Cosima Stubenrauch

Universität Stuttgart, Stuttgart, Baden-Württemberg, Germany

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Publications (109)393.02 Total impact

  • Anne K Steudle · Bettina M Nestl · Bernhard Hauer · Cosima Stubenrauch
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    ABSTRACT: The paper at hand deals with biocatalysis in bicontinuous microemulsions. The latter consist of a dynamic network of oil and water domains separated by a monolayer of surfactant molecules, i.e. the interfacial layer. A microemulsion with the composition buffer - n-octane - nonionic surfactant was tested as reaction medium for an enzyme-catalysed reaction with a focus on the conversion of hydrophobic substrates, which are difficult to convert in aqueous buffer solutions. For the study at hand, we chose to investigate the activity of the squalene-hopene cyclase from Alicyclobacillus acidocaldarius (AacSHC) towards its natural substrate squalene in bicontinuous microemulsions. Firstly, the study revealed that the activity of AacSHC depends linearly on the enzyme concentration. Secondly, a hyperbolic curve was found for the dependence of the activity on the substrate concentration and a saturation of the AacSHC at substrate concentrations above 20mM was observed. Thirdly, the composition of the interfacial layer was found to have no significant influence on the activity or on the conformation of AacSHC. Surprisingly and unexpectedly, a distinctly enhanced selectivity towards hopene was discovered in the microemulsion. To conclude, bicontinuous microemulsions were found to be a suitable reaction medium for biocatalytic reactions with the enzyme AacSHC. Copyright © 2015 Elsevier B.V. All rights reserved.
    Colloids and surfaces B: Biointerfaces 08/2015; 135:735-741. DOI:10.1016/j.colsurfb.2015.08.034 · 4.15 Impact Factor
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    ABSTRACT: In our previous work we were able to prove that gelled bicontinuous microemulsions are a novel type of orthogonal self-assembled system. The study at hand aims at complementing our previous work by answering the question of whether gelled lyotropic liquid crystals are also orthogonal self-assembled systems. For this purpose we studied the same system, namely, water-n-decane/12-hydroxyoctadecanoic acid (12-HOA)-n-decyl tetraoxyethylene glycol ether (C10E4). The phase boundaries of the nongelled and the gelled lyotropic liquid crystals were determined visually and with (2)H NMR spectroscopy. Oscillating shear measurements revealed that the absolute values of the storage and loss moduli of the gelled liquid crystalline (LC) phases do not differ very much from those of the binary organogel. While both the phase behavior and the rheological properties of the LC phases support the hypothesis that gelled lyotropic liquid crystals are orthogonal self-assembled systems, freeze-fracture electron microscopy (FFEM) seems to indicate an influence of the gel network on the structure of the Lα phase and vice versa.
    Langmuir 07/2015; 31(31). DOI:10.1021/acs.langmuir.5b01992 · 4.46 Impact Factor
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    Mireia Subinya · Anne K Steudle · Tomasz P Jurkowski · Cosima Stubenrauch
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    ABSTRACT: The paper at hand deals with the influence of the pH-value on the conformation and activity of the lipase B from Candida antarctica (CalB) which is incorporated in a bicontinuous microemulsion. The microemulsion used for this purpose consists of water/NaCl, n-octane, and the non-ionic surfactant penthaethylene glycol monodecylether (C10E5). The conformational study clearly shows (1) that CalB molecules are partitioned between the interfacial monolayer and the water domains and (2) that the pH-value of the microemulsion's water domains strongly influences the conformation of CalB at the interfacial monolayer. From these observations we conclude that there is a continuous exchange between the CalB molecules, which are located at the interfacial monolayer and those which are located in the water domains of the microemulsion. This exchange strongly influences the CalB conformation in both regions. In addition to the conformation, we also studied the catalytic activity of CalB. The catalytic measurements revealed a bell-shaped dependence between the CalB activity and the pH-value. The maximum catalytic activity of CalB in bicontinuous microemulsions was observed at pH=5.5. At this pH we observed the highest amount of α-helix conformation of the CalB molecules that are located at the interfacial monolayer, which, in turn, allows connecting the activity with the conformation. Copyright © 2015 Elsevier B.V. All rights reserved.
