Tuning the solution organization of cationic polymers through interactions with bovine serum albumin


There has been extensive research studying the association of proteins and polyelectrolytes especially in regard to protein/peptide drug delivery, protein separation and tissue engineering. Imidazolium quaternized polymers based on poly(chloromethylstyrene) were used in this experiment. The polymers were obtained by the use of nitroxide mediated radical polymerization and post-polymerization functionalization. The quaternization reaction substitutes the chlorine groups with cations in order to ensure that the polymers are soluble and positively charged in water. The polymers that were used include QIm-PCMS1 and QIm-PCMS2. The degree of quaternization of the two polymers was 73% and 100% respectively, which leads to QIm-PCMS1 being more hydrophobic than QIm-PCMS2.

The successful investigation of the complexation with globular proteins has been conducted with small angle scattering methods. Quaternized polymers are anticipated to define their own association state in aqueous media. In any case, it is important to keep in mind that even after quaternization, they still remain hydrophobic polyelectrolytes. The protein chosen is Bovine Serum Albumin (BSA), a negatively charged protein at neutral pH, which serves as a model protein in the small angle neutron scattering complexation studies with the aforementioned cationic polyelectrolytes,

Researchers led by Dr. Stergios Pispas at Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation in Greece in collaboration with Helmholtz-Zentrum Berlin in Germany demonstrated the ability to tune the polyelectrolyte/protein interactions and polyelectrolyte chain–chain associations by modifying the hydrophobic content of the polyelectrolytes.

Quaternized polymer chains are capable of forming aggregates with dimensions much larger than their own size. The dimension scales investigated by small angle neutron scattering (Figure 1a) are in a range that includes the size of the Bovine Serum Albumin. Based on established formulae and equations characteristic parameters for the polyelectrolyte solutions and polyelectrolyte/protein mixtures are deduced. Through these formulae the electrostatic and hydrophobic interactions were found to be of fundamental importance to Bovine Serum Albumin/polymer complexes. Electrostatic interactions are defined by the salt content while hydrophobic interactions are related to the degree of quaternization.

Although different polymer quaternization levels showed no difference in the solutions of the quaternized polymers, they interacted differently with Bovine Serum Albumin. As stated above, they still have different hydrophobic content. At another level however, there was the loss of the alpha-helix structural form of the Bovine Serum Albumin once its process of complexation with the polymers took place (Figure 1b). The alpha-helix form is the basic state in which the secondary structure of the Bovine Serum Albumin exists. Bovine Serum Albumin complexation with the quaternized polymers leads it to be denatured of its secondary structure. This case is similar to the aggregation of casein micelles in milk where the proteins are also met in their denatured state. It can be said that quaternized polymers may act as a medium to associations driven by protein denaturation.

By using light scattering measurements, the polymer structural organization especially at larger length scales is investigated. This organization is mostly affected by the interactions that exist with the Bovine Serum Albumin. Therefore an increase in the Bovine Serum Albumin content leads to a systematic increase in the scattered intensity. In the establishment of high clusters, the associations of polymer chains that were formed at the beginning are strenghtened by the Bovine Serum Albumin molecules. This increase in the mass of clusters ranges in the order of 10. This also implies inter-aggregate associations.

Through the use of small angle neutron scattering, the local interactions that have been presented can be said to be answerable for the assembly at larger length scale. Hence, the interactions that exist between the hydrophobic and positively charged groups that are present in the quaternized polymers, as well as the hydrophobic and negative parts of Bovine Serum Albumin are very conceivable.

The research work is a comprehensive study of protein/hydrophobic polyelectrolyte interactions at a wide range of length scales that demonstrates the tunability of the formed complexes by both hydrophobic and electrostatic effects, and gives insights for the designed construction of polyelectrolyte/protein nanoparticulate structures for biomedical applications.

Tuning solution organization of cationic polymers through interactions with bovine serum albumin. Advances in Engineering

Figure legend: SANS profiles from QIm-PCMS1 (16 mg ml-1) (blue) and QIm-PCMS1 (16 mg ml-1)/BSA(4 mg ml-1) in D2O with no added salt (red). Lines are fits to the experimental data.


