TY - JOUR A1 - Rackwitz, Jenny A1 - Kopyra, Janina A1 - Dabkowska, Iwona A1 - Ebel, Kenny A1 - Rankovic, MiloS Lj. A1 - Milosavljevic, Aleksandar R. A1 - Bald, Ilko T1 - Sensitizing DNA Towards Low-Energy Electrons with 2-Fluoroadenine JF - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition N2 - 2-Fluoroadenine ((2F)A) is a therapeutic agent, which is suggested for application in cancer radiotherapy. The molecular mechanism of DNA radiation damage can be ascribed to a significant extent to the action of low-energy (<20 eV) electrons (LEEs), which damage DNA by dissociative electron attachment. LEE induced reactions in (2F)A are characterized both isolated in the gas phase and in the condensed phase when it is incorporated into DNA. Information about negative ion resonances and anion-mediated fragmentation reactions is combined with an absolute quantification of DNA strand breaks in (2F)A-containing oligonucleotides upon irradiation with LEEs. The incorporation of (2F)A into DNA results in an enhanced strand breakage. The strand-break cross sections are clearly energy dependent, whereas the strand-break enhancements by (2F)A at 5.5, 10, and 15 eV are very similar. Thus, (2F)A can be considered an effective radiosensitizer operative at a wide range of electron energies. KW - ab initio calculations KW - dissociative electron attachment KW - DNA origami KW - DNA radiation damage KW - fludarabine Y1 - 2016 U6 - https://doi.org/10.1002/anie.201603464 SN - 1433-7851 SN - 1521-3773 VL - 55 SP - 10248 EP - 10252 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Meiling, Till T. A1 - Cywinski, Piotr J. A1 - Bald, Ilko T1 - White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis JF - Scientific reports N2 - In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification. The CNDs are stable over a long period of time (> 1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1% up to 28% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst. Y1 - 2016 U6 - https://doi.org/10.1038/srep28557 SN - 2045-2322 VL - 6 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Sun, Jing A1 - Cernoch, Peter A1 - Völkel, Antje A1 - Wei, Yuhan A1 - Ruokolainen, Janne A1 - Schlaad, Helmut T1 - Aqueous Self-Assembly of a Protein-Mimetic Ampholytic Block Copolypeptide JF - Macromolecules : a publication of the American Chemical Society N2 - This report describes the aggregation behavior of an ABC-type ampholytic block copolypeptide, poly(ethylene oxide)-block-poly(L-lysine)-block-poly(L-glutamate), in aqueous media in dependence of pH. Polypeptide secondary structures and self-assemblies are investigated by circular dichroism (CD), Fourier transform infrared (FT-IR) and NMR spectroscopy, zeta potential measurements, analytical ultracentrifugation (AUC), dynamic/static light scattering (DLS/SLS), and cryogenic transmission electron microscopy (cryoTEM). The polymer chains tend to form vesicles when the hydrophobic polypeptide helix is located at the chain end (acidic pH) and are existing as single chains when it is located in the center and flanked by the two hydrophilic segments (basic pH). Precipitation occurs in the intermediate pH range due to polyion complexation of the charged polypeptide segments. Y1 - 2016 U6 - https://doi.org/10.1021/acs.macromol.6b00817 SN - 0024-9297 SN - 1520-5835 VL - 49 SP - 5494 EP - 5501 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Hardy, John G. A1 - Torres-Rendon, Jose Guillermo A1 - Leal-Egana, Aldo A1 - Walther, Andreas A1 - Schlaad, Helmut A1 - Coelfen, Helmut A1 - Scheibel, Thomas R. T1 - Biomineralization of Engineered Spider Silk Protein-Based Composite Materials for Bone Tissue Engineering JF - Materials N2 - Materials based on biodegradable polyesters, such as poly(butylene terephthalate) (PBT) or poly(butylene terephthalate-co-poly(alkylene glycol) terephthalate) (PBTAT), have potential application as pro-regenerative scaffolds for bone tissue engineering. Herein, the preparation of films composed of PBT or PBTAT and an engineered spider silk protein, (eADF4(C16)), that displays multiple carboxylic acid moieties capable of binding calcium ions and facilitating their biomineralization with calcium carbonate or calcium phosphate is reported. Human mesenchymal stem cells cultured on films mineralized with calcium phosphate show enhanced levels of alkaline phosphatase activity suggesting that such composites have potential use for bone tissue engineering. KW - spider silk KW - recombinant protein KW - biodegradable polymers KW - biomaterials KW - biomineralization KW - bone tissue engineering Y1 - 2016 U6 - https://doi.org/10.3390/ma9070560 