Pore formation in fluctuating membranes

We study the nucleation of a single pore in a fluctuating lipid membrane, specifically taking into account the membrane fluctuations, as well as the shape fluctuations of the pore. For large enough pores, the nucleation free energy is well-described by shifts in the effective membrane surface tension and the pore line tension. Using our framework, we derive the stability criteria for the various pore formation regimes. In addition to the well-known large-tension regime from the classical nucleation theory of pores, we also find a low-tension regime in which the effective line and surface tensions can change sign from their bare values. The latter scenario takes place at sufficiently high temperatures, where the opening of a stable pore of finite size is entropically favorable.     

Selective detection of Fe(III) ions in aqueous solution with a 1,8-diacridylnaphthalene-derived fluorosensor

The syn-isomer of 1,8-bis(4,4′-diisopropyl-9,9′-diacridyl)naphthalene, 1, has been prepared by two consecutive Pd(PPh₃)₄-catalyzed Stille cross-coupling steps. This highly congested sensor undergoes Fe(III)-selective fluorescence quenching in water/acetonitrile even in the presence of excess of other metal ions.     

Préparation d'isoxazoles trisubstitués par réduction chimique et électrochimique d'α-acyl β-nitrostilbènes

Nitration of α-acylstilbenes with dinitrogen tetroxide leads to corresponding Z-α-acyl-β-nitrostilbenes. By chemical or electochemical reduction of these compounds, trisubstituted isoxazoles were prepared in good yields.     

Adducts of niobium(V) and tantalum(V) halides. XIV. Structure and relative stability of the adducts with some phosphoryl compounds

The adducts of niobium(V) and tantalum(V) halides with some phosphoryl compounds have been studied in chloroform solution by ¹H- and ¹⁹F-FT-NMR. spectroscopy. These octahedral adducts of general formula MX₅ · L (M = Nb, Ta; X = F, Cl, Br; L = phosphoryl ligand) are monomeric and neutral. Their relative stability constants have been determined at ?60°. The stabilities are controlled by electronic effects of substituents on the phosphoryl group.     

Stereochemical memory versus Curtin-Hammett behavior in the rearrangement of 1,3-cyclopentanediyl radical cations derived from housanes through structural effects on conformational control

The electron-transfer-catalyzed rearrangement of the housanes 1 affords regioselectively the two cyclopentenes 2 and 3 by 1,2-migration of a group at the methano bridge. Appropriate ring annelation in the intermediary cyclopentane-1,3-diyl radical cation 1(*+) changes the stereochemical course of the rearrangement from complete stereoselectivity (stereochemical memory) for the structurally simple housane 1b to partial loss of stereoselectivity through competing conformational interconversion for the tricyclic housane 1c. Additional cyclohexane annelation, as in the tetracyclic housane 1a, results in complete loss of stereocontrol through Curtin-Hammett behavior, as substantiated by the viscosity dependence on the product ratio of the rearrangement. Whereas in the radical cations 1b(*+) and 1c(*+) the 1,2-shifts (k(2) and k(3)) are faster than the conformational anti <==> syn change (k(1), k(-1)), the reverse applies for the radical cation 1a(*+). Such structural manipulation of conformational effects in radical cation rearrangements has hitherto not been documented.     

Amidine als Zwischenprodukte bei Umamidierungsreaktionen. 9. Mitteilung über Umamidierungsreaktionen

Amidines as Intermediates in Transamidation Reactions By loss of water in the presence of p-toluenesulfonic acid/xylole N-aminoalkyllactames form bicyclic amidines. The corresponding N-alkylaminoalkyl-lactames' react to bicyclic amidinium salts or to transamidated products, ring-enlarged by the N-alkylamino residue, respectively (s. Scheme 1). The bicyclic amidines and amidinium salts are partially hydrolyzed by KOH/H₂O to lactames (s. Scheme 2). Which of the two possible isomeric lactames are formed is discussed.     

Pheromone, 3.Mitt.: Eine einfache Methode zur Steuerung der Reduktion von α-Alkoxy-carbonylverbindungen

Summary Enantiomerically pure 1,2-diols bearing optionallysyn oranti configurated secondary hydroxylic groups are synthesized from acetal-protected cyanohydrins. After resolution of the diastereomers the cyanohydrins are converted into -alkoxy-ketones by Grignard-reaction followed by reduction using common chelating or non-chelating agents. Among others syntheses of enantiomerically pure pheromones,endo-Brevicomin,exo-Brevicomin and Dispalure are given as examples.

Prof. Dr. Hans Berbalk zum 70. Geburtstag gewidmet     

Cyclic homology of differential operators,the Virasoro algebra and aq-analogue

We show how methods from cyclic homology give easily an explicit 2-cocycle on the Lie algebra of differential operators of the circle such that restricts to the cocycle defining the Virasoro algebra. The same methods yield also aq-analogue of as well as an infinite family of linearly independent cocycles arising when the complex parameterq is a root of unity. We use an algebra ofq-difference operators andq-analogues of Koszul and the Rham complexes to construct these quantum cocycles.