    Colloids and surfaces B: Biointerfaces 04/2015; 131. DOI:10.1016/j.colsurfb.2015.04.041 · 4.15 Impact Factor
  • Michaela Laupheimer · Natalie Preisig · Cosima Stubenrauch
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    ABSTRACT: The paper at hand deals with the properties of a particular organogel, namely the binary system n-decane/12-hydroxyoctadecanoic acid (12-HOA). To provide a complete characterisation we firstly determined the sol–gel transition temperatures as a function of the gelator concentration with DSC and rheometry. Moreover, we calculated thermodynamic parameters from the DSC measurements such as the sol–gel transition enthalpy. Secondly, we studied the rheological properties with an oscillating shear rheometer. Thirdly, we investigated the structure of the gel network and of the gelator fibers. For this purpose, we carried out SANS measurements from which we obtained structural parameters such as the mean radius of the fibers and the mean thickness of the fiber nodes, but also the mole fraction of gelator involved in building up the gelator network. Additionally we present electron microscopy (EM) pictures of a 12-HOA gel prepared with the freeze-fracture method (FFEM). FFEM allows imaging a sample in its original state due to cryofixation while other EM methods require modifications like evaporation of the gel solvent. From our pictures we were able to determine the sense of the helical twist of the gelator fibers and we also observed a layered fine structure, which – to the best of our knowledge – has not been seen in EM pictures of 12-HOA gels yet. Our study allows an in-depth understanding of the gelator network in the model system n-decane/12-HOA. Moreover, our results are in perfect agreement with all data published for binary organogels consisting of an oil and 12-HOA, which, in turn, will help to understand many of the unanswered questions that still exist in relation to gels.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 03/2015; 469. DOI:10.1016/j.colsurfa.2015.01.039 · 2.75 Impact Factor
  • Ramona Yvette Genevieve König · Cosima Stubenrauch
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    ABSTRACT: This study deals with the synthesis of Pt nanoparticles via oil-inwater microemulsions formulated with the technical grade surfactant BIODAC (R) 510. For this purpose we studied the influence of the Platinum precursor dimethyl(cyclooctadiene) platinum (Pt(COD) Me-2) on the phase behavior of the base microemulsion. It was found that the addition of Pt(COD) Me-2 has nearly no effect on the phase boundaries even at relatively high concentrations. Small angle X-ray scattering data confirmed that the addition of the metal organyl also does not influence the size of the microemulsion droplets. According to transmission electron microscopy (TEM) the size of the resulting platinum nanoparticles is independent on the amount of Pt(COD) Me-2 in the templating microemulsion. This result was rather surprising since it indicates that a greater amount of precursor in the o/w-microemulsion leads to more rather than to larger nanoparticles.
    Tenside Surfactants Detergents 03/2015; 52(2):106-112. DOI:10.3139/113.110354 · 0.74 Impact Factor
  • Aggeliki Quell · Jonas Elsing · Wiebke Drenckhan · Cosima Stubenrauch
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    ABSTRACT: We have developed a templating route for the synthesis of monodisperse and highly ordered polystyrene foams. The route is based on the generation of monodisperse templates, namely of foamed emulsions and emulsions, respectively, via microfluidic techniques. The polymerization of the templates leads to polystyrene foams with controllable pore size, pore size distribution and connectivity and thus opens up a new arena for the synthesis of tailor‐made polymer foams. Microfluidic techniques can be used to generate highly monodisperse polystyrene foams with periodic pore organization. For this purpose, monodisperse foamed emulsions and emulsions, respectively, are to be used as templates. The polymerization of the templates leads to tailor‐made polystyrene foams with controllable pore size, pore size distribution, and connectivity.
    Advanced Engineering Materials 03/2015; 17(5). DOI:10.1002/adem.201500040 · 1.76 Impact Factor
  • Christiaan Ridings · Cosima Stubenrauch · Gunther G. Andersson
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    ABSTRACT: The effect of sodium halides on the surface structure of foam films stabilized by the nonionic surfactant dodecyldimethyl phosphine oxide (C12DMPO) was investigated using a combination of neutral impact collision ion scattering spectroscopy and thin film pressure balance. The former technique was used to determine the concentration depth profiles of the elements at the liquid surface, while the latter technique was used to provide film thickness information. An excess of iodide was found at the liquid surface in the presence of C12DMPO. Upon formation of the foam film, iodide was shifting closer to the surface showing that the foam film surface is more negatively charged than the surface of the respective bulk liquid. In contrast, an excess of chloride was found at the surface only in the presence of the surfactant and formation of a foam film. The iodide-containing films were slightly thicker than the chloride-containing films, which is concluded to be due to the increased surface charge of the iodide-containing films.
