(689d) Self Consistent Field Theory Study of Multivalent Cation Effect on Semiflexible End-Grafted Random Polyelectrolytes

Biopolymers such as DNA, aptamers and proteins have long been a matter of interest for diverse applications. Modeling these biopolymers requires indepth understanding of random (heterogeneous) polyelectrolytes due to their resemblance in structure and property. Randomness of the sequence creates more variation in the local environment surrounding a random polyelectrolyte chain than a regular homogeneous polyelectrolyte. Presence of multivalent cations largely effects the structure and chemistry of these polyelectrolytes due to strong electrostatic interactions and salting out effect ^[2] and is critically important in biosensing and drug delivery applications.This study aims to elucidate the underlying physics of multivalent cation effect on surface-grafted random polyelectrolytes from a statistical thermodynamic viewpoint.

This theoretical study implements a Self Consistent Field Theory (SCFT) approach to build the molecular model for the random polyelectrolytes grafted to a surface and surrounded by multivalent cations. Structural rigidity of the polyelectrolyte chain is taken into account by using the Wormlike Chain Model of semi-flexible polymers. The molecular model properly accounts for the structural, thermodynamic and electrostatic properties of all the species present in the system. The highly non-additive coupling between various interactions creates a varying local environment near each polyelectrolyte chains that ultimately results in collapse of the chain. Formation of salt bridge between different chains with the aid of multivalent cations is considered in this theory by using a chemical reaction formalism. Poor solvent quality due to presence of thermodynamically controlled salting out effect is accounted with a Flory-Huggins Chi parameter . Variation of the cation effect is analyzed at different pH, salt concentration, polymer grafting density and polymer chain length. This model gives an exhaustive framework to demonstrate multivalent cation induced structural change in random polyelectrolytes tethered to nano surfaces for drug delivery and biosensing applications and also in colloid chemistry.

 

References

1. Borukhov, I., Andelman, D., and Orland, H. (1998). Random polyelectrolytes and polyampholytes in solution, Eur. Phys. J. B 5, 869–880.
2. Djabourov, M., Nishinari, K., and Ross-Murphy, S. B. (2013).Physical Gels from Biological and Synthetic Polymers, Cambridge University Press.