@article{SeckerBrosnanLimbergetal.2015, author = {Secker, Christian and Brosnan, Sarah M. and Limberg, Felix Rolf Paul and Braun, Ulrike and Trunk, Matthias and Strauch, Peter and Schlaad, Helmut}, title = {Thermally Induced Crosslinking of Poly(N-Propargyl Glycine)}, series = {Macromolecular chemistry and physics}, volume = {216}, journal = {Macromolecular chemistry and physics}, number = {21}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1352}, doi = {10.1002/macp.201500223}, pages = {2080 -- 2085}, year = {2015}, abstract = {As polypeptoids become increasingly popular, they present a more soluble and processable alternative to natural and synthetic polypeptides; the breadth of their potential functionality slowly comes into focus. This report analyzes the ability of an alkyne-functionalized polypeptoid, poly(N-propargyl glycine), to crosslink upon heating. The crosslinking process is analyzed by thermal analysis (differential scanning calorimetry and thermogravimetric analysis), Fourier-transform infrared, electron paramagnetic resonance, and solid-state NMR spectroscopy. While a precise mechanism cannot be confidently assigned, it is clear that the reaction proceeds by a radical mechanism that exclusively involves the alkyne functionality, which, upon crosslinking, yields alkene and aromatic products.}, language = {en} } @article{KoshkinaLangThiermannetal.2015, author = {Koshkina, Olga and Lang, Thomas and Thiermann, Raphael and Docter, Dominic and Stauber, Roland H. and Secker, Christian and Schlaad, Helmut and Weidner, Steffen and Mohr, Benjamin and Maskos, Michael and Bertin, Annabelle}, title = {Temperature-Triggered Protein Adsorption on Polymer-Coated Nanoparticles in Serum}, series = {Langmuir}, volume = {31}, journal = {Langmuir}, number = {32}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.5b00537}, pages = {8873 -- 8881}, year = {2015}, abstract = {The protein corona, which forms on the nanoparticle's surface in most biological media, determines the nanoparticle's physicochemical characteristics. The formation of the protein corona has a significant impact on the biodistribution and clearance of nanoparticles in vivo. Therefore, the ability to influence the formation of the protein corona is essential to most biomedical applications, including drug delivery and imaging. In this study, we investigate the protein adsorption on nanoparticles with a hydrodynamic radius of 30 nm and a coating of thermoresponsive poly(2-isopropyl-2-oxazoline) in serum. Using multiangle dynamic light scattering (DLS) we demonstrate that heating of the nanoparticles above their phase separation temperature induces the formation of agglomerates, with a hydrodynamic radius of 1 mu m. In serum, noticeably stronger agglomeration occurs at lower temperatures compared to serum-free conditions. Cryogenic transmission electron microscopy (cryo-TEM) revealed a high packing density of agglomerates when serum was not present. In contrast, in the presence of serum, agglomerated nanoparticles were loosely packed, indicating that proteins are intercalated between them. Moreover, an increase in protein content is observed upon heating, confirming that protein adsorption is induced by the alteration of the surface during phase separation. After cooling and switching the surface back, most of the agglomerates were dissolved and the main fraction returned to the original size of approximately 30 nm as shown by asymmetrical flow-field flow fractionation (AF-FFF) and DLS. Furthermore, the amounts of adsorbed proteins are similar before and after heating the nanoparticles to above their phase-separation temperature. Overall, our results demonstrate that the thermoresponsivity of the polymer coating enables turning the corona formation on nanoparticles on and off in situ. As the local heating of body areas can be easily done in vivo, the thermoresponsive coating could potentially be used to induce the agglomeration of nanopartides and proteins and the accumulation of nanoparticles in a targeted body region.}, language = {en} } @article{SeckerBrosnanLuxenhoferetal.2015, author = {Secker, Christian and Brosnan, Sarah M. and Luxenhofer, Robert and Schlaad, Helmut}, title = {Poly(alpha-Peptoid)s Revisited: Synthesis, Properties, and Use as Biomaterial}, series = {Macromolecular bioscience}, volume = {15}, journal = {Macromolecular bioscience}, number = {7}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-5187}, doi = {10.1002/mabi.201500023}, pages = {881 -- 891}, year = {2015}, abstract = {Polypeptoids have been of great interest in the polymer science community since the early half of the last century; however, they had been basically forgotten materials until the last decades in which they have enjoyed an exciting revival. In this mini-review, we focus on the recent developments in polypeptoid chemistry, with particular focus on polymers synthesized by the ring-opening polymerization (ROP) of amino acid N-carboxyanhydrides (NCAs). Specifically, we will review traditional monomer synthesis (such as Leuchs, Katchalski, and Kricheldorf) and recent advances in polymerization methods to yield both linear, cyclic, and functional polymers, solution and bulk thermal properties, and preliminary results on the use of polypeptoids as biomaterials (i.e immunogenicity, biodistribution, degradability, and drug delivery).