Raaijmakers M.J.T.,MESA Institute for Nanotechnology |
Wessling M.,DWI Leibniz Institute for Interactive Materials |
Nijmeijer A.,MESA Institute for Nanotechnology |
Benes N.E.,MESA Institute for Nanotechnology
Chemistry of Materials | Year: 2014
Macromolecular network rigidity of synthetic membranes is essential for sieving of hot gases. Hyper-cross-linked polyPOSS-imide membranes with tailored intercage spacing are presented. The length and flexibility of their imide bridges enables tuning of gas permeability and selectivity in a broad temperature range. The facile synthesis allows for large-scale production of membranes designed for specific process conditions. © 2014 American Chemical Society.
Mate D.M.,DWI Leibniz Institute for Interactive Materials |
Alcalde M.,CSIC - Institute of Catalysis
Biotechnology Advances | Year: 2015
Laccases are multicopper oxidoreductases considered by many in the biotechonology field as the ultimate "green catalysts". This is mainly due to their broad substrate specificity and relative autonomy (they use molecular oxygen from air as an electron acceptor and they only produce water as by-product), making them suitable for a wide array of applications: biofuel production, bioremediation, organic synthesis, pulp biobleaching, textiles, the beverage and food industries, biosensor and biofuel cell development. Since the beginning of the 21st century, specific features of bacterial and fungal laccases have been exhaustively adapted in order to reach the industrial demands for high catalytic activity and stability in conjunction with reduced production cost. Among the goals established for laccase engineering, heterologous functional expression, improved activity and thermostability, tolerance to non-natural media (organic solvents, ionic liquids, physiological fluids) and resistance to different types of inhibitors are all challenges that have been met, while obtaining a more comprehensive understanding of laccase structure-function relationships. In this review we examine the most significant advances in this exciting research area in which rational, semi-rational and directed evolution approaches have been employed to ultimately convert laccases into high value-added biocatalysts. © 2014 Elsevier Inc.
Thavanesan T.,RWTH Aachen |
Herbert C.,DWI Leibniz Institute for Interactive Materials |
Plamper F.A.,RWTH Aachen
Langmuir | Year: 2014
The thermoresponsive and pH-sensitive behavior of poly(N,N- dimethylaminoethyl methacrylate) (PDMAEMA), poly(N,N-diethylaminoethyl methacrylate) (PDEAEMA), and poly(N,N-diisopropylaminoethyl methacrylate) (PDiPAEMA) is compared by use of different techniques. We employed temperature- and pH-dependent turbidimetry, fluorescence spectroscopy (of the polarity indicator 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran, 4HP, which is sometimes also abbreviated as DCM), and IR spectroscopy (of the carbonyl band). Within specific pH windows, all polymers showed phase separation at elevated temperatures (showing a lower critical solution temperature behavior, an LCST behavior). By increasing the hydrophobicity of the dialkylaminoethyl substituent, the phase separation is shifted to lower pH (at constant temperatures; pHPDMAEMA > pHPDEAEMA > pHPDiPAEMA) or to lower temperatures (at constant pH; T PDMAEMA > TPDEAEMA > TPDiPAEMA). While PDMAEMA does not exhibit pronounced changes in polarity upon phase separation (as seen by fluorescence spectroscopy), PDEAEMA and PDiPAEMA provide a nonpolar surrounding for the 4HP uptake above their collapse. In addition, PDiPAEMA causes the sharpest transition (as seen by the 4HP probe), although the carbonyl hydration experiences a more gradual (sigmoidal) transition for all polymers (as seen by IR). These observations allow a distinction of the phase separation mechanisms. While the LCST properties of PDMAEMA are mainly caused by backbone/carbonyl interactions, its rather polar dimethylaminoethyl group does not inflict pronounced hydrophobicity, but promotes a higher water content within the phase-separated polymer. In contrast, the phase separation of PDEAEMA and PDiPAEMA is mainly influenced by the less polar dialkylaminoethyl groups, leading to drastic changes in the hydrophobicity around the cloud points. Further, the IR data suggest that the diisopropylaminoethyl groups of PDiPAEMA tend to backfold to the carbonyl groups/backbone to minimize water-polymer contact already in its soluble state. Finally, this study might lead to advanced lasing applications of the laser dye 4HP. © 2014 American Chemical Society.
Wang B.,DWI Leibniz Institute for Interactive Materials |
Walther A.,DWI Leibniz Institute for Interactive Materials
ACS Nano | Year: 2015
Natural high-performance materials inspire the pursuit of ordered hard/soft nanocomposite structures at high fractions of reinforcements and with balanced molecular interactions. Herein, we develop a facile, waterborne self-assembly pathway to mimic the multiscale cuticle structure of the crustacean armor by combining hard reinforcing cellulose nanocrystals (CNCs) with soft poly(vinyl alcohol) (PVA). We show iridescent CNC nanocomposites with cholesteric liquid-crystal structure, in which different helical pitches and photonic band gaps can be realized by varying the CNC/PVA ratio. We further show that multilayered crustacean-mimetic materials with tailored periodicity and layered cuticular structure can be obtained by sequential preparation pathways. The transition from a cholesteric to a disordered structure occurs for a critical polymer concentration. Correspondingly, we find a transition from stiff and strong mechanical behavior to materials with increasing ductility. Crack propagation studies using scanning electron microscopy visualize the different crack growth and toughening mechanisms inside cholesteric nanocomposites as a function of the interstitial polymer content for the first time. Different extents of crack deflection, layered delamination, ligament bridging, and constrained microcracking can be observed. Drawing of highly plasticized films sheds light on the mechanistic details of the transition from a cholesteric/chiral nematic to a nematic structure. The study demonstrates how self-assembly of biobased CNCs in combination with suitable polymers can be used to replicate a hierarchical biological structure and how future design of these ordered multifunctional nanocomposites can be optimized by understanding mechanistic details of deformation and fracture. © 2015 American Chemical Society.
Heinen L.,DWI Leibniz Institute for Interactive Materials |
Walther A.,DWI Leibniz Institute for Interactive Materials
Soft Matter | Year: 2015
Self-regulating reconfigurable soft matter systems are of great interest for creating adaptive and active material properties. Such complex functionalities emerge from non-linear and interactive behavior in space and time as demonstrated by a plethora of dynamic, self-organizing biological structures (e.g., the cytoskeleton). In man-made self-assemblies, patterning of the spatial domain has advanced to creating hierarchical structures via precise molecular programming. However, orchestration of the time domain of self-assemblies is still in its infancy and lacks universal design principles. In this Emerging Area article we outline major strategies for programming the time domain of self-assemblies following the concepts of regulatory reaction networks, energy dissipation and kinetic control. Such concepts operate outside thermodynamic equilibrium and pave the way for temporally patterned, dynamic, and autonomously acting functional materials. © The Royal Society of Chemistry.