Structural effects on encapsulation as probed in redox-active core dendrimer isomers

Area of Science:

• Supramolecular Chemistry
• Nanotechnology
• Electrochemistry

Background:

• Dendrimers are highly branched macromolecules with unique properties.
• Iron-sulfur clusters are important in biological and chemical systems.
• Controlling the encapsulation of core molecules within dendrimers is crucial for their function.

Purpose of the Study:

• To synthesize and characterize isomeric iron-sulfur core dendrimers.
• To investigate the effect of dendrimer architecture on core encapsulation.
• To understand how encapsulation influences electrochemical properties and electron transfer.

Main Methods:

• Synthesis of three pairs of isomeric iron-sulfur core dendrimers with distinct aromatic substitution patterns (extended vs. backfolded).
• Electrochemical studies (cyclic voltammetry) to assess reduction potentials.
• Heterogeneous electron-transfer rate measurements.
• Diffusion measurements using pulsed field gradient spin-echo Nuclear Magnetic Resonance (NMR) and chronoamperometry.
• Proton relaxation (T(1)) measurements to probe dendrimer conformation.

Main Results:

• Backfolded isomers demonstrated more effective encapsulation of iron-sulfur cores compared to extended isomers.
• Backfolded dendrimers exhibited more difficult electrochemical reduction, suggesting a more hydrophobic microenvironment.
• Heterogeneous electron-transfer rates were attenuated in backfolded dendrimers relative to extended ones.
• Diffusion measurements and T(1) relaxation data indicated smaller, more compact structures for backfolded dendrimers.

Conclusions:

• Dendrimer architecture significantly influences the encapsulation efficiency of iron-sulfur cores.
• The backfolded isomeric structure leads to a more hydrophobic environment and altered electrochemical behavior.
• Effective electron-transfer distance, dictated by core position and mobility, is more critical than overall dendrimer size for electron transfer attenuation.