X-ray crystal structure of bis(4-nitropyrazol-1-yl)methane,and some empirical rules concerning the bond angles in pyrazoles

The crystal structure of bis(4-nitropyrazol-1-yl)methane has been determined by X-ray diffraction. The nitro groups form angles of 16.45(6) and 11.83(7)°, respectively, with the pyrazole ring to which they are attached. The internal and external angles of the pyrazole rings follow a set of empirical rules: (1) N(1)-N(2)-C(3) is smaller than N(2)-N(1)-C(5); (2) N(2)-C(3)-C(4) is larger than N(1)-N(2)-C(3) and at least one chosen between C(3)-C(4)-C(5) and C(4)-C(5)-N(1); (3) C3-C4-C5 is not the largest internal angle; (4) R1-N1-N2 is smaller than R1-N1-C5; (5) N2-C3-R3 is smaller than R3-C3-C4, or R5-C5-N1 is smaller than C4-C5-R5; (6) C3-C4-R4 and R4-C4-C5 are nearly the same. Provided that the angle considered is not part of another ring, the first five rules are valid for all the pyrazoles investigated up to now, while violation of the last rule is good evidence for steric hindrance or marked asymmetry of the 3- and 5-substituents.     

Theoretical study of aminoalkylation in the Mannich reaction of furan with methyleneimminium salt

The potential energy surface for the reaction of furan and methyleneimminium cation with formation of a Mannich base has been studied using AM1 and PM3 semiempirical calculations. Nonspecific solvent effects were taken account of in the framework of the multicavity self-consistent reaction field approach. Characteristics of the reaction path elucidated for various media are discussed. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 359–366, 1998     

Cover Picture: Angew. Chem. Int. Ed. 6/2002

The cover picture shows the electric eel, Electrophorus electricus, a source for commercially available acetylcholinesterase. In an experiment described by K. B. Sharpless and M. G. Finn and co‐workers on pp. 1053–1057, a femtomolar inhibitor was assembled by the enzyme from a collection of building blocks containing azide and alkyne functional groups, shown floating in solution. The templated 1,3‐dipolar cycloaddition reaction, producing the inhibitor, is represented by the flare of light at the center of the image.     

Portfolio selection with probabilistic utility

Inspired by statistical physics, we present a probabilistic approach to portfolio selection. Instead of seeking the global extremum of some chosen utility function, we reinterpret the latter as a probability distribution of ‘optimal’ portfolios, and select the portfolio that is given by the mean value with respect to that distribution. Compared to the standard maximization of expected utility, this approach has several attractive features. First, it significantly reduces the excessive sensitivity to external parameters that often plague optimization procedures. Second, it mitigates the commonly observed concentration on too few assets; and third, it provides a natural and consistent way to account for the incompleteness of information and the aversion to uncertainty. Supportive empirical evidence is derived by using artificial data to simulate finite-sample behavior and out-of-sample performance.     

Disposable Electrospun Electrodes Based on Conducting Nanofibers

A new approach for the fabrication of disposable electrochemical surfaces is presented. Conducting fibers have been produced by a two‐step process. Firstly, a fine web mat composed of nylon‐6 and ferric chloride fibers (with diameters of about 200 nm) were electrospun on a flat collector. Afterwards, the electrospun mat was exposed to pyrrole vapor under controlled dry atmosphere until each nylon thread was fully coated with a conducting polypyrrole layer. The conducting fiber mat was finally integrated within an electrochemical cell and used as a disposable sensor device. The suitability of the sensor was tested using phosphate and carbonate organic anions. The large scale fabrication of conducting tissue, in the form of a fine web of spun nanofibers, is relatively fast and inexpensive, and it paves the way to the build up of new disposable electrodes.     

Copper(II) and zinc(II) complexes with 2-formylpyridine-derived hydrazones

In the present work 2-formylpyridine-para-chloro-phenyl hydrazone (H2FopClPh) and 2-formylpyridine-para-nitro-phenyl hydrazone (H2FopNO₂Ph) were obtained, as well as their copper(II) and zinc(II) complexes [Cu(H2FopClPh)Cl₂] (1), [Cu(2FopNO₂Ph)Cl] (2), [Zn(H2FopClPh)Cl₂] (3) and [Zn(H2FopNO₂Ph)Cl₂] (4). Upon re-crystallization in DMSO:acetone conversion of 2 into [Cu(2FopNO₂Ph)Cl(DMSO)] (2a) and of 4 into [Zn(2FopNO₂Ph)Cl(DMSO)] (4a) occurred. The crystal structures of 1, 2a, 3 and 4a were determined.     

On the Foundation of Combinatorial Theory. X. A Categorical Setting for Symmetric Functions

This paper examines surface gravity waves in a shallow channel with periodic or random bottom irregularities. Three types of bottom topography are distinguished, allowing a simplification of the basic shallow-water-wave equations. For two of them, asymptotic equations of the Korteveg-de Vries type are derived (the third type has been considered earlier by other authors).