Tuning the solution organization of cationic polymers through interactions with bovine serum albuminTuning the solution organization of cationic polymers through interactions with bovine serum albumin. Advances in Engineering

Schematic illustration of the interaction of BSA with QIm-PCMS polymers.

About the author

Aristeidis Papagiannopoulos is a postdoctoral research associate at the TPCI-NHRF. He has studied Physics at the University of Patras, Greece and owns a Masters Degree in Polymer Science and Technology from the same University. He obtained his PhD in Physics from the University of Leeds, United Kingdom in 2005 in the Polymers and Complex Fluids Group. He has worked as a postdoctoral researcher in several institutes and Universities as the University of Leeds, the University of Manchester and the Foundation of Research and Technology (Greece). He uses small angle neutron scattering to study complexation of stimuli responsive self-assembled block copolymers with proteins and associative biopolymers.

His research interests cover development of microrheological, light scattering and interfacial instrumentation  for the investigation of biomacromolecular systems in solution and at interfaces. He is active in the field of interfaces research with focus on adsorption of polyelectrolytes and proteins. He also investigates complex fluids from biopolymers with rheology and microrheology methods. He is the author of 30 research articles, and 6 invited chapters in books.

About the author

Eleni Vlassi obtained her PhD in Chemistry from the University of Athens, Greece in 2015. She graduated from the department of Chemical Engineering of the University of Patras, Greece in 2009 and obtained her MSc on Energy and Environment from the same university in 2012. She has received Recognition for distinction in undergraduate studies from the Technical Chamber of Greece in 2012 and awards of distinction in undergraduate studies and morality from the Greek National State Scholarship Foundation for 2 successive years 2004-2006. Lately she was selected as candidate of State Scholarships Foundation (IKY) for the financial support of her postdoctoral research through the ”IKY FELLOWSHIPS OF EXCELLENCE FOR POSTGRADUATE STUDIES IN GREECE – SIEMENS PROGRAM’ (2016-017-0173-10237)”. She is the author of 7 research articles and her research interests are in polymer and food science.

She works in polymer synthesis (such as cationic polymerization and hydrolysis) and physicochemical characterization of self-assembled systems (including magnetic nanoparticles, drug/gene delivery) with a variety of methods as Fourier transform infrared spectroscopy, scattering methods (light scattering, small angle neutron scattering) and ultraviolet-visble spectroscopy.

About the author

Stergios Pispas studied Chemistry at the University of Athens, Greece and obtained his PhD on Polymer Chemistry from the same university in 1994. During 1994 and 1995 he was a Postdoctoral Fellow at the Chemistry Department of the University of Alabama at Birmingham,USA. He then returned to Greece and joined again the Chemistry Department of the University of Athens as a Research Associate. In 2004 he became an Associate Researcher at the Theoretical and Physical Chemistry Institute at the National Hellenic Research Foundation, Athens, Greece, introducing the first Polymer Science oriented activities.

Since 2014 he is Director of Research at TPCI-NHRF. He serves as the chairman of the Scientific Council of TPCI-NHRF (since 2016) and an Advisory Board Member of the European Polymer Journal (since 2017). He has been awarded the American Institute of Chemists Foundation Award for Outstanding Post-doctoral Fellow (1995) and the A. K. Doolittle Award of the American Chemical Society (2003).

He has published more than 270 research articles in referred journals, several invited review articles and chapters in books and encyclopedias, and he is the co-author of two books and a patent. His research work has received more than 7000 citations (h-index=38). His current research focuses on the synthesis of functional block copolymers and polyelectrolytes by controlled polymerization methodologies, the study of their self-assembly properties, as well as the development of complex, hybrid, self-organized nanostructures based on designed synthetic polymers and inorganic nanomaterials and biomacromolecules with applications in nanomedicine and biotechnology.


Papagiannopoulos A, Vlassi E, Pispas S, Jafta CJ. Tuning the solution organization of cationic polymers through interactions with bovine serum albumin. Physical Chemistry Chemical Physics. 2017; 19(28):18471-80.


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