}, language = {en} } @article{SeckerRobinsonSchlaad2015, author = {Secker, Christian and Robinson, Joshua W. and Schlaad, Helmut}, title = {Alkyne-X modification of polypeptoids}, series = {European polymer journal}, volume = {62}, journal = {European polymer journal}, publisher = {Elsevier}, address = {Oxford}, issn = {0014-3057}, doi = {10.1016/j.eurpolymj.2014.08.028}, pages = {394 -- 399}, year = {2015}, abstract = {Poly(N-propargyl glycine) (PNPG) can be readily prepared by ring-opening polymerization of N-propargyl glycine N-carboxyanhydride (NCA) and modified using various addition reactions such as copper catalyzed [3+2] cycloaddition of azide, radical (photo-)addition of thiol, nucleophilic addition of ethylene oxide, and thermal induced cross-linking. It is demonstrated that PNPG can serve as a modular platform to produce a bibliography of novel functional polypeptoid or pseudopeptide materials, including polypeptoid ionic liquids and graft copolymers.}, language = {en} } @article{SeckerVoelkelTierschetal.2016, author = {Secker, Christian and Voelkel, Antje and Tiersch, Brigitte and Koetz, Joachim and Schlaad, Helmut}, title = {Thermo-Induced Aggregation and Crystallization of Block Copolypeptoids in Water}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {49}, journal = {Macromolecules : a publication of the American Chemical Society}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/acs.macromol.5b02481}, pages = {979 -- 985}, year = {2016}, abstract = {Block copolypeptoids comprising a thermosensitive, crystallizable poly(N-(n-propyl)glycine) block and a watersoluble poly(N-methylglycine) block, P70My (y = 23, 42, 76, 153, and 290), were synthesized bY ring-opening polymerization of the corresponding N-alkylglycine N-carboxyanhydrides (NCAs) and examined according to their thermo-induced aggregation and crystallization in water by turbidimetty, micro-differential scanning calorimetry (micro-DSC); cryogenic scanning electron microscopy (cryo-SEM), analytical ultracentrifugation (AUC), and static light scattering (SLS). At a temperature above the cloud point temperature, the initially formed micellar aggregates started to crystallize and grow into larger complex assemblies of about 100-500 nm, exhibiting flower-like (P70M23), ellipsoidal (P70M42 and P70M72) or irregular shapes (P70M153 and.P70M290).}, language = {en} } @article{ThielkeSeckerSchlaadetal.2016, author = {Thielke, Michael W. and Secker, Christian and Schlaad, Helmut and Theato, Patrick}, title = {Electrospinning of Crystallizable Polypeptoid Fibers}, series = {Macromolecular rapid communications}, volume = {37}, journal = {Macromolecular rapid communications}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1336}, doi = {10.1002/marc.201500502}, pages = {100 -- 104}, year = {2016}, abstract = {A unique fabrication process of low molar mass, crystalline polypeptoid fibers is described. Thermoresponsive fiber mats are prepared by electrospinning a homogeneous blend of semicrystalline poly(N-(n-propyl) glycine) (PPGly; 4.1 kDa) with high molar mass poly(ethylene oxide) (PEO). Annealing of these fibers at approximate to 100 degrees C selectively removes the PEO and produces stable crystalline fiber mats of pure PPGly, which are insoluble in aqueous solution but can be redissolved in methanol or ethanol. The formation of water-stable polypeptoid fiber mats is an important step toward their utilization in biomedical applications such as tissue engineering or wound dressing.}, language = {en} } @article{BogomolovaSeckerKoetzetal.2017, author = {Bogomolova, Anna and Secker, Christian and Koetz, Joachim and Schlaad, Helmut}, title = {Thermo-induced multistep assembly of double-hydrophilic block copolypeptoids in water}, series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, volume = {295}, journal = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, publisher = {Springer}, address = {New York}, issn = {0303-402X}, doi = {10.1007/s00396-017-4044-6}, pages = {1305 -- 1312}, year = {2017}, abstract = {The aqueous solution behavior of thermoresponsive-hydrophilic block copolypeptoids, i.e., poly(N-(n-propyl)glycine) (x) -block-poly(N-methylglycine) (y) (x = 70; y = 23, 42, 76), in the temperature range of 20-45 A degrees C is studied. Turbidimetric analyses of the 0.1 wt\% aqueous solutions reveal two cloud points at T (cp)similar to 30 and 45 A degrees C and a clearing point in between at T (cl)similar to 42 A degrees C. Temperature-dependent dynamic light scattering (DLS) suggest that right above the first collapse temperature, single polymer molecules assemble into large structures which upon further heating, i.e., at the clearing point temperature, disassemble into micelle-like structures. Upon further heating, the aggregates start to grow again in size, as recognized by the second cloud point, through a crystallization process.}, language = {en} } @phdthesis{Secker2014, author = {Secker, Christian}, title = {Polypeptoid block coloymers}, pages = {128}, year = {2014}, language = {en} }