@article{GuRisseLuetal.2019, author = {Gu, Sasa and Risse, Sebastian and Lu, Yan and Ballauff, Matthias}, title = {Mechanism of the oxidation of 3,3′,5,5′-tetramethylbenzidine catalyzed by peroxidase-like Pt nanoparticles immobilized in spherical polyelectrolyte brushes}, series = {ChemPhysChem}, volume = {21}, journal = {ChemPhysChem}, number = {5}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1439-4235}, doi = {10.1002/cphc.201901087}, pages = {450 -- 458}, year = {2019}, abstract = {Experimental and kinetic modelling studies are presented to investigate the mechanism of 3,3 ',5,5 '-tetramethylbenzidine (TMB) oxidation by hydrogen peroxide (H2O2) catalyzed by peroxidase-like Pt nanoparticles immobilized in spherical polyelectrolyte brushes (SPB-Pt). Due to the high stability of SPB-Pt colloidal, this reaction can be monitored precisely in situ by UV/VIS spectroscopy. The time-dependent concentration of the blue-colored oxidation product of TMB expressed by different kinetic models was used to simulate the experimental data by a genetic fitting algorithm. After falsifying the models with abundant experimental data, it is found that both H2O2 and TMB adsorb on the surface of Pt nanoparticles to react, indicating that the reaction follows the Langmuir-Hinshelwood mechanism. A true rate constant k, characterizing the rate-determining step of the reaction and which is independent on the amount of catalysts used, is obtained for the first time. Furthermore, it is found that the product adsorbes strongly on the surface of nanoparticles, thus inhibiting the reaction. The entire analysis provides a new perspective to study the catalytic mechanism and evaluate the catalytic activity of the peroxidase-like nanoparticles.}, language = {en} } @misc{WalkowiakLuGradzielskietal.2020, author = {Walkowiak, Jacek and Lu, Yan and Gradzielski, Michael and Zauscher, Stefan and Ballauff, Matthias}, title = {Thermodynamic analysis of the uptake of a protein in a spherical polyelectrolyte brush}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1}, issn = {1866-8372}, doi = {10.25932/publishup-51730}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-517307}, pages = {10}, year = {2020}, abstract = {A thermodynamic study of the adsorption of Human Serum Albumin (HSA) onto spherical polyelectrolyte brushes (SPBs) by isothermal titration calorimetry (ITC) is presented. The SPBs are composed of a solid polystyrene core bearing long chains of poly(acrylic acid). ITC measurements done at different temperatures and ionic strengths lead to a full set of thermodynamicbinding constants together with the enthalpies and entropies of binding. The adsorption of HSA onto SPBs is described with a two-step model. The free energy of binding Delta Gb depends only weakly on temperature because of a marked compensation of enthalpy by entropy. Studies of the adsorbed HSA by Fourier transform infrared spectroscopy (FT-IR) demonstrate no significant disturbance in the secondary structure of the protein. The quantitative analysis demonstrates that counterion release is the major driving force for adsorption in a process where proteins become multivalent counterions of the polyelectrolyte chains upon adsorption. A comparison with the analysis of other sets of data related to the binding of HSA to polyelectrolytes demonstrates that the cancellation of enthalpy and entropy is a general phenomenon that always accompanies the binding of proteins to polyelectrolytes dominated by counterion release.}, language = {en} } @article{WalkowiakLuGradzielskietal.2019, author = {Walkowiak, Jacek and Lu, Yan and Gradzielski, Michael and Zauscher, Stefan and Ballauff, Matthias}, title = {Thermodynamic analysis of the uptake of a protein in a spherical polyelectrolyte brush}, series = {Macromolecular rapid communications}, volume = {41}, journal = {Macromolecular rapid communications}, number = {1}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1336}, doi = {10.1002/marc.201900421}, pages = {8}, year = {2019}, abstract = {A thermodynamic study of the adsorption of Human Serum Albumin (HSA) onto spherical polyelectrolyte brushes (SPBs) by isothermal titration calorimetry (ITC) is presented. The SPBs are composed of a solid polystyrene core bearing long chains of poly(acrylic acid). ITC measurements done at different temperatures and ionic strengths lead to a full set of thermodynamicbinding constants together with the enthalpies and entropies of binding. The adsorption of HSA onto SPBs is described with a two-step model. The free energy of binding Delta Gb depends only weakly on temperature because of a marked compensation of enthalpy by entropy. Studies of the adsorbed HSA by Fourier transform infrared spectroscopy (FT-IR) demonstrate no significant disturbance in the secondary structure of the protein. The quantitative analysis demonstrates that counterion release is the major driving force for adsorption in a process where proteins become multivalent counterions of the polyelectrolyte chains upon adsorption. A comparison with the analysis of other sets of data related to the binding of HSA to polyelectrolytes demonstrates that the cancellation of enthalpy and entropy is a general phenomenon that always accompanies the binding of proteins to polyelectrolytes dominated by counterion release.