Highlight Publications 2019

Dual-Responsive Photocatalytic Polymer Nanogels
Calum T. J. Ferguson, Niklas Huber, Katharina Landfester and Kai A. I. Zhang
Dual-Responsive Photocatalytic Polymer Nanogels
Selective activation of photocatalysts under constant light conditions has recently been targeted to produce multi-responsive systems. However, controlled activation, with easy recovery of the photocatalysts, induced by external stimuli remains a major challenge. Mimicking the responsibilities of biological systems by multiple triggers can offer a promising solution. Herein, we report dual-responsive polymer photocatalysts in form of nanogels consisting of a cross-linked poly-N-isopropylacrylamide nanogel, copolymerised with a photocatalytically active monomer. Dual-responsive polymer nanogels undergo a stark reduction in diameter with the increase in temperature, above the lower critical solution temperature, shielding photocatalytic sites retarding activity. Temperature-dependent photocatalytic formation of the enzyme cofactor nicotinamide adenine dinucleotide (NAD+) in water demonstrates the ability to switch on/off photocatalysis. Moreover, photocatalysis of fine chemicals (benzaldehyde, benzyl-1-phenylmethanimine and 1,2-dioctyldisulfane) has been conducted in the nanogels swollen state, demonstrating the utility of the designed material.
© WILEY-VCH (2019)
Stimuli-induced polymer for photocatalytic reactions upon temperature and light
Possibilities and Limitations of Different Separation Techniques for the Analysis of the Protein Corona
C. Weber, S. Morsbach, K. Landfester
Possibilities and Limitations of Different Separation Techniques for the Analysis of the Protein Corona
One of the challenges in nanomedicine is the formation of a protein corona (PC) around nanomaterials (NMs) upon contact with a biological medium, which later determines the in vitro/in vivo behavior. However, the outcome of the PC analysis cannot easily be compared among different techniques, since different sample preparation procedures exist. Depending on the applied procedure, the NM–protein system is altered, so that it is necessary to consider the individual influence on the PC. Accordingly, we give an overview of applied sample preparation methods for the PC analysis and evaluate their influence on the outcome of the results especially with regard to the terms “soft” and “hard PC”.
© © 2019 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim (2019)
The application of different separation techniques to nanomaterial-protein complexes influences the obtained protein corona depending on the forces acting on the sample.
Surface Premelting and Interfacial Interactions of Semi-Clathrate Hydrate
Ngoc N. Nguyen, Rüdiger Berger, Hans-Jürgen Butt
Surface Premelting and Interfacial Interactions of Semi-Clathrate Hydrate
Clathrate hydrates are a demanding field of research because of their fundamental impact on human life and the environment. Interfacial forces involving hydrates are vital factors in numerous natural and industrial processes, but the topic has been relatively neglected in the scientific literature. By using atomic force microscopy, we are now able to measure for the first time the forces between a semi-clathrate hydrate formed by tetrabutyl ammonium bromide and a silica microsphere in air and in undecane. Significantly, the analyses of jump-in (attractive) and pull-off (adhesive) forces in force–distance curves indicate the presence of a quasi-liquid layer (QLL) on the hydrate surface resulting from interfacial premelting. We have shown that interfacial forces between the sphere and the hydrate surface are dominated by the capillary formation between the QLL and the sphere. van der Waals forces are still active in the region several nm above the QLL, prior to the sphere touching the QLL. Our study introduces a new quantitative parameter to the hydrate literature, that is, the thickness of the QLL on the hydrate surface. This parameter, being around 11 nm at −4 °C, is crucial to the modeling of hydrate interactions and agglomerations.
© American Chemical Society (2019)
The Ultrafast Assembly of a Dipeptide Supramolecular Organogel and its Phase Transition from Gel to Crystal
Tingting Yuan, Dr. Youqian Xu, Dr. Jinbo Fei, Huimin Xue, Xianbao Li, Chenlei Wang, Prof. Dr. George Fytas, Prof. Dr. Junbai Li
The Ultrafast Assembly of a Dipeptide Supramolecular Organogel and its Phase Transition from Gel to Crystal
MPIP researchers in collaboration with Junbai Li (CAS Key Lab, Chinese Academy of Science, Beijing, China) investigated the assembly of a dipeptide revealing the intermediate structures from the molecule to supramolecular organogel via a conformation transition in dilute aqueous solutions.
