Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    New insights into the liquid crystal behaviour of hydrogen-bonded mixtures provided by temperature-dependent FTIR spectroscopy
    Paterson, D.A. ; Martínez-Felipe, A. ; Jansze, S.M. ; Marcelis, A.T.M. ; Storey, J.M.D. ; Imrie, C.T. - \ 2015
    Liquid Crystals 42 (2015)5-6. - ISSN 0267-8292 - p. 928 - 939.
    low molar-mass - side-chain - carboxylic-acids - benzoic-acid - amorphous polymers - pyridyl moieties - ir-spectra - dimers - phase - complexes
    The phase behaviour of equimolar mixtures of 6-(4'-cyanobiphenyl-4-yl)hexyloxybenzoic acid (CB6OBA) with either 1-(4-butylazobenzene-4'-oxy)-5-(4-oxypyridine)pentane (BuABO5OPyr) or 1-(4-butylazobenzene-4'-oxy)-6-(4-oxypyridine)hexane (BuABO6OPyr) is reported. CB6OBA shows a monotropic twist-bend nematic phase and an enantiotropic nematic phase whereas the two pyridyl-based components do not exhibit liquid crystallinity. Both equimolar mixtures (CB6OBA/BuABOnOPyr) show enantiotropic nematic phases. The nematic-isotropic transition temperature and associated entropy change are higher for the CB6OBA/BuABO6OPyr mixture than for the CB6OBA/BuABO5OPyr mixture. This may be accounted for in terms of the average shapes of the hydrogen-bonded 1:1 complexes formed between the two differing components in the mixtures. However, Fourier transform infrared spectroscopy reveals that this complex is not formed quantitatively, but instead a complex mixture exists over the complete temperature range studied, involving the 1:1 complex, both cyclic and open acid dimers, free acid and hence, free BuABOnOPyr molecules.
    Designed Enclosure Enables Guest Binding Within the 4200 A Cavity of a Self-Assembled Cube
    Ramsay, W.J. ; Szczypinski, F.T. ; Weissman, H. ; Ronson, T.K. ; Smulders, M. ; Rybtchinski, B. ; Nitschke, J.R. - \ 2015
    Angewandte Chemie-International Edition 54 (2015)19. - ISSN 1433-7851 - p. 5636 - 5640.
    molecular recognition - supramolecular chemistry - coordination cage - shape-persistent - encapsulation - exchange - host - architectures - complexes - polyhedra
    Metal–organic self-assembly has proven to be of great use in constructing structures of increasing size and intricacy, but the largest assemblies lack the functions associated with the ability to bind guests. Here we demonstrate the self-assembly of two simple organic molecules with CdII and PtII into a giant heterometallic supramolecular cube which is capable of binding a variety of mono- and dianionic guests within an enclosed cavity greater than 4200 Å3. Its structure was established by X-ray crystallography and cryogenic transmission electron microscopy. This cube is the largest discrete abiological assembly that has been observed to bind guests in solution; cavity enclosure and coulombic effects appear to be crucial drivers of host–guest chemistry at this scale. The degree of cavity occupancy, however, appears less important: the largest guest studied, bound the most weakly, occupying only 11¿% of the host cavity.
    Considerations on the shuttle mechanism of FeEDDHA chelates at the soil-root interface in case of Fe deficiency
    Schenkeveld, W.D.C. ; Reichwein, A.M. ; Temminghoff, E.J.M. ; Riemsdijk, W.H. van - \ 2014
    Plant and Soil 379 (2014)1-2. - ISSN 0032-079X - p. 373 - 387.
    strategy i plants - calcareous soil - lolium-perenne - metal uptake - iron uptake - complexes - eddha - chlorosis - isomers - montmorillonite
    A mechanism of action for the performance of Fe chelates as soil-applied fertilizer has been hypothesized by Lindsay and Schwab (J Plant Nutr 5:821-840, 1982), in which the ligand participates in a cyclic process of delivering Fe at the root surface and mobilizing Fe from the soil. This "shuttle mechanism" seems appealing in view of fertilizer efficiency, but little is known about its performance. The chelate FeEDDHA is a commonly used Fe fertilizer on calcareous soils. In this study, the performance of the shuttle mechanism has been examined for FeEDDHA chelates in soil interaction and pot trial experiments. The specificity of EDDHA ligands for chelating Fe from soils of low Fe availability is limited. Experimental support for a shuttle mechanism in soil-plant systems with FeEDDHA was found: specific metal mobilization only occurred upon FeEDDHA-facilitated Fe uptake. The mobilized metals originated at least in part from the root surface instead of the soil. The results from this study support the existence of a shuttle mechanism with FeEDDHA in soil application. If the efficiency of the shuttle mechanism is however largely controlled by metal availability in the bulk soil, it is heavily compromised by complexation of competing cations: Al, Mn and particularly Cu.
