Designed Beta‐Turn Mimic Based on the Allylic‐Strain Concept: Evaluation of Structural and Biological Features by Incorporation into a Cyclic RGD Peptide (Cyclo(‐L‐arginylglycyl‐L‐α‐aspartyl‐))

The (3R,5S,6E,8S,10R)‐11‐amino‐3,5,8,10‐tetramethylundec‐6‐enoic acid (ATUA; 1 ), which was designed as a βII′‐turn mimic according to the concepts of allylic strain and 2,4‐dimethylpentane units, was incorporated into a cyclic RGD peptide. The three‐dimensional structure of cyclo(‐RGD‐ATUA‐) (=cyclo(‐Arg‐Gly‐Asp‐ATUA‐)) 4 in H₂O was determined by NMR techniques, distance geometry calculations and molecular‐dynamics simulations. The RGD sequence of 4 shows high conformational flexibility but some preference for an extended conformation. The structural features of the RGD sequence of 4 were compared with the RGD moiety of cyclo(‐RGDfV‐) (=cyclo(‐Arg‐Gly‐Asp‐D ‐Phe‐Val‐)). In contrast to cyclo(‐RGDfV‐), which is a highly active αvβ3 antagonist and selective against αIIbβ3, cyclo(‐RGD‐ATUA‐) shows a lower activity and selectivity. The structure of the ATUA residue in the cyclic peptide resembles a βII′‐turn‐like conformation. Its middle part, adjacent to the C?C bond, strongly prefers the designed and desired structure.     

CdSe and CdSe/CdS nanorod solids

We demonstrate the self-organization of CdSe nanorods into nematic, smectic, and crystalline solids. Layered colloidal crystals of CdSe nanorods grow by slow destabilization of a nanocrystal solution upon allowing the diffusion of a nonsolvent into the colloidal solution of nanocrystals. The colloidal crystals of nanorods show characteristic birefringence, which we assign to specific spherulite-like texture of each nanorod assembly. To demonstrate the general character of nanorod self-assembly technique, CdSe/CdS heterostructure nanorods were organized into highly luminescent superlattices.     

Optical properties of bis(cyclopentadienyl)magnesium: excimer-type luminescence of the bis(cyclopentadienyl) ligand frame

The electronic spectra of solid MgCp₂ (Cp = cyclopentadienyl) show features which indicate the presence of intramolecular interligand interactions. The fluorescence of MgCp₂ (λ_max = 363 nm) undergoes a considerable Stokes shift which is apparently caused by a bonding attraction between both Cp rings in the excited state. An additional phosphorescence of the (Cp⁻)₂ fragment (λ_max = 535 nm) appears at 77 K.     

Selektivierung geringer Mengen Kupfer mit Polyäthylenimin-Zellulose

Zusammenfassung Polyäthyleniminzellulosen sorbieren Cu²⁺ durch koordinative Bindung als Zentralion des sekundären Stickstoffs des Polyäthylenimins im P_H-Bereich 3,5 bis 4,5 selektiv aus verd. Lösungen. 10g Kupfer können von 10⁵fachen Überschüssen anderer Übergangsmetalle separiert, mit verd. Salzsäure eluiert und mit Diäthyldithiocarbamat photometrisch bestimmt werden. Das Verfahren eignet sich zur Erfassung von 0,001% Kupfer in Zink, Mangan, Kobalt, Nickel, Cadmium und Aluminium sowie aus Lösungen, deren Kupfergehalt 0,02 ppm beträgt.

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Selectivation of small amounts of copper with polyethyleneimine-cellulose

Summary Polyethyleneimine celluloses selectively sorb Cu²⁺ from dilute solutions through coordinative bonding as central ion of the secondary nitrogen of polyethyleneimine in the p_H-range of 3.5–4.5. 10g of copper may be separated from 10₅-fold excesses of other transition metals, then eluted with dilute hydrochloric acid and determined photometrically with diethyldithiocarbamate. The method is suitable for determining 0.001% copper in zinc, manganese, cobalt, nickel, cadmium, and aluminium as well as in solutions whose coppercontent is 0.02 ppm.