SN - 1996-1944 VL - 9 SP - 93 EP - 108 PB - MDPI CY - Basel ER - TY - JOUR A1 - Prinz, Julia A1 - Matkovic, Aleksandar A1 - Pesic, Jelena A1 - Gajic, Rados A1 - Bald, Ilko T1 - Hybrid Structures for Surface-Enhanced Raman Scattering: DNA Origami/Gold Nanoparticle Dimer/Graphene JF - Small N2 - A combination of three innovative materials within one hybrid structure to explore the synergistic interaction of their individual properties is presented. The unique electronic, mechanical, and thermal properties of graphene are combined with the plasmonic properties of gold nanoparticle (AuNP) dimers, which are assembled using DNA origami nanostructures. This novel hybrid structure is characterized by means of correlated atomic force microscopy and surface-enhanced Raman scattering (SERS). It is demonstrated that strong interactions between graphene and AuNPs result in superior SERS performance of the hybrid structure compared to their individual components. This is particularly evident in efficient fluorescence quenching, reduced background, and a decrease of the photobleaching rate up to one order of magnitude. The versatility of DNA origami structures to serve as interface for complex and precise arrangements of nanoparticles and other functional entities provides the basis to further exploit the potential of the here presented DNA origami-AuNP dimer-graphene hybrid structures. Y1 - 2016 U6 - https://doi.org/10.1002/smll.201601908 SN - 1613-6810 SN - 1613-6829 VL - 12 SP - 5458 EP - 5467 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Vacogne, Charlotte D. A1 - Schopferer, Michael A1 - Schlaad, Helmut T1 - Physical Gelation of alpha-Helical Copolypeptides JF - Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences N2 - Owing to its rod-like alpha-helical secondary structure, the synthetic polypeptide poly(gamma-benzyl-L-glutamate) (PBLG) can form physical and thermoreversible gels in helicogenic solvents such as toluene. The versatility of PBLG can be increased by introducing functionalizable comonomers, such as allylglycine (AG). In this work we examined the secondary structure of PBLG and a series of statistical poly(gamma-benzyl-L-glutamate-co-allylglycine) copolypeptides, varying in composition and chain length, by circular dichroism (CD), Fourier-transform infrared (FTIR) and Raman spectroscopy, and wide-angle X-ray scattering (WAXS). The secondary structure of PBLG and the copolypeptides presented dissimilarities that increased with increasing AG molar fraction, especially when racemic AG units were incorporated. The physical gelation behavior of these copolypeptides was analyzed by temperature-sweep H-1 NMR and rheological measurements. The study revealed that both copolypeptide composition and chain length affected secondary structure, gelation temperature, and gel stiffness. Y1 - 2016 U6 - https://doi.org/10.1021/acs.biomac.6b00427 SN - 1525-7797 SN - 1526-4602 VL - 17 SP - 2384 EP - 2391 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Guiet, Amandine A1 - Unmüssig, Tobias A1 - Göbel, Caren A1 - Vainio, Ulla A1 - Wollgarten, Markus A1 - Driess, Matthias A1 - Schlaad, Helmut A1 - Polte, Jörg A1 - Fischer, Anna T1 - Yolk@Shell Nanoarchitectures with Bimetallic Nanocores - Synthesis and Electrocatalytic Applications JF - Earth & planetary science letters KW - AgAu alloy nanoparticles KW - tin-rich ITO KW - yolk@shell materials KW - nanoreactor KW - soft-templating KW - inverse micelles KW - polystyrene-block-poly(4-vinylpyridine) Y1 - 2016 U6 - https://doi.org/10.1021/acsami.6b06595 SN - 1944-8244 VL - 8 SP - 28019 EP - 28029 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Demirel, A. Levent A1 - Guner, Pinar Tatar A1 - Verbraeken, Bart A1 - Schlaad, Helmut A1 - Schubert, Ulrich S. A1 - Hoogenboom, Richard T1 - Revisiting the Crystallization of Poly(2-alkyl-2-oxazoline)s JF - Journal of polymer science : B, Polymer physics N2 - Poly(2-alkyl-2-oxazoline)s (PAOx) exhibit different crystallization behavior depending on the length of the alkyl side chain. PAOx having methyl, ethyl, or propyl side chains do not show any bulk crystallization. Crystallization in the heating cycle, that is, cold crystallization, is observed for PAOx with butyl and pentyl side chains. For PAOx with longer alkyl side chains crystallization occurs in the cooling cycle. The different crystallization behavior is attributed to the different polymer chain mobility in line with the glass transition temperature (T-g) dependency on alkyl side chain length. The decrease in chain mobility with decreasing alkyl side chain length hinders the relaxation of the polymer