Dynamic Fourier transform infrared spectroscopy in polymer research

The rapid-scanning capability of FTIR instrumentation has revitalized the field of vibrational spectroscopy in polymer research and will be discussed with reference to the study of polyurethane kinetics, the temperature dependence of hydrogen bonding in polyamide 6 and strain-induced crystallization in a polydimethylsiloxane elastomer.     

The Chemistry of Dichloromethylenammonium Salts (“Phosgenimonium Salts”)

Dichloromethylenammonium salts, particularly dichloromethylenedimethylammonium chloride, occupy a unique place as stable but reactive building blocks for synthesis. They contain three mobile chlorine atoms activated by an amino group on the same carbon atom. These salts can be regarded as chlorinated Vilsmeier or Mannich reagents and are thus at a higher oxidation level. As in the Mannich or Vilsmeier reaction, the carbon condenses here as an electrophile with formation of C? C or C? hetero atom bonds in a variety that is still far from being exhausted.     

(Benzylthio)- und (Arylthio)-substituierte Nitril-ylide: Thermische Erzeugung und Reaktionen

Thermal Generation and Reactions of (Benzylthio)-and (Arylthio)-Substituted Nitrile Ylides Thermolysis of 4-(benzylthio)- and 4-(arylthio)-1,3-oxazol-5(2H)-ones 6 , at 110–155° in the presence of dipolarophiles with activated C≡C, C?C, C?O, C?S, and N?N bonds, led to 5-membered cyclo-adducts and CO² (cf. Schemes 3, 5-7). Heating 6a and 6c in the presence of ethyl propiolate yielded ethyl quinoline-3-carboxylate ( 19 ) and ethyl pyridine-3-carboxylate( 22 ), respectively (cf. Scheme 8). These results are rationalized on the basis of the intermediate formation of thio-substituted nitrile ylides of type 7 (cf. Scheme 2), which undergo regioselective 1,3-dipolar cycloadditions with reactive dipolarophiles. In the absence of such a dipolarophile, the nitrile ylides isomerize via a [1,4]-H shift to give 2-aza-1,3-butadienes of type 20 . The latter are trapped in a Diels-Alder reaction with ethyl propiolate (cf. Scheme 8).     

3-(Dimethylamino)-2,2-dimethyl-2H-azirin als α-Aminoisobuttersäure(Aib)-Äquivalent: Cyclische Depsipeptide durch direkte Amid-Cyclisierung

3-(Dimethylamino)-2,2-dimethyl-2H,-azirine as an α-Aminoisobutyric-Acid (Aib) Equivalent: Cyclic Depsipeptides via Direct Amid Cyclization In MeCN at room temperature, 3-(dimethylamino)-2,2-dimethyl-2H-azirine ( 1 ) and α-hydroxycarboxylic acids react to give diamides of type 8 (Scheme 3). Selective cleavage of the terminal N,N-dimethylcarboxamide group in MeCN/H₂O leads to the corresponding carboxylic acids 13 (Scheme 4). In toluene/Ph SH , phenyl thioesters of type 11 are formed (see also Scheme 5). Starting with diamides 8 , the formation of morpholin-2,5- diones 10 has been achieved either by direct amide cyclization via intermediate 1,3-oxazol-5(4H)-ones 9 or via base-catalyzed cyclization of the phenyl thioesters 11 (Scheme 3). Reaction of carboxylic acids with 1 , followed by selective amide hydrolysis, has been used for the construction of peptides from α-hydroxy carboxylic acids and repetitive α-aminoisobutyric-acid (Aib) units (Scheme 4). Cyclization of 14a, 17a , and 20a with HCI in toluene at 100° gave the 9-, 12-, and 15-membered cyclic depsipeptides 15, 18 , and 21 , respectively.     

Beiträge zur Chemie der Pyrrolpigmente, 26. Mitt.: Zur anaeroben Photochemie von Gallenpigmenten: Die Lumineszenz von Gallenpigment-Partialstruktursystemen und integralen Farbstoffen

The luminescence properties of about twentyfive model compounds representing the three main partial structures of bile pigments (namely pyrromethenes, pyrromethenones and methylenepyrrolylmethylenepyrrolinones) as well as tripyrrines and the geometrical isomers of aetiobiliverdin-IV- are reported. In these compounds there is usually only a very faint or even no fluorescence and phosphorescene as the pathway of deexcitation. Vibrational internal conversion and photoisomerizations at the exocyclic double bonds are the main anaerobic paths of radiationless decay of the excited states.

H. Falk, K. Grubmayr, E. Haslinger, T. Schlederer undK. Thirring, Mh. Chem.109, 1451 (1978).     

1,6-dithia-spiro[4.4]nonadiene aus 2-thiazolin-5-thionen

4,4-Dimethyl-2-phenyl-2-thiazolin-5-thione ($\text{4}$) reacts with 2,3-diphenylcyclopropenone ($\text{2a}$) at 145°C and with benzonitrilio-2-propanide ($\text{6}$) at room temperature to yield the 1,6-dithia-spiro[4.4]nonadienes $\text{5}$ and $\text{7}$, respectively.     

