.5).Abbreviations: PTH=phenylthiohydantoin, TLC=thin-layer chromatography, HPTLC=high-performance TLC; other abbreviations: see end of text. Proportions in solvent mixtures are v/v except where otherwise indicated.     

New method of preparing β-lactams

Summary A method has been devised for the synthesis of -lacrams from amides of -ha!ocarboxylic acids. Some new azetidinones with residues containing carboxyl groups on the nitrogen have been piepated. The method permits the conversion of $-amino acids trio difficulty accessible mixed (secondary) amino acids.This paper is publised under the regulations governing Brief Communications.     

A constitutional diagram of the system VC0.88−HfC0.98−(MoC)

The system VC_0.88–HfC_0.98–MoC was investigated by means of melting point, differential-thermoanalytical, X-ray diffraction and metallographic techniques on hot pressed and heat treated as well as melted alloy specimens and a constitutional diagram from 1500°C through the melting range established.The small miscibility gap within the HfC–MoC system (T _c=1630°C) interacts at lower temperatures with the solvus in a monotectoid-like reaction at 1575°C. Additions of VC to the HfC–MoC solid solution gradually increase its critical temperature.Solid state phase behaviour and melting behaviour was established within the isopleths VC_0.88–MoC as well as within (V_0.5Hf_0.5)C–MoC and (V_0.75Hf_0.25)C–(Hf_0.75Mo_0.25)C.Phase equilibria within VC_0.88–HfC–MoC are characterized by an extreme large miscibility gap at 1500°C connecting the VC–HfC and HfC–MoC systems.Originating at the VC–HfC binary an eutectic trough proceeds into the VC–HfC–MoC ternary with rising temperatures, connecting the maximum critical point of the disappearing miscibility gap [(V_0.31Hf_0.49Mo_0.20)C] by a limiting tie line (2750±20°C). Isothermal sections have been calculated assuming regular solutions.With 5 Figures