Category: Doctoral Students Seminar

Maria Camilles on “Investigation of effect of thermal denaturation on eye lens crystallin proteins using NMR spectroscopy”

and Muhammad Tariq on “Epitaxial Crystallization of Polyethylene on Molybdenum Disulfide Substrate via Prefreezing”

Continue reading “Doctoral students seminar (March 13, 2018)”

Effect of End-Capping Motifs on Conformational Dynamics and Stability of α-Helices

by Stefan Wicht

Recent results revealed that stabilizing or destabilizing the ends of the helix affects helix unfolding but not refolding in the center. Thus, helix stability in the center is changed remote from the region of stabilization or destabilization and this non-local effect was attributed either to an impact on boundary diffusion or boundary diffusion distances. We tested the effect of differently charged capping motifs at the N-cap and C-cap position of helical peptides on boundary diffusion or diffusion distances by triplet-triplet-energy-transfer (TTET). It could be demonstrated that introducing opposite charges at the helix termini leads to a global stabilization of the helix, whereas introducing similar charges at the helix termini lead to a global destabilization. This stability effect is in accordance with the helix macro-dipole. However, our results showed that capping motifs do not lead to a change in the diffusion coefficient for boundary diffusion which indicates that longer or shorter diffusion distances are the origin of this stability effect. Temperature dependence measurements revealed that the activation energy of boundary diffusion is also not affected by capping motifs, which was reproduced by calculations using the Lifson-Roig theory for helix-coil transition. These results suggest that capping motifs simply elongate helices by hydrogen bonding of additional residues.

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Monte Carlo Simulations of Thiophene and Polythiophene Chains of Various Lengths in Vacuum and in Contact with Substrates

by Momchil Ivanov

Thiophene and polythiophenes are a subject of study in the SFB. Poly(3-hexylthiophene-2,5-diyl) or P3HT in particular is a polymer used in organic photovoltaics, therefore, a large amount of experimental data for it exists. Some theoretical models of this particular polymer that exist in the literature as well. I will give a brief introduction into the method of Monte Carlo sampling as a method of simulating the existing models and will present results on simulations of thiophene and P3HT in vacuum as well as in the presence of a substrate.

Location: UL, Linnéstr. 5, SR 218
Time: 3.30pm-5.00pm

Geometrical stiffness studied by a coarse grained homopolymer model

by Benno Werlich

Morphologies of biopolymers depend on the interaction energies and on stiffness. We use a coarse grained homopolymer model to study geometrical stiffness as bond length variation. Therefore we show a wide range of stable structures which are known from different stiffness approaches and also from experiments. With the help of canonical and microcanonical analysis we created a state diagram for a broad range of stiffness from flexible to very stiff chains. Simulations were performed by Stochastic Monte Carlo Simulations (SAMC).

 

Location: MLU, Von-Danckelmann-Platz 3, SR E.04
Time: 3.30pm-5.00pm

Solid state NMR investigations and MD simulations of amphiphilic triblock copolymers in lipid bilayers

Pluronics are triblock copolymers widely used in pharmacological industry that consist of hydrophilic poly(ethylene oxide) end blocks and a hydrophobic poly(propylene oxide) middle block. Depending on the lengths of the different blocks, Pluronics can influence membrane properties in a variety of ways.

Using solid-state nuclear magnetic resonance (NMR), we investigated the structure and dynamics of different Pluronics interacting with a number of phosphatidylcholine membranes with variable bilayer thickness and acyl chain saturation. Continue reading “Talk by Ruth Bärenwald at MLU (December 12, 2017)”

UV-B induced changes of eye-lens crystallins

Age related cataract is the major cause of blindness worldwide. With the age of 75 years, more than 50% of all people are affected and so far, surgery is the only effective treatment available. For this reason it is important to understand the complex system of the eye lens especially effects of aging like chronic UV-B irradiation.

Many modifications of crystallins by UV-B on already aggregated and destroyed protein have been found. So far, changes in the soluble fractions of the protein are not well investigated. Answering this question, different techniques of solution NMR have been applied to native and irradiated hgD-crystallin to identify and characterize a modified but still soluble state of the protein. This would highlight the first structural changes on the transition from functional soluble protein to dysfunctional aggregates.

Location: MLU, Von-Danckelmann-Platz 3, SR 1.06
Time: 3.30pm

Molecular Dynamics and Charge Transport in highly-conductive Polymeric Ionic Liquids

Glassy dynamics and charge transport are studied for the polymeric ionic liquid (PIL) poly[tris(2-(2-methoxyethoxy)ethyl)ammonium acryloxypropyl sulfonate] (PAAPS) with varying molecular weight (9700, 44200, 51600, and 99500 g/mol) by broadband dielectric spectroscopy (BDS) in a wide frequency (10⁻²−10⁷ Hz) and temperature range (100−400 K) and by DSC- and AC-chip calorimetry.

The dielectric spectra are characterized by a superposition of (i) relaxation processes, (ii) charge transport, and (iii) electrode polarization. Continue reading “Talk by F. Frenzel at UL (October 24, 2017)”