Work hardening and recovery in fully lamellar TiAl: relative activity of deformation systems

The relative activity of deformation systems during work hardening and thermal recovery has been investigated in fully lamellar TiAl. This has been done by a combination of a series of deformation/static recovery experiments and numerical simulations based on a defect density-based crystal plasticity model. Firstly, active deformation systems in differently oriented polysynthetically twinned crystals/single lamellar colonies have been studied. Subsequently, numerical experiments on a polycolony microstructure have been used to investigate the inhomogeneous microplasticity (i.e. the typical microyield) in fully lamellar TiAl. From this, it has been possible to analyse how changes in the lamella thickness, domain size and colony size influence the onset of macroscopic yield. Based on static recovery experiments with differently oriented polysynthetically twinned crystals, numerical studies have revealed trends in the recovery of work hardening in both polysynthetically twinned crystals and polycolony microstructures.     

Synthesis of Diacetylene‐Containing Peptide Building Blocks and Amphiphiles,Their Self‐Assembly and Topochemical Polymerization in Organic Solvents

A series of functional iodoacetylenes was prepared and converted into the corresponding diacetylene‐substituted amino acids and peptides via Pd/Cu‐promoted sp–sp carbon cross‐coupling reactions. The unsymmetrically substituted diacetylenes can be incorporated into oligopeptides without a change in the oligopeptide strand's directionality. Thus, a series of oligopeptide‐based, amphiphilic diacetylene model compounds was synthesized, and their self‐organization as well as their UV‐induced topochemical polymerizability was investigated in comparison to related polymer‐substituted macromonomers. Solution‐phase IR spectroscopy, gelation experiments, and UV spectroscopy helped to confirm that a minimum of five N‐H???O?C hydrogen‐bonding sites was required in order to obtain reliable aggregation into stable β‐sheet‐type secondary structures in organic solvents. Furthermore, the non‐equidistant spacing of these hydrogen‐bonding sites was proven to invariably lead to β‐sheets with a parallel β‐strand orientation, and the characteristic IR‐spectroscopic signatures of the latter in organic solution was identified. Scanning force micrographs of the organogels revealed that compounds with six hydrogen‐bonding sites gave rise to high aspect ratio nanoscopic fibrils with helical superstructures but, in contrast to the related macromonomers, did not lead to uniform supramolecular polymers. The UV‐induced topochemical polymerization within the β‐sheet aggregates was successful, proving parallel β‐strand orientation and highlighting the effect of the number and pattern of N‐H???O?C hydrogen‐bonding sites as well as the hydrophobic residue in the molecular structure on the formation of higher structures and reactivity.     

1H- und 13C-NMR-spektroskopische Untersuchungen zur Ladungsverteilung in substituierten 1,3-Dioxan-2-ylium-Salzen

The ¹H and ¹³C NMR spectra of a series of 1,3-dioxan-2-ylium salts substituted at C-2 and C-4, C-5, C-6 have been measured. The atomic charge distribution in 1,3-dioxan- and 1,3-dioxolan-2-ylium cations has been calculated with the MINDO/3 method, leading to a linear correlation between π-charge and ¹³C chemical shift at C-2. The strong C-21-proton downfield shift is caused by the anisotropic influence of the mesomeric cation system. The conformations of substituted 1,3-dioxan-2-ylium cations are discussed.     

Control of Crystallinity of Vinylene-Linked Two-Dimensional Conjugated Polymers by Rational Monomer Design

The interest in two-dimensional conjugated polymers (2D CPs) has increased significantly in recent years. In particular, vinylene-linked 2D CPs with fully in-plane sp²-carbon-conjugated structures, high thermal and chemical stability, have become the focus of attention. Although the Horner-Wadsworth-Emmons (HWE) reaction has been recently demonstrated in synthesizing vinylene-linked 2D CPs, it remains largely unexplored due to the challenge in synthesis. In this work, we reveal the control of crystallinity of 2D CPs during the solvothermal synthesis of 2D-poly(phenylene-quinoxaline-vinylene)s (2D-PPQVs) and 2D-poly(phenylene-vinylene)s through the HWE polycondensation. The employment of fluorinated phosphonates and rigid aldehyde building blocks is demonstrated as crucial factors in enhancing the crystallinity of the obtained 2D CPs. Density functional theory (DFT) calculations reveal the critical role of the fluorinated phosphonate in enhancing the reversibility of the (semi)reversible C−C single bond formation.     

