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Bauer D.M.,Karlsruhe Institute of Technology | Rogge A.,Karlsruhe Institute of Technology | Stolzer L.,Karlsruhe Institute of Technology | Barner-Kowollik C.,Institute For Technische Chemie Und Polymerchemie | And 2 more authors.
Chemical Communications

DNA was modified with a photo-reactive caged diene allowing for the modification of dienophile containing proteins under mild irradiation conditions to afford fully functional DNA-protein conjugates. This journal is © 2013 The Royal Society of Chemistry. Source

Glassner M.,Institute For Technische Chemie Und Polymerchemie | Delaittre G.,Institute For Technische Chemie Und Polymerchemie | Delaittre G.,Karlsruhe Institute of Technology | Kaupp M.,Institute For Technische Chemie Und Polymerchemie | And 3 more authors.
Journal of the American Chemical Society

Tailor-made water-soluble macromolecules, including a glycopolymer, obtained by living/controlled RAFT-mediated polymerization are demonstrated to react in water with diene-functionalized poly(ethylene glycol)s without pre- or post-functionalization steps or the need for a catalyst at ambient temperature. As previously observed in organic solvents, hetero-Diels-Alder (HDA) conjugations reached quantitative conversion within minutes when cyclopentadienyl moieties were involved. However, while catalysts and elevated temperatures were previously necessary for open-chain diene conjugation, additive-free HDA cycloadditions occur in water within a few hours at ambient temperature. Experimental evidence for efficient conjugations is provided via unambiguous ESI-MS, UV/vis, NMR, and SEC data. © 2012 American Chemical Society. Source

Altintas O.,Institute For Technische Chemie Und Polymerchemie | Barner-Kowollik C.,Institute For Technische Chemie Und Polymerchemie
Macromolecular Rapid Communications

The present feature article highlights the preparation of polymeric nanoparticles and initial attempts towards mimicking the structure of natural biomacromolecules by single chain folding of well-defined linear polymers through covalent and non-covalent interactions. Initially, the discussion focuses on the synthesis and characterization of single chain self-folded structures by non-covalent interactions. The second part of the article summarizes the folding of single chain polymers by means of covalent interactions into nanoparticle systems. The current state of the art in the field of single chain folding indicates that covalent-bond-driven nanoparticle preparation is well advanced, while the first encouraging steps towards building reversible single chain folding systems by the use of mutually orthogonal hydrogen-bonding motifs have been made. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Wolf T.J.A.,Karlsruhe Institute of Technology | Voll D.,Institute For Technische Chemie Und Polymerchemie | Barner-Kowollik C.,Institute For Technische Chemie Und Polymerchemie | Unterreiner A.-N.,Karlsruhe Institute of Technology

The excited states and dynamics of the three triplet radical photoinitiators benzoin (2-hydroxy-1,2-diphenylethanone, Bz), 2,4,6-trimethylbenzoin (2-hydroxy-1-mesityl-2-phenylethanone, TMB), and mesitil (1,2-bis(2,4,6-trimethylphenyl)-1,2-ethanedione, Me)-employed in our previous studies for quantifying net initiation efficiencies in pulsed laser polymerization with methacrylate monomers [Voll, D.; Junkers, T.; Barner-Kowollik, C. Macromolecules2011, 44, 2542-2551]-are investigated via both femtosecond transient absorption (TA) spectroscopy and density functional theory (DFT) methods to elucidate the underlying mechanisms causing different initiation efficiencies when excited at 351 nm. Bz and TMB are found to have very similar properties in the calculated excited states as well as in the experimentally observed dynamics. After excitation into the first excited singlet state (S 1) Bz and TMB undergo rapid intersystem crossing (ISC). The ISC can compete with ultrafast internal conversion (IC) processes because an excited triplet state (T n) of nearly the same energy is present in both cases. ISC is therefore the dominating depopulation channel of S 1, and subsequent α-cleavage to produce radicals takes place on the picosecond time scale. In contrast, Me is excited into the second excited singlet state (S 2). In this case no isoenergetic triplet state is available, which inhibits ISC from competing with ultrafast deactivation processes. ISC is therefore assigned to be a minor deactivation channel in Me. Employing these findings, quantitative photoinitiation efficiency relations of Bz, TMB, and Me obtained by pulsed laser polymerization can be directly correlated with the relative TA intensities found in the femtosecond experiments. The ISC efficiency is thus a critical parameter for evaluating the overall photoinitiation efficiency and demonstrates that the employment of the herein presented method represents a powerful tool for attaining a quantitative picture on the suitability of a photoinitiator. © 2012 American Chemical Society. Source

Wolf T.J.A.,Karlsruhe Institute of Technology | Wolf T.J.A.,Center for Functional Nanostructures | Fischer J.,Center for Functional Nanostructures | Fischer J.,Institute For Angewandte Physik | And 9 more authors.
EPJ Web of Conferences

Different photoinitiators are investigated by femtosecond transient absorption spectroscopy and DFT calculations. Their initiation properties are critically governed by competition between intersystem crossing, fluorescence and internal conversion partly taking place on comparable time scales. It is thereby shown that the S* lifetime cannot serve as a measure for the photoinitiation efficiency. © Owned by the authors, published by EDP Sciences, 2013. Source

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