    The Journal of Physical Chemistry C 01/2015; 119(1):441-448. DOI:10.1021/jp510258r · 4.77 Impact Factor
  • Anne K. Steudle · Mireia Subinya · Bettina M. Nestl · Cosima Stubenrauch
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    ABSTRACT: Selective enzyme-catalysed biotransformations offer great potential in organic chemistry. However, special requirements are needed to achieve optimum enzyme activity and stability. A bicontinuous microemulsion is proposed as reaction medium because of its large connected interface between oil and water domains at which a lipase can adsorb and convert substrates in the oil phase of the microemulsion. Herein, a microemulsion consisting of buffer–n-octane–nonionic surfactant CiEj was used to investigate the key factors that determine hydrolyses of p-nitrophenyl esters catalysed by the lipase B from Candida antarctica (CalB). The highest CalB activity was found around 44 °C in the absence of NaCl and substrates with larger alkyl chains were better hydrolysed than their short-chained homologues. The CalB activity was determined using two different co-surfactants, namely the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and the sugar surfactant decyl β-D-glucopyranoside (β-C10G1). The results show the CalB activity as linear function of both enzyme and substrate concentration with an enhanced activity when the sugar surfactant is used as co-surfactant.
    Chemistry - A European Journal 12/2014; 21(6). DOI:10.1002/chem.201405335 · 5.73 Impact Factor
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    Kathrin Schellmann · Natalie Preisig · Per Claesson · Cosima Stubenrauch
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    ABSTRACT: The critical micelle concentration (cmc), the surface excess (Γ), as well as the micelle aggregation number (m) of the surfactant dodecyldimethylamine oxide (C12DMAO) have been reported to strongly depend on the pH-value of the aqueous surfactant solution. At high ionic strength, the cmc displays a minimum, while both Γ and m have a maximum at a pH-value close to the pKa of the surfactant. These experimental observations have been explained as being due to specific hydrogen bonds between the head groups, which are formed once the surfactant is partly or fully protonated. This investigation addresses the question of whether the pH also affects the foaming properties of C12DMAO solutions. To answer this question we measured the foamability and the foam stability of C12DMAO solutions at a fixed C12DMAO concentration of 5 cmc for five different pH-values, namely pH = 2, 3, 5, 8, and 10. We found that the foamability is hardly affected by the pH-value, while the foam stability strongly depends on the pH. As is the case for the above mentioned properties, the foam stability also displays an extremum in the studied pH-range, namely a maximum at pH = 5. We discuss our results in terms of the hydrogen bond hypothesis and show that this hypothesis indeed is in line with the observed trend for the foam stability. Moreover, we discuss that hydrogen bond formation may rationalize how the molecular structure of a surfactant affects foam stability.
    Soft Matter 11/2014; 11(3). DOI:10.1039/c4sm02476a · 4.03 Impact Factor
  • Michaela Laupheimer · Thomas Sottmann · Ralf Schweins · Cosima Stubenrauch
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    ABSTRACT: An orthogonal self-assembled system consists of different structures which coexist independently. Furthermore, the characteristic properties of the respective “base systems”, i.e. of the systems which contain only one of the structures, are retained in the orthogonal self-assembled system. We have identified gelled bicontinuous microemulsions as orthogonal self-assembled systems and reported in a preceding paper (Soft Matter, 2013, 9, 3661) that their phase behaviour and rheological properties are in perfect agreement with those of the two base systems, namely a non-gelled bicontinuous microemulsion and a binary gel. In the paper at hand we present the results of structural investigations. With FT-PGSE 1H-NMR measurements we verified the bicontinuity of our gelled model system H2O–n-decane/12-hydroxyoctadecanoic acid (12-HOA)–tetraethylene glycol monodecyl ether (C10E4) at appropriate temperatures. Apart from that, we proved the coexistence of the bicontinuous microemulsion domains with the gelator network in a small angle neutron scattering (SANS) study. A qualitative comparison between the SANS data of the gelled bicontinuous microemulsion and those of its base systems reveals that the characteristic scattering features of both base systems are present. Moreover, we were able to quantitatively describe and interpret the SANS data, yielding at the same time the structural parameters of the bicontinuous microemulsion and the gelator network.