}, language = {en} } @article{RotheZhaoKewesetal.2019, author = {Rothe, Martin and Zhao, Yuhang and Kewes, G{\"u}nter and Kochovski, Zdravko and Sigle, Wilfried and van Aken, Peter A. and Koch, Christoph and Ballauff, Matthias and Lu, Yan and Benson, Oliver}, title = {Silver nanowires with optimized silica coating as versatile plasmonic resonators}, series = {Scientific reports}, volume = {9}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-019-40380-5}, pages = {12}, year = {2019}, abstract = {Metal nanoparticles are the most frequently used nanostructures in plasmonics. However, besides nanoparticles, metal nanowires feature several advantages for applications. Their elongation offers a larger interaction volume, their resonances can reach higher quality factors, and their mode structure provides better coupling into integrated hybrid dielectric-plasmonic circuits. It is crucial though, to control the distance of the wire to a supporting substrate, to another metal layer or to active materials with sub-nanometer precision. A dielectric coating can be utilized for distance control, but it must not degrade the plasmonic properties. In this paper, we introduce a controlled synthesis and coating approach for silver nanowires to fulfill these demands. We synthesize and characterize silver nanowires of around 70 nm in diameter. These nanowires are coated with nm-sized silica shells using a modified Stober method to achieve a homogeneous and smooth surface quality. We use transmission electron microscopy, dark-field microscopy and electron-energy loss spectroscopy to study morphology and plasmonic resonances of individual nanowires and quantify the influence of the silica coating. Thorough numerical simulations support the experimental findings showing that the coating does not deteriorate the plasmonic properties and thus introduce silver nanowires as usable building blocks for integrated hybrid plasmonic systems.}, language = {en} } @article{QuanGoubardBretescheHaerketal.2019, author = {Quan, Ting and Goubard-Bretesche, Nicolas and Haerk, Eneli and Kochovski, Zdravko and Mei, Shilin and Pinna, Nicola and Ballauff, Matthias and Lu, Yan}, title = {Highly Dispersible Hexagonal Carbon-MoS2-Carbon Nanoplates with Hollow Sandwich Structures for Supercapacitors}, series = {Chemistry - a European journal}, volume = {25}, journal = {Chemistry - a European journal}, number = {18}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.201806060}, pages = {4757 -- 4766}, year = {2019}, abstract = {MoS2, a typical layered transition-metal dichalcogenide, is promising as an electrode material in supercapacitors. However, its low electrical conductivity could lead to limited capacitance if applied in electrochemical devices. Herein, a new nanostructure composed of hollow carbon-MoS2-carbon was successfully synthesized through an L-cysteine-assisted hydrothermal method by using gibbsite as a template and polydopamine as a carbon precursor. After calcination and etching of the gibbsite template, uniform hollow platelets, which were made of a sandwich-like assembly of partial graphitic carbon and two-dimensional layered MoS2 flakes, were obtained. The platelets showed excellent dispersibility and stability in water, and good electrical conductivity due to carbon provided by the calcination of polydopamine coatings. The hollow nanoplate morphology of the material provided a high specific surface area of 543 m(2) g(-1), a total pore volume of 0.677 cm(3) g(-1), and fairly small mesopores (approximate to 5.3 nm). The material was applied in a symmetric supercapacitor and exhibited a specific capacitance of 248 F g(-1) (0.12 F cm(-2)) at a constant current density of 0.1 Ag-1; thus suggesting that hollow carbon-MoS2 carbon nanoplates are promising candidate materials for supercapacitors.}, language = {en} } @article{XuAngiolettiUbertiLuetal.2018, author = {Xu, Xiao and Angioletti-Uberti, Stefano and Lu, Yan and Dzubiella, Joachim and Ballauff, Matthias}, title = {Interaction of Proteins with Polyelectrolytes}, series = {Langmuir}, volume = {35}, journal = {Langmuir}, number = {16}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.8b01802}, pages = {5373 -- 5391}, year = {2018}, abstract = {We discuss recent investigations of the interaction of polyelectrolytes with proteins. In particular, we review our recent studies on the interaction of simple proteins such as human serum albumin (HSA) and lysozyme with linear polyelectrolytes, charged dendrimers, charged networks, and polyelectrolyte brushes. In all cases discussed here, we