     

Auftrennung von gemischten Hexa(bromochloro)-rhenaten(IV) und -osmaten(IV) auf Dünnschichtcelluloseplatten

The ions ReBr_nCl _6?n ^2? (0?n?6) and OsBr_nCl _6?n ^2? , respectively, ReO₄ ^? and Br^? have been separated on cellulose using the thin-layer chromatographic technique with 3.2 M sulphuric acid as the mobile phase.     

Solid-Phase Synthesis of a Sialyl-Tn-Glycoundecapeptide of the MUC1 Repeating Unit

The synthesis of glycopeptides carrying tumour-associated antigens is of interest for cancer diagnosis and treatment. Here, a very efficient route lo disaccharide threonine building block 8 is presented which allows the introduction of the sialyl-Tn antigen into a peptide. The syntheses of the undecapeptide and the sialyl-Tn-containing glycoundecapeptide, which are a part of the repeating unit of MUC1, were performed by solid-phase synthesis with an allylic anchor cleavable under neutral conditions. After detachment from the resin, the peptide and the glycopeptide arc completely deprotected giving the target compounds 13 and 15 , respectively.     

Methylmetall-bis(trimethylsilyl)amidoderivate des Aluminiums,Galliums und Arsens

Methyl Metal Bis(trimethylsilyl)amido Derivatives of Aluminium, Gallium, and Arsenic MeAl[N(SiMe₃)₂]₂ (Me ? CH₃) has been prepared by the reaction of AlMe₃ with HN(SiMe₃)₂ in a 1:2 molar ratio. The homologue Gallium compound (as well as the Aluminium derivative) is formed in good yields by the interaction of MeMcl₂ (M = Al, Ga) with Li- and Na[N(SiMe₃)₂], respectively. MeAs[N(SiMe₃)₂]₂ is formed by the reaction of AsCl₃ and Na[N(SiMe₃)₂] in a 1:3 molar ratio. These colourless amido derivatives are monomeric in solution, they have been characterized by analyses, mass, n.m.r. (¹H and ¹³C), and especially by i.r. and Raman spectra.     

Mass spectrometric analysis of ceramic components for solid oxide fuel cells

For the determination of trace impurities in ceramic components of solid oxide fuel cells (SOFCs), some mass spectrometric methods have been applied such as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and inductively coupled plasma mass spectrometry (ICP-MS). Due to a lack of suitable standard reference materials for quantifying of analytical results on La _x Sr _y MnO₃ cathode material a matrix-matched synthetic standard-high purity initial compounds doped with trace elements-was prepared in order to determine the relative sensitivity coefficients in SSMS and LA-ICP-MS. Radiofrequency glow discharge mass spectrometry (rf-GDMS) was developed for trace analysis and depth profiling of thick non-conducting layers. Surface analytical techniques, such as secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS), were used to determine the element distribution on surfaces (homogeneity) and the surface contaminants of SOFC ceramic layers.Dedicated to Professor Dr. rer. nat. Hubertus Nickel on the occasion of his 65th birthday     

Über die Darstellung von Dimethyl(mercapto)sulfonium-hexa-chloroantimonat [(CH3)2SSH]+SbCl6−

Preparation of Dimethyl(mercapto)sulfonium-hexachloroantimonate [(CH₃)₂SSH]⁺SbCl₆^? The preparation of [(CH₃)₂SSH]⁺SbCl₆^? from [(Ch₃)₂SCl]⁺SbCl₆^? and H₂S at 223 K is reported. This salt is stable below 243 K and is characterized by vibrational spectroscopy.     

Interplay between Auger and ionization processes in nanocrystal quantum dots

We study the interplay between Auger effects and ionization processes in the limit of strong electronic confinement in core/shell CdSe/ZnS semiconductor nanocrystal quantum dots. Spectrally resolved fluorescence decay measurements reveal a monotonic increase of the photoluminescence decay rate on excitation density. Our results suggest that Auger recombination accelerates ionization processes that lead to the occupation of dark, nonemissive nanocrystal states. A model is proposed in the quantized Auger regime describing these experimental observations and providing an estimate of the Auger assisted ionization rates.