Toward uniform polymer architecture through stereospecific living polymerization and chromatographic separation technique

Isotactic (it-) and syndiotactic (st-) poly(methyl methacrylate)s (PMMAs) were fractionated into uniform PMMAs (without molecular weight distribution) by supercritical fluid chromatography (SFC). The SFC technique was applied to the isolation of uniform it- and st-PMMAs with a hydroxy group (it- and st-PMMA-OH) at the chain end. Equimolar amounts of uniform it- and st-PMMA-OHs were coupled with sebacoyl dichloride to form uniform stereoblock PMMA. The reaction of uniform st-PMMA-OH with methacryloyl chloride gave uniform PMMA macromonomer with methacryloyl group at the chain end. The resulting uniform macromonomer was polymerized radically and the products were fractionated into uniform comblike polymers (1mer to 4mer) by means of gel-permeation chromatography (GPC). The uniform st-PMMA-OH was reacted with 1, 3, 5-benzenetricarbonyl trichloride to form uniform st-tri-armed star polymer. Some of the properties of these uniform stereoregular polymer architectures were studied.     

Chemists and Biochemists during the National Socialist Era

Chemistry and biochemistry in Germany was notably affected by the dismissal and emigration of Jewish scientists. The expulsion of Jewish scientists aided to significantly reduce the international regard for German science, particularly in biochemistry, physical chemistry, and quantum chemistry, after 1945. In most cases remaining scientists adjusted quickly after 1933 to the new political circumstances, with a few exceptions. A number of them even actively supported the politics of National Socialism. This fact as well as the common stance to forget the 12 years of National Socialist rule complicated the exchange of international scientific knowledge after 1945 and delayed affiliation of the weakened fields of research to the level of international research.     

Tris(dialkylamino)benzylphosphoniumbromide – Phosphoniumsalze mit drei nahezu planar konfigurierten N‐Atomen

Tris(dialkylamino)benzylphosphonium Bromides – Phosphonium Salts with three N Atoms configurated nearly planar Tris(dialkylamino)benzylphosphonium bromides [(R₂N)₃PCH₂C₆H₅]⁺Br^– (R: Me, Et, n‐Pr, n‐Bu) have been obtained by the reaction of the corresponding tris(dialkylamino)phosphines with benzylbromide in good yields. The compounds crystallize as colorless solids from acetonitrile or methylene chloride after addition of diethylether. The corresponding tris(dialkylamino)‐benzylphosphonium tribromides have been prepared by treating of the simple bromides with equimolar quantities of elemental bromine. The orange‐red precipitates have been recrystallized from the same solvents by addition of diethylether. In all compounds investigated the crystal structure analyses showing three N atoms with a nearly planar configuration.     

Coumarin-Rhodamine Hybrids—Novel Probes for the Optical Measurement of Viscosity and Polarity

A comprehensive systematic study of absorption and fluorescence properties in solvents of varying viscosity and polarity of three novel and red-emitting coumarin-rhodamine hybrid derivatives with differences in the rigidity of their substituents is presented. This includes ethanol-polyethylene glycol, toluene-polyethylene glycol, and toluene-paraffin mixtures. Moreover, protonation-induced effects on the spectroscopic properties are studied. A viscosity-induced emission enhancement was observed for all coumarin-rhodamine hybrid derivatives. MCR2 bearing a julolidine donor showed the expected low sensitivity to viscosity whereas MCR3 with its freely rotatable diphenylamino substituent revealed a particularly pronounced sensitivity to this parameter. Moreover, MCR2 shows an enhancement in emission in the open, i.e., protonated form in conjunction with a largely Stokes shift fluorescence in the deep red spectral region. This enables the application of these dyes as viscosity sensors and as far red emitting pH-sensitive probes.     

Photophysics of 1-ethynylpyrene-modified RNA base adenine

The photophysical behaviour of a pyrene-modified adenine base is examined. Time-dependent absorption and fluorescence spectroscopy is used to shed light on the fluorescence behavior and the charge transfer between the fluorophore and the nucleobase. The results from TCSPC, fluorescence upconversion and pump-probe absorption spectroscopy are reported, compared and analyzed. This study is a prerequisite for the detailed characterization of RNA dynamics in real time and on a molecular time scale.     