Beiträge zur Chemie der Pyrrolpigmente, 19. Mitt.: Die elektrochemische Oxidation von Pyrromethenonen und Pyrromethenen (Gallenpigment-Partialstrukturen)

The electrochemical oxidation of arylmethylene-pyrrolinones, pyrromethenones and pyrromethenes as representative bile pigment partial structure models was investigated by means of a rotating disc platinum electrode using acetonitrile as the solvent. Two different oxidation reactions were found. The first reaction being a reversible one-electron oxidation with compounds of the arylmethylene-pyrrolinone series and pyrromethenones which are unsubstituted in position 5 of the pyrrole ring. A two step reaction (the first one reversible, the second irreversible) on the other hand was found to be typical for pyrromethenones bearing a methyl group in this position.Through protonation the first step is at a higher potential, whereas the second one is lowered and becomes reversible. The resulting oxidation pattern can be interpreted analogous to the oxidation of hydroquinones in aprotic solvents.The geometrical isomers of a pyrromethenone were oxidized at appr. the same potential, but there is a strong dependence of the potential of the first oxidation step on the substitution: a higher degree of alkylation favours oxidation by lowering the oxidation potential.

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Beitr?ge zur Bestimmung von Spurenverunreinigungen in UO2-Kernbrennstoff

Zusammenfassung Die für die Bestimmung geringer Gehalte an Phosphor, Silicium, Fluor, Chlor, Lithium, Natrium, Calcium und Kohlenstoff in UO₂-Kernbrennstoff angewandten chemischen Analysenverfahren werden beschrieben. Durch Kombination einfacher und blindwertfreier Abtrennungsverfahren (Extraktionen und Pyrohydrolysen) mit empfindlichen physikalischchemischen Bestimmungsmethoden (Spektralphotometrie, Flammenphotometrie, coulometrische Titration) lassen sich Nachweisgrenzen zwischen 0,1 und 10 ppm bei Probeneinwaage von 0,5–1 g UO₂ erreichen. Der Zeitaufwand für die Analysen kann durch simultane Bestimmung zweier oder dreier Elemente in einem Arbeitsgang niedriggehalten werden. Die beschriebenen Verfahren haben sich bei Reinheitskontrollen von Kernbrennstoffen gut bewährt.

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Summary Analytical methods have been developed for the determination of trace amounts of phosphorus, silicon, fluorine, chlorine, lithium, sodium, calcium, and carbon in UO₂ of nuclear purity. By combination of simple and rapid separation procedures (extraction, pyrohydrolysis) with highly sensitive methods of determination (spectrophotometry, flame photometry, coulometric titration) detection limits of 0.1–10 ppm have been obtained with sample sizes of 0.5–1 g. In order to reduce the time needed for analysis, some of the above elements are determined simultaneously. The methods described have been successfully applied to the purity control of nuclear fuels.

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Herrn Dr. W. Gebauhr danken wir für wertvolle Anregungen und Diskussionen.     

Kraftfeldrechnungen an linearen Oligopyrrolen: 2,2′-Bipyrrol, 2,2′-Furylpyrrol und Prodigiosen

Using a specific force field model, relative stabilities of 2,2-bipyrrole and 2,2-furylpyrrole conformers as well as of prodigiosene tautomers, configurations, and conformations, are studied. 2,2-Bipyrrole adopts anantiperiplanar conformation in accord with other theoretical calculations and experimental findings. Its rotational barrier calculated by this method compares favourably to the one derived by other means. For the parent prodigiosene the (Z)sp,sp arrangement is found to be the most stable one. The two possible tautomers within its dipyrrin fragment do not show a significant energy difference.

     

A Biokinetic Model to Describe Consequences of Inhibition/Stimulation in DNA-Proofreading and -Repair,Part 2. Calibration of the Model

Summary.  A biokinetic model has been developed to describe the mathematical consequences of inhibition, respectively stimulation of proofreading. According to data reported in the literature, a first approximative calibration of the model has been carried out in an attempt to make it both: practically applicable and comparable with experimental data and clinical facts. The model is open for further improvements and adjustable according to results of further researches via the parameters chosen. In a first test of the model it is shown that it does well reflect the results described in the literature upon proof-reading-inhibition and its consequences, i.e., the reduction of replication-fidelity (→ exponential increase of malignant cells with time). As a further result it is shown that the model also does well describe in its kinetic approach opposite effects as, e.g., a reduction of wrong genetic information by classical cancer-therapies like chemotherapy and surgergy. The system is orientated towards known biochemical relations and chemical similarities together with a discussion of the potential chance which offer special combinations of chemically identifyable substances (like nucleotides’ precursors or effector-molecules contained in low-molecular-human-placenta-extracts as an alternative to umbilical cords’-blood/cells) as stimulators of the enzymatic proof-reading- and -repair-machinery. E-mail: Haschke.H@isovolta.com Received January 20, 2002; accepted (revised) June 26, 2002