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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    Understanding functionality of sucrose in cake for reformulation purposes
    Sman, R.G.M. van der; Renzetti, S. - \ 2020
    Critical Reviews in Food Science and Nutrition (2020). - ISSN 1040-8398 - p. 1 - 17.
    Cake - ingredient functionality - state diagram - sugar replacement - thermodynamics

    We review the functionality of sucrose during the manufacture of cakes from the perspective of sugar replacement. Besides providing sweetness, sucrose has important functionalities concerning structure formation. These functionalities also need to be mimicked in reformulated cakes. First, we review the hypotheses, concerning the development of structure and texture of cakes during manufacturing, which are conveniently summarized in a qualitative way using the Complex Dispersed Systems methodology. Subsequently, we represent the changes of the state of the cake during manufacturing in a supplemented state diagram, which indicates the important phase transitions occurring during baking. From the analysis, we have learned that sucrose act both as a plasticizer and as a humectant, modifying the phase transitions of biopolymers, dough viscosity, and water activity. If sugar replacers exactly mimick this behavior of sucrose, similar textures in reformulated cakes can be obtained. Physical theories exist for characterizing the plasticizing and hygroscopic behavior of sugars and their replacers. We have shown that the starch gelatinization and egg white denaturation can be predicted by the volumetric density of hydrogen bonds present in the solvent, consisting of water, sugar or its replacers, such as polyols or amino-acids.

    Modeling food matrix effects on chemical reactivity : Challenges and perspectives
    Capuano, Edoardo ; Oliviero, Teresa ; Boekel, Martinus A.J.S. van - \ 2018
    Critical Reviews in Food Science and Nutrition 58 (2018)16. - ISSN 1040-8398 - p. 2814 - 2828.
    activity coefficients - fingerprinting - Food matrix - kinetics - modeling - thermodynamics

    The same chemical reaction may be different in terms of its position of the equilibrium (i.e., thermodynamics) and its kinetics when studied in different foods. The diversity in the chemical composition of food and in its structural organization at macro-, meso-, and microscopic levels, that is, the food matrix, is responsible for this difference. In this viewpoint paper, the multiple, and interconnected ways the food matrix can affect chemical reactivity are summarized. Moreover, mechanistic and empirical approaches to explain and predict the effect of food matrix on chemical reactivity are described. Mechanistic models aim to quantify the effect of food matrix based on a detailed understanding of the chemical and physical phenomena occurring in food. Their applicability is limited at the moment to very simple food systems. Empirical modeling based on machine learning combined with data-mining techniques may represent an alternative, useful option to predict the effect of the food matrix on chemical reactivity and to identify chemical and physical properties to be further tested. In such a way the mechanistic understanding of the effect of the food matrix on chemical reactions can be improved.

    Exergy analysis in industrial food processing
    Zisopoulos, F.K. - \ 2016
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Atze Jan van der Goot. - Wageningen : Wageningen University - ISBN 9789462578326 - 229
    thermodynamics - energy - physical properties - food production - drying - food industry - efficiency - thermodynamica - energie - fysische eigenschappen - voedselproductie - drogen - voedselindustrie - efficiëntie

    The sustainable provision of food on a global scale in the near future is a very serious challenge. This thesis focuses on the assessment and design of sustainable industrial food production chains and processes by using the concept of exergy which is an objective metric based on the first and second law of thermodynamics. Three case studies are presented, two on a chain level (industrial bread and mushroom production), and one on a process level (conceptual spray drying of a lactose solution). Furthermore, industrial food production chains are categorized as thermodynamic archetypes and general rules are derived for their sustainable design exergy-wise. Additional methodological aspects related to e.g. the impact of system boundaries, the allocation of exergy values to waste streams, and the influence of the selection of the environment of reference on the outcome of the analysis, are also discussed.

