Towards light-driven catalysis in block copolymer micelles

Im Rahmen dieser Arbeit wurden die Synthese, Charakterisierung und Untersuchungen polymerbasierter, sogenannter „weicher“ Materie als Matrizen für lichtgetriebene Redoxreaktionen behandelt. Der erste Teil dieser Arbeit umfasste die Präparation von pH-responsiven Mizellen in Wasser auf Grundlage von maßgeschneiderten, amphiphilen Blockcopolymeren, wobei unter anderem die im hydrophilen Teil vorhandenen Liganden zur Anbindung von Übergangsmetallkomplexen genutzt wurden. Auf diese Weise konnten (photo)katalytisch aktive Zentren innerhalb der pH-sensitiven Corona der Mizellen integriert werden. Mit diesem Ansatz war es möglich, mittels Konformationsänderungen der Corona der Mizellen deren Aktivität in verschiedenen, photokatalytischen Systemen experimentell zu kontrollieren und mit theoretischen Modellen zu analysieren. Der zweite Teil dieser Abhandlung widmete sich der Verwendung eines alternativen, polaren und funktionalisierbaren Monomer zum Aufbau analoger Blockcopolymerarchitekturen in methanolischen Lösungen sowie einer Anwendung in photokatalytischen Prozessen. Es ließen sich auf der chemischen Struktur basierende Indizien einer weit über die bloße mechanische Integration hinausreichende Funktion der Matrix feststellen. Dies wurde auch durch eine gesamtheitliche Betrachtung beider Systeme herausgearbeitet. Der dritte Teil dieser Arbeit fokussierte sich auf photokatalytische Modellsysteme, um Fallstudien zur Reproduzierbarkeit in einem modularen Photoreaktor durchzuführen. Ein weiteres Modellsystem wurde für eine didaktische Anwendung zugänglich gemacht. Mit dieser Arbeit war es möglich einen substanziellen Beitrag zur weichen Materie-vermittelten lichtgetriebenen Katalyse zu leisten. Dies geschah sowohl durch die Präsentation von Konzepten zur Integration derartiger Systeme in weicher Materie als auch der resultierenden Möglichkeit stoffliche und energetische Mechanismen in solchen Matrizen nachzuvollziehen

Triple‐responsive polyampholytic graft copolymers as smart sensors with varying output

Abstract Three triggers result in two measurable outputs from polymeric sensors: multiresponsive polyampholytic graft copolymers respond to pH‐value and temperature, as well as the type and concentration of metal cations and therefore, allow the transformation of external triggers into simply measurable outputs (cloud point temperature (T CP ) and surface plasmon resonance (SPR) of encapsulated silver nanoparticles). The synthesis relies on poly(dehydroalanine) (PDha) as the reactive backbone and gives straightforward access to materials with tunable composition and output. In particular, a rather high sensitivity toward the presence of Cu 2+ , Co 2+ , and Pb 2+ metal cations is found

In Situ SERS Sensing by a Laser-Induced Aggregation of Silver Nanoparticles Templated on a Thermoresponsive Polymer

A stimuli-responsive (pH- and thermoresponsive) micelle-forming diblock copolymer, poly(1,2-butadiene) 290 - block -poly( N , N -dimethylaminoethyl methacrylate) 240 (PB- b -PDMAEMA), was used as a polymer template for the in situ synthesis of silver nanoparticles (AgNPs) through Ag + complexation with PDMAEMA blocks, followed by the reduction of the bound Ag + with sodium borohydride. A successful synthesis of the AgNPs on a PB- b -PDMAEMA micellar template was confirmed by means of UV–Vis spectroscopy and transmission electron microscopy, wherein the shape and size of the AgNPs were determined. A phase transition of the polymer matrix in the AgNPs/PB- b -PDMAEMA metallopolymer hybrids, which results from a collapse and aggregation of PDMAEMA blocks, was manifested by changes in the transmittance of their aqueous solutions as a function of temperature. A SERS reporting probe, 4-mercaptophenylboronic acid (4-MPBA), was used to demonstrate a laser-induced enhancement of the SERS signal observed under constant laser irradiation. The local heating of the AgNPs/PB- b -PDMAEMA sample in the laser spot is thought to be responsible for the triggered SERS effect, which is caused by the approaching of AgNPs and the generation of “hot spots” under a thermo-induced collapse and the aggregation of the PDMAEMA blocks of the polymer matrix. The triggered SERS effect depends on the time of a laser exposure and on the concentration of 4-MPBA. Possible mechanisms of the laser-induced heating for the AgNPs/PB- b -PDMAEMA metallopolymer hybrids are discussed

A novel class of microRNA-recognition elements that function only within open reading frames.