    Tetramer formation in Arabidopsis MADS domain proteins: analysis of a protein-protein interaction network
    Espinosa-Soto, C. ; Immink, R.G.H. ; Angenent, G.C. ; Alvarez-Buylla, E.R. ; Folter, de, S. - \ 2014
    BMC Systems Biology 8 (2014). - ISSN 1752-0509 - 17 p.
    box transcription factors - floral organ identity - flower development - gene duplication - adaptive evolution - homeotic proteins - factor family - in-vitro - dna - complexes
    Background: MADS domain proteins are transcription factors that coordinate several important developmental processes in plants. These proteins interact with other MADS domain proteins to form dimers, and it has been proposed that they are able to associate as tetrameric complexes that regulate transcription of target genes. Whether the formation of functional tetramers is a widespread property of plant MADS domain proteins, or it is specific to few of these transcriptional regulators remains unclear. Results: We analyzed the structure of the network of physical interactions among MADS domain proteins in Arabidopsis thaliana. We determined the abundance of subgraphs that represent the connection pattern expected for a MADS domain protein heterotetramer. These subgraphs were significantly more abundant in the MADS domain protein interaction network than in randomized analogous networks. Importantly, these subgraphs are not significantly frequent in a protein interaction network of TCP plant transcription factors, when compared to expectation by chance. In addition, we found that MADS domain proteins in tetramer-like subgraphs are more likely to be expressed jointly than proteins in other subgraphs. This effect is mainly due to proteins in the monophyletic MIKC clade, as there is no association between tetramer-like subgraphs and co-expression for proteins outside this clade. Conclusions: Our results support that the tendency to form functional tetramers is widespread in the MADS domain protein-protein interaction network. Our observations also suggest that this trend is prevalent, or perhaps exclusive, for proteins in the MIKC clade. Because it is possible to retrodict several experimental results from our analyses, our work can be an important aid to make new predictions and facilitates experimental research on plant MADS domain proteins.
    Influence of soil humic and fulvic acid on the activity and stability of lysozyme and urease
    Li, Y. ; Tan, W. ; Koopal, L.K. ; Wang, M. ; Liu, Fan ; Norde, W. - \ 2013
    Environmental Science and Technology 47 (2013). - ISSN 0013-936X - p. 5050 - 5056.
    isothermal titration calorimetry - insecticidal cry1ab protein - ionic-strength - prion protein - ph - adsorption - complexes - binding - substances - fractions
    Humic substances (HS), including humic acids (HA) and fulvic acids (FA), are important components of soil systems. HS form strong complexes with oppositely charged proteins, which will lead to changes in the enzyme activity. The effect of soil HS on the activity and stability of two enzymes was investigated as a function of pH, ionic strength, and mass ratio HS/enzyme. Humic acid (JGHA) and fulvic acid (JGFA) are negatively charged, lysozyme is net positive at pH values below 10.4, and urease is net positive below pH 5.2 or net negative above pH 5.2. The enzyme activities in the HS-enzyme complexes were suppressed when the enzymes were oppositely charged to the HS. The largest activity suppression was observed around the mass ratio HS/enzyme where the HS-protein complex was at its isoelectric point (IEP). At the IEP strong aggregation of the complexes led to encapsulation of the enzyme. The ionic strength was important; an increase decreased complex formation, but increased aggregation. Due to the larger hydrophobicity of JGHA than JGFA, the reduction in enzyme activity was stronger for JGHA. The enzyme stability also decreased maximally at mass ratio around the IEP of the complex when HS and protein were oppositely charged. When urease and HS were both negatively charged no complexes were formed, but the presence of JGHA or JGFA improved the activity and stability of the enzyme.