Docking to heme proteins

In silico screening has become a valuable tool in drug design, but some drug targets represent real challenges for docking algorithms. This is especially true for metalloproteins, whose interactions with ligands are difficult to parametrize. Our docking algorithm, EADock, is based on the CHARMM force field, which assures a physically sound scoring function and a good transferability to a wide range of systems, but also exhibits difficulties in case of some metalloproteins. Here, we consider the therapeutically important case of heme proteins featuring an iron core at the active site. Using a standard docking protocol, where the iron–ligand interaction is underestimated, we obtained a success rate of 28% for a test set of 50 heme‐containing complexes with iron‐ligand contact. By introducing Morse‐like metal binding potentials (MMBP), which are fitted to reproduce density functional theory calculations, we are able to increase the success rate to 62%. The remaining failures are mainly due to specific ligand–water interactions in the X‐ray structures. Testing of the MMBP on a second data set of non iron binders (14 cases) demonstrates that they do not introduce a spurious bias towards metal binding, which suggests that they may reliably be used also for cross‐docking studies. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Silicon-containing polyphilic bent-core molecules: the importance of nanosegregation for the development of chirality and polar order in liquid crystalline phases formed by achiral molecules

Polyphilic molecules composed of a bent aromatic core, oligo(siloxane) units, and alkyl segments were synthesized, and the self-organization of these molecules was investigated. Most materials organize into polar smectic liquid crystalline phases. The switching process of these mesophases changes from antiferroelectric for the nonsilylated compounds via superparaelectric to surface-stabilized ferroelectric with increasing segregation of the silylated segments. It is proposed that the siloxane sublayers stabilize a polar synclinic ferroelectric (SmC(s)P(F)) structure, and the escape from a macroscopic polar order as well as steric effects leads to a deformation of the layers with formation of disordered microdomains, giving rise to optical isotropy. Another striking feature is the spontaneous formation of chiral domains with opposite handedness. For two compounds, a temperature-dependent inversion of the optical rotation of these domains was found, and this is associated with an increase of the tilt angle of the molecules from < 45 degrees to > 50 degrees. This observation confirms the recently proposed concept of layer optical chirality (Hough, L. E.; Clark, N. A. Phys. Rev. Lett. 2005, 95, 107802), which is a new source of optical activity in supramolecular systems. With increasing length of the alkyl chains, segregation is lost and a transition from smectic to a columnar phase is found. In the columnar phase, the switching process is antiferroelectric and takes place by rotation of the molecules around the long axes, which reverses the layer chirality; that is, the racemic ground-state structure is switched into a homogeneous chiral structure upon application of an electric field.     

Studies into the Early Degradation Stages of Cellulose by Different Iron Gall Ink Components

Selective fluorescence labelling of oxidized cellulose functionalities followed by GPC-MALLS was used to get a deeper insight into ink-induced degradation processes. As the method is very sensitive towards oxidation and molecular weight changes, slight variations at the very beginning of aging processes, e.g. during ink corrosion of cellulose, can be studied. Five different ink modifications were applied on model papers and underwent mild accelerated aging at 55 °C and cycling humidity (7 days) followed by a short period of static humid aging at 80 °C (2 days). Pure ink constituents like tannic acid or iron sulphate do not result in the same degree of oxidation or chain scission as complete inks. Balanced ink degrades paper more than single compounds, but less than unbalanced inks. Interestingly, some degradation occurs already during or shortly after the application process of unbalanced inks on paper. It could be demonstrated that this oxidation proceeded in a rather high Mw area, while the subsequent aging steps affected predominantly regions of shorter cellulose chains.     

Stable Peptides Instead of Stapled Peptides: Highly Potent αvβ6‐Selective Integrin Ligands

The αvβ6 integrin binds the RGD‐containing peptide of the foot and mouth disease virus with high selectivity. In this study, the long binding helix of this ligand was downsized to an enzymatically stable cyclic peptide endowed with sub‐nanomolar binding affinity toward the αvβ6 receptor and remarkable selectivity against other integrins. Computational studies were performed to disclose the molecular bases underlying the high binding affinity and receptor subtype selectivity of this peptide. Finally, the utility of the ligand for use in biomedical studies was also demonstrated here.