© Wiley (2019)
The Ultrafast Assembly of a Dipeptide Supramolecular Organogel and its Phase Transition from Gel to Crystal
Temperature-Dependent Thermoelastic Anisotropy of the Phenyl Pyrimidine Liquid Crystal
Meguya Ryu, Yu Cang, Zuyuan Wang, George Fytas and Junko Morikawa
Temperature-Dependent Thermoelastic Anisotropy of the Phenyl Pyrimidine Liquid Crystal
MPIP researchers in collaboration with Meguya Ryu and Junko Morikawa (Tokyo Institute of Technology) investigated the thermomechanical properties of a liquid crystal in five consecutive phases, revealing a much stronger anisotropy and temperature-dependency of the thermal diffusivity than those of the elastic moduli and yielding insights into structure-based phonon engineering.
© ACS (2019)
The liquid crystal undergoes crystalline, smectic C, smectic A, nematic, and isotropic phases in order with temperature rise. The thermal and elastic anisotropies are experimentally observed to decrease with the phase variation.
Hydrophobic Metal–Organic Frameworks
Kolleboyina Jayaramulu, Florian Geyer, Andreas Schneemann, Štěpán Kment, Michal Otyepka, Radek Zboril, Doris Vollmer, Roland A. Fischer
Hydrophobic Metal–Organic Frameworks
Metal–organic frameworks (MOFs) have diverse potential applications in catalysis, gas storage, separation, and drug delivery because of their nanoscale periodicity, permanent porosity, channel functionalization, and structural diversity. Despite these promising properties, the inherent structural features of even some of the best‐performing MOFs make them moisture‐sensitive and unstable in aqueous media, limiting their practical usefulness. This problem could be overcome by developing stable hydrophobic MOFs whose chemical composition is tuned to ensure that their metal–ligand bonds persist even in the presence of moisture and water. However, the design and fabrication of such hydrophobic MOFs pose a significant challenge. Reported syntheses of hydrophobic MOFs are critically summarized, highlighting issues relating to their design, characterization, and practical use. First, wetting of hydrophobic materials is introduced and the four main strategies for synthesizing hydrophobic MOFs are discussed. Afterward, critical challenges in quantifying the wettability of these hydrophobic porous surfaces and solutions to these challenges are discussed. Finally, the reported uses of hydrophobic MOFs in practical applications such as hydrocarbon storage/separation and their use in separating oil spills from water are summarized. Finally, the state of the art is summarized and promising future developments of hydrophobic MOFs are highlighted.
© MPI-P (2019)
On the origin of the extremely different solubilities of polyethers in water
Bernd Ensing, Ambuj Tiwari, Martijn Tros, Johannes Hunger, Sérgio R. Domingos, Cristóbal Pérez, Gertien Smits, Mischa Bonn, Daniel Bonn & Sander Woutersen
On the origin of the extremely different solubilities of polyethers in water
The solubilities of polyethers in water are surprisingly counter-intuitive. The best-known example is the difference between polyethylene glycol ([-CH2-CH2-O-]n) which dissolves up to 0.5 kg/l, and polyoxymethylene ([-CH2-O-]n) which is completely insoluble in water, exactly the opposite of what one expects from the ratio of hydrophobic to hydrophilic parts in these molecules. Using advanced spectroscopic and theoretical tools, a team of researchers from the University of Amsterdam and MPIP in the MaxWater consortium (https://www.maxwater.mpg.de/) find that the dynamics of water molecules solvating polyethers is fundamentally different depending on their C/O composition, as a result of the varying partial charge on the O atoms. The results show that quantum effects can have a major impact on aqueous solubilities.