    Emission enhancement and lifetime modification of phosphorescence on silver nanoparticle aggregates
    Gill, R. ; Tian, L. ; Amerongen, H. van; Subramaniam, V. - \ 2013
    Physical Chemistry Chemical Physics 15 (2013). - ISSN 1463-9076 - p. 15734 - 15739.
    single-molecule fluorescence - oxygen generation - luminescence - spectroscopy - photochemistry - complexes - yields
    Silver nanoparticle aggregates have been shown to support very large enhancements of fluorescence intensity from organic dye molecules coupled with an extreme reduction in observed fluorescence lifetimes. Here we show that for the same type of aggregates, similar enhancement factors (similar to 75 x in intensity and similar to 3400 x in lifetime compared to the native radiative lifetime) are observed for a ruthenium-based phosphorescent dye (when taking into account the effect of charge and the excitation/emission wavelengths). Additionally, the inherently long native phosphorescence lifetimes practically enable more detailed analyses of the distribution of lifetimes (compared with the case with fluorescence decays). It was thus possible to unambiguously observe the deviation from mono-exponential decay which we attribute to emission from a distribution of fluorophores with different lifetimes, as we could expect from a random aggregation process. We believe that combining phosphorescent dyes with plasmonic structures, even down to the single dye level, will offer a convenient approach to better characterize plasmonic systems in detail.
    Chemodynamics of soft Charged nanoparticles in aquatic media: Fundamental concepts
    Town, R.M. ; Buffle, J. ; Duval, J.F.L. ; Leeuwen, H.P. van - \ 2013
    The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 117 (2013)33. - ISSN 1089-5639 - p. 7643 - 7654.
    metal speciation dynamics - aqueous-solutions - solvent exchange - complexes - relaxation - nmr - ion - approximation - temperature - membranes
    Multi-responsive physical gels formed by a biosynthetic asymmetric triblock protein polymer and a polyanion
    Pham, T.H.T. ; Wang, J. ; Werten, M.W.T. ; Snijkers, F. ; Wolf, F.A. de; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2013
    Soft Matter 9 (2013)37. - ISSN 1744-683X - p. 8923 - 8930.
    controlled drug-delivery - aqueous-solution - block-copolymers - hydrogels - ph - chitosan - aggregation - terpolymers - temperature - complexes
    We report the design, production and characterization of a biosynthetic asymmetric triblock copolymer which consists of one collagen-like and one cationic block spaced by a hydrophilic random coiled block. The polymer associates into micelles when a polyanion is added due to the electrostatic interaction between the cationic block and the polyanion. The collagen-like block self-assembles into thermo-responsive triple helices upon cooling. When both end blocks are induced to self-assemble, a physical gel is formed via thermo-responsive association of the charge-driven micelles. The self-assembly of both end blocks and the effects of salt and temperature thereon were characterized by light scattering and rheology
    Understanding the extraordinary ionic reactivity of aqueous nanoparticles
    Leeuwen, H.P. van; Buffle, J. ; Duval, J.F.L. ; Town, R.M. - \ 2013
    Langmuir 29 (2013)33. - ISSN 0743-7463 - p. 10297 - 10302.
    soft - chemodynamics - size - coagulation - relaxation - complexes - ligands - binding - cu(ii)
    Nanoparticles (NPs) are generally believed to derive their high reactivity from the inherently large specific surface area. Here we show that this is just the trivial part of a more involved picture. Nanoparticles that carry electric charge are able to generate chemical reaction rates that are even substantially larger than those for similar molecular reactants. This is achieved by Boltzmann accumulation of ionic reactants and the Debye acceleration of their transport. The ensuing unique reactivity features are general for all types of nanoparticles but most prominent for soft ones that exploit the accelerating mechanisms on a 3D level. These features have great potential for exploitation in the catalysis of ionic reactions: the reactivity of sites can be enhanced by increasing the indifferent charge density in the NP body
    Role of nanoparticles in analytical solid phase microextraction (SPME)
    Zielinska, K. ; Leeuwen, H.P. van - \ 2013
    Environmental Chemistry 10 (2013)2. - ISSN 1448-2517 - p. 120 - 126.