    Electrically excited liquid water : lessons from floating water bridge
    Wexler, A.D. - \ 2016
    Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): J. Woisetschläger; E.C. Fuchs. - Wageningen : Wageningen University - ISBN 9789462577039 - 223
    water - liquids - electric field - thermodynamics - bridges - equilibrium - disequilibrium - electrodynamics - nuclear magnetic resonance - neutron scattering - infrared spectroscopy - spectroscopy - gas chromatography - electrical conductivity - interferometry - spectral analysis - physics - water - vloeistoffen (liquids) - elektrisch veld - thermodynamica - bruggen - evenwicht - verstoord evenwicht - elektrodynamica - kernmagnetische resonantie - neutronenverstrooiing - infraroodspectroscopie - spectroscopie - gaschromatografie - elektrische geleidbaarheid - interferometrie - spectraalanalyse - fysica

    Water is essential to a healthy and secure world. Developing new technologies which can take full advantage of the unique attributes of water is important for meeting the ever increasing global demand while reducing the production footprint. Water exhibits unexpected departures in more than 70 physical and chemical properties compared to other molecular species of similar chemical composition. The principal cause for this behavior is ascribed to the large number of hydrogen bonds which form between neighboring water molecules. Hydrogen bonds are moderately strong in water and exhibit both electrostatic as well as covalent character. When examining the liquid state these interactions play a significantly role in moderating the interchange between dynamics and structure. In disordered materials such as a liquid there are three length scales of importance: 1) at the microscopic molecular level interactions dominate, 2) the macroscopic level where classical forces act upon the statistically isotropic medium, and 3) the mesoscopic level where heterogeneous interactions dominate through evolving transient structures each with unique dynamical behaviors. The mesoscale is important to most environmental and biological processes and is even more poorly understood than the liquid state in general. The aim of this thesis is to explore the extended molecular behavior of liquid water excited by strong electric field gradients.

    The floating water bridge belongs to a larger class of phenomena called electrohydrodynamic (EHD) liquid bridges. These self-suspending liquid catenaries can occur in a number of polar liquids provided the conductivity is low. They exhibit elevated temperatures and bidirectional flow patterns, as well as sub-Hz diameter oscillations. The flow behavior and dynamics of these bridges is complex but can be addressed by continuum level EHD theory. The polarizing effect of the electric field gradient accelerates the fluid tangentially along the surface resulting in a Taylor pump which supplies the bridge with liquid. The free hanging section is stable against gravity within a band of operational parameters whereby the electric field strength is sufficient confine fluid elements within the bridge. A standardized protocol for operating stable EHD bridges in multiple configurations is developed and presented. This is the primary tool used throughout the thesis and provides a macroscopic object for the experimental examination of how forces which typically only occur over a few nanometers in nature affect the organization of polar liquids, notably water. In order to examine the role that the electric field gradient plays in the observed molecular changes found in EHD bridges a simple point-plane electrode system was also employed.

    There are available a number of tools which provide complimentary information on chemical and physical processes occurring in the liquid state. A brief introduction is given on the interaction between electromagnetic waves and matter with respect to field theory and methods from atomic physics. The basis for interaction over different length scales is established. Electrochemical characterization includes the quantification and identification of the charge carrying species present, the relative proton concentration, and the complex dielectric response. The vibrational and rotational motion of molecules is measured with a combination of infrared emission spectroscopy and imaging and permits the detection of both the thermal bath and non-equilibrium molecular excited states. The local structure of the liquid matter contained in the bridge can be elucidated through the methods discussed here. X-rays provide information on the electron density whereas neutrons reveal nuclear positions. Together with isotope substitution a complete picture of the motionally averaged local structure of the liquid in the bridge can be recovered. QENS is a special case of inelastic scattering which permits the measurement of diffusion, relaxation, and other slow energy or mass transfer modes in materials using a time-of-flight spectrometer. This data compliments the NMR methods used herein specifically to probe the environment of protons in the system; and to provide clues about the strength of both intra- intermolecular coupling in the system. Very small perturbations in the optical properties of a liquid can be detected using interferometry; these ultimately reflect changes in the polarizability of the liquid which can arise from changes in physical properties. Raman scattering is an inelastic method which can probe changes to the polarizability of a liquid that reflect shifts in the local molecular environment and can be used to determine both local and non-local vibrational coupling.