© MPI-P (2019)
Hydration of polyethers determines their vastly different solubility
Targeted Drug Delivery in Plants: Enzyme-Responsive Lignin Nanocarriers for the Curative Treatment of the Worldwide Grapevine Trunk Disease Esca
Jochen Fischer, Sebastian J. Beckers, Doungporn Yiamsawas, Eckhard Thines, Katharina Landfester, Frederik R. Wurm
Targeted Drug Delivery in Plants: Enzyme-Responsive Lignin Nanocarriers for the Curative Treatment of the Worldwide Grapevine Trunk Disease Esca
Nanocarrier (NC)-mediated drug delivery is a widely researched field of medicine but to date has not been used in agriculture. Developed is the first curative NC-based treatment of the worldwide occurring grapevine trunk disease Esca with more than 2 billion infected plants causing a loss yearly of $1.5 billion. To date, only repetitive spraying of fungicides is used to reduce the chances of infection. We developed a nanocarrier (NC)-based treatment for grapevines against the fungal disease Esca. In contrast to extensive spraying, this long-term effective treatment uses minimum amounts of fungicide encapsulated in biobased and biodegradable lignin (a natural component of wood) NCs. The fungicide is released only on demand in case of infection due to ligninolytic enzymes, secreted by the Esca-associated fungi, which degrade the carrier matrix. We conducted field studies in different vineyards and prove a curative effect of the nanocarrier-mediated treatment over a period of up to five years.
© MPI-P (2019)
Benzo-Fused Periacenes or Double Helicenes? Different Cyclodehydrogenation Pathways on Surface and in Solution
Qigang Zhong, Yunbin Hu, Kaifeng Niu, Haiming Zhang, Daniel Ebeling, André Schirmeisen, Klaus Müllen, Akimitsu Narita, Lifeng Chi
Benzo-Fused Periacenes or Double Helicenes? Different Cyclodehydrogenation Pathways on Surface and in Solution
Controlling the regioselectivity of C−H activation in unimolecular reactions is of great significance for the rational synthesis of functional graphene nanostructures, which are called nanographenes. Here, we demonstrate that the adsorption of tetranaphthyl-p-terphenyl precursors on metal surfaces can completely change the cyclodehydrogenation route and lead to obtaining planar benzo-fused perihexacenes rather than double [7]helicenes obtained in solution. The course of the on-surface planarization reaction is monitored using scanning probe microscopy, which unambiguously reveals the formation of dibenzoperihexacenes and the structures of reaction intermediates. The regioselective planarization can be attributed to the flattened adsorption geometries and reduced flexibility of the precursors on the surfaces, in addition to the different mechanism of the on-surface cyclodehydrogenation from that of the solution counterpart. We have further achieved an on-surface synthesis of dibenzoperioctacene by employing a tetra-anthryl-p-terphenyl precursor. The energy gaps of the new nanographenes are measured to be approximately 2.1 eV (dibenzoperihexacene) and 1.3 eV (dibenzoperioctacene) on a Au(111) surface. Our findings shed new light on the regioselectivity in cyclodehydrogenation reactions, which will be important for exploring the synthesis of unprecedented nanographenes.
© ACS (2019)
Different cyclodehydrogenation pathways of a tetranaphthyl-p-terphenyl precursor, demonstrating the regioselective planarization on-surface to form benzo-fused periacenes instead of double helicenes formed in solution.
Regioselective Hydrogenation of a 60-Carbon Nanographene Molecule toward a Circumbiphenyl Core
Xuelin Yao, Xiao-Ye Wang, Christopher Simpson, Giuseppe M. Paternò, Michele Guizzardi, Manfred Wagner, Giulio Cerullo, Francesco Scotognella, Mark D. Watson, Akimitsu Narita, and Klaus Müllen
Regioselective Hydrogenation of a 60-Carbon Nanographene Molecule toward a Circumbiphenyl Core
Regioselective peripheral hydrogenation of a nanographene molecule with 60 contiguous sp2 carbons provides unprecedented access to peralkylated circumbiphenyl. Conversion to the circumbiphenyl core structure was unambiguously validated by MALDI-TOF mass spectrometry, NMR, FTIR, and Raman spectroscopy. UV-vis absorption spectra and DFT calculations demonstrated the significant change of the optoelectronic properties upon peripheral hydrogenation. Stimulated emission of the peralkylated circumbiphenyl, observed via ultrafast transient absorption measurements, indicates potential as an optical gain material.
