Homogeneity and Canonical Connections of Isoparametric Manifolds

On every isoparametric submanifold M a connection with parallel second fundamental form is constructed geometrically such that M is an orbit of an s-representation if and only if the connection is a canonical one. If the rank of M is greater than one this connection is in case of homogeneity the canonical connection of the reductive decomposition given by the orbit of s-representation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Sensitized photoconduction in a polydiacetylene crystal (DCHD)

The photoconductivity of DCHD displays a maximum near 3.6 eV coinciding with the maximum of the S_o → S₁ absorption of the carbazole group. It is attributed to a sensitization involving charge transfer from the excited chromophore to the chain. The rate constant for non-radiative decay of the carbazole singlet due to energy transfer to the chain is 1.6 × 10¹³ s^?1, and for charge transfer ≈ 3 × 10¹¹ s^?1.     

Defect Structure in Te-doped GaAs Single Crystals after Plastic Deformation (II). Dislocation Slip and Cell Formation

At temperatures above the brittle-to-ductile transition (490 °C) in Te-doped GaAs three types of predominant defect configurations have been observed after uniaxial compression along a [001] direction: (i) twins and stacking faults (500 … 520 °C), (ii) slip zones of dislocations (≈550 °C) and (iii) dislocation cells (580 … 590 °C). In Part II quantitative details of the appearance of slip and cell formation are given. Leading segments of gliding half loops are mainly of 60° type. Cell walls were formed by multiple slip of perfect dislocations.     

On self-majorizing elements in Archimedean vector lattices

A finite element in an Archimedean vector lattice is called self-majorizing if its modulus is a majorant. Such elements exist in many vector lattices and naturally occur in different contexts. They are also known as semi-order units as the modulus of a self-majorizing element is an order unit in the band generated by the element. In this paper the properties of self-majorizing elements are studied systematically, and the relations between the sets of finite, totally finite and self-majorizing elements of a vector lattice are provided. In a Banach lattice an element \(\varphi \) is self-majorizing , if and only if the ideal and the band both generated by \(\varphi \) coincide.     

Phenanthrene-fused boron-dipyrromethenes as bright long-wavelength fluorophores

A new class of boron-dipyrromethene (BDP or BODIPY) dyes was obtained by phenanthrene fusion to the beta-pyrrole positions, absorbing in the wavelength range of important laser sources. Despite a 'propeller-like' distorted structure in the crystalline state, the chromophore absorbs (log epsilon > or = 5) and fluoresces (Phif > or = 0.8) strongly and can be easily turned into a fluorescence light-up probe. Incorporation into latex beads produces bright and photostable single-dye and F?rster Resonance Energy Transfer (FRET) particles for microscopy applications.     

Membrane-mediated induction and sorting of K-Ras microdomain signaling platforms

The K-Ras4B GTPase is a major oncoprotein whose signaling activity depends on its correct localization to negatively charged subcellular membranes and nanoclustering in membrane microdomains. Selective localization and clustering are mediated by the polybasic farnesylated C-terminus of K-Ras4B, but the mechanisms and molecular determinants involved are largely unknown. In a combined chemical biological and biophysical approach we investigated the partitioning of semisynthetic fully functional lipidated K-Ras4B proteins into heterogeneous anionic model membranes and membranes composed of viral lipid extracts. Independent of GDP/GTP-loading, K-Ras4B is preferentially localized in liquid-disordered (l(d)) lipid domains and forms new protein-containing fluid domains that are recruiting multivalent acidic lipids by an effective, electrostatic lipid sorting mechanism. In addition, GDP-GTP exchange and, thereby, Ras activation results in a higher concentration of activated K-Ras4B in the nanoscale signaling platforms. Conversely, palmitoylated and farnesylated N-Ras proteins partition into the l(d) phase and concentrate at the l(d)/l(o) phase boundary of heterogeneous membranes. Next to the lipid anchor system, the results reveal an involvement of the G-domain in the membrane interaction process by determining minor but yet significant structural reorientations of the GDP/GTP-K-Ras4B proteins at lipid interfaces. A molecular mechanism for isoform-specific Ras signaling from separate membrane microdomains is postulated from the results of this study.     

Activation and Coordination of Ammonia at [Cp*Ir(H)2]: NMR and Matrix Isolation Studies

¹H NMR exchange spectroscopy of a reaction mixture of [Cp*Ir(H)₄] ( 1 ; Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) and ammonia suggests an exchange of hydrogen atoms between the hydrido ligands and ammonia. Treatment of 1 with ND₃ led to an H/D exchange between ND₃ and the hydrido ligands of 1 . Subsequent studies showed that photolysis of 1 isolated in frozen argon matrices leads to the formation of the iridium compounds [Cp*Ir(H)₂] ( 2 ) and [Cp*Ir(H)₃] ( 4 ), as it was confirmed by IR spectroscopy. In the presence of water the aqua complex [Cp*Ir(H)₂(OH₂)] ( 3 ) was generated simultaneously. Accordingly, photolysis of 1 in an argon matrix doped with ammonia gave rise to the ammine complex [Cp*Ir(H)₂(NH₃)] ( 5 ). IR assignments were supported by calculations of the gas‐phase IR spectra of 1 – 5 by DFT methods.     

Mononuclear Tetraamineplatinum(II) Complexes: Synthesis,Anticancer Activity,DNA Binding,and Cellular Uptake

The synthesis of three bis[(tert‐butoxy)carbonyl]‐protected (tetramine)dichloroplatinum complexes 2a – c of formula cis‐[PtCl₂(LL)] and of their cationic deprotected analogs 3a – c and their evaluation with respect to in vitro cytotoxicity, intramolecular stability, DNA binding, and cellular uptake is reported. The synthesis comprises the complexation of K₂[PtCl₄] with di‐N‐protected tetramines 1a – c to give 2a – c and subsequent acidolysis, yielding 3a – c . The cytotoxicity of the complexes is in direct relation to the length of the polyamine. Complexes 3a – c display a significant higher affinity for CT DNA as well as for cellular DNA in A2780 cells than cisplatin.