    Soft Matter 10/2014; 10(43). DOI:10.1039/C4SM01639D · 4.03 Impact Factor
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    ABSTRACT: Water-in-oil (w/o) microemulsions were used as a template for the synthesis of mono- and bi-metallic nanoparticles. For that purpose, w/o-microemulsions containing H2PtCl6, H2PtCl6 + Pb(NO3)(2) and H2PtCl6 + Bi(NO)(3), respectively, were mixed with a w/o-microemulsion containing the reducing agent, NaBH4. The results revealed that it is possible to synthesize Pt, PtPb and PtBi nanoparticles of similar to 3-8 nm in diameter at temperatures of about 30 degrees C. The catalytic properties of the bimetallic PtBi and PtPb nanoparticles were studied and compared with monometallic platinum nanoparticles. Firstly, the electrochemical oxidation of formic acid to carbon monoxide was investigated, and it was found that the resistance of the PtBi and PtPb nanoparticles against the catalyst-poisoning carbon monoxide was significantly higher compared to the Pt nanoparticles. Secondly, investigating the reduction of 4-nitrophenol to 4-aminophenol, we found that the bimetallic NPs are most active at 23 degrees C, while the order of the activity changes at higher temperatures, i.e., that the Pt nanoparticles are the most active ones at 36 and 49 degrees C. Furthermore, we observed a strong influence of the support, which was either a polymer or Al2O3. Thirdly, for the hydrogenation of allylbenzene to propylbenzene, the monometallic Pt NPs turned out to be the most active catalysts, followed by the PtPb and PtBi NPs. Comparing the two bimetallic nanoparticles, one sees that the PtPb NPs are significantly more active than the respective PtBi NPs.
    Catalysts 09/2014; 4(3):256-275. DOI:10.3390/catal4030256 · 2.00 Impact Factor
  • Jan C Thater · Violaine Gérard · Cosima Stubenrauch
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    ABSTRACT: In this study, we investigate properties of microemulsions which consist of the ionic liquid (IL) ethylammonium nitrate (EAN), the nonionic surfactant C12E3 and an n-alkane, namely n-dodecane or n-octane. The compositions of the coexisting phases are calculated from the densities and volumes of the respective phases. Since the interfacial tension between the water-rich and the oil-rich phase in traditional microemulsions (containing water and oil) relates to the microstructure, spinning drop tensiometry is used to measure the interfacial tension σab and to estimate the domain sizes. Finally, measuring the self-diffusion coefficients of all components via the Fourier Transform Pulsed Gradient Spin Echo (FTPGSE) NMR technique allowed distinguishing between continuous and discrete structures. Our results indicate that the general principles underlying water-n-alkane-CiEj microemulsions can indeed be transferred to oil-in-EAN droplet and the respective bicontinuous microemulsions, while differences are observed for EAN-in-oil droplet microemulsions.
    Langmuir 07/2014; 30(28). DOI:10.1021/la501899c · 4.46 Impact Factor
  • Laurie Saulnier · Julia Boos · Cosima Stubenrauch · Emmanuelle Rio
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    ABSTRACT: The purpose of this article is to compare experiments carried out with single vertical foam films and with foams. We focus on the generation of films and foams and measure (i) the quantity of water entrained and (ii) the stability of the systems. The surfactants we used are C12E6, β-C12G2 and their 1 : 1 mixture because those systems are very well characterised in the literature and are known to stabilise foams with very different properties. We show that the quantity of water uptake in foams and single vertical films scales in the same way with the velocity of generation. However, the different surfactant solutions have different foamabilities, whereas the films they stabilise have exactly the same thickness. Moreover, the foamability of a C12E6 solution is much lower than that of a β-C12G2 solution or of a solution of the 1 : 1 mixture. This is due to the rapid rupture of the C12E6 foam films during foam generation. Surprisingly, the isolated films have exactly the same lifetime for all the surfactant solutions. We conclude that, though drawing a correlation between films and foams is tempting, the results obtained do not allow correlating of film and foam stability during the generation process. The only difference we observed between the single films stabilised by the different solutions is the stability of their respective black films. We thus suggest that the stability of black films during foam generation plays an important role which should be explored further in future work.