© ACS (2019)
π-Truncation, a direct and efficient strategy, serves as a general approach to unique aromatic structures.
Correlated interfacial water transport and proton conductivity in perfluorosulfonic acid membranes
Xiao Ling, Mischa Bonn, Katrin F. Domke, and Sapun H. Parekh
Correlated interfacial water transport and proton conductivity in perfluorosulfonic acid membranes
Fuel cell proton exchange membranes (PEMs) are central to hydrogen fuel cell technology. The mechanism and optimization of proton transport in these materials is intimately linked with hydration and water transport. Studies of water transport in PEMs have previously been limited to macroscopic permeability measurements. Our real-time vibrational microscopy experiments connect the macroscopic proton transport in PEMs to the molecular water arrangement: Two distinct types of water, differing in their degree of molecular coordination, transit the membrane at very different rates. The more weakly coordinated water species consistently exhibits faster transit across five different PEMs and shows a direct correlation to the proton conductivity, suggesting that designing PEMs to maximize the fraction of under-coordinated water is key for maximizing overall transport.
© Sapun Parekh (2019)
The correlation between proton- and water transport in fuel cell membranes has been discovered using time-resolved Raman microscopy
Prevention of Dominant IgG Adsorption on Nanocarriers in IgG‐Enriched Blood Plasma by Clusterin Precoating
Domenik Prozeller, Jorge Pereira, Johanna Simon, Volker Mailänder, Svenja Morsbach, Katharina Landfester
Prevention of Dominant IgG Adsorption on Nanocarriers in IgG‐Enriched Blood Plasma by Clusterin Precoating
Nanocarriers for medical applications must work reliably within organisms, independent of the individual differences in the blood proteome. Variation in the blood proteome, such as immunoglobulin levels, is a result of environmental, nutrition, and constitution conditions. This variation, however, should not influence the behavior of nanocarriers in biological media. The composition of the protein corona is investigated to understand the influence varying immunoglobulin levels in the blood plasma have on the interactions with nanocarriers. Specifically, the composition of the nanocarriers' coronas is analyzed after incubation in plasma with normal or elevated immunoglobulin G (IgG) levels, and cellular uptake is monitored in cell lines containing different immunoglobulin receptors. Here, it is reported that upon doubling the IgG concentration in plasma, the IgG fraction in the protein corona increases by a factor of 40 independent of the nanocarrier material. This results in a significant increase in uptake in cells exhibiting IgG binding receptors. Furthermore, precoating nanocarriers with clusterin successfully prevents dominant IgG‐adsorption and additionally reduces cellular internalization, after incubation with IgG‐enriched plasma. Therefore, precoating nanocarriers may be utilized as a powerful method to reduce the influence of individual variations in blood composition on the protein corona.
© Wiley-VCH, Advanced Science (2019)
Clusterin shields nanocarriers from adsorption of immunoglobulins in blood plasma with elevated IgG levels.
The Surface of Ice under Equilibrium and Nonequilibrium Conditions
Yuki Nagata, Tetsuya Hama, Ellen H. G. Backus, Markus Mezger, Daniel Bonn, Mischa Bonn, and Gen Sazaki
The Surface of Ice under Equilibrium and Nonequilibrium Conditions
How does ice surface look like? How does ice surface vary with temperature? How do molecules adsorbed into the ice? Why is ice surface slippery? A review article focusing on sum-frequency generation spectroscopy, molecular dynamics simulation, and confocal microscopy reveal the presence of different quasi-liquid states; disordered layer, quasi-liquid droplet, and quasi-liquid film. We overview how these different quasi-liquid states emerge and how these affects the gas uptakes and ice friction.