    human blood-serum - speciation analysis - aqueous matrices - quo-vadis - nd-spme - protein - aggregation - complexes - chemicals - kinetics
    Solid phase microextraction (SPME) is commonly used to measure the free concentration of fairly hydrophobic substances in aqueous media on the basis of their partitioning between sample solution and a solid phase. Here we study the role of nanoparticles that may sorb the analyte in the sample medium. As an example case, the solid phase poly(dimethylsiloxane) (PDMS) is exposed to an aqueous dispersion containing silica nanoparticles with 10-nm radius. Confocal laser microscopic data show that these SiO2 nanoparticles do enter the PDMS and partition between the sample solution and solid phase. Moreover, they form aggregates at the surface of the solid phase. The overall partitioning of the SiO2 nanoparticles in the aqueous sample–PDMS system is examined and potential effects on the SPME analysis of organic analytes are indicated
    A predicted functional gene network for the plant pathogen Phytophthora infestans as a framework for genomic biology
    Seidl, M.F. ; Schneider, A. ; Govers, F. ; Snel, B. - \ 2013
    BMC Genomics 14 (2013). - ISSN 1471-2164 - 16 p.
    protein-protein interactions - zoospore motility - complexes - reveals - yeast - families - tool - organization - translation - innovations
    Background - Associations between proteins are essential to understand cell biology. While this complex interplay between proteins has been studied in model organisms, it has not yet been described for the oomycete late blight pathogen Phytophthora infestans. Results - We present an integrative probabilistic functional gene network that provides associations for 37 percent of the predicted P. infestans proteome. Our method unifies available genomic, transcriptomic and comparative genomic data into a single comprehensive network using a Bayesian approach. Enrichment of proteins residing in the same or related subcellular localization validates the biological coherence of our predictions. The network serves as a framework to query existing genomic data using network-based methods, which thus far was not possible in Phytophthora. We used the network to study the set of interacting proteins that are encoded by genes co-expressed during sporulation. This identified potential novel roles for proteins in spore formation through their links to proteins known to be involved in this process such as the phosphatase Cdc14. Conclusions - The functional association network represents a novel genome-wide data source for P. infestans that also acts as a framework to interrogate other system-wide data. In both capacities it will improve our understanding of the complex biology of P. infestans and related oomycete pathogens
    Fractionation of technical lignins as a tool for improvement of their antioxidant properties
    Arshanitsa, A. ; Ponomarenko, J. ; Dizhbite, T. ; Andersone, A. ; Gosselink, R.J.A. ; Putten, J. van der; Lauberts, M. ; Telysheva, G. - \ 2013
    Journal of Analytical and Applied Pyrolysis 103 (2013). - ISSN 0165-2370 - p. 78 - 85.
    radical scavenging activity - extraction - complexes
    The modern biorefinery concept is aimed at the elaboration of sustainable processes with the most profitable utilization of all biomass products obtained at the technological cycle. Lignin separated as by-product in the lignocellulosic chemical processing is recognized as an important component of polymer systems. The presence of sterically hindered phenolic hydroxyl groups in the lignin macromolecule opens the possibility of its application as antioxidant for composites, e.g. polyurethanes (PU), which are considered as one of the most versatile polymeric materials. In the present work, the object of investigations was lignin obtained as a product, so-called BIOLIGNIN™, of wheat straw organosolv processing for pulp and fuel ethanol production (CIMV pilot plant, France). However, heterogeneity of the lignin obtained negatively influences its applicability that can be overcome by fractionation. Three soluble fractions were isolated from CIMV lignin by a sequential extraction with dichloromethane (A fraction), methanol (B fraction) and mixture of both the solvents (C fraction) and characterized in terms of their composition, functionality and structure using analytical pyrolysis (Py-GC/MS), 31P NMR and Size Exclusion Chromatography (SEC) methods. Antioxidant properties of BIOLIGNIN™ fractions were assessed in the tests with free radicals ABTS+ and DPPH. Application of Py-GC/MS for characterization of the fractions opened an opportunity to found some novel “structure–activity” correlations needed for understanding and tuning of antioxidant properties of lignins. The antioxidant activity of the fractions under investigation was tested by their influence on thermo-oxidative destruction of prepared model PU films. The data of TGA method (oxidative conditions) clearly testified the antioxidant effect of all three fractions with the most prominent activity for C fraction. The shifting of the exothermal maxima connected with oxidizing of volatile products of PU destruction to the higher temperature region by 20–30 K and 30–40 K was registered.