    Magnetic resonance imaging was used to track the flow field present in the bridge without the use of tracer particles; revealing that the bridge has a layered structure, with distinct flow regimes lying one on top of the other. Investigation of the electrochemistry in the water bridge found that protons account for 87% of the charge transport in the bridge. Impedance spectroscopy and pH measurement corroborate the finding that a proton gradient forms across the entire system. The results from elastic neutron and X-ray scattering reveal that the static structure is unchanged within the given accuracy of the employed measurements. However, the systematic analysis of the data using a reverse Monte Carlo computer simulation revealed significant dynamical changes that are reliable above the limited instrument precision. The imposed electric field of an EHD bridge distorts the local Coulombic interactions between molecules altering the dielectric relaxation pathway so that it becomes more favorable for the absorbed energy to become trapped locally for a longer period of time. The electric field in the bridge system is not uniform. Strong field gradients are present which stimulate changes in the molecular polarizability, generating gradients of physical properties, and restricting the allowed rotational-vibrational relaxation transitions. These trends are comparable to those from ultrafast relaxation measurements where the vibrational lifetime of the OH stretch of HDO was found to be significantly shorter in the bridge than in the neat liquid. This absorbed energy, however, remained trapped in a local intermediate state longer in the bridge before being released as a thermal perturbation. The nuclear relaxation dynamics in a glycerol bridge showed similar behavior where the transverse and longitudinal magnetization lifetimes diverged from the expectation values given the systems temperature.

    From the experimental observations several features of electrically excited water appear. At the gross continuum level the operation of a floating water bridge results in the production of a charge imbalance between anolyte and catholyte. This is in part due to the enhanced proton mobility in the bridge. Protons no longer are confined to the hydrogen bond mediated Grotthuss mechanism but can travel even faster through a delocalized state. This means that charge can be pumped faster than it can be neutralized resulting in the observed electrochemical differences. The energy level of protons in the conduction channel is the difference between the ground and excited state levels observed as a non-thermal emission feature in the mid-infrared. The proton channel will be active over relatively short distances and will experience interruptions due to fluctuations in molecular position driven by local force gradients. These channels are localized and discontinuous providing the physical basis for the onset of mesoscale dynamic heterogeneity in the excited liquid. The picture begins to emerge whereby local trapping states and long-range cooperative coupling modes dynamically exchange energy. The energy exchange is far from equilibrium and supports multiple transfer mechanisms. At the mesoscale the excited state exhibits traits of a chaotic dynamical system and provides a varied energetic landscape whereby rotational-vibrational transition dipoles, nuclear spin states, and thermodynamic potentials, such as the configurational entropy, non-adiabatically – that is there is a pumping of heat in response to the induced fluctuating gradient fields. The transfer of perturbations from local to collective modes and vice versa requires that the chemical, thermal, and electromagnetic potentials present in the molecular milieu be linked to the entropy production.

    This early foray into the non-equilibrium dynamics and mesoscale organization of electrically excited liquid water opens an opportunity to develop technologies which better mimic nature. Taking biological systems as the exemplary standard by which to compare it is necessary to develop soft matter based technical systems which take advantage of the link between electric, magnetic, and thermal fields to drive chemical and physical processes with higher efficiency. Water, as well as other polar liquids, can be locally controlled so as to induce spatial variation in the chemical potential whereby one can imagine a reactor where disparate physical or chemical process can occur in close proximity without the need for rigid segregating structures. Furthermore, this level of control is dynamical such that the organization of the partitioning in the liquid can be changed in time so that the total energy requirement of the intended process is optimized. With such an approach it is conceivable that the size, complexity, and energetic costs of performing many industrial and municipal processes can be reduced. Rather than treating liquids as bulk fluids the opportunity presents itself to use the internal structure and dynamics of liquids to build fluid technologies.