Insight into the Supramolecular Architecture of Intact Diatom Biosilica from DNP‐Supported Solid‐State NMR Spectroscopy

Diatom biosilica is an inorganic/organic hybrid with interesting properties. The molecular architecture of the organic material at the atomic and nanometer scale has so far remained unknown, in particular for intact biosilica. A DNP‐supported ssNMR approach assisted by microscopy, MS, and MD simulations was applied to study the structural organization of intact biosilica. For the first time, the secondary structure elements of tightly biosilica‐associated native proteins in diatom biosilica were characterized in situ. Our data suggest that these proteins are rich in a limited set of amino acids and adopt a mixture of random‐coil and β‐strand conformations. Furthermore, biosilica‐associated long‐chain polyamines and carbohydrates were characterized, thereby leading to a model for the supramolecular organization of intact biosilica.     

Protein tyrosine phosphatase oligomerization studied by a combination of 15N NMR relaxation and 129Xe NMR. Effect of buffer containing arginine and glutamic acid

15N NMR relaxation and 129Xe NMR chemical shift measurements offer complementary information to study weak protein-protein interactions. They have been applied to study the oligomerization equilibrium of a low-molecular-weight protein tyrosine phosphatase in the presence of 50 mM arginine and 50 mM glutamic acid. These experimental conditions are shown to enhance specific protein-protein interactions while decreasing nonspecific aggregation. In addition, 129Xe NMR chemical shifts become selective reporters of one particular oligomer in the presence of arginine and glutamic acid, indicating that a specific Xe binding site is created in the oligomerization process. It is suggested that the multiple effects of arginine and glutamic acid are related to their effective excluded volume that favors specific protein association and the destabilization of partially unfolded forms that preferentially interact with xenon and are responsible for nonspecific protein aggregation.     

Kit for unsymmetric dinucleating double-Schiff-base ligands: facile access to a versatile new ligand system and its first heterobimetallic copper-zinc complex

The synthetic route toward new unsymmetric compartmental "end-off" Schiff-base ligands in a straightforward two-step reaction of 2,6-diformyl-4-methylphenol and two different amine components is presented. To demonstrate the versatility of this method, we have synthesized two different single-Schiff-base proligands, Hbpahmb and Hphmb, utilizing (2-aminoethyl)bis(2-pyridylmethyl)amine and (2-aminomethyl)pyridine, respectively. Subsequent reaction with thiosemicarbazide as the second amine component leads to the novel unsymmetric double-Schiff-base ligands {1-[3-[2-[bis(pyridin-2-ylmethyl)amino]ethyliminomethyl]-2-hydroxy-5-methylphenyl]methylidene}hydrazine carbothioamide (H2bpamptsc) and {1-[3-(pyridin-2-ylmethyliminomethyl)-2-hydroxy-5-methylphenyl]methylidene}hydrazine carbothioamide (H2pmptsc). Both ligands provide two distinctly different coordination pockets: a rigid tridentate N,O,S donor set of the hydrazide compartment versus a rather flexible pentadentate (H2bpamptsc) or tridentate (H2pmptsc) nitrogen-rich chelating side arm. The reaction of the ligand H2bpamptsc with zinc(II) acetate and copper(II) perchlorate yields the heterobinuclear Cu-Zn complex [CuZn(bpamptsc)(mu2,eta1-OAc)(MeCN)](ClO4) (1).