    16 kDa Heat Shock Protein from Heat-Inactivated Mycobacterium tuberculosis Is a Homodimer – Suitability for Diagnostic Applications with Specific Llama VHH Monoclonals
    Srivastava, S.K. ; Ruigrok, V.J.B. ; Thompson, N.J. ; Trilling, A.K. ; Heck, A.J.R. ; Rijn, C.J.M. van; Beekwilder, M.J. ; Jongsma, M.A. - \ 2013
    PLoS ONE 8 (2013)5. - ISSN 1932-6203
    hiv-associated tuberculosis - immunological diagnosis - antibody fragments - mass-spectrometry - skin-test - antigen - complexes - responses - peptides - epitopes
    Background: The 16 kDa heat shock protein (HSP) is an immuno-dominant antigen, used in diagnosis of infectious Mycobacterium tuberculosis (M.tb.) causing tuberculosis (TB). Its use in serum-based diagnostics is limited, but for the direct identification of M.tb. bacteria in sputum or cultures it may represent a useful tool. Recently, a broad set of twelve 16 kDa specific heavy chain llama antibodies (VHH) has been isolated, and their utility for diagnostic applications was explored. Methodology/Principal Findings: To identify the epitopes recognized by the nine (randomly selected from a set of twelve 16 kDa specific VHH antibodies) distinct VHH antibodies, 14 overlapping linear epitopes (each 20 amino acid long) were characterized using direct and sandwich ELISA techniques. Seven out of 14 epitopes were recognized by 8 out of 9 VHH antibodies. The two highest affinity binders B-F10 and A-23 were found to bind distinct epitopes. Sandwich ELISA and SPR experiments showed that only B-F10 was suitable as secondary antibody with both B-F10 and A-23 as anchoring antibodies. To explain this behavior, the epitopes were matched to the putative 3D structure model. Electrospray ionization time-of-flight mass spectrometry and size exclusion chromatography were used to determine the higher order conformation. A homodimer model best explained the differential immunological reactivity of A-23 and B-F10 against heat-treated M.tb. lysates. Conclusions/Significance: The concentrations of secreted antigens of M.tb. in sputum are too low for immunological detection and existing kits are only used for identifying M.tb. in cultures. Here we describe how specific combinations of VHH domains could be used to detect the intracellular HSP antigen. Linked to methods of pre-concentrating M.tb. cells prior to lysis, HSP detection may enable the development of protein-based diagnostics of sputum samples and earlier diagnosis of diseases.
    Discovery of T cell epitopes implementing HLA-peptidomics into a reverse immunology approach
    Hombrink, P. ; Hassan, C. ; Kester, M.G.D. ; Ru, A.H. ; Bergen, C.A.M. ; Nijveen, H. ; Drijfhout, J.W. ; Falkenburg, J.H.F. ; Heemskerk, M.H.M. ; Veelen, P.A. van - \ 2013
    The Journal of Immunology 190 (2013)8. - ISSN 0022-1767 - p. 3869 - 3877.
    minor histocompatibility antigens - versus-host-disease - restricted tissue distribution - identification - peptides - leukemia - gene - immunotherapy - lymphocytes - complexes
    T cell recognition of minor histocompatibility Ags (MiHA) plays an important role in the graft-versus-tumor effect of allogeneic stem cell transplantation. Selective infusion of T cells reactive for hematopoiesis-restricted MiHA presented in the context of HLA class I or II molecules may help to separate the graft-versus-tumor effects from graft-versus-host disease effects after allogeneic stem cell transplantation. Over the years, increasing numbers of MiHA have been identified by forward immunology approaches, and the relevance of these MiHA has been illustrated by correlation with clinical outcome. As the tissue distribution of MiHA affects the clinical outcome of T cell responses against these Ags, it would be beneficial to identify additional predefined MiHA that are exclusively expressed on hematopoietic cells. Therefore, several reverse immunology approaches have been explored for the prediction of MiHA. Thus far, these approaches frequently resulted in the identification of T cells directed against epitopes that are not naturally processed and presented. In this study we established a method for the identification of biologically relevant MiHA, implementing mass spectrometry–based HLA-peptidomics into a reverse immunology approach. For this purpose, HLA class I binding peptides were eluted from transformed B cells, analyzed by mass spectrometry, and matched with a database dedicated to identifying polymorphic peptides. This process resulted in a set of 40 MiHA candidates that were evaluated in multiple selection steps. The identification of LB-NISCH-1A demonstrated the technical feasibility of our approach. On the basis of these results, we present an approach that can be of value for the efficient identification of MiHA or other T cell epitopes.
