Development of a redox active colloidal system for dissipative self-assembly

Abstract

Dissipative self-assembly (DSA) is a process that leads to the formation of structures and materials away from the thermodynamic equilibrium state through a controlled exchange of energy and/or matter with the environment1. This form of self-assembly is key in numerous biological processes, and, in living organisms, it enables properties such as self-healing, self-replication, signal processing and motility, among others. Recently, there is a growing interest in developing synthetic supramolecular and colloidal systems that can undergo dissipative self-assembly, for example controlled by the consumption of chemical fuel(s). The overall goal of this TFG project is to develop a colloidal system based on ferrocene-functionalized silica (SiO2) particles whose assembly can be controlled via redox-responsive host-guest interactions between the ferrocene (Fc) moiety and a β-cyclodextrin-dimer that can act as a linker between the particles. The addition of suitable chemical fuels (an oxidant and a reductant) will allow us to regulate the assembly/disassembly of the colloidal system, which depends on the kinetics of the redox process. To achieve this goal, monodisperse non-fluorescent and fluorescent core-shell SiO2 particles were synthesized, and subsequently functionalized with Fc moieties using ‘click’ chemistry. Full physicochemical and size characterization of the particles proved the success of the synthesis and functionalization steps, demonstrating the formation of spherical, monodisperse Fc-functionalized particles with size around 500 nm. Redox kinetic studies with a variety of oxidants and reductants were performed using molecular ferrocene, in order to optimize the experimental conditions to be used for the dissipative self-assembly. These studies showed that FeCl3 and ascorbic acid are the most suitable pair of redox agents for fast redox switching of Fc, whilst H2O2 is more suitable for fine-tuning the redox kinetics. Preliminary self-assembly studies revealed that in the presence of β-cyclodextrin-dimer, Fc-functionalized particles assemble, and could then be disassembled by addition of an oxidant. This result is promising for the development of DSA, and further studies are being carried out to investigate this system in more depth