    Self-assembled structures of PMAA-PMMA block copolymers: Synthesis, characterization, and self-consistent field computations
    Li, F. ; Schellekens, J. ; Bont, J.A.M. de; Peters, R. ; Overbeek, A. ; Leermakers, F.A.M. ; Tuinier, R. - \ 2015
    Macromolecules 48 (2015)4. - ISSN 0024-9297 - p. 1194 - 1203.
    controlled radical polymerization - laser-light scattering - emulsion polymerization - association behavior - aqueous-medium - micelles - surfactants - vesicles - thermodynamics - morphologies
    Block copolymers composed of methacrylic acid (MAA) and methyl methacrylate (MMA) blocks are interesting candidates for replacing surfactants in emulsion polymerization methods. Here the synthesis and experimental characterization of well-defined PMAA–PMMA block copolymers made via RAFT polymerization are reported. It is shown that these block copolymers self-organize in water into micellar spherical or cylindrical structures or into highly size disperse structures (probably vesicles) in aqueous salt solutions upon increasing the pH. The physical properties of the polymer dispersions depend on the self-organization morphology which is determined by the diblock copolymer PMAA and PMMA block lengths. The relation between diblock copolymer block lengths and the self-organized structures is rationalized using self-consistent field theory (SCFT). Theoretically predicted self-assembled structures of MAAx–MMAy block copolymers are compared with the results obtained from experiments. Size and morphology of the self-assembled structures are in good agreement with SCFT.
    Modelling the rheology of anisotropic particles adsorbed on a two-dimensional fluid interface
    Luo, A.M. ; Sagis, L.M.C. ; Oettinger, H.C. ; Michele, C. de; Ilg, P. - \ 2015
    Soft Matter 11 (2015). - ISSN 1744-683X - p. 4383 - 4395.
    complex fluids - capillary interactions - constitutive equation - general formalism - liquid-crystals - dynamics - thermodynamics - emulsions
    We present a general approach based on nonequilibrium thermodynamics for bridging the gap between a well-defined microscopic model and the macroscopic rheology of particle-stabilised interfaces. Our approach is illustrated by starting with a microscopic model of hard ellipsoids confined to a planar surface, which is intended to simply represent a particle-stabilised fluid-fluid interface. More complex microscopic models can be readily handled using the methods outlined in this paper. From the aforementioned microscopic starting point, we obtain the macroscopic, constitutive equations using a combination of systematic coarse-graining, computer experiments and Hamiltonian dynamics. Exemplary numerical solutions of the constitutive equations are given for a variety of experimentally relevant flow situations to explore the rheological behaviour of our model. In particular, we calculate the shear and dilatational moduli of the interface over a wide range of surface coverages, ranging from the dilute isotropic regime, to the concentrated nematic regime.
    General Laws and Centripetal Science
    Jagers Op Akkerhuis, G.A.J.M. - \ 2014
    European Review 22 (2014). - ISSN 1062-7987 - p. S113 - S144.
    lipid vesicles - evolution - thermodynamics - organization - systems - hierarchy - selection
    The large number of discoveries in the last few decades has caused a scientific crisis that is characterised by overspecialisation and compartmentalisation. To deal with this crisis, scientists look for integrating approaches, such as general laws and unifying theories. Representing what can be considered a general form law, the operator hierarchy is used here as a bridge between existing integrating approaches, including: a cosmic timeline, hierarchy and ontology, a periodic table of periodic tables, the unification of evolutionary processes, a general evolution concept, and general aspects of thermodynamics. At the end of the paper an inventory of unifying concepts is presented in the form of a cross table. The study ends with a discussion of major integrating principles in science.