combined experimental work with molecular dynamics (MD) simulations and mean-field theories. In particular, isothermal titration calorimetry (ITC) has been employed to obtain the respective binding constants K-b and the Gibbs free energy of binding. MD simulations with explicit counterions but implicit water demonstrate that counterion release is the main driving force for the binding of proteins to strongly charged polyelectrolytes: patches of positive charges located on the surface of the protein become multivalent counterions of the polyelectrolyte, thereby releasing a number of counterions condensed on the polyelectrolyte. The binding Gibbs free energy due to counterion release is predicted to scale with the logarithm of the salt concentration in the system, which is verified by both simulations and experiment. In several cases, namely, for the interaction of proteins with linear polyelectrolytes and highly charged hydrophilic dendrimers, the binding constant could be calculated from simulations to very good approximation. This finding demonstrated that in these cases explicit hydration effects do not contribute to the Gibbs free energy of binding. The Gibbs free energy can also be used to predict the kinetics of protein uptake by microgels for a given system by applying dynamic density functional theory. The entire discussion demonstrates that the direct comparison of theory with experiments can lead to a full understanding of the interaction of proteins with charged polymers. Possible implications for applications, such as drug design, are discussed.}, language = {en} } @article{MeiKochovskiRoaetal.2019, author = {Mei, Shilin and Kochovski, Zdravko and Roa, Rafael and Gu, Sasa and Xu, Xiaohui and Yu, Hongtao and Dzubiella, Joachim and Ballauff, Matthias and Lu, Yan}, title = {Enhanced Catalytic Activity of Gold@Polydopamine Nanoreactors with Multi-compartment Structure Under NIR Irradiation}, series = {Nano-Micro Letters}, volume = {11}, journal = {Nano-Micro Letters}, number = {1}, publisher = {Shanghai JIAO TONG univ press}, address = {Shanghai}, issn = {2311-6706}, doi = {10.1007/s40820-019-0314-9}, pages = {16}, year = {2019}, abstract = {Photothermal conversion (PTC) nanostructures have great potential for applications in many fields, and therefore, they have attracted tremendous attention. However, the construction of a PTC nanoreactor with multi-compartment structure to achieve the combination of unique chemical properties and structural feature is still challenging due to the synthetic difficulties. Herein, we designed and synthesized a catalytically active, PTC gold (Au)@polydopamine (PDA) nanoreactor driven by infrared irradiation using assembled PS-b-P2VP nanosphere as soft template. The particles exhibit multi-compartment structure which is revealed by 3D electron tomography characterization technique. They feature permeable shells with tunable shell thickness. Full kinetics for the reduction reaction of 4-nitrophenol has been investigated using these particles as nanoreactors and compared with other reported systems. Notably, a remarkable acceleration of the catalytic reaction upon near-infrared irradiation is demonstrated, which reveals for the first time the importance of the synergistic effect of photothermal conversion and complex inner structure to the kinetics of the catalytic reduction. The ease of synthesis and fresh insights into catalysis will promote a new platform for novel nanoreactor studies.}, language = {en} } @article{MeiJaftaLauermannetal.2017, author = {Mei, Shilin and Jafta, Charl J. and Lauermann, Iver and Ran, Qidi and Kaergell, Martin and Ballauff, Matthias and Lu, Yan}, title = {Porous Ti4O7 Particles with Interconnected-Pore Structure as a High-Efficiency Polysulfide Mediator for Lithium-Sulfur Batteries}, series = {Advanced functional materials}, volume = {27}, journal = {Advanced functional materials}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.201701176}, pages = {10}, year = {2017}, abstract = {Multifunctional Ti4O7 particles with interconnected-pore structure are designed and synthesized using porous poly(styrene-b-2-vinylpyridine) particles as a template. The particles can work efficiently as a sulfur-host material for lithium-sulfur batteries. Specifically, the well-defined porous Ti4O7 particles exhibit interconnected pores in the interior and have a high-surface area of 592 m(2) g(-1); this shows the advantage of mesopores for encapsulating of sulfur and provides a polar surface for chemical binding with polysulfides to suppress their dissolution. Moreover, in order to improve the conductivity of the electrode, a thin layer of carbon is coated on the Ti4O7 surface without destroying its porous structure. The porous Ti4O7 and carbon-coated Ti4O7 particles show significantly improved electrochemical performances as cathode materials for Li-S batteries as compared with those of TiO2 particles.}, language = {en} }