One-Pot Synthesis of Water-Soluble Glycosyl Azobenzenes and Their Photoswitching Properties in Water

Molecular photoswitches capable of reversible photoswitching in aqueous media are highly demanded for various biological applications and photopharmacology. Carbohydrates, as natural and abundant raw materials, provide opportunity to make photoswitches water-soluble through linking sugar to the photoswitching molecules. We have developed a one-pot synthesis method to prepare water-soluble glycosyl azobenzenes through DMC (2-chloro-1,3-dimethylimidazolinium chloride)-mediated glycosylation between sugar and dihydroxyazobenzenes (DHABs) in aqueous media. The scope of the method has been investigated with different mono- and disaccharides, as well as with p,p'- and o,o'-DHAB, with excellent 1,2-trans stereoselectivity. Diglycosylation products can also be obtained with an excess amount of monosaccharides in one step. We have also demonstrated the possibility of further functionalization on the azobenzene moiety of glycosyl azobenzene. Both mono- and diglycosyl azobenzenes showed excellent photoswitching properties in water with high fatigue resistance and good thermostability for the Z-isomers. Excellent E → Z photoisomerization of both mono- and diglycosylated azobenzenes (Z/E = 99/1) is observed under illumination at 365 nm, while back Z → E photoisomerization can be achieved with blue light (with E/Z = 80/20 at PSS₄₈₅ for the diglycosyl derivative).

Controlling Antibacterial Activity Exclusively with Visible Light: Introducing a Tetra-ortho-Chloro-Azobenzene Amino Acid

The introduction of a novel tetra-ortho-chloroazobenzene amino acid (CEBA) has enabled photoswitching of the antimicrobial activity of tyrocidine A analogues by using exclusively visible light, granting spatiotemporal control under benign conditions. Compounds bearing this photoswitchable amino acid become active upon irradiation with red light, but quickly turn-off upon exposure to other visible light wavelengths. Critically, sunlight quickly triggers isomerisation of the red light-activated compounds into their original trans form, offering an ideal platform for self-deactivation upon release into the environment. Linear analogues of tyrocidine A were found to provide the best photocontrol of their antimicrobial activity, leading to compounds active against Acinetobacter baumannii upon isomerisation. Exploration of their N- and C-termini has provided insights into key elements of their structure and has allowed obtaining new antimicrobials displaying excellent strain selectivity and photocontrol.

Design and synthesis of an azobenzene-betaine surfactant for photo-rheological fluids

HYPOTHESIS

Morphology of surfactant self-assemblies are governed by the intermolecular interactions and packing constraints of the constituent molecules. Therefore, rational design of surfactant structure should allow targeting of the specific self-assembly modes, such as wormlike micelles (WLMs). By inclusion of an appropriate photo-responsive functionality to a surfactant molecule, light-based control of formulation properties without the need for additives can be achieved.

EXPERIMENTS

A novel azobenzene-containing surfactant was synthesised with the intention of producing photo-responsive wormlike micelles. Aggregation of the molecule in its cis and trans isomers, and its concomitant flow properties, were characterised using UV-vis spectroscopy, small-angle neutron scattering, and rheological measurements. Finally, the fluids capacity for mediating particle diffusion was assessed using dynamic light scattering.

FINDINGS

The trans isomer of the novel azo-surfactant was found to form a viscoelastic WLM network, which transitioned to inviscid ellipsoidal aggregates upon photo-switching to the cis isomer. This was accompanied by changes in zero-shear viscosity up to 16,000×. UV-vis spectroscopic and rheo-SANS analysis revealed π-π interactions of the trans azobenzene chromophore within the micelles, influencing aggregate structure and contributing to micellar rigidity. Particles dispersed in a 1 wt% surfactant solution showed a fivefold increase in apparent diffusion coefficient after UV-irradiation of the mixture.

Photomodulation of bacterial growth and biofilm formation using carbohydrate-based surfactants

Naturally occurring and synthetic carbohydrate amphiphiles have emerged as a promising class of antimicrobial and antiadhesive agents that act through a number of dynamic and often poorly understood mechanisms. In this paper, we provide the first report on the application of azobenzene trans-cis photoisomerization for effecting spatial and temporal control over bacterial growth and biofilm formation using carbohydrate-based surfactants. Photocontrollable surface tension studies and small angle neutron scattering (SANS) revealed the diverse geometries and dimensions of self-assemblies (micelles) made possible through variation of the head group and UV-visible light irradiation. Using these light-addressable amphiphiles, we demonstrate optical control over the antibacterial activity and formation of biofilms against multi-drug resistant (MDR) Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative Escherichia coli. To probe the mechanism of bioactivity further, we evaluated the impact of trans-cis photoisomerization in these surfactants on bacterial motility and revealed photomodulated enhancement in swarming motility in P. aeruginosa. These light-responsive amphiphiles should attract significant interest as a new class of antibacterial agents and as investigational tools for probing the complex mechanisms underpinning bacterial adhesion and biofilm formation.

Carbohydrate-based surfactants as photocontrollable inhibitors of ice recrystallization

We report the synthesis and photocontrollable ice recrystallization inhibition (IRI) activity of a panel of carbohydrate-based surfactants.