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Interaction between lysozyme and colloidal poly(NIPAM-co-AAc) microgels
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. (Pharmaceutical Physical Chemistry)
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
School of Chemistry, University of Bristol, United Kingdom.
School of Chemistry, University of Bristol, United Kingdom.
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2010 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 347, no 2, 241-251 p.Article in journal (Refereed) Published
Abstract [en]

The interaction between lysozyme and colloidal poly(NIPAM-co-acrylic acid) microgels is investigated in aqueous solutions at neutral pH. Lysozyme binding isotherms, obtained within the ionic strength range 10-220 mM, indicate that the maximum uptake at 10 mM is 2.4 g lysozyme per gram dry gel, and that the uptake capacity decreases with increasing ionic strength to approximately 0 at 220 mM. Swelling isotherms, obtained from photon correlation spectroscopy measurements, show that the binding is accompanied by a substantial deswelling of the microgels. The microgel suspension is stable up to a protein-to-polymer charge ratio in the microgels of about 0.6, largely independent of ionic strength, whereas flocculation/sedimentation occurs at higher charge ratios. The charge ratio 0.6 corresponds to a zeta-potential of about -6 mV, as obtained from measurements of electrophoretic mobility. Binding and swelling isotherms are analyzed in detail and compared with predictions of theoretical model calculations. The influence of protein-protein attraction is highlighted, as well as the interplay between electrostatic interactions and network elasticity.

Place, publisher, year, edition, pages
2010. Vol. 347, no 2, 241-251 p.
Keyword [en]
microgel, NIPAM, acrylic acid, lysozyme, protein, colloidal stability, electrophoretic mobility
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-101244DOI: 10.1016/j.jcis.2010.03.072ISI: 000278707400012PubMedID: 20417522OAI: oai:DiVA.org:uu-101244DiVA: diva2:212201
Available from: 2009-04-21 Created: 2009-04-21 Last updated: 2010-12-16Bibliographically approved
In thesis
1. Interaction Between Microgels and Oppositely Charged Proteins
Open this publication in new window or tab >>Interaction Between Microgels and Oppositely Charged Proteins
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis reports on interactions between microgels and oppositely charged proteins. Two types of negatively charged microgels are investigated: poly(acrylic acid) microgels of 60-80 µm in diameter, and colloidal poly(NIPAM-co-acrylic acid) microgels of around 1 µm in diameter. The proteins used are lysozyme and cytochrome c, which both have positive net charge. The experimental techniques used in the studies of the larger microgels are mainly micromanipulator-assisted microscopy and confocal microscopy, while the smaller microgels are studied mainly with dynamic light scattering.

It is observed that large amounts of protein are absorbed by the microgels, and that the uptake involves a substantial deswelling of the microgel. The uptake generally decreases as the ionic strength is increased, which is characteristic of electrostatic interactions. An ionic strength optimum is however observed in the case of lysozyme and poly(acrylic acid) microgels, where the highest uptake (10 gram lysozyme / gram microgel) is observed at ionic strength 40 mM. Cytochrome c uptake in poly(acrylic acid) microgels results in homogenous cytochrome c distribution throughout the microgel, whereas lysozyme uptake results in core-shell formation; the lysozyme concentration becomes much higher in the shell (outer part of the microgel) than in the core (inner part of the microgel). The shell constitutes a stress-bearing network which is sufficiently porous to allow protein diffusion through the shell. The different protein distributions are associated with different protein-protein interactions; strong protein-protein attraction promotes shell formation.

In the case of colloidal microgels, lysozyme uptake decreases the electrophoretic mobility and the colloidal stability of the microgels. The microgels flocculate as the uptake reaches charge ratio 0.6-0.7 (positive lysozyme charges/negative microgel charges), largely independent of ionic strength. Initial experiments on the combination of cytochrome c and colloidal microgels show that colloidal stability is maintained at a range of conditions (ionic strength, protein concentration) where flocculation occurred in the case of lysozyme.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 71 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 98
Series
Keyword
microgel, protein, uptake, distribution, core-shell, colloidal stability
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-101246 (URN)978-91-554-7526-0 (ISBN)
Public defence
2009-06-05, B21, BMC, Husargatan 3, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2009-05-15 Created: 2009-04-21 Last updated: 2009-05-15Bibliographically approved

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Johansson, Christian

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