A continuous fl ow microwave system based on a transmission line short-circuited waveguide reactor concept is described. The continuous fl ow reactor is capable of operating in a genuine high-temperature/high-pressure process window (310 ° C/60 bar), applying a microwave transparent and chemical resistant cylindrical γ -Al 2 O 3 tube as reaction zone. The system can be operated in an extremely energy effi cient manner, utilizing 0.6 -6 kW microwave power (2.45 GHz). The application of the reactor for processing four chemical transformations in a high-temperature/high-pressure regime with a throughout of 3.5 -6.0 l/h is demonstrated.

The impact damage resistance of Fibre Metal Laminates (FML) is studied. FML is a new family of laminated materials which consist of thin aluminium layers bonded together by intermediate fibrelepoxy layers. Different glass fibre FML variants are compared with A1 2024-T3, and carbodPEI composites. The effect of the relative glasslepoxy content in FML is determined. FML shows an equal to 15% better minimum cracking energy at low velociry impact compared to monolithic aluminium, but behaves much better ( 2 -3 . 5~ higher minimum c r a c h g energy) at high velocities. The impact damage resistance of FML increases with an increasing glasslepoxy content. This is panly due to the strain rate sensitivity of the glass fibres. FML are also superior because during irnpacr delamination occurs, and the laminae consequently will be loaded in a more efficient membrane deformation compared to the dominant bending defonnation of the monolithic material. CarbodPEI thermoplastic composites have a poor impact damage resistance.Rkum6:La resistance aux digits de percussion de Fibre Metal Laminates (FML) est h d i e e . Les FML sont une nouveIie familie de materiaux iamelles, qui consistent de iamelles d'aluminium collees les unes contre fes aulres par des couches intermediaires de fibreslepoxy. Plusieurs sortes de FML de fibres de verre sont comparees a Al 2024-T3, et a des composites carbonIPEI. L'effet du contenu relatif verrelepoxy dans les FML est determine. A percussion a basse vitesse, les FML montrent une energie minimum d'eclatement egale ou 15% meilleure compares a I'aluminium monolithe, mais a vitesses elevees les FML se comportent beaucoup m i e u (une energie minkurn d'tclatement 2 -3 . 5~ plus elevee). La resistance aux digits de percussion des FML augmente avec le rapport verrelepoxy. Ceci est due partiellement a la sensitivite des fibres de verre a la vitesse de contrainte. Les FML sont aussi superieurs car pendant la percussion les lamelles se detachent, et par consequence les FML seront charges dans une deformation de membranes qui est plus efficace que la deformation de flechissement du materiau monolithe. Les composites thermoplastes carboniPE1 ont une resistance aux deglts de percussion peu dlevee.

Several bolaform amphiphiles (bolaamphiphiles) with a rigid polyene as hydrophobic core have been prepared from bixin. Concentrated solutions or precipitates tend to the formation of colorless polymers in the dark. A phenylenediamine-bridged dimer with carboxylate head groups dissolved in DPPC vesicle membranes promotes migration of borohydride and dithionite ions through the membrane. Entrapped indigodisulfonic acid is reduced to two different "leucoindigo" dyes. Surface monolayers of bolaamphiphiles with a cis-bixin Chromophore show characteristic plateau regions beginning at approximately 1.0 nm2/molecule and with fully reproducible overshoots. Surface pressure/area diagrams are interpreted with the formation and reversible pileup of islands of aggregated molecules lying parallel to the water surface. Surface potential measurements and reflection spectroscopy support this conclusion. Bolaamphiphiles with an all-trans-bixin chromophore only produce steep slopes around 0.3 nm2/ molecule. Plateaus are not found. A first interpretation favors an erect position of these amphiphiles in surface aggregates, but the spectroscopic data are not unequivocal. Bixin derivates with a gluconamide head group were effectively integrated into helical micellar gluconamide fibers, which is demonstrated by induced circular dichroism in Pand M-helices.Bolaform amphiphilic (bolaamphiphilic) molecules with a hydrophobic core and two hydrophilic head groups form vesicles with a monolayer membrane,' if the hydrophobic core is made of oligomethylene chains. These membranes can be as thin as 1.5 nm and are nevertheless very efficient barriers to ion and electron t r a n~p o r t .~.~ Several natural and synthetic amphiphiles with one hydrophilic and one hydrophobic edge act as ion pores in monolayer membra ne^.^" They form hydrophilic domains and water channels within the membrane. It should, however, also be possible to transport electrons over lipid membranes by reversible redox reactions of the polyene chains as observed in polyacetylene.6 We chose bixin as a possible "electron wire" because we anticipated a reversible "Michael type addition of electrons" to the activated polyene.Bixin (la) is a natural, unsymmetric bolaamphiphile' from seeds of Bixa orellana? which is commercially available in gram q~a n t i t i e s .~ One head group is a carboxylic acid, the other a carbomethoxy group. The hydrophobic chain consists of a rigid polyene with a cisconfigurated double bond toward the methyl ester end and four methyl groups at regular intervals. The nonsymmetry of the bolaamphiphile can be removed by methylation, hydrolysis, or dimerization via a diol or diamine. It can also be accentuated by one-sided condensation with bulky hydrophilic groups. Furthermore, the cis double bond is "straightened out" (trans isomerized) by iodine (5) Fuhrhop, J.-H.; Liman, U.; Koesling, V. J. Am. Chem. SOC. 1988, 2 IO. fiA4MA45. ---, ----(6) Calvert, P. Nature 1987,327,371. (7) Fuhrop, J.-H.; Mathieu, J. Angew. Chem. 1984,96, 124-137. (8) Kaner, P.; Jucker, ...

thanks the Studienstiftung des Deutschen Volkes for a Dissertation Stipend (1985-1987). 700 0 V C H Verlagsgesellschaji mbH. 0-6940 Weinheirn, 1987 OS70-0833/87/0707-0700 $ 02 S0/0 Angew. Chem lnf. Ed. Engl. 26 (1587) No. 7

Die spontane Umwandlung von löslichen Polypeptid‐Helices in unlösliche Blattstrukturen beim Vereinen der beiden enantiomeren Helices (schematisch im Bild rechts) impliziert, daß metastabile Überstrukturen in Lösung nur dann langlebig sind, wenn sie aus chiralen Untereinheiten aufgebaut sind. Beim Vereinen von über Wochen stabilen, klaren Lösungen der Titelverbindungen fällt sofort und praktisch quantitativ das Racemat aus. Offensichtlich verhindert die aufgrund der Kurvatur der Helices extrem große Oberfläche(nenergie) die Kristallisation, während im Racemat Kristallebenen ohne Kurvatur gebildet werden können.