Thermal elimination of isobutene from meta and para tert-di-butyl pyromellitic acid

An investigation of the kinetics of the thermal elimination of isobutene from the meta and para isomers of the tert-butyl diesters of pyromellitic acid has been carried out using Fourier transform-Raman spectroscopy and mass spectroscopy. These studies indicate that the elimination of the tert-butyl group occurs at a temperature 26°C lower for the meta isomer than for the para isomer; the maximum rate of elimination occurs at 184°C for the former and at 210°C for the latter. Analysis of the Raman spectra of the compounds indicates that this effect results from the better packing arrangement in the para monomer compared with the meta monomer. Formation of pyromellitic dianhydride in the tert-butyl diesters of pyromellitic acid occurred only after formation of the pyromellitic acid; thus it occurred at lower temperatures for the meta isomer. When the meta and para tert-butyl diesters of pyromellitic acid are dissolved at 1% concentration in poly (vinyl acetate), the elimination of isobutene occurs at 173°C for both isomers, indicating that it is the differences in crystal packing which give rise to the 26°C difference in the solid-state samples. For the meta, para, and 50/50 mixed isomers of the tert-butyl esters of oxydianiline/pyromellitic dianhydride polyamic acid, the elimination of the tert-butyl group occurs at the same temperature (177°C). This result indicates that the packing arrangement of the tert-butyl group is disrupted in the polymer chain, so that intermolecular bonding does not hinder thermal deprotection of the tert-butyl group from the polymer. © 1992 John Wiley & Sons, Inc.     

Synthesis and anticancer activity of the proposed structure of caldoramide,an N-peptidyltetramate from the cyanobacterium Caldora penicillata

The structure proposed in the literature for caldoramide, a formal pentapeptide metabolite of the marine cyanobacterium Caldora penicillata, was synthesised in 12 steps and 16% yield (longest linear sequence from isoleucine) following the strategy of a stepwise consecutive extension of an N-oligopeptidyl chain on a tetramate anchor. The synthetic product differed from the natural isolate in optical rotation, some NMR data, and cytotoxicities. Its antiproliferative effect on three human cancer cell lines was distinctly lower than that of related dolastatin 10 and belamide A.     

Infrarotspektroskopische Charakterisierung von Carbons?uren durch ihre Trimethylsilylester

Zusammenfassung 91 Carbonsäuren wurden mit Dialkoxytrimethylsiloxy-N-trimethylsilylphosphoriminen (besonders Diäthoxytrimethylsiloxy-N-trimethylsilylphosphorimin, DASPI) oder mit Trimethylsilylmethyl acetamid, TMSMA, silyliert. Die C=O-Frequenzen der entsprechenden Trimethylsilylester können zur Ermittlung des Substitutionstyps am-C-Atom der Carbonsäuren dienen.-Aminosäuren bilden eine Ausnahme. Diese Säuren wurden wegen ungenügender Silylierung mit DASPI nur mit TMSMA silyliert. Folgende Frequenzbereiche der Silylesterbande wurden gefunden: aliphatisch, aliphatisch-verzweigt 1713 bis 1733 (1722±4) cm^–1;-heterosubstituiert, einschließlich-Acylamino- 1721–1754 (1737±11) cm^–1, in den meisten Fällen von einer zweiten, längerwelligen Bande begleitet im Abstand von 10–25 cm^–1:-unge-sättigt 1687–1736 (1701±13) cm^–1; aromatisch 1673–1721 (1705+10) cm^–1;-Amino- 1702–1731 (1719±7) cm^–1. (In Klammern: Mittelwerte mit Standardabweichung.)

