Beiträge zur Chemie der Pyrrolpigmente, 70. Mitt.: Zum aktiven Transport mit tripyrrinoiden Liganden

The tripyrrin carboxylic acid6 exhibits a pronounced efficiency for carrier mediated proton driven secondary active transport (counter transport) for a series of toxic or valuable cations in a bulk chloroform membrane. In case of Zn⁺⁺ ions the mechanism including complete concentration profiles forNerst diffusion layers and bulk phase have been established. This compound might be used for detoxification or enrichment of precious metals using membrane separation systems.

Herrn Prof. Dr.A. Neckel mit den besten Wünschen zum 60. Geburtstag gewidmet.     

A microcomputer-controlled titrator for automated individual analysis

A titration unit for automatic analysis systems is described. The titrator performs different titrations specified by strings of digital parameters. It has 4 independent titration stations with individual electrode systems. A multiburette with 20 cylinders provides all stations with the necessary reagents. End-point titrations, and incremental and equilibrium titrations are controlled by a microcomputer. In combination with a sample transport and a desk calculator, the titrator can be used to process automatically samples of different natures which require different treatment.     

Synthesis and structure of a stabilized 10-membered cyclic enediyne

The synthesis and structure of an acetal protected 10-membered cyclic enediyne-1,2-diol rac-10 is reported. The conformational constrain of the unsaturated macrocycle by the acetal protection group prevents the thermal cyclization reaction of the endiyne during synthesis and purification.     

Rotational fluctuations of water inside the nanopores of SBA-type molecular sieves

The rotational molecular dynamics of water confined to nanoporous molecular sieves of a regular hexagonal (SBA-15) and of a foamlike pore structure was studied by dielectric spectroscopy in the frequency range from 10(-2) to 10(9) Hz and in a broad temperature interval. Two relaxation processes were observed: the process at lower frequencies is related to water molecules forming a layer, which is strongly adsorbed at the pore surface, whereas the relaxation process at higher frequencies is assigned to fluctuations of water molecules situated close to the center of the pore. The relaxation times of the low-frequency process for both materials and of the high-frequency process for the SBA-15 material have an unusual saddlelike temperature dependence, reported here for the first time. To describe this temperature dependence, a model developed for water confined to nanoporous glasses by Ryabov et al. [J. Phys. Chem. B 2001, 105, 1845] was applied, which considers two competing effects. The characteristic features of these two competing processes were compared with those reported for other porous systems.     

Das Verhalten der WÄrmeleitfÄhigkeit von Kautschuk bei der Dehnung

Zusammenfassung Mit einer Me\apparatur, die nach einer Relativmethode die W?rmeleitung in fadenf?rmigen Kautschukvulkanisaten zu messen gestattet, wird der Einflu\ der Dehnung auf die W?rmeleitf?higkeit untersucht. Es ergibt sich ein wesentlicher Anstieg der W?rmeleitung mit der Dehnung bei allen untersuchten Materialien. Bei stark vulkanisiertem Kautschuk ist dieser Anstieg am geringsten, bei Polybutadienen ist er h?her als bei Naturkautschuk. Auf Grund von bekannten Vorstellungen über die Kinetik der hochpolymeren Moleküle bei Dehnung und über die Ausbreitung von W?rmewellen in Festk?rpern werden die Beobachtungsergebnisse gedeutet. Dabei wird festgestellt, da\ der Anstieg der W?rmeleitf?higkeit auf eine zunehmende Ausrichtung von Molekülkettenabschnitten in Dehnungsrichtung — die zugleich Richtung des W?rmestromes ist- und auf eine Abnahme der Zahl der Streuzentren für die W?rmewellen zurückzuführen ist. Auch Unterschiede bezüglich des Betrages des Anstiegs, den die einzelnen Materialien zeigen, k?nnen z. T. auf Grund dieser Vorstellungen erkl?rt werden.     

Continuous flow in open microfluidics using controlled evaporation

This paper presents a method for programming the flow rate of liquids inside open microfluidic networks (MFNs). A MFN comprises a number of independent flow paths, each of which starts with an open filling port, has a sealed microchannel in which assays can be performed, and an open capillary pump (CP). The MFN is placed over Peltier elements and its flow paths initially fill owing to capillary forces when liquids are added to the filling ports. A cooling Peltier element underneath the filling ports dynamically prevents evaporation in all filling ports using the ambient temperature and relative humidity as inputs. Another Peltier element underneath the CPs heats the pumps thereby inducing evaporation in the CPs and setting the flow rate in the microchannels. This method achieves flow rates in the microchannels ranging from approximately 1.2 nL s(-1) to approximately 30 pL s(-1), and is able to keep 90% of a 0.6 microL solution placed in an open filling port for 60 min. This simple and efficient method should be applicable to numerous assays or chemical reactions that require small and precise flow of liquids and reagents inside microfluidics.     

Zur Chemie der Pyrrolpigmente, 56. Mitt.

From an investigation of the ICD of bilatrienes-abc and 2,3-dihydrobilatrienes-abc induced by mixtures of CCl₄ with (+)-cis-Pinane, (–)-lactic and (+)-tartaric acid esters it is concluded that specific interactions between chromophore and the chiral reagents afford a partial resolution of the labile racemate of helices. Attaching chiral residues covalently to the chromophore induces very low resolution of the same kind in case of apolar ligands like a cholesteryl-residue. However, with polar ligands as in the case ofBoc-lysyl derivatives enantiomeric excesses up to 90% are achieved depending on the solvent used.

Herrn Prof. Dr.Karl Schlögl zu seinem 60. Geburtstag gewidmet.