Matthias Ballauff

Bio: Matthias Ballauff is an academic researcher from Free University of Berlin. The author has contributed to research in topics: Polyelectrolyte & Small-angle X-ray scattering. The author has an hindex of 77, co-authored 399 publications receiving 23083 citations. Previous affiliations of Matthias Ballauff include Helmholtz-Zentrum Berlin & Karlsruhe Institute of Technology.

Kinetic Analysis of Catalytic Reduction of 4-Nitrophenol by Metallic Nanoparticles Immobilized in Spherical Polyelectrolyte Brushes

Abstract: We present a study on the catalytic reduction of 4-nitrophenol by sodium borohydride in the presence of metal nanoparticles. The nanoparticles are embedded in spherical polyelectrolyte brushes, which consist of a polystyrene core onto which a dense layer of cationic polyelectrolyte brushes are grafted. The average size of the nanoparticles is approximately 2 nm. The kinetic data obtained by monitoring the reduction of 4-nitrophenol by UV/vis-spectroscopy could be explained in terms of the Langmuir−Hinshelwood model: The borohydride ions transfer a surface-hydrogen species in a reversible manner to the surface. Concomitantly 4-nitrophenol is adsorbed and the rate-determining step consists of the reduction of nitrophenol by the surface-hydrogen species. The apparent reaction rate can therefore be related to the total surface S of the nanoparticles, to the kinetic constant k related to the rate-determining step, and to the adsorption constants KNip and KBH4 of nitrophenol and of borohydride, respectively. In...

Catalysis by metallic nanoparticles in aqueous solution: model reactions.

Abstract: Catalysis by metallic nanoparticles is certainly among the most intensely studied problems in modern nanoscience. However, reliable tests for catalytic performance of such nanoparticles are often poorly defined, which makes comparison and benchmarking rather difficult. We tackle in this tutorial review a subset of well-studied reactions that take place in aqueous phase and for which a comprehensive kinetic analysis is available. Two of these catalytic model reactions are under consideration here, namely the reduction of (i) p-nitrophenol and (ii) hexacyanoferrate (III), both by borohydride ions. Both reactions take place at the surface of noble metal nanoparticles at room temperature and can be accurately monitored by UV-vis spectroscopy. Moreover, the total surface area of the nanoparticles in solution can be known with high precision and thus can be directly used for the kinetic analysis. Hence, these model reactions represent cases of heterogeneous catalysis that can be modelled with the accuracy typically available for homogeneous catalysis. Both model reactions allow us to discuss a number of important concepts and questions, namely the dependence of catalytic activity on the size of the nanoparticles, electrochemistry of nanoparticles, surface restructuring, the use of carrier systems and the role of diffusion control.

Thermosensitive core--shell particles as carriers for Ag nanoparticles : modulating the catalytic activity by a phase transition in networks

Abstract: Metal nanoparticles have properties that are significantly different from the bulk properties of the metals. Moreover, their high surface-to-volume ratio renders them ideal candidates for application as catalysts. However, the pronounced tendency of nanoparticles to aggregate must be overcome by using suitable carrier systems. Recently, a number of systems have been discussed that are suitable for applications in aqueous environments. These include polymers, dendrimers, microgels, 18] and other colloidal systems. 20] In all the cases studied so far, these carrier systems only provide a suitable support for the nanoparticles and prevent them from aggregating. In this way the carrier system of, for example, dendrimers or microgels acts much in the same way as a “nanoreactor” that immobilizes the particles and leads to their more convenient handling. Here we report on the first system that allows us to modulate the activity of nanoparticles through a thermodynamic transition that takes place within the carrier system. Figure 1 displays the principle. Metallic nanoparticles are embedded in a polymeric network attached to a colloidal core particle. In all the cases discussed here the core consists of poly(styrene) (PS) while the network consists of poly(Nisopropylacrylamide) (PNIPA) cross-linked with N,N’-methylenebisacrylamide (BIS). The particles are suspended in water, which swells the PNIPA at room temperature. The PNIPA network, however, undergoes a phase transition around 30 8C, during which most of the water is expelled. Previous experiments have demonstrated that this transition is perfectly reversible and the process of shrinking and reswelling can be repeated without degradation or coagulation of the particles. Metallic nanoparticles embedded in such a network are fully accessible to reactants at low temperature. Above the phase transition, however, the marked shrinkage of the network should be followed by a concomitant slowing down of the diffusion of the reactants within the network. The rate of reactions catalyzed by the nanoparticles should thus be slowed down considerably. In this way, the network could act as a “nanoreactor” that can be opened or closed to a certain extent. Herein we demonstrate that thermosensitive core–shell networks may indeed be used as such a nanoreactor. The activity of the catalyst can be modulated by temperature over a wide range. As the model reaction we chose the reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride. The reaction was repeatedly performed to check the catalytic activity of the metal nanoparticles, and the results obtained in the present study can be directly compared to literature data. The carrier particles having a PS core and a PNIPA shell were prepared as described recently. 24] Figure 2 shows a schematic representation of the silver nanoparticles being