    Controlled mixing of lanthanide(III) ions in coacervate
    Wang, J. ; Velders, A.H. ; Gianolio, E. ; Aime, S. ; Vergeldt, F.J. ; As, H. van; Yan Yun, ; Drechsler, M. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2013
    Chemical Communications 49 (2013)36. - ISSN 1359-7345 - p. 3736 - 3738.
    mri contrast agents - coordination polymers - nanoparticles - luminescent - complexes - ligand - assemblies - stability - sensors - design
    This article presents a facile strategy to combine Eu3+ and Gd3+ ions into coacervate core micelles in a controlled way with a statistical distribution of the ions. Consequently, the formed micelles show a high tunability between luminescence and relaxivity. These highly stable micelles present great potential for new materials, e.g. as bimodal imaging probes.
    The edible mushroom Laetiporus sulphureus as potential source of natural antioxidants
    Klaus, A. ; Kozarski, M. ; Niksic, M. ; Jakovljevic, D. ; Todorovic, N. ; Stefanoska, I. ; Griensven, L.J.L.D. van - \ 2013
    International Journal of Food Sciences and Nutrition 64 (2013)5. - ISSN 0963-7486 - p. 599 - 610.
    ganoderma-lucidum - feruloyl oligosaccharides - chemical-characterization - polysaccharide extracts - agaricus-bisporus - diabetic-rats - fruit-bodies - components - complexes - amylose
    Hot water extract (LN), partially purified polysaccharides (LP) and hot alkali extracted polysaccharides (LNa) obtained from fruiting bodies of the wild basidiomycete Laetiporus sulphureus were examined for their antioxidant activities. LNa was the most active antioxidant, as shown by the median effective concentrations (EC50 values) of 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity (0.5 +/- 0.2 mg/ml), reducing power (4.0 +/- 0.3 mg/ml) and ferrous ion-chelating ability (1.5 +/- 0.1 mg/ml). LNa contained the highest level of alpha-glucan (17.3 +/- 1.2 g/100 g dw), whereas LP contained mostly beta-glucans (66.8 +/- 1.3 g/100 g dw). The prevalent monosaccharide in all extracts was glucose. The EC50 values of all three antioxidant activity assays were well-correlated with the alpha-glucan content. Strong and significant correlation was found between total phenolic compounds and DPPH scavenging ability and also reducing power. The three investigated extracts (at concentrations of 0.1-10 mg/ml) were not toxic to HTR-8/SVneo trophoblast cell line.
    Direct synthesis of inverse hexagonally ordered diblock copolymer/polyoxometalate nanocomposite films
    Lunkenbein, T. ; Kamperman, M.M.G. ; Li, Z. ; Bojer, C. ; Drechsler, M. ; Forster, S. ; Wiesner, U. ; Muller, A. ; Breu, J. - \ 2012
    Journal of the American Chemical Society 134 (2012)30. - ISSN 0002-7863 - p. 12685 - 12692.
    surfactant-encapsulated polyoxometalate - block-copolymer surfactants - transition-metal oxides - lyotropic phases - catalysis - nanoparticles - composites - complexes - chemistry - clusters
    Nanostructured inverse hexagonal polyoxometalate composite films were cast directly from solution using poly(butadiene-block-2-(dimethylamino)ethyl methacrylate) (PB-b-PDMAEMA) diblock copolymers as structure directing agents for phosphomolybdic acid (H(3)[PMo(12)O(40)], H(3)PMo). H(3)PMo units are selectively incorporated into the PDMAEMA domains due to electrostatic interactions between protonated PDMAEMA and PMo(3-) anions. Long solvophilic PB chains stabilized the PDMAEMA/H(3)PMo aggregates in solution and reliably prevented macrophase separation. The choice of solvent is crucial. It appears that all three components, both blocks of the diblock copolymer as well as H(3)PMo, have to be soluble in the same solvent which turned out to be tetrahydrofuran, THF. Evaporation induced self-assembly resulted in highly ordered inverse hexagonal nanocomposite films as observed from transmission electron microscopy and small-angle X-ray scattering. This one-pot synthesis may represent a generally applicable strategy for integrating polyoxometalates into functional architectures and devices.
