A reparametrization of the CNDO method I. Hydrocarbons

The empirical evaluation of the core matrix elements in the CNDO method is modified and the parameters are adjusted to give optimal values for heats of atomization, bond lengths, bond angles and force constants.

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Zusammenfassung Die empirischen Ansätze der CNDO-Methode für die Core-Matrixelemente werden modifiziert und die Parameter abgeändert, um möglichst gute Werte für Bildungswärmen aus den Atomen, Bindungslängen, Valenzwinkel und Kraftkonstanten zu erhalten.

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Resumé L'évaluation empirique des éléments de matrice de coeur dams la méthode CNDO et les paramèters sont modifiés en vue de dormer des valeurs optimaux pour les énergies d'atomisation, les distances interatomiques, les angles de valence et les constants de force.

     

A general method for the n-alkylation of thioamides.

Thioamides are N-alkylated in a two-step procedure: (i) Reaction with an aldehyde and benzotriazole yields an adduct which is (ii) reduced to the N-alkylthiomide by NaBH₄.     

A facile spectrophotometric method for the determination of selenium.

A rapid and sensitive spectrophotometric method is described for the determination of trace amounts of selenium using Variamine Blue (VB) as a chromogenic reagent. The proposed method is based on the reaction of selenium with potassium iodide in an acidic medium to liberate iodine, which oxidizes Variamine Blue to form a violet-colored species having an absorption maximum at 546 nm. Beer's law is obeyed in the range 2-20 g of selenium in a final volume of 10 ml. The molar absorptivity and Sandell's sensitivity were found to be 2.6 x 10(4) l mol-1 cm-1 and 0.003 microgram cm-2, respectively. The optimum reaction conditions and other analytical parameters were evaluated. The effect of interfering ions on the determination is described. The proposed method has been successfully applied to the determination of selenium in real samples of water, soil, plant materials, human hair, and synthetic samples of cosmetics and pharmaceutical preparations.     

Regular copolyamides. I. A facile method for the preparation of diamine-oxamides

α,ω-Diamine-oxamides with 2–12 CH₂ groups between the two amino groups were obtained by the reaction of the diamines and diethyl or dimethyl oxalate. Diethyl oxalate is added slowly to a substantial excess of diamine in the proper solvent over a period of time under controlled temperature conditions. All variables are very important for each individual diamine in order to obtain optimal conversions to the diamine-oxamides under the most favorable conditions. Diamine-oxamides were obtained in approximately 80% yield with only small amounts (5–10%) of the corresponding polyoxamides as the side product. Diamine-oxamides from diamines with less than six methylene groups are water-soluble. All diamine-oxamides show an alternation of their melting points and are useful intermediates for the preparation of regular copolyoxamides.     

A simple method for the preparation of N-sulfonylsulfilimines from sulfides.

While excellent methods exist for the oxidation of sulfides to sulfoxides R1R2S-->R1R2SO, the azaversion of this atom transfer redox process, i.e., R1R2S-->R1R2S=N-SO2R3, has been less reliable. In sulfilimine synthesis, sulfoxide has been an inevitable byproduct in all cases to date, and the yields of sulfilimine have varied widely. A nearly ideal procedure for the sulfide to sulfonyl sulfilimine transformation is described. Almost quantitative yields are achieved from a diverse set of sulfides and a broad range of the readily available sulfonyl nitrenoid sources known as chloramine salts (R3SO2NClNa), essentially by simply stirring them together in acetonitrile.     

A class of new silylating reagents. I. A mild method for introduction of the tert-butyldimethylsilyl group.

$\text{t}$-Butyldimethylsilyl enol ethers of pentane-2,4-dione and methyl acetoacetate react rapidly at room temperature to give high isolated yields of the t-butyldimethylsilyl ethers of a variety of alcohols.     

A building block method for the synthesis of higher cycloamides.