    A possible simplification of the Goss-modified Abraham solvation equation
    Noort, P.C.M. van - \ 2013
    Chemosphere 93 (2013)9. - ISSN 0045-6535 - p. 1742 - 1746.
    partition-coefficients - organic-compounds - gas-phase - water - thermodynamics - temperature - equilibrium - descriptors - solutes - model
    Abraham solvation equations find widespread use in environmental chemistry and pharmaco-chemistry. Recently Goss proposed a modified Abraham solvation equation. For various partitioning processes, the present study investigates the consequences for the fit when the Abraham solvation parameter V is left out of this modified solvation equation. For air-organic solvent partition, the Abraham solvation parameter V can be omitted from the Goss-modified Abraham solvation equation without any loss of statistical quality. For air–water partitioning, organic biphasic system partitioning, as well as water-organic solvent partitioning, omitting the V parameter from the Goss-modified Abraham solvation equation leads to only a small deterioration of statistic quality.
    Bending rigidities of surfactant bilayers using self-consistent field theory
    Leermakers, F.A.M. - \ 2013
    Journal of Chemical Physics 138 (2013). - ISSN 0021-9606 - 11 p.
    interacting chain molecules - lipid-bilayers - curvature elasticity - statistical-theory - adsorption - membranes - size - thermodynamics - interface - relevance
    Self-consistent field (SCF) theory is used to find bending moduli of surfactant and lipid bilayers. Recently, we successfully applied low-memory search methods to solve the SCF equations. Using these we are now able to directly evaluate the Gaussian bending modulus for molecularly detailed models of bilayers by evaluating the excess Helmholtz energy of tensionless bilayers in a (part of the) Im3m cubic phase. The result prompted us to reconsider the protocol that has been used thus far to find the mean bending modulus k c and Gaussian bending modulus k¯. With respect to previous predictions, the value of k c is reduced by a factor of two and the Gaussian bending modulus is less negative and much closer to zero. In line with experimental data we now find that k¯can also become positive. In this paper we use the non-ionic surfactants series of the type C n E m for illustration.
    Normal stresses in surface shear experiments
    Sagis, L.M.C. - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 99 - 103.
    in-water emulsions - interfacial permeability - general formalism - bending rigidity - complex fluids - dynamics - viscoelasticity - thermodynamics - liquid/liquid - gas/liquid
    When viscoelastic bulk phases are sheared, the deformation of the sample induces not only shear stresses, but also normal stresses. This is a well known and well understood effect, that leads to phenomena such as rod climbing, when such phases are stirred with an overhead stirrer, or to die swell in extrusion. Viscoelastic interfaces share many commonalities with viscoelastic bulk phases, with respect to their response to deformations. There is however little experimental evidence that shear deformations of interfaces can induce in-plane normal stresses (not to be confused with stresses normal to the interface). Theoretical models for the stress-deformation behavior of complex fluid-fluid interfaces subjected to shear, predict the existence of in-plane normal stresses. In this paper we suggest methods to confirm the existence of such stresses experimentally.
    Distant residues mediate picomolar binding affinity of a protein cofactor
    Bollen, Y.J.M. ; Westphal, A.H. ; Lindhoud, S. ; Berkel, W.J.H. van; Mierlo, C.P.M. van - \ 2012
    Nature Communications 3 (2012). - ISSN 2041-1723
    azotobacter-vinelandii apoflavodoxin - hydrogen-exchange - ligand-binding - oxidized flavodoxin - energy landscape - nmr relaxation - dynamics - kinetics - thermodynamics - topology
    Numerous proteins require cofactors to be active. Computer simulations suggest that cooperative interaction networks achieve optimal cofactor binding. There is a need for the experimental identification of the residues crucial for stabilizing these networks and thus for cofactor binding. Here we investigate the electron transporter flavodoxin, which contains flavin mononucleotide as non-covalently bound cofactor. We show that after binding flavin mononucleotide with nanomolar affinity, the protein relaxes extremely slowly (time constant ~5 days) to an energetically more favourable state with picomolar-binding affinity. Rare small-scale openings of this state are revealed through H/D exchange of N(3)H of flavin. We find that H/D exchange can pinpoint amino acids that cause tight cofactor binding. These hitherto unknown residues are dispersed throughout the structure, and many are located distantly from the flavin and seem irrelevant to flavodoxin's function. Quantification of the thermodynamics of ligand binding is important for understanding, engineering, designing and evolving ligand-binding proteins
    Exergy landscapes: Exploration of second-law thinking towards sustainable landscape design
    Stremke, S. ; Dobbelsteen, A. van den; Koh, J. - \ 2011
    International Journal of Exergy 8 (2011)2. - ISSN 1742-8297 - p. 148 - 174.
