Hairdressing shish-kebabs; comprehensive survey and theoretical discussion of overgrowth crystallization

The platelet component of shish-kebabs crystallizes after the core, during cooling or storage below the formation temperature of the core. Three basic platelet morphologies were previously identified which were mutually interconvertible, a process we have termed “hairdressing”. In this paper we show that these three categories are special cases of a continuous range of overgrowth spacings. Crystallization at high temperatures gives widely spaced overgrowths and, as the crystallization temperature is reduced, so the overgrowth spacing decreases gradually. In the extreme case (only obtainable by quenching) the overgrowths become so close as to overlap and appear continuous. We also report a variety of further effects which were caused by exposing the shish-kebabs, while in solvent, to temperatures above their initial formation temperature. A new theoretical approach is described which considers the depletion of material available to form new overgrowths during crystallization. Two versions of this theory are presented (one a computer simulation and one analytic); interpreting our results on the basis of this theory we show that shish-kebabs crystallize at high temperatures even when quenched (90°C and above except in a few exceptional circumstances) and we are able to explain all the features of shish-kebab crystallization that we have observed.     

A doubly deprotonated form of calix[6]arene: Crystal and molecular structure of (calix[6]arene-2H)2−·(HNEt 3 + )2

The doubly deprotonated form of calix[6]arene, with two protonated triethylamines as counter-ions, crystallizes in the monoclinic system: space groupP2₁/n,a=8.465(4),b=17.822(8),c=15.182(6) Å,=90.18(4)°,V=2291(2) ų,Z=2. Refinement led to a final conventionalR value of 0.063 for 1046 reflections. The macrocycle conformation is not apinched cone, usual for freeR-calix[6]arene, but a distorted 1,2,3-alternate cone, since the molecule lies on a symmetry center. Furthermore, one of the torsion angles defined by the methylene bridges is near to zero, which is unusual in calixarene structures. Supplementary Data relating to this article (atomic coordinates for hydrogen atoms, anisotropic displacement parameters for oxygen and nitrogen atoms, and observed and calculated structure factors) are deposited with the British Library as Supplementary Publication No. SUP 82182 (7 pages).     

Identifizierung von sechs Komponenten des Spurpheromons der Ameisenart Lasius fuliginosus. Vorläufige Mitteilung

Hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, and dodecanoic acid are components of the trail pheromone of the ant species Lasius fuliginosus. The acids were extracted from the contents of the rectal ampullae and identified by the mass spectra and gas chromatographic retention times of the corresponding methyl esters.     

NMR parameters of the tetrahedrane [Fe2(CO)6(μ-SNH)], studied by experiment and DFT

The intramolecular dynamic behavior of the tetrahedrane-type cluster [Fe₂(CO)₆(μ-SNH)] 1 was studied by ¹³C NMR spectroscopy. The ⁵⁷Fe chemical shift of 1 and the coupling constants ¹ J(⁵⁷Fe,¹³C) were measured. These NMR parameters, and also ¹ J(⁵⁷Fe,¹⁵N), were found to be in good agreement with data calculated by using density functional theory (DFT) methods (B3LYP), based on the geometry calculated at the 6-311+G(d,p) level of theory. The isolobal replacement of the Fe(CO)₃ with BH fragments leads to the tetrahedranes [Fe(CO)₃(BH)(μ-SNH)] 2 and [(HB)₂(μ-SNH)] 3. Both were identified by calculations as minima on the respective potential energy surface (PES). However, the tetrahedrane-type structure of 3 is much higher in energy when compared with the planar cyclic isomers 3a and 3b.     

Totalsynthese von natürlichem α-Tocopherol. 2. Mitteilung. Aufbau der Seitenkette aus (−)-(S)-3-Methyl-γ-butyrolacton

Total Synthesis of Natural α-Tocopherol A short and efficient route to optically pure (+)-(3 R, 7 R)-trimethyldodecanol ( 14 ) is demonstrated, 14 serving as side chain unit in the preparation of natural vitamin E. The synthesis of 14 is based on the concept of using a single optically active C₅-synthon of suitable configuration and functionalization to introduce both asymmetric centres in 14 . (?)-(S)-3-Methyl-γ-butyrolacton ( 1 ) and ethyl (?)-(S)-4-bromo-3-methylbutyrate ( 2 ), respectively, is used in a sequence of either two Grignard C,C-coupling reactions 5 → 8 and 12 → 13 or two Wittig reactions 17a → 18 and 20 → 21 to achieve this goal. 14 is converted to (2 R, 4′R, 8′R)-α-tocopherol (= vitamin E) by coupling with a chroman unit in known manner. Optical purity of products and intermediates is established.     

