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Rehm T.H.,Fraunhofer Institute for Chemical Technology
Chemical Engineering and Technology | Year: 2016

The unique properties of fluorine resulting from its tremendously high electronegativity make it a key player in the quest of enabling new and advanced qualities for chemical compounds and materials. With the advent of fluorinating reagents, a great diversity of synthetic methodologies has been developed to incorporate fluorine or fluorine-containing groups into small molecules with high conversion and selectivity. Especially photochemically catalyzed fluorination reactions proved their potential for the synthesis of fluorine-containing fine chemicals due to their mild reaction conditions. This tutorial review gives an overview of recently published synthesis strategies that use (visible-) light-absorbing catalysts for the activation of fluorinating reagents. A special focus lies on the use of continuous-flow microreactors for photochemically catalyzed fluorination reactions due to the excellent utilization of this reactor equipment for photochemistry. Photochemically catalyzed fluorination reactions allow the mild and selective incorporation of fluorine and fluorine-containing groups into small molecules. In conjunction with continuous-flow microreactors this strategy is a powerful tool for enabling the facile and efficient synthesis of high-value chemical products for a broad field of applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Zydziak N.,Karlsruhe Institute of Technology | Zydziak N.,Fraunhofer Institute for Chemical Technology | Yameen B.,Karlsruhe Institute of Technology | Barner-Kowollik C.,Karlsruhe Institute of Technology
Polymer Chemistry | Year: 2013

To meet the ever growing demand for carbon nanomaterials with tailored properties, Diels-Alder reactions are emerging as an efficient alternative to other synthetic methods. From an application perspective, the development of convenient surface functionalization strategies for carbon nanostructures is of paramount importance. Pristine carbon nanostructures display a natural tendency to undergo Diels-Alder reactions with a range of functional dienes and dienophiles without the need of a catalyst. This has sparked significant scientific interest in exploiting the Diels-Alder reaction as a powerful strategy for their synthesis as well as for their subsequent surface functionalization. The present review highlights the remarkable role of Diels-Alder reactions for the synthesis of fullerenes, carbon nanotubes and graphene, and its promise as a facile carbon nanostructure functionalization strategy with small molecules and polymer chains. A critical overview of the recent developments evidencing the potential of Diels-Alder reactions as an efficient route to carbon based functional materials is presented. This journal is © 2013 The Royal Society of Chemistry. Source

Dietrich M.,Karlsruhe Institute of Technology | Dietrich M.,Fraunhofer Institute for Chemical Technology | Delaittre G.,Karlsruhe Institute of Technology | Blinco J.P.,Karlsruhe Institute of Technology | And 3 more authors.
Advanced Functional Materials | Year: 2012

The nitrile imine-mediated tetrazole-ene cycloaddition reaction (NITEC) is introduced as a powerful and versatile conjugation tool to covalently ligate macromolecules onto variable (bio)surfaces. The NITEC approach is initiated by UV irradiation and proceeds rapidly at ambient temperature yielding a highly fluorescent linkage. Initially, the formation of block copolymers by the NITEC methodology is studied to evidence its efficacy as a macromolecular conjugation tool. The grafting of polymers onto inorganic (silicon) and bioorganic (cellulose) surfaces is subsequently carried out employing the optimized reaction conditions obtained from the macromolecular ligation experiments and evidenced by surface characterization techniques, including X-ray photoelectron spectroscopy and FT-IR microscopy. In addition, the patterned immobilization of variable polymer chains onto profluorescent cellulose is achieved through a simple masking process during the irradiation. Photoinduced nitrile imine-alkene 1,3-dipolar cycloaddition (NITEC) is employed to covalently bind well-defined polymers onto silicon oxide or cellulose. A diaryl tetrazole-functionalized molecule is grafted via silanization or amidification, respectively. Under UV light, a reactive nitrile imine rapidly forms and reacts with maleimide-functionalized polymers yielding a fluorescent linkage. Via a masking method, polymeric fluorescent patterns are achieved. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Treuel L.,Karlsruhe Institute of Technology | Treuel L.,University of Duisburg - Essen | Treuel L.,Fraunhofer Institute for Chemical Technology | Brandholt S.,Karlsruhe Institute of Technology | And 5 more authors.
ACS Nano | Year: 2014

Recent studies have firmly established that cellular uptake of nanoparticles is strongly affected by the presence and the physicochemical properties of a protein adsorption layer around these nanoparticles. Here, we have modified human serum albumin (HSA), a serum protein often used in model studies of protein adsorption onto nanoparticles, to alter its surface charge distribution and investigated the consequences for protein corona formation around small (radius ∼5 nm), dihydrolipoic acid-coated quantum dots (DHLA-QDs) by using fluorescence correlation spectroscopy. HSA modified by succinic anhydride (HSAsuc) to generate additional carboxyl groups on the protein surface showed a 3-fold decreased binding affinity toward the nanoparticles. A 1000-fold enhanced affinity was observed for HSA modified by ethylenediamine (HSAam) to increase the number of amino functions on the protein surface. Remarkably, HSAsuc formed a much thicker protein adsorption layer (8.1 nm) than native HSA (3.3 nm), indicating that it binds in a distinctly different orientation on the nanoparticle, whereas the HSAam corona (4.6 nm) is only slightly thicker. Notably, protein binding to DHLA-QDs was found to be entirely reversible, independent of the modification. We have also measured the extent and kinetics of internalization of these nanoparticles without and with adsorbed native and modified HSA by HeLa cells. Pronounced variations were observed, indicating that even small physicochemical changes of the protein corona may affect biological responses. © 2013 American Chemical Society. Source

Konig A.,Fraunhofer Institute for Chemical Technology | Kroke E.,TU Bergakademie Freiberg
Fire and Materials | Year: 2012

The chemical nature of flexible polyurethane (flex PU) foams, the low density, the high air permeability and the open cell structure cause this material to be highly flammable. The new phosphorus flame-retardant (FR) methyl-DOPO (9, 10-dihydro-9-oxa-methylphosphaphenanthrene-10-oxide) is known to show an excellent flame retarding behavior in flex PU foam by acting mainly in the gas phase. In this study, the FR working mechanism of methyl-DOPO and its ring-opened analogue MPPP (methylphenoxyphenyl-phosphinate) is investigated by TGA, TG-MS, FMVSS 302 and Cone Calorimeter measurements. Under TG-MS conditions comparable concentrations of low molecular weight species such as HPO, mathrmCH 3PO or PO 2 are released. These species are able to scavenge the H- and OH-radicals in the radical chain reactions of the flame leading to a significant increase in the CO/CO 2 ratio and the smoke density during cone calorimeter experiments. Finally, the flame retardancy of MPPP is determined to be less efficient in flex PU foam because of the higher vapor pressure compared with methyl-DOPO. Here, the vaporization of methyl-DOPO occurs in the same temperature region as the depolymerization of the urethane and the bisubstituted urea groups during pyrolysis of the foam leading to an optimal interaction. Copyright © 2010 John Wiley & Sons, Ltd. Source

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