Supramolecular Control of Azobenzene Switching on Nanoparticles

Abstract

The reversible photoisomerization of azobenzene has been utilized to construct a plethora of systems in which optical, electronic, catalytic, and other properties can be controlled by light. However, owing to azobenzene’s hydrophobic nature, most of these examples have been realized only in organic solvents, and systems operating in water are relatively scarce. Here, we show that by coadsorbing the inherently hydrophobic azobenzenes with water-solubilizing ligands on the same nanoparticulate platforms, it is possible to render them essentially water-soluble. To this end, we developed a modified nanoparticle functionalization procedure allowing us to precisely fine-tune the amount of azobenzene on the functionalized nanoparticles. Molecular dynamics simulations helped us to identify two distinct supramolecular architectures (depending on the length of the background ligand) on these nanoparticles, which can explain their excellent aqueous solubilities. Azobenzenes adsorbed on these water-soluble nanoparticles exhibit highly reversible photoisomerization upon exposure to UV and visible light. Importantly, the mixed-monolayer approach allowed us to systematically investigate how the background ligand affects the switching properties of azobenzene. We found that the nature of the background ligand has a profound effect on the kinetics of azobenzene switching. For example, a hydroxy-terminated background ligand is capable of accelerating the back-isomerization reaction by more than 6000-fold. These results pave the way toward the development of novel light-responsive nanomaterials operating in aqueous media and, in the long run, in biological environments.

A new azobenzene-based design strategy for detergents in membrane protein research

“…[14][15][16] Research on azobenzene detergents has been focused on photoresponsive surface coatings, [17][18][19][20] catalysis systems, 21 and supramolecular aggregates. [22][23][24][25][26][27] The utility of anionic 4-hexylphenylazosulfonate for denaturing top-down proteomics has been outlined very recently. 28 As ionic detergents commonly denature membrane proteins more than non-ionic detergents, 29 this inspired us to investigate whether non-ionic azobenzene detergents can be used for the non-denaturing structural analysis of membrane proteins.…”

Self-Assembly of Nanoparticles Decorated by Liquid Crystalline Groups: Computer Simulations

“…Therefore, computer simulation studies indicate the possibility for the Sm A phase self-assemble by quenching the system in a broad temperature interval under illumination, otherwise impossible for the non-illuminated system. Although, these simulation findings cannot be compared straightaway with the particular experiments, they are very much in-tune with the general applications of the azobenzene chromophores to control LC alignment, aggregation and self-assembly in the systems of DNPs [24][25][26][27][28].…”

“…These are not the artefacts of the model or the simulation approach, but reflect physical properties of the LC polymers, which are relatively viscous and characterised by slow relaxation and strong tendencies for metastability attributed to the presence of a transient network [23]. One of the ways to stimulate/control the self-assembly of DNPs is to use the light [24][25][26][27][28]. To utilise this approach, the chromophores (e.g.…”

Driving Smart Molecular Systems by Artificial Molecular Machines

“…In response to irradiation, the azo group (NN) of azobenzene undergoes photoisomerization, inducing a transition from thermally stable trans ‐isomer to the photostable cis ‐isomer, with the reverse process observed upon exposure of the latter isomer to long wavelength or heating. This reversibility, along with the relative ease of chemical modification, makes azobenzene and its derivatives popular components of stimuli‐responsive systems . 3) Molecular motors, representing the third type of molecular machines, undergo unidirectional motion under external energy input and are fundamentally different from molecular switches; i.e., the former can progressively drive systems away from equilibrium and continuously perform work in nonequilibrium environments for a full cycle, whereas the latter cannot.…”