Series of cyclic amides containing optically active helicene, (P)-1,12-dimethylbenzo[c]phenanthrene, are synthesized using a building block method. The building block consists of one (P)-helicene unit and one dianiline unit with its amino-terminal-protected with benzyloxycarbonyl and its acid terminal activated as acid chloride. The coupling with (P,P....)-[(n - 3) + (n - 2)]diamine followed by deprotection gives (P,P....)-[(n - 1) + n]diamine, which possesses n - 1 parts of (P)-helicene and n parts of dianiline. Cyclization of the (P,P....)-[(n - 1) + n]diamine with helicenediacid dichloride gives (P,P....)-[n + n]cycloamide. All the members of (P,P)-[2 + 2]cycloamide to (P,P,P,P,P,P,P,P,P,P)-[10 + 10]cycloamide are synthesized using this method, and are compared spectroscopically.     

A study of the AMO method as applied to the lithium metal. III. A method for calculating the total electronic energy of crystals in the LCAO approximation

A method is given for accurate calculation of the expectation value of the Hamiltonian of a crystal with respect to a single-determinant wave function of LCAO type. The method is partly based on numerical integration over one Wigner-Seitz cell. In principle, the calculations involve infinite summations over lattice sites; suitable truncation methods are devised.     

A simple method for tosylation with inversion.

In this paper we describe a simple one-step procedure for tosylation with inversion, using zinc tosylate, diethylazodicarboxylate and triphenylphosphine.     

Determination of lipids. A density gradient method

Summary A method is described by which chloroform droplets containing dissolved lipids may be analyzed for their lipid content by comparison with similar solutions in a density gradient tube with aqueous cadmium chloride solution. The procedure offers a very simple way in which lipids may be determined regardless of their source. The absolute limit of detection was of the order of 0.15 micrograms.

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Zusammenfassung Die Konzentration in Chloroformtröpfchen gelöster Lipide kann durch Vergleich der Dichte dieser Lösungen mit jener von Lipidlösungen bekannter Konzentration ermittelt werden. Zum Dichtevergleich nach der Schwebemethode dient eine 50-ml-Bürette, die mit einer Cadmiumchloridlösung gleichmäßig abfallender Konzentration gefüllt ist. Lipide irgendwelcher Herkunft können auf diese einfache Art bestimmt werden. Die absolute Erfassungsgrenze beträgt 0,15.

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Résumé La concentration des lipoïdes dissous dans des gouttelettes de chloroforme peut être déterminée par comparaison de la densité de ces solutions avec celles de solutions de lipoïdes de concentration connue. Pour la comparaison de densité par la méthode d'immersion, on se sert d'une burette de 50 ml remplie d'une solution de chlorure de cadmium s'écoulant régulièrement. Les lipoïdes de n'importe quelle origine peuvent être simplement déterminés par ce procédé. La sensibilité absolue atteint 0,15.

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This investigation was supported in part by Veterans Administration, under contract No. V 100 1M-1979, the National Cancer Institute of the National Institutes of Health, Public Health Service, and by the Committee on Research of the University of California.     

A method for UV-bonding in the fabrication of glass electrophoretic microchips.

This paper presents an approach for the development of methodologies amenable to simple and inexpensive microchip fabrication, potentially applicable to dissimilar materials bonding and chip integration. The method involves a UV-curable glue that can be used for glass microchip fabrication bonding at room temperature. This involves nothing more than fabrication of glue "guide channels" into the microchip architecture that upon exposure to the appropriate UV light source, bonds the etched plate and cover plate together. The microchip performance was verified by capillary zone electrophoresis (CZE) of small fluorescent molecules with no microchannel surface modification carried out, as well as with a DNA fragment separation following surface modification. The performance of these UV-bonded electrophoretic microchips indicates that this method may provide an alternative to high temperature bonding.     

A conformational analysis method for understanding the energy landscapes of clusters.

A newly developed unbiased structural optimization method, named dynamic lattice searching (DLS), is proposed as an approach for conformational analysis of atomic/molecular clusters and used in understanding the energy landscape of large clusters. The structures of clusters are described in terms of the number of basic tetrahedron (BT) units they contain. We found that the hit numbers of different structural motifs in DLS runs is proportional to the number of BTs. A parameter T(max) is defined to limit the maximal number of atoms moved in a structural transition. Results show that T(max) is a key parameter for modulating the efficiency of the DLS method and has a great influence on the hit number of different motifs in DLS runs. Finally, the effect of potential range on the conformational distribution of the (Morse)(98) cluster is also discussed with different potential-range parameters.