MicroRNAs (miRNAs) are well known to target 3' untranslated regions (3' UTRs) in mRNAs, thereby silencing gene expression at the post-transcriptional level. Multiple reports have also indicated the ability of miRNAs to target protein-coding sequences (CDS); however, miRNAs have been generally believed to function through similar mechanisms regardless of the locations of their sites of action. Here, we report a class of miRNA-recognition elements (MREs) that function exclusively in CDS regions. Through functional and mechanistic characterization of these 'unusual' MREs, we demonstrate that CDS-targeted miRNAs require extensive base-pairing at the 3' side rather than the 5' seed; cause gene silencing in an Argonaute-dependent but GW182-independent manner; and repress translation by inducing transient ribosome stalling instead of mRNA destabilization. These findings reveal distinct mechanisms and functional consequences of miRNAs that target CDS versus the 3' UTR and suggest that CDS-targeted miRNAs may use a translational quality-control-related mechanism to regulate translation in mammalian cells

Phenolic Polymers as Model Melanins

Melanins are a class of conjugated biopolymers with varying compositions and functions, which have a variety of potential medical and technical applications. Here we examine the conjugated polymers derived from a variety of phenolic monomers (catechol (CAT), levodopa (DOPA) and homogentisic acid (HGA)), using a selection of different analytical chemistry techniques to compare their properties with a view to understanding structure-function relations. The polymers displayed measurable conductivity, with electronic properties tuned by the functional groups pendant on the polymer backbones (which served as dopants) suggesting their potential for application in electronic devices

Effect of hot calendering on physical properties and water vapor transfer resistance of bacterial cellulose films

This work investigates the effect of hot calendering on bacterial cellulose (BC) films properties, aiming the achievement of good transparency and barrier property. A comparison was made using vegetal cellulose (VC) films on a similar basis weight of around 40 g.m-2. The optical-structural, mechanical and barrier property of BC films were studied and compared with those of highly beaten VC films. The Youngs moduli and tensile index of the BC films are much higher than those obtained for VC (14.5 16.2 GPa vs 10.8 8.7 GPa and 146.7 64.8 N.m.g-1 vs 82.8 40.5 N.m.g-1), respectively. Calendering increased significantly the transparency of BC films from 53.0 % to 73.0 %. The effect of BC ozonation was also studied. Oxidation with ozone somewhat enhanced the brightness and transparency of the BC films, but at the expenses of slightly lower mechanical properties. BC films exhibited a low water vapor transfer rate, when compared to VC films and this property decreased by around 70 % following calendering, for all films tested. These results show that calendering could be used as a process to obtain films suitable for food packaging applications, where transparency, good mechanical performance and barrier properties are important. The BC films obtained herein are valuable products that could be a good alternative to the highly used plastics in this industry.The authors thank FCT (Fundação para a Ciência e Tecnologia) and FEDER (Fundo Europeu de Desenvolvimento Regional) for the financial support of the project FCT PTDC/AGR-FOR/3090/2012— FCOMP-01-0124-FEDER-027948 and the awarding of a research grant for Vera Costa

On the use of nanocellulose as reinforcement in polymer matrix composites

AbstractNanocellulose is often being regarded as the next generation renewable reinforcement for the production of high performance biocomposites. This feature article reviews the various nanocellulose reinforced polymer composites reported in literature and discusses the potential of nanocellulose as reinforcement for the production of renewable high performance polymer nanocomposites. The theoretical and experimentally determined tensile properties of nanocellulose are also reviewed. In addition to this, the reinforcing ability of BC and NFC is juxtaposed. In order to analyse the various cellulose-reinforced polymer nanocomposites reported in literature, Cox–Krenchel and rule-of-mixture models have been used to elucidate the potential of nanocellulose in composite applications. There may be potential for improvement since the tensile modulus and strength of most cellulose nanocomposites reported in literature scale linearly with the tensile modulus and strength of the cellulose nanopaper structures. Better dispersion of individual cellulose nanofibres in the polymer matrix may improve composite properties