Electrochemical C−H Functionalization of (Hetero)Arenes—Optimized by DoE

A novel approach towards the activation of different arenes and purines including caffeine and theophylline is presented. The simple, safe and scalable electrochemical synthesis of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) aryl ethers was conducted using an easy electrolysis setup with boron-doped diamond (BDD) electrodes. Good yields up to 59 % were achieved. Triethylamine was used as a base as it forms a highly conductive media with HFIP, making additional supporting electrolytes superfluous. The synthesis was optimized using Design of Experiment (DoE) techniques giving a detailed insight to the significance of the reaction parameters. The mechanism was investigated by cyclic voltammetry (CV). Subsequent transition metal-catalyzed as well as metal-free functionalization led to interesting motifs in excellent yields up to 94 %.     

Enhanced protein crystallization around the metastable critical point

We report on a computer-simulation study of homogeneous crystal nucleation in a model for globular proteins. We find that the presence of a metastable vapour-liquid critical point drastically changes the pathway for the formation of a critical nucleus. But what is more important, the large density fluctuations near the critical point also lowers the free-energy barrier to nucleation and hence increases the nucleation rate. As␣the location of the vapour-liquid critical point can be controlled by changing the solvent conditions, our simulation results suggest a guided approach to protein crystallization. Received: 4 June 1998/Accepted: 3 September 1998 / Published online: 10 December 1998     

Ordering of PCDTBT Revealed by Time‐Resolved Electron Paramagnetic Resonance Spectroscopy of Its Triplet Excitons

Time‐resolved electron paramagnetic resonance (TREPR) spectroscopy is shown to be a powerful tool to characterize triplet excitons of conjugated polymers. The resulting spectra are highly sensitive to the orientation of the molecule. In thin films cast on PET film, the molecules’ orientation with respect to the surface plane can be determined, providing access to sample morphology on a microscopic scale. Surprisingly, the conjugated polymer investigated here, a promising material for organic photovoltaics, exhibits ordering even in bulk samples. Orientation effects may significantly influence the efficiency of solar cells, thus rendering proper control of sample morphology highly important.     

Linear stability of stationary solutions of the Vlasov-Poisson system in three dimensions

Rigorous results on the stability of stationary solutions of the Vlasov-Poisson system are obtained in the contexts of both plasma physics and stellar dynamics. It is proved that stationary solutions in the plasma physics (stellar dynamics) case are linearly stable if they are decreasing (increasing) functions of the local, i.e., particle, energy. The main tool in the analysis is the free energy, a conserved quantity of the linearized system. In addition, an appropriate global existence result is proved for the linearized Vlasov-Poisson system and the existence of stationary solutions which satisfy the above stability condition is established.     

A stability result for the relativistic Vlasov-Maxwell system

We consider a space-periodic version of the relativistic Vlasov-Maxwell system describing a collisionless plasma consisting of electrons and positively charged ions. As our main result, we prove that certain spacially homogeneous stationary solutions are nonlinearly stable. To this end we also establish global existence of weak solutions to the corresponding initial value problem. Our investigation is motivated by a corresponding result for the Vlasov-Poisson system, cf. [1, 14].     

Phase transitions in ultraoriented polyethylene fibers under moderate pressures: A synchrotron X-ray study

The effect of pressure on phase transformations of ultradrawn ultra-high-molecular-weight polyethylene (UHMWPE) fibers was examined by in situ X-ray diffraction measurements with synchrotron radiation. The mesomorphic hexagonal phase was metastable even at a relatively low pressure of about 100 bar. The effect of pressure on the melting transitions was larger than in chain-folded structures. The existence and metastability of the hexagonal phase is the basis of compaction technology of UHMWPE fibers in composite materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 53–59, 2004     

Multipole Radiation in a Collisionless Gas Coupled to Electromagnetism or Scalar Gravitation

We consider the relativistic Vlasov-Maxwell and Vlasov-Nordström systems which describe large particle ensembles interacting by either electromagnetic fields or a relativistic scalar gravity model. For both systems we derive a radiation formula analogous to the Einstein quadrupole formula in general relativity.Supported in parts by DFG priority research program SPP 1095     

Sequence-Tunable Phase Behavior and Intrinsic Fluorescence in Dynamically Interacting Peptides

A conceptual framework towards understanding biological condensed phases is emerging, derived from biological, biomimetic, and synthetic sequences. However, de novo peptide condensate design remains a challenge due to an incomplete understanding of the structural and interactive complexity. We designed peptide modules based on a simple repeat motif composed of tripeptide spacers (GSG, SGS, GLG) interspersed with adhesive amino acids (R/H and Y). We show, using sequence editing and a combination of computation and experiment, that n→π* interactions in GLG backbones are a dominant factor in providing sufficient backbone structure, which in turn regulates the water interface, collectively promoting liquid droplet formation. Moreover, these R(GLG)Y and H(GLG)Y condensates unexpectedly display sequence-dependent emission that is a consequence of their non-covalent network interactions, and readily observable by confocal microscopy.