backbone to the thermodynamic equilibrium crystalline structure. Double melting behavior is observed for PButOx and PiPropOx which is explained by the melt-recrystallization mechanism. Isothermal crystallization experiments of PButOx between 60 and 90 degrees C and PiPropOx between 90 and 150 degrees C show that PAOx can crystallize in bulk when enough time is given. The decrease of Tg and the corresponding increase in chain mobility at T > T-g with increasing alkyl side chain length can be attributed to an increasing distance between the polymer backbones and thus decreasing average strength of amide dipole interactions. (C) 2015 Wiley Periodicals, Inc. KW - chain mobility KW - crystallization KW - differential scanning calorimetry (DSC) KW - effect of alkyl side chains KW - glass transition temperature KW - melt KW - melt-recrystallization KW - polymer crystallization Y1 - 2016 U6 - https://doi.org/10.1002/polb.23967 SN - 0887-6266 SN - 1099-0488 VL - 54 SP - 721 EP - 729 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Tritschler, Ulrich A1 - Zlotnikov, Igor A1 - Fratzl, Peter A1 - Schlaad, Helmut A1 - Gruener, Simon A1 - Coelfen, Helmut T1 - Gas barrier properties of bio-inspired Laponite-LC polymer hybrid films JF - PLoS one N2 - Bio-inspired Laponite (clay)-liquid crystal (LC) polymer composite materials with high clay fractions (>80%) and a high level of orientation of the clay platelets, i.e. with structural features similar to the ones found in natural nacre, have been shown to exhibit a promising behavior in the context of reduced oxygen transmission. Key characteristics of these bio-inspired composite materials are their high inorganic content, high level of exfoliation and orientation of the clay platelets, and the use of a LC polymer forming the organic matrix in between the Laponite particles. Each single feature may be beneficial to increase the materials gas barrier property rendering this composite a promising system with advantageous barrier capacities. In this detailed study, Laponite/LC polymer composite coatings with different clay loadings were investigated regarding their oxygen transmission rate. The obtained gas barrier performance was linked to the quality, respective Laponite content and the underlying composite micro-and nanostructure of the coatings. Most efficient oxygen barrier properties were observed for composite coatings with 83% Laponite loading that exhibit a structure similar to sheet-like nacre. Further on, advantageous mechanical properties of these Laponite/LC polymer composites reported previously give rise to a multifunctional composite system. KW - gas permeation KW - liquid crystal KW - Laponite KW - liquid crystal polymer KW - bio-inspired KW - organic-inorganic composite material KW - self-organization Y1 - 2016 U6 - https://doi.org/10.1088/1748-3190/11/3/035005 SN - 1748-3182 SN - 1748-3190 VL - 11 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Schürmann, Robin Mathis A1 - Bald, Ilko T1 - Decomposition of DNA Nucleobases by Laser Irradiation of Gold Nanoparticles Monitored by Surface-Enhanced Raman Scattering JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Different approaches have been proposed to treat cancer cells using gold nanoparticles (AuNPs) in combination with radiation ranging from infrared lasers to high-energy ion beams. Here we study the decomposition of the DNA/RNA nucleobases thymine (T) and uracil (U) and the well-known radiosensitizer 5-bromouracil (BrU) in close vicinity to AuNPs, which are irradiated with a nanosecond pulsed laser (532 nm) matching the surface plasmon resonance of the AuNPs. The induced damage of nucleobases is analyzed by UV-vis absorption spectroscopy and surface-enhanced Raman scattering (SERS). A clear DNA damage is observed upon laser irradiation. SERS spectra indicate the fragmentation of the aromatic ring system of T and U as the dominant form of damage, whereas with BrU mainly the cleavage of the Br-C bond and formation of Br- ions is observed. This is accompanied by a partial transformation of BrU into U. The observed damage is at least partly ascribed to the intermediate formation of low energy electrons from the laser-excited AuNPs and subsequent dissociative electron attachment to T, U, and BrU. These reactions represent basic DNA damage pathways occurring on the one hand in plasmon-assisted cancer therapy and on the other hand in conventional cancer radiation therapy using AuNPs as sensitizing agents. Y1 - 2016 U6 - https://doi.org/10.1021/acs.jpcc.5b10564 SN - 1932-7447 VL - 120 SP - 3001 EP - 3009 PB - American Chemical Society CY - Washington ER -