    Coating of Single DNA Molecules by Genetically Engineered Protein Diblock Copolymers
    Hernandez Garcia, A. ; Werten, M.W.T. ; Cohen Stuart, M.A. ; Wolf, F.A. de; Vries, R.J. de - \ 2012
    Small 8 (2012). - ISSN 1613-6810 - p. 3491 - 3501.
    gene delivery - block-copolymer - plasmid dna - drug-delivery - condensation - complexes - length - efficiency - polyplexes - filaments
    Coating DNA is an effective way to modulate its physical properties and interactions. Current chemosynthetic polymers form DNA aggregates with random size and shape. In this study, monodisperse protein diblock copolymers are produced at high yield in recombinant yeast. They carry a large hydrophilic colloidal block (˜400 amino acids) linked to a short binding block (˜12 basic amino acids). It is demonstrated that these protein polymers complex single DNA molecules as highly stable nanorods, reminiscent of cylindrical viruses. It is proposed that inter- and intramolecular bridging of DNA molecules are prevented completely by the small size of the binding block attached to the large colloidal stability block. These protein diblocks serve as a scaffold that can be tuned for application in DNA-based nanotechnology.
    A silica sol-gel design strategy for nanostructured metallic materials
    Warren, S.C. ; Perkins, M.R. ; Adams, A.M. ; Kamperman, M.M.G. - \ 2012
    Nature Materials 11 (2012)5. - ISSN 1476-1122 - p. 460 - 467.
    single-source precursors - electrical-properties - transparent conductors - oxygen reduction - thin-films - fuel-cells - complexes - oxide - fabrication - electrodes
    Batteries, fuel cells and solar cells, among many other high-current-density devices, could benefit from the precise meso- to macroscopic structure control afforded by the silica sol–gel process. The porous materials made by silica sol–gel chemistry are typically insulators, however, which has restricted their application. Here we present a simple, yet highly versatile silica sol–gel process built around a multifunctional sol–gel precursor that is derived from the following: amino acids, hydroxy acids or peptides; a silicon alkoxide; and a metal acetate. This approach allows a wide range of biological functionalities and metals—including noble metals—to be combined into a library of sol–gel materials with a high degree of control over composition and structure. We demonstrate that the sol–gel process based on these precursors is compatible with block-copolymer self-assembly, colloidal crystal templating and the Stöber process. As a result of the exceptionally high metal content, these materials can be thermally processed to make porous nanocomposites with metallic percolation networks that have an electrical conductivity of over 1,000¿S¿cm-1. This improves the electrical conductivity of porous silica sol–gel nanocomposites by three orders of magnitude over existing approaches, opening applications to high-current-density devices.
    Direct measurement of the strength of single ionic bonds between hydrated charges
    Spruijt, E. ; Berg, S.A. van den; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2012
    ACS Nano 6 (2012)6. - ISSN 1936-0851 - p. 5297 - 5303.
    molecule force spectroscopy - microscopy - afm - proteins - dna - complexes - chromatin - brushes - chains
    The strength of ionic bonds is essentially unknown, despite their widespread occurrence in natural and man-made assemblies. Here, we use single-molecule force spectroscopy to measure their strength directly. We disrupt a complex between two oppositely charged polyelectrolyte chains and find two modes of rupture: one ionic bond at a time, or cooperative rupture of many bonds at once. For both modes, disruption of the ionic bonds can be described quantitatively as an activated process. The height of the energy barrier is not only lowered by added salt, but also by the applied force. We extract unperturbed ionic bond lifetimes that range from milliseconds for single ionic bonds at high salt concentration to tens of years for small complexes of five ionic bonds at low salt concentration.
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