    Soft Matter 05/2014; 10(29). DOI:10.1039/c4sm00326h · 4.03 Impact Factor
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    ABSTRACT: Surface properties, miscibility and self-assembly of mixtures of a food-grade αs-casein and the triblock copolymer PE6400 (PEO13-PPO30-PEO13) were examined. The properties at the surface were determined by surface pressure measurements for a 1:1 molar mixture. Comparison of the measured with the calculated isotherms show attractive interactions at surface pressures above 9mN/m. The miscibility gaps of solutions containing 0.004-0.2mmol/l αs-casein and 0.02-0.1mol/l polymer were examined. It was found that a one-phase region exists at distinct mixing ratios and temperatures. Comparison of the cloud points of mixtures of αs-casein and PE6400 with pure αs-casein showed that the presence of the triblock copolymer enhanced the solubility of the protein. The ζ-potential of the αs-casein solution decreased by addition of PE6400 to zero. Our results thus suggest that αs-casein and PE6400 are miscible. The results of the cloud point and ζ-potential measurements were explained by formation of a mixed aggregate where the PPO chains are anchored inside the hydrophobic part of the αs-casein while the PEO chains cover the charged hydrophilic part of the αs-casein thereby leading to an increase of the cloud point and a decrease in ζ-potential. This is in agreement with the attractive interactions between αs-casein and PE6400 as observed via surface pressure measurements at the surface.
    Colloids and surfaces B: Biointerfaces 03/2014; 118C:49-56. DOI:10.1016/j.colsurfb.2014.03.030 · 4.15 Impact Factor
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    ABSTRACT: Biotechnology involves applying enzymes in organic synthesis to convert non-natural substrates into enantiomerically pure products under mild reaction conditions. Non-natural substrates are often lipophilic molecules that can hardly be accessed and converted by enzymes in their natural aqueous environment. Bicontinuous microemulsions provide a sponge-like nanostructure with a large interfacial area between aqueous and oil domains, which makes them valuable alternative reaction media. In the present study we introduced the lipase B from Candida antarctica into a bicontinuous microemulsion of composition H2O/NaCl- n-octane - pentaethylene glycol monodecylether (C10E5). Phase behavior, partitioning studies and pulsed-field-gradient NMR measurements revealed that the lipase is mostly adsorbed at the microemulsions interface. Phase diagrams showed a maximum in efficiency with increasing amount of lipase added to the water phase of the microemulsion. It was observed that the ratio between the mass of lipase which is introduced into the system and the mass of lipase which is located at the interface stays constant. Self-diffusion coefficients of all components showed that the presence of the lipase is not influencing the bicontinuity of the microemulsion.
    Langmuir 02/2014; 30(11). DOI:10.1021/la4042088 · 4.46 Impact Factor
  • Michaela Laupheimer · Cosima Stubenrauch
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    ABSTRACT: We present a quantitative method to determine the phase transition temperatures between one-phase and two-phase regions of multi-component liquid mixtures via temperature-dependent transmission measurements with an UV/Vis spectrometer. The method is based on the fact that multi-phase samples are turbid, while one-phase samples are transparent. We describe the method in detail and discuss the choice of the experimental parameters (wavelength, sample layer thickness), a suitable temperature program as well as the data analysis. We prove the validity of our method by measuring the phase diagrams of two model systems, namely a liquid and a gelled microemulsion. The results are in good agreement with those obtained with the conventional visual method used for phase studies.
