First direct lithiation of 2-pyridylpiperazine on solid phase

[reaction: see text] The first direct lithiation of a pyridine derivative on solid phase has been realized. Metalation of polymer-bound 2-pyridylpiperazine with the BuLi-LiDMAE reagent followed by electrophilic quenching and subsequent cleavage provided a range of new useful C-6 substituted 2-piperazinylpyridines.     

Identification of organic compounds by microscopy and X-ray diffractometry

Summary Primary and secondary crystallographic constants can be utilized conveniently for identifications of crystalline organic and inorganic materials by microscopy and X-ray diffractometry. Several specific properties can be measured under the petrographical microscope, including optic axial angle, character, dispersion, and in addition, refractive index directions can be established. The d spacings and their intensities as determined with the X-ray diffractometer serve to identify crystalline materials. The two instruments should be considered as supplementary tools for identifying crystals.Both instruments supply a means for identification and semiquantitative analysis of mixed crystal systems. Data are presented for the systems: acetic-propionic p-bromoanilides and acet-propion-2.4-dinitro-phenylhydrazones.

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Zusammenfassung Primäre und sekundäre kristallographische Konstanten können zur Identifizierung kristallisierter organischer und anorganischer Stoffe auf mikroskopischem Wege und durch Röntgendiffraktometrie gut herangezogen werden. Einzelne spezifische Eigenschaften können unter dem petrographischen Mikroskop gemessen werden, so der optische Achsenwinkel, der Charakter, die Dispersion. Außerdem kann man Angaben über den Brechungsindex erhalten. Die mit dem Röntgendiffraktometer bestimmten Netzebenenabstände d und deren Intensitäten dienen zur Identifizierung kristallisierter Stoffe. Die beiden Instrumente sind als Hilfsmittel zur Erkennung von Kristallen anzusehen.Sie bieten die Möglichkeit zur Identifizierung und halbquantitativen Analyse von Mischkristallsystemen. Daten für die Systeme Essigsäure-Propionsäure-p-Bromanilid und Acetaldehyd-Propionaldehyd-2,4-Dinitrophenylhydrazon werden mitgeteilt.

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Résumé Les constantes cristallographiques primaires et secondaires sont utilisables pour l'identification de composés cristallins organiques et minéraux par microscopie et diffractométrie de rayons X. Il est possible de mesurer diverses propriétés spécifiques sous le microscope pétrographique, savoir: l'angle des axes optiques, le caractère et la dispersion optiques. Il est en outre possible de déterminer les directions des indices de réfraction primaires. Les espacements «d» et leurs intensités déterminés par le diffractomètre à rayons X permettent d'identifier les substances cristallines. Les deux instruments doivent être considérés comme complémentaires pour l'identification de cristaux. Chacun d'entre eux fournit un moyen d'identification et d'analyse semi quantitative des systèmes de cristaux mixtes. On rend compte de résultats obtenus pour les systèmes: p-bromoanilides acétique et propionique ainsi que 2, 4-dinitro phénylhydrazones de l'acétaldéhyde et du propionaldéhyde.

     

From bouncing to floating: noncoalescence of drops on a fluid bath

When a drop of a viscous fluid is deposited on a bath of the same fluid, it is shown that its coalescence with this substrate is inhibited if the system oscillates vertically. Small drops lift off when the peak acceleration of the surface is larger than g. This leads to a steady regime where a drop can be kept bouncing for any length of time. It is possible to inject more fluid into the drop to increase its diameter up to several centimeters. Such a drop remains at the surface, forming a large sunk hemisphere. When the oscillation is stopped, the two fluids remain separated by a very thin air film, which drains very slowly (approximately 30 min). An analysis using lubrication theory accounts for most of the observations.     

Sigmatropic 1.5-hydrogen shift and concomitant cyclopropane bond cleavage on thermolysis of trans-1-isopropenyl-4-methylene spiro[2.x]alkanes into 1-methylene-(3′-methylbut-2′-enyl)-cycloalk-2-enes

Thermolysis of several trans-1-isopropenyl-4-methylene-spiro[2.x]- alkanes (x = 4,5) in xylene solution at 130° causes quantitative rearrangement to 1-methylene-2-(3′-methylbut-2′-enyl)cycloalkanes ($\text{3}$ – $\text{4}$).     

Thermodynamics of nonequilibrium radiation. (II) Irreversible evolution and experimental setup

Giving continuation to the study of the thermodynamics of nonequilibrium radiation presented in the preceding article [Physica A 300 (2001) 386], we derive the evolution in time of its macroscopic nonequilibrium state. The case of a semiconductor sample and the coupling of radiation and transverse optical phonons is explicitly considered. Excitation of the latter drives the radiation field out of equilibrium. Under constant excitation, a steady state sets in which is analyzed. It is shown that the quasitemperature per mode of the radiation field, which has been defined in the preceding paper, can be determined in optical experiments such as Raman scattering.     

Hibernating Bears,Antibiotics, and the Evolving Ribosome (Nobel Lecture)

High‐resolution structures of ribosomes, the cellular machines that translate the genetic code into proteins, revealed the decoding mechanism, detected the mRNA path, identified the sites of the tRNA molecules in the ribosome, elucidated the position and the nature of the nascent proteins exit tunnel, illuminated the interactions of the ribosome with non‐ribosomal factors, such as the initiation, release and recycling factors. Notably, these structures proved that the ribosome is a ribozyme whose active site, namely where the peptide bonds are being formed, is situated within a universal symmetrical region that is embedded in the otherwise asymmetric ribosome structure. As this symmetrical region is highly conserved and provides the machinery required for peptide bond formation and for ribosome polymerase activity, it may be the remnant of the proto‐ribosome, a dimeric prebiotic machine that formed peptide bonds and non‐coded polypeptide chains. Structures of complexes of ribosomes with antibiotics targeting them revealed the principles allowing for their clinical use, identified resistance mechanisms and showed the structural bases for discriminating pathogenic bacteria from hosts, hence providing valuable structural information for antibiotics improvement and for the design of novel compounds that can serve as antibiotics.