© Yuki Nagata / MPI-P (2019)
Ice structure changes with temperature
Disentangling the Role of Chain Conformation on the Mechanics of Polymer Tethered Particle Materials
Jiarul Midya, Yu Cang, Sergei A. Egorov, Krzysztof Matyjaszewski, Michael R. Bockstaller, Arash Nikoubashman, and George Fytas
Disentangling the Role of Chain Conformation on the Mechanics of Polymer Tethered Particle Materials
MPIP researchers in collaboration with Dr. Midya, Dr. Nikoubashman (Johannes Gutenberg University Mainz), Prof. Egorov (University of Virginia), Prof. Bockstaller and Prof. Matyjaszewski (Carnegie Mellon University) revealed the role of chain conformation on the mechanics of one-component nanocomposites. Polymer-tethered nanoparticle (alternatively called brush particle) assemblies represent a novel class of materials with unprecedented combinations of properties. The grafted polymer chains effectively control the particle interactions, and hence are instrumental for overcoming the phase separation issue in two-component nanocomposites. To achieve the desired material properties and further advance the opportunities presented by brush particle systems, understanding the microscopic origin of macroscopic properties is crucial. However, despite recent scientific efforts there remain still many open questions, especially regarding the mechanical behavior in one-component systems. In this work, we complement experimental non-invasive Brillouin light spectroscopy measurements with microscopically resolved molecular dynamics simulations to elucidate the role of graft architecture in the elasticity of brush particle systems. The experimental results revealed a significant mechanical reinforcement in the sparsely grafted nanoparticles compared to the systems with almost same particle loading but dense and short chains. Our simulations demonstrated that the stiffening is caused by the coil-like conformations of the sparsely grafted long chains, which led to significantly stronger polymer-polymer interactions compared to densely grafted NPs. Our results offer novel opportunities to tailor physical properties of composite materials by the strategic design of the ‘molecular architecture’ of constituents.
© Katharina Maisenbacher (2019)
Schematic figure of mechanical reinforcement found in a sparsely grafted particle film compared to a system with same particle loading but grafted with dense and short chains.
Engineering of robust topological quantum phases in graphene nanoribbons
Oliver Gröning, Shiyong Wang, Xuelin Yao, Carlo A. Pignedoli, Gabriela Borin Barin, Colin Daniels, Andrew Cupo, Vincent Meunier, Xinliang Feng, Akimitsu Narita, Klaus Müllen, Pascal Ruffieux & Roman Fasel
Engineering of robust topological quantum phases in graphene nanoribbons
Boundaries between distinct topological phases of matter support robust, yet exotic quantum states such as spin–momentum locked transport channels or Majorana fermions. It is desirable to rationally engineer topological electronic phases into stable and processable materials to exploit the corresponding quantum states. Here we present a flexible strategy based on atomically precise graphene nanoribbons to design robust nanomaterials exhibiting the topological boundary states. Namely, when the width of a narrow graphene nanoribbon changes, in the current case from seven to nine atoms, a special zone is created at the transition: because the electronic properties of the two areas differ in a special, so-called topological way, a "protected" and thus very robust new quantum state is created in the transition zone. We demonstrate the controlled periodic coupling of topological boundary states at junctions of graphene nanoribbons with armchair edges to create quasi-one-dimensional trivial and non-trivial electronic quantum phases. The topological end states occur at the ends of certain graphene nanoribbon segments. This offers the possibility of using them as elements of so-called qubits for the application in a quantum computer.
© Oliver Gröning (2019)
When graphene nanoribbons contain sections of varying width, robust new quantum states can be created in the transition zone.