    ecosystem development - built environment - energy - systems - thermodynamics - optimization - indicator - strategy - ecology - law
    Depletion of fossil fuels and climate change necessitate a transition to sustainable energy systems that make efficient use of renewable energy sources. During recent decades, the Second Law of Thermodynamics has helped to increase energy efficiencies. More recently, the disciplines of building engineering, architecture and urban planning have begun embracing this ‘second-law thinking’ in order to reduce energy consumption in the built environment. Second-law thinking, however, is not yet a part of spatial planning and landscape design. This is especially problematic because the concepts of exergy and entropy are imperative to sustainable development. This paper explores the Laws of Thermodynamics and related concepts in order to advance the planning and design of sustainable landscapes. The discussion in this paper is based on ‘research by design’ – a research approach that includes literature and case-study research, as well as the design of several sustainable energy landscapes in the Netherlands. From our studies, we conclude that second-law thinking should be embraced in spatial planning and landscape design practice. To facilitate this integration, we propose a number of exergy-conscious design principles, each one supporting sustainable energy transition.
    Nonlinear rheological models for structured interfaces
    Sagis, L.M.C. - \ 2010
    Physica A 389 (2010)10. - ISSN 0378-4371 - p. 1993 - 2006.
    thermodynamics - fluids
    The GENERIC formalism is a formulation of nonequilibrium thermodynamics ideally suited to develop nonlinear constitutive equations for the stress–deformation behavior of complex interfaces. Here we develop a GENERIC model for multiphase systems with interfaces displaying nonlinear viscoelastic stress–deformation behavior. The link of this behavior to the microstructure of the interface is described by including a scalar and a tensorial structural variable in the set of independent surface variables. We derive an expression for the surface stress tensor in terms of these structural variables, and a set of general nonlinear time evolution equations for these variables, coupling them to the deformation field. We use these general equations to develop a number of specific models, valid for application near equilibrium, or valid for application far beyond equilibrium.
    Interfacial tension between a complex coacervate phase and its coexisting aqueous phase
    Spruijt, E. ; Sprakel, J.H.B. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2010
    Soft Matter 6 (2010). - ISSN 1744-683X - p. 172 - 178.
    atomic-force microscope - microencapsulation - thermodynamics - micelles - polymer - system
    Complex coacervation is the associative phase separation in a solution of positively and negatively charged macroions. Despite the widespread use of coacervation in e.g. micellar assemblies (complex coacervate core micelles), drug carriers and thin films, there is virtually no experimental data on the interfacial tension between such coacervate phases (polyelectrolyte complexes) and their coexisting aqueous phases or on the influence of salt thereon. In this paper we use colloidal probe AFM measurements of capillary adhesion forces to obtain the interfacial tension between a complex coacervate phase of two polyelectrolytes with high charge density and its coexisting aqueous phase. We find that the interfacial tension is of order 100 µN/m, decreases with increasing salt concentration and vanishes at the critical point. Interestingly, we find that the critical scaling exponent for the interfacial tension found in segregative demixing also applies here
    Expanding the exergy concept to the urban water cycle
    Leduc, W.R.W.A. ; Agudelo Vera, C.M. ; Rovers, R. ; Mels, A.R. - \ 2009
    In: SASBE 2009 Book of Abstracts of the 3rd CIB International Conference on Smart and Sustainable Built Environments, Delft, The Netherlands, 15-19 June 2009. - Delft, NL : Delft University of Technology - ISBN 9789052693729 - p. 101 - 101.
