Conformational Effects in Non-Stoichiometric Complexes of Two Hyperbranched Molecules with a Linear Polyelectrolyte

George Dalakoglou,Anatoly Darinskii,Alexey Lyulin,Sergey Larin,Sergey Lyulin,Kostas Karatasos

doi:10.3390/polym4010240

Abstract

We report results from Brownian dynamics computer simulations of systems comprised by two terminally charged hyperbranched molecules preferentially branched in the periphery, with an oppositely charged linear chain of varying length. Comparison of the findings from the present study to stoichiometric counterparts and to analogous dendrimer-based complexes, reveal that the presence of the second hyperbranched molecule incurs significant changes in the conformational characteristics of both components of the complex. Instead of step-like changes in the average size and shape of the hyperbranched component that were noted in the previously studied stoichiometric systems, a rather smooth change is observed upon increase of the length of the linear component. In addition, a markedly different behavior is also noticed in the conformational characteristics of the linear chain when compared to that in similar dendrimer-based systems. The above findings are consistent with the higher degree of deformability of the peripherally branched molecules which allow appropriate rearrangements in shape in order to accommodate the favorable Coulombic interactions between the two components of the complex. This behavior offers new insight towards the design of more efficient hyperbranched-based systems which can take advantage of the multifunctionality and the structural properties of the highly branched polymer components.

Highlights

Hyperbranched polymers have emerged in the last few years as a new promising category of non-viral vehicles for drug and gene delivery applications [1,2,3]
We considered the Bjerrum length λB to be equal to l without loss of generality, while the Debye radius was taken as rD = 8.96l For comparison purposes, the aforementioned parameters were taken to be identical to those utilized in the previous study concerning the non-stoichiometric linear polyelectrolytes (LPE)/dendrimer complexes
To check c the efffects triggeered by the realization r o of thhe “linker” conformattion in non-stooichiometriic complexees c comprised b HBPs off the MAX topology, by t w have calcculated the dependencee of the sem we miaxes of thhe e ellipsoid of inertia i of thhe HBP com mponents off the compleexes as a funnction of thhe length of the LPE

Summary

Introduction

Hyperbranched polymers have emerged in the last few years as a new promising category of non-viral vehicles for drug and gene delivery applications [1,2,3]. The advantages related to their use as complexation and delivery agents, such as their structural features, their multifunctionality and their favorable transport and thermodynamic properties, have surged the scientific as well as the industrial interest towards an effort for a better control of their physicochemical behavior [4,5,6,7,8,9,10] To this end, a large number of theoretical and experimental studies have been devoted to the elucidation of the structure/properties relation of complexes comprised by hyperbranched molecules (HBP) and linear polyelectrolytes (LPE), with complexes including nucleic acids being the most characteristic examples [11,12,13,14,15]. These studies aimed at the elucidation of the generic behavior related to their conformational characteristics and to phenomena of key importance regarding their action as complexation agents and delivery vehicles, such as overcharging [27,31,33,34]

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Conclusion