Naturstoffe aus Mikroorganismen. 8. Mitteilung [1]. Optimale Gewinnung von Proferrorosamin A aus Pseudomonas roseus fluorescens J. C. MARCHAL 1937

Optimum Obtention of Proferrorosamine A from Pseudomonas roseus fluorescens J. C. MARCHAL 1937. We have developed the best conditions for the culture of Pseudomonas roseus fluorescens, and a quantitative isolation of the Proferrorosamine A produced in the culture solution, in order to study the incorporation of 1-[¹⁴C]-glycerol in this propigment.     

Resonant oscillations in open tubes

Summary The problem of a gas-filled tube excited by sinusoidal piston motion at one end and open at the other end is reinvestigated.It is shown that the key idea for the solution of the problem is a suitable combination of the usual amplitude nonlinearity and distortion effects. The main consequence of this is that the solution cannot be expressed in terms of a hierarchy associated with an expansion in the Mach number. Nevertheless an equation can be constructed which describes the behaviour of the flow in the limit of small Mach numbers. At the open end shock waves appear in the solution within a well-defined frequency band at each resonant frequency. Two different models which have been proposed by Wijngaarden and Jimenez respectively are used to define the boundary condition. It is seen that some basic properties of the resonant oscillations are independent of the boundary condition. Wijngaarden's model leads to very good agreement with results from several different experimenters. In this case, the width of the frequency interval where shocks occur is of the orderO(M); the width of the resonance band is of the orderO(M ^1/2), just as for the closed end tube.

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Zusammenfassung Betrachtet wird ein mit Gas gefülltes Rohr, welches an einem Ende offen ist und am andern Ende von einem harmonisch schwingenden Kolben angetrieben wird. Der Schlüssel zur Lösung dieses Problems ist eine geeignete Kombination der üblichen Amplitudennichtlinearität mit den Dispersionseffekten. Dies führt auf die grundlegende Konsequenz, dass es nicht möglich ist, die Lösung im Rahmen einer Hierarchie auszudrücken, welche aus einer Entwicklung in der Machzahl hervorgeht. Es ist gleichwohl möglich, eine Gleichung zu konstruieren, welche die Gasschwingungen für kleine Machzahlen beschreibt. Am offenen Ende treten innerhalb eines wohldefinierten Frequenzbandes (bei jeder Resonanzfrequenz) Stosswellen auf. Zur Definition der Randbedingung am offenen Ende werden zwei Modelle benützt, die (beziehungsweise) von Wijngaarden und Jimenez vorgeschlagen wurden. Einige der grundlegenden Eigenschaften der Lösungen sind unabhängig von der Randbedingung. Wijngaardens Modell führt auf sehr gute Übereinstimmung mit typischen Experimenten. In diesem Fall ist die Breite des Intervalls, in welchen Stösse auftreten, von der Ordnung O(M); die Breite des Resonanzbandes ist (in Übereinstimmung mit den Ergebnissen vom geschlossenen Rohr) von der OrdnungO(M ^1/2).

     

Nonlinear acoustic resonances in shock tubes with varying cross-sectional area

Summary Second-order resonance effects in closed tubes with varying cross-sectional area are investigated. It is seen that for tubes with cross-sectional areasA(x)x ^–2 solutions for the pressure disturbances can be found, as was done by W. Chester in case of tubes with constant cross-sectional area.

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Zusammenfassung Es werden Resonanzeffekte zweiter Ordnung in Rohren mit veränderlicher Querschnittsfläche betrachtet. Ist die QuerschnittsflächeA(x)x ^–2, so können die Druckstörungen in Analogie zu Chesters Theorie analytisch berechnet werden.

     

Assessment of supporting electrolyte contributions in electrochemically modulated liquid chromatography

This paper reports the results of an investigation on the role of the supporting electrolyte in separations using electrochemically modulated liquid chromatography (EMLC) with a porous graphitic carbon stationary phase. With respect to the identity of the supporting electrolyte, the elution strength of the electrolyte anion increased as F- < OH- < BF4- < ClO4- < PF6- for injections of negatively charged aromatic molecules, whereas a 10-fold increase in electrolyte concentration induced a 60% change in retention for the same solutes. Furthermore, both the concentration and composition of the supporting electrolyte affected retention in a manner that varied with the charge of the analyte and applied potential. This behavior is explained using Gouy-Chapman diffuse double layer theory, coupled with comparisons of this theory with closely related models for ion-pair chromatography. Insights into the retention mechanism reveal that an ion-exchange mechanism controls the retention of negatively charged solutes at applied potentials removed from the potential of zero charge (PZC). At potentials close to the PZC, the electrostatic model is less effective with the predominant retention mechanism likely involving hydrophobic interactions with the carbonaceous stationary phase. The combined effects of these findings are demonstrated by using a temporal gradient in supporting electrolyte concentration to optimize an EMLC separation.