TY - JOUR A1 - Machatschek, Rainhard Gabriel A1 - Heuchel, Matthias A1 - Lendlein, Andreas T1 - Thin-layer studies on surface functionalization of polyetherimide BT - hydrolysis versus amidation JF - Journal of materials research : JMR / Materials Research Society N2 - Among the high-performance and engineering polymers, polyimides and the closely related polyetherimide (PEI) stand out by their capability to react with nucleophiles under relatively mild conditions. By targeting the phthalimide groups in the chain backbone, post-functionalization offers a pathway to adjust surface properties such as hydrophilicity, solvent resistance, and porosity. Here, we use ultrathin PEI films on a Langmuir trough as a model system to investigate the surface functionalization with ethylene diamine and tetrakis(4-aminophenyl)porphyrin as multivalent nucleophiles. By means of AFM, Raman spectroscopy, and interfacial rheology, we show that hydrolysis enhances the chemical and mechanical stability of ultrathin films and allows for the formation of EDC/NHS-activated esters. Direct amidation of PEI was achieved in the presence of a Lewis acid catalyst, resulting in free amine groups rather than cross-linking. When comparing amidation with hydrolysis, we find a greater influence of the latter on material properties. KW - Membrane KW - Nanostructure KW - Polymer KW - Raman spectroscopy KW - Scanning probe microscopy (SPM) KW - Surface reaction KW - Thin film Y1 - 2021 U6 - https://doi.org/10.1557/s43578-021-00339-7 SN - 0884-2914 SN - 2044-5326 VL - 37 IS - 1 SP - 67 EP - 76 PB - Springer CY - Berlin ER - TY - GEN A1 - Hess, Anne-Katrin A1 - Saffert, Paul A1 - Liebeton, Klaus A1 - Ignatova, Zoya T1 - Optimization of translation profiles enhances protein expression and solubility T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - mRNA is translated with a non-uniform speed that actively coordinates co-translational folding of protein domains. Using structure-based homology we identified the structural domains in epoxide hydrolases (EHs) and introduced slow-translating codons to delineate the translation of single domains. These changes in translation speed dramatically improved the solubility of two EHs of metagenomic origin in Escherichia coli. Conversely, the importance of transient attenuation for the folding, and consequently solubility, of EH was evidenced with a member of the EH family from Agrobacterium radiobacter, which partitions in the soluble fraction when expressed in E. coli. Synonymous substitutions of codons shaping the slow-transiting regions to fast-translating codons render this protein insoluble. Furthermore, we show that low protein yield can be enhanced by decreasing the free folding energy of the initial 5'-coding region, which can disrupt mRNA secondary structure and enhance ribosomal loading. This study provides direct experimental evidence that mRNA is not a mere messenger for translation of codons into amino acids but bears an additional layer of information for folding, solubility and expression level of the encoded protein. Furthermore, it provides a general frame on how to modulate and fine-tune gene expression of a target protein. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 518 KW - transfer-RNA genes KW - codon usage KW - Escherichia coli KW - Epoxide hydrolases KW - messenger-RNA KW - sequence KW - elongation KW - Ribosome KW - mechanism KW - Membrane Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-409574 SN - 1866-8372 IS - 518 ER - TY - JOUR A1 - Machatschek, Rainhard Gabriel A1 - Heuchel, Matthias A1 - Lendlein, Andreas T1 - Hydrolytic stability of polyetherimide investigated in ultrathin films JF - Journal of materials research : JMR / Materials Research Society N2 - Increasing the surface hydrophilicity of polyetherimide (PEI) through partial hydrolysis of the imide groups while maintaining the length of the main-chain was explored for adjusting its function in biomedical and membrane applications. The outcome of the polymer analogous reaction, i.e., the degree of ring opening and chain cleavage, is difficult to address in bulk and microstructured systems, as these changes only occur at the interface. Here, the reaction was studied at the air-water interface using the Langmuir technique, assisted by atomic force microscopy and vibrational spectroscopy. Slow PEI hydrolysis sets in at pH > 12. At pH = 14, the ring opening is nearly instantaneous. Reduction of the layer viscosity with time at pH = 14 suggested moderate chain cleavage. No hydrolysis was observed at pH = 1. Hydrolyzed PEI films had a much more cohesive structure, suggesting that the nanoporous morphology of PEI can be tuned via hydrolysis. KW - 2D materials KW - Membrane KW - Polymer KW - Water KW - Nanostructure Y1 - 2021 U6 - https://doi.org/10.1557/s43578-021-00267-6 SN - 0884-2914 SN - 2044-5326 VL - 36 IS - 14 SP - 2987 EP - 2994 PB - Springer CY - Berlin ER - TY - JOUR A1 - Draude, Felix A1 - Körsgen, Martin A1 - Pelster, Andreas A1 - Schwerdtle, Tanja A1 - Müthing, Johannes A1 - Arlinghaus, Heinrich F. T1 - Characterization of freeze-fractured epithelial plasma membranes on nanometer scale with ToF-SIMS JF - Analytical & bioanalytical chemistry N2 - Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to characterize the freeze-fracturing process of human epithelial PANC-1 and UROtsa cells. For this purpose, phosphatidylcholine, sphingomyelin, phosphatidylethanolamine, and phosphatidylserine standard samples were investigated to find specific signals with both high specificity and signal intensity. The results were used to investigate single cells of subconfluent cell layers prepared with a special silicon wafer sandwich preparation technique. This freeze-fracturing technique strips cell membranes off the cells, isolating them on opposing silicon wafer substrates. Criteria were found for defining regions with stripped off cell membranes and, on the opposing wafer, complementary regions with the remaining cells. Measured ethanolamine/choline and serine/choline ratios in these regions clearly showed that in the freeze-fracturing process, the lipid bilayer of the plasma membrane is split along its central zone. Accordingly, only the outer lipid monolayer is stripped off the cell, while the inner lipid monolayer remains attached to the cell on the opposing wafer, thus allowing detailed analysis of a single lipid monolayer. Furthermore, it could be shown that using different washing procedures did not influence the transmembrane lipid distribution. Under optimized preparation conditions, it became feasible to detect lipids with a lateral resolution of approximately 100 nm. The data indicate that ToF-SIMS would be a very useful technique to study with very high lateral resolution changes in lipid composition caused, for example, by lipid storage diseases or pharmaceuticals that interfere with the lipid metabolism. KW - ToF-SIMS imaging KW - Life science KW - Lipid KW - Freeze-fracturing KW - Membrane KW - Transmembrane asymmetry Y1 - 2015 U6 - https://doi.org/10.1007/s00216-014-8334-2 SN - 1618-2642 SN - 1618-2650 VL - 407 IS - 8 SP - 2203 EP - 2211 PB - Springer CY - Heidelberg ER -