    Tenside Surfactants Detergents 01/2014; 51(1):17-25. DOI:10.3139/113.110281 · 0.74 Impact Factor
  • Colloids and surfaces B: Biointerfaces 01/2014; 118:49–56. · 4.15 Impact Factor
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    ABSTRACT: Micelles are a potential encapsulation system for bioactive compounds. In previous studies we were able to show that the triblock copolymer PEO13-PPO30-PE013 and alphas-casein are miscible within distinct temperature and concentration ranges. In this study, we wanted to test our hypothesis that mixed micelles are formed which, in turn, are able to solubilize hydrophobic compounds. Additionally we want to gain insight into the specific arrangement of individual molecules in these micelles. For that purpose, mixtures containing increasing mole fractions of casein (alphacas = 4.3 x 10(-4) to alphacas = 7.2 x 10(-3)) were examined at 30 degreeC. The hydrophobic fluorescence probe pyrene was used as a model solute. Emission spectra were recorded and I1/I3 and lex/I1 ratios were evaluated. Furthermore, the emission spectra of tryptophan were recorded and the maximum emission wavelength was evaluated. The determined parameters showed that micelles are formed in all solutions and that the solubilization of pyrene occurred. The calculated interaction parameter betaindicated that the mixing was antagonistic, possibly due to steric hindrances between the casein and the polymer. It seems that the mixed micelles are formed in such a way that the hydrophobic part of the polymer is attached to the hydrophobic parts of the caseins (a necklace and bead model) since the tryptophan residues are located in a hydrophobic environment above the CMC. We suggest a first structural arrangement model, recognizing that further studies will be required to prove and refine it.
    Faraday Discussions 12/2013; 166:399-416. DOI:10.1039/c3fd00102d · 4.61 Impact Factor
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    ABSTRACT: In this study, the surface tension, miscibility, and particle size distribution of a solution containing an αs-casein (CN)-rich CN fraction (54 wt % αs-CN, 32 wt % β-CN, and 15 wt % κ-CN) were determined at pH 6.6. The nondialyzed CN fraction was compared with a dialyzed one. In the nondialyzed sample, every charge on the protein was compensated by 0.3 charges coming from counterions, whereas in the dialyzed sample, only 0.2 charges could be assigned to each charge on the protein. This relation was determined by calculating the charges at the proteins, taking the measured mineral content into account. The surface tension was measured as a function of the protein concentration by the du Noüy ring method at room temperature. Results indicated alterations in the surface properties after reduction of counterions. The equilibrium surface tension above the critical micelle concentration increased from 40.1 × 10(-3) to 45 × 10(-3) N/m, the critical micelle concentration increased from 0.9 × 10(-4) to 2 × 10(-3) mol/L, and the minimal area occupied per molecule at the surface increased from 2.4 × 10(-18) to 4.6 × 10(-18) m(2). Cloud points were determined by measuring the absorbance of CN solutions as a function of the temperature. The cloud points were found to be concentration dependent and had a minimum at 0.2 wt % at 34°C for nondialyzed CN and at 0.25 wt % at 28°C for dialyzed CN, again demonstrating the influence of counterion reduction. Below the cloud point, a micellar phase was found to exist. The hydrodynamic diameter of the micelles were characterized by dynamic light scattering in both auto- and cross-correlation mode. However, no influence of reduction in counterions could be observed, possibly due to the fact that dynamic light scattering is not a suitable method for this type of system. The presence of self-assembled structures was verified by freeze-fracture electron microscopy. The observed differences between dialyzed and nondialyzed samples were explained by changes in the counterion cloud surrounding the proteins. Consequently, the electrostatic interactions between as well as within the CN are altered by dialysis, which, in turn, affects the behavior at the surface as well as the properties in the solution.
    Journal of Dairy Science 07/2013; 96(9). DOI:10.3168/jds.2013-6788 · 2.57 Impact Factor
  • Journal of Dairy Science 06/2013; · 2.57 Impact Factor

Publication Stats

1k Citations
393.02 Total Impact Points


  • 2009–2015
    • Universität Stuttgart
      • • Institute of Physical Chemistry
      • • Institute of Technical Biochemistry
      Stuttgart, Baden-Württemberg, Germany
  • 2005–2011
    • University College Dublin
      • School of Chemical and Bioprocess Engineering
      Dublin, L, Ireland
  • 2000–2006
    • University of Cologne
      • • Institute of Organic Chemistry
      • • Institute of Physical Chemistry
      Köln, North Rhine-Westphalia, Germany