Single photon emission from graphene quantum dots at room temperature
Shen Zhao, Julien Lavie, Loïc Rondin, Lucile Orcin-Chaix, Carole Diederichs, Philippe Roussignol, Yannick Chassagneux, Christophe Voisin, Klaus Müllen, Akimitsu Narita, Stéphane Campidelli & Jean-Sébastien Lauret
Single photon emission from graphene quantum dots at room temperature
Graphene being a zero-gap material, considerable efforts have been made to develop semiconductors whose structure is compatible with its hexagonal lattice. Size reduction is a promising way to achieve this objective. The reduction of both dimensions of graphene leads to graphene quantum dots. Here, we report on a single-emitter study that directly addresses the intrinsic emission properties of graphene quantum dots. In particular, we show that they are efficient and stable single-photon emitters at room temperature and that their emission wavelength can be modified through the functionalization of their edges. Finally, the investigation of the intersystem crossing shows that the short triplet lifetime and the low crossing yield are in agreement with the high brightness of these quantum emitters. These results represent a step-forward in performing chemistry engineering for the design of quantum emitters.
© Jean-Sébastien Lauret (2019)
Emission of single photons from graphene quantum dot C96. Second-order correlation function showed a strong antibunching.
Polyhedral Liquid Marbles
Florian Geyer, Yuta Asaumi, Doris Vollmer, Hans-Jürgen Butt, Yoshinobu Nakamura, and Syuji Fujii
Polyhedral Liquid Marbles
A new type of armored droplet, a so-called polyhedral liquid marble, is introduced. These liquid marbles consist of liquid droplets stabilized by hydrophobic hexagonal plates made of poly(ethylene terephthalate), which adsorb to the liquid–air interface. Depending on the specific combination of plate size and droplet diameter, the plates self-assemble into highly ordered hexagonally arranged domains. Even tetrahedral-, pentahedral-, and cube-shaped liquid marbles composed of only 4 to 6 plates are demonstrated. During evaporation of the internal liquid, due to the high adsorption energy of the plates at the liquid–air interface, the overall surface area stays constant, resulting in strongly deformed polyhedral liquid marbles. In line with this, highly asymmetric polyhedral liquid marbles and letters are obtained due to the strong interfacial jamming exerted by the rigid hexagonal plates. This is particularly pronounced for larger plate sizes, leading to liquid marbles with unusually sharp edges (for example, rectangular edges). The polyhedral liquid marbles exhibit various stimuli-responsive behaviors simultaneously being exposed to water, ammonia, or tetrahydrofuran vapors. Air-driven polyhedral liquid marbles floating on water can reach velocities of several centimeters per second.
© MPI-P / Wiley-VCH (2019)
Polyhedral liquid marbles prepared using 2.48 mm sized hexagonal plates and 15 µL dyed water droplets (left) and solidified polyhedral liquid marble using cyanoacrylate (right).
Chemisorption of Atomically Precise 42-Carbon Graphene Quantum Dots on Metal Oxide Films Greatly Accelerates Interfacial Electron Transfer
Peng Han, Ian Cheng-Yi Hou, Hao Lu, Xiao-Ye Wang, Klaus Müllen, Mischa Bonn, Akimitsu Narita, Enrique Cánovas
Chemisorption of Atomically Precise 42-Carbon Graphene Quantum Dots on Metal Oxide Films Greatly Accelerates Interfacial Electron Transfer
Atomically precise graphene quantum dots (GQDs) are graphene nanostructures which have size-dependent band-gaps; furthermore, they are metal-free and hence low-cost and environmentally friendly. These features make GQDs promising building blocks in novel solar energy conversion schemes, e.g. constituting a promising alternative to organometallic dyes employed in sensitized solar cells. However, current GQD-based sensitized solar cells are characterized by modest efficiencies; which were correlated with the low affinity towards the oxide electrode of the employed physisorbed GQDs sensitizers. Here we demonstrate that chemisorption of atomically precise GQDs onto mesoporous metal oxides, enabled by their functionalization with a carboxylate group, substantially enhances electron collection in the metal oxide electrode. Chemisorption boost electron transfer rates by almost 2 orders of magnitude when compared with physisorbed sensitizers. The accelerated interfacial electron transfer can be traced to stronger donor−acceptor coupling strength enabled by chemisorption.
© ACS / MPI-P (2019)
 
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