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Infrared-spectroscopic characterisation of carboxylic acids by their trimethylsilyl esters

91 Carboxylic acids were silylated by dialkyltrimethylsilyl-N-trimethylsilyl phosphorimidates (mainly diethyltrimethylsilyl-N-trimethylsilyl phosphorimidate, DESPI) or trimethylsilylmethyl acetamide, TMSMA, and the C=O frequencies of the corresponding trimethylsilyl esters were investigated. Exceptions were -amino acids. Due to uncomplete silylation by DESPI these were silylated by TMSMA, but investigations in the region lower than 1690 cm^–1 could not be made because of the strong absorption by the amide I band of TMSMA.The following frequency regions of the silyl ester band were found: aliphatic, aliphatic-branched 1713–1733 (1722±4) cm^–1;-heterosubstituted, including-acylamino- 1721–1754 (1737±11) cm^–1 and, in most cases a second, lower frequency band at a distance of 10–25 cm^–1 originating from conformational isomers:-unsa-turated 1687–1736 (1701±13) cm^–1; aromatic 1673–1721 (1705±10) cm^–1;-amino-1702–1731 (1719±7) cm^–1. (In brackets: mean value ± standard deviation.)

     

A Self‐Binding,Melt‐Castable,Crystalline Organic Electrolyte for Sodium Ion Conduction

The preparation and characterization of the cocrystalline solid–organic sodium ion electrolyte NaClO₄(DMF)₃ (DMF=dimethylformamide) is described. The crystal structure of NaClO₄(DMF)₃ reveals parallel channels of Na⁺ and ClO₄⁻ ions. Pressed pellets of microcrystalline NaClO₄(DMF)₃ exhibit a conductivity of 3×10⁻⁴ S cm⁻¹ at room temperature with a low activation barrier to conduction of 25 kJ mol⁻¹. SEM revealed thin liquid interfacial contacts between crystalline grains, which promote conductivity. The material melts gradually between 55–65 °C, but does not decompose, and upon cooling, it resolidifies as solid NaClO₄(DMF)₃, permitting melt casting of the electrolyte into thin films and the fabrication of cells in the liquid state and ensuring penetration of the electrolyte between the electrode active particles.     

Spectroscopic and redox properties of amine-functionalized K2[OsII(bpy)(CN)4] complexes

We report the first examples of amine-functionalized K(2)[Os(II)(bpy)(CN)(4)] (bpy = 2,2'-bipyridine) complexes. The tetracyanoosmate complexes were prepared by UV irradiation (λ = 254 nm) of K(4)[Os(II)(CN)(6)] and primary amine-functionalized bpy ligands in acidic aqueous media. The aqueous solution pH dependences of the spectroscopic and redox properties of 4,4'- and 5,5'-substituted complexes have been investigated. The pendant amine functional groups and coordinated cyanide ligands are basic sites that can be sequentially protonated, thereby allowing systematic tuning of electrochemical and optical spectroscopic properties.     

Synthesen und Kristallstrukturen neuer sulfidoverbrückter Rutheniumclusterverbindungen

Syntheses and Crystal Structures of New Sulfido‐bridged Ruthenium Clusters The reaction of S(SiMe₃)₂ or NaSH with [RuCl₂(PPh₃)₃] or [Ru₃Cl₈(PEt₃)₄] leads to the formation of sulfidobridged ruthenium clusters. In this publication the compounds [Ru₆S₈(PPh₃)₆][PF₆] ( 1 ), [Ru₆S₈(PPh₃)₆][RuCl₄(PPh₃)₂] ( 2 ), [Ru₆S₈(PEt₃)₆] ( 3 ) and [Ru₃S₄Cl₂(PPh₃)₃]₂ ( 4 ) are described. The structures of these compounds were elucidated by single crystal X‐ray structural analyses.     

Electroactive self-assembled monolayers on gold via bipodal dithiazepane anchoring groups

Novel dithiazepane-functionalized ferrocenyl-phenylethynyl oligomers 1 and 2 have been synthesized. Self-assembled monolayers (SAMs) of these ferrocene derivatives have been studied by X-ray photoelectron spectroscopy, ellipsometry, and cyclic voltammetry. It has been shown by XPS that monolayers of the dithiazepane-anchored molecules on gold electrodes contain gold-thiolate species. Cyclic voltammetry of the SAMs were characteristic of stable electroactive monolayers even for single-component SAMs of 1 and 2, with the more ideal responses recorded for the two-component SAMs diluted with undecanethiol. The small variation in peak splittings at progressively higher scan rates in these SAMs makes dithiazepane-bridged redox species promising candidates for further studies on molecular wires with bipodal anchoring.