    waterbeheer - water - energiebronnen - watergebruik - stedelijke gebieden - duurzaamheid (sustainability) - energiebehoud - thermodynamica - steden - stedelijke planning - hydrologische cyclus - water management - water - energy sources - water use - urban areas - sustainability - energy conservation - thermodynamics - towns - urban planning - hydrological cycle
    Natural energy and water cycles are modified by metabolic profiles of the cities. The metabolic profile varies with the local resource availability and the level of technological development. To cope with this complexity, the concept of Exergy, based on Thermodynamic laws, and defined as the non-used fraction of energy, has been used to understand the energy cycle in the built environment. This will lead to new approaches towards urban planning and better resources use. This paper aims to find out if the exergy concept can be expanded to the water cycle defined as the use of the non-used water(-fraction). This way the cycle can be optimized and closed at a high efficiency level. In order to achieve this, we want to study to what extend the energy and water cycles are comparable, and how they can learn from each other in order to optimize their management.
    Impact of ligand protonation on eigen-type metal complexation kinetics in aqueous systems
    Leeuwen, H.P. van; Town, R.M. ; Buffle, J. - \ 2007
    The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 111 (2007)11. - ISSN 1089-5639 - p. 2115 - 2121.
    deposition potential sscp - stripping chronopotentiometry - dissociation kinetics - speciation analysis - planar diffusion - lability - association - cadmium - ions - thermodynamics
    The impact of ligand protonation on metal speciation dynamics is quantitatively described. Starting from the usual situation for metal complex formation reactions in aqueous systems, i.e., exchange of water for the ligand in the inner coordination sphere as the rate-determining step (Eigen mechanism), expressions are derived for the lability of metal complexes with protonated and unprotonated ligand species being involved in formation of the precursor outer-sphere complex. A differentiated approach is developed whereby the contributions from all outer-sphere complexes are included in the rate of complex formation, to an extent weighted by their respective stabilities. The stability of the ion pair type outer-sphere complex is given particular attention, especially for the case of multidentate ligands containing several charged sites. It turns out that in such cases, the effective ligand charge can be considerably different from the formal charge. The lability of Cd(II) complexes with 1,2-diaminoethane-N,N'-diethanoic acid at a microelectrode is reasonably well predicted by the new approach.
    Tertiary structure in 7.9 M guanidinium chloride: the role of Glu-53 and Asp-287 in Pyrococcus furiosus endo-beta-1,3-glucanase
    Chiaraluce, R. ; Florio, R. ; Angelaccio, S. ; Gianese, G. ; Lieshout, J.F.T. van; Oost, J. van der; Consalvi, V. - \ 2007
    FEBS Journal 274 (2007). - ISSN 1742-464X - p. 6167 - 6179.
    denatured state - staphylococcal nuclease - protein stability - unfolded state - thermophilic proteins - residual structure - m-values - intermediate - thermodynamics - salt
    The thermodynamic stability of family 16 endo-ß-1,3-glucanase (EC 3.2.1.39) from the hyperthermophilic archaeon Pyrococcus furiosus is decreased upon single (D287A, E53A) and double (E53A/D287A) mutation of Asp287 and Glu53. In accordance with the homology model prediction, both carboxylic acids are involved in the composition of a calcium binding site, as shown by titration of the wild-type and the variant proteins with a chromophoric chelator. The present study shows that, in P. furiosus, endo-ß-1,3-glucanase residues Glu53 and Asp287 also make up a calcium binding site in 7.9 m guanidinium chloride. The persistence of tertiary structure in 7.9 m guanidinium chloride, a feature of the wild-type enzyme, is observed also for the three variant proteins. The ¿GH2O values relative to the guanidinium chloride-induced equilibrium unfolding of the three variants are approximatelty 50% lower than that of the wild-type. The destabilizing effect of the combined mutations of the double mutant is non-additive, with an energy of interaction of 24.2 kJ·mol¿1, suggesting a communication between the two mutated residues. The decrease in the thermodynamic stability of D287A, E53A and E53A/D287A is contained almost exclusively in the m-values, a parameter which reflects the solvent-exposed surface area upon unfolding. The decrease in m-value suggests that the substitution with alanine of two evenly charged repulsive side chains induces a stabilization of the non-native state in 7.9 m guanidinium chloride comparable to that induced by the presence of calcium on the wild-type. These results suggest that the stabilization of a compact non-native state may be a strategy for P. furiosus endo-ß-1,3-glucanase to thrive under adverse environmental conditions.