Catalytic Activity of Palladium Nanoparticles Encapsulated in Spherical Polyelectrolyte Brushes and Core−Shell Microgels

Abstract: We present a quantitative comparison of the catalytic activity of palladium nanoparticles immobilized in different colloidal carrier systems, namely, in (i) spherical polyelectrolyte brushes (SPB) and (ii) core−shell microgels. The first system given by the SPB carrier particles consist of a solid core of polystyrene onto which long chains of poly((2-methylpropenoyloxyethyl) trimethylammonium chloride) (PMPTAC) are grafted. These positively charged polyelectrolyte chains form a dense layer on the surface of the core particles which binds the divalent PdCl42- ions. Reduction leads to metallic Pd particles. System 2 is given by core−shell microgels which consists of a solid core of polystyrene and a shell of cross-linked poly(N-isopropylacrylamide) (PNIPA). The metal ions were strongly localized within the network because of complexation of the PdCl42- ions and the nitrogen atoms of PNIPA. Reduction of these ions leads to nearly monodisperse nanoparticles of metallic palladium that are only formed within th...

Protein interactions with polymer coatings and biomaterials.

Abstract: Protein adsorption is considered to be the most important factor of the interaction between polymeric biomaterials and body fluids or tissues. Water-mediated hydrophobic and hydration forces as well as electrostatic interactions are believed to be the major factors of protein adsorption. A systematic analysis of various monolayer systems has resulted in general guidelines, the so-called "Whitesides rules". These concepts have been successfully applied for designing various protein-resistant surfaces and are being studied to expand the understanding of protein-material interactions beyond existing limitations. Theories on the mechanisms of protein adsorption are constantly being improved due to the fast-developing analytical technologies. This Review is aimed at improving these empirical guidelines with regard to present theoretical and analytical advances. Current analytical methods to test mechanistic hypotheses and theories of protein-surface interactions will be discussed. Special focus will be given to state-of-the-art bioinert and biospecific coatings and their applications in biomedicine.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Emerging applications of stimuli-responsive polymer materials

Abstract: Responsive polymer materials can adapt to surrounding environments, regulate transport of ions and molecules, change wettability and adhesion of different species on external stimuli, or convert chemical and biochemical signals into optical, electrical, thermal and mechanical signals, and vice versa. These materials are playing an increasingly important part in a diverse range of applications, such as drug delivery, diagnostics, tissue engineering and 'smart' optical systems, as well as biosensors, microelectromechanical systems, coatings and textiles. We review recent advances and challenges in the developments towards applications of stimuli-responsive polymeric materials that are self-assembled from nanostructured building blocks. We also provide a critical outline of emerging developments.

Electrospinning: A Fascinating Method for the Preparation of Ultrathin Fibers

Abstract: Electrospinning is a highly versatile method to process solutions or melts, mainly of polymers, into continuous fibers with diameters ranging from a few micrometers to a few nanometers. This technique is applicable to virtually every soluble or fusible polymer. The polymers can be chemically modified and can also be tailored with additives ranging from simple carbon-black particles to complex species such as enzymes, viruses, and bacteria. Electrospinning appears to be straightforward, but is a rather intricate process that depends on a multitude of molecular, process, and technical parameters. The method provides access to entirely new materials, which may have complex chemical structures. Electrospinning is not only a focus of intense academic investigation; the technique is already being applied in many technological areas.

Stochastic Processes in Physics and Chemistry

Abstract: N G van Kampen 1981 Amsterdam: North-Holland xiv + 419 pp price Dfl 180 This is a book which, at a lower price, could be expected to become an essential part of the library of every physical scientist concerned with problems involving fluctuations and stochastic processes, as well as those who just enjoy a beautifully written book. It provides an extensive graduate-level introduction which is clear, cautious, interesting and readable.