    Direct measurement of depletion and hydrodynamic forces in solutions of a reversible supramolecular polymer
    Knoben, W. ; Besseling, N.A.M. ; Cohen Stuart, M.A. - \ 2007
    Langmuir 23 (2007)11. - ISSN 0743-7463 - p. 6095 - 6105.
    equilibrium polymers - chain stoppers - surface forces - particles - dispersions - microscope - stability - thermodynamics - suspensions - dynamics
    In this paper, the investigation of surface forces in semidilute solutions of a nonadsorbing hydrogen-bonded reversible supramolecular polymer is described. Colloidal probe atomic force microscopy was used for direct measurement of depletion forces. Hydrodynamic drag on the AFM cantilever with the colloidal probe was measured both far away from and close to the planar substrate surface. The results indicate that the presence of the depletion layer causes slip at the surfaces with a large apparent slip length. Our analysis explains how the presence of slip enables the measurement of (relatively weak) depletion forces in solutions with a high viscosity by significantly reducing the hydrodynamic forces. The range and magnitude of the measured depletion forces are qualitatively in agreement with previous experiments and theoretical predictions. Due to the relatively large experimental error, no quantitative conclusions can be drawn. Depletion-induced phase separation of suspensions of stearylated silica particles was also observed. Phase separation becomes more pronounced with increasing polymer concentration. --------------------------------------------------------------------------------
    Opposing effects of cation binding and hydration on the bending rigidity of anionic lipid bilayers
    Claessens, M.M.A.E. ; Leermakers, F.A.M. ; Hoekstra, F.A. ; Cohen Stuart, M.A. - \ 2007
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 111 (2007)25. - ISSN 1520-6106 - p. 7127 - 7132.
    vesicles - adsorption - membranes - phases - thermodynamics - curvature - liposomes - dilute - salt
    We correlate the molecularly realistic self-consistent field predictions for the mean bending modulus kc of charged lipid vesicles with experimental observations of the size R of corresponding vesicles that are produced by the freeze-thaw method. We elaborate on the Ansatz that the bending modulus is related to the membrane persistence length and that this length scale sets the radius of the vesicles. Alkali cations have a remarkable effect on the mean bending modulus and thus on the equilibrium radius of negatively charged entropically stabilized dioleoylphosphatidylglycerol (DOPG) vesicles. Where cation hydration typically results in thicker and thus stiffer membranes, specific adsorption to the bilayer surface results in a decrease of the surface charge density and the thickness of the membrane-associated electric double layer. As a result of these opposing effects on kc and R, the largest DOPG vesicles are found in the presence of K+, which combines an intermediate hydration enthalpy and PG-binding affinity.
    Interfacial Transport Phenomena (Second edition)
    Slattery, J.C. ; Sagis, L.M.C. ; Oh, E.S. - \ 2007
    New York (US) : Springer - ISBN 9780387384382 - 830
    engineering - mechanica - materialen - thermodynamica - oppervlakten - grensvlak - engineering - mechanics - materials - thermodynamics - surfaces - interface
    Gives a presentation of transport phenomena or continuum mechanics focused on momentum, energy, and mass transfer at interfaces. This work includes a discussion of transport phenomena at common lines or three-phase lines of contact, and a theory for the extension of continuum mechanics to the nanoscale region immediately adjacent to the interface.
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