Sulfur and Azobenzenes, a Profitable Liaison: Straightforward Synthesis of Photoswitchable Thioglycosides with Tunable Properties

Azobenzene photoswitches are valuable tools for controlling properties of molecular systems with light. We have been investigating azobenzene glycoconjugates to probe carbohydrate‐protein interactions and to design glycoazobenzene macrocycles with chiroptical and physicochemical properties modulated by light irradiation. To date, direct conjugation of glycosides to azobenzenes was performed by reactions providing target compounds in limited yields. We therefore sought a more effective and reliable coupling method. In this paper, we report on a straightforward thioarylation of azobenzene derivatives with glycosyl thiols as well as other thiols, thereby increasing the scope of azobenzene conjugation. Even challenging unsymmetrical conjugates can be achieved in good yields via sequential or one‐pot procedures. Importantly, red‐shifted azoswitches, which are addressed with visible light, were easily functionalized. Additionally, by oxidation of the sulfide bridge to the respective sulfones, both the photochromic and the thermal relaxation properties of the core azobenzene can be tuned. Utilizing this option, we realized orthogonal three‐state photoswitching in mixtures containing two distinct azobenzene thioglycosides.

Near-Infrared Light Regulation of Capture and Release of ctDNA Platforms Based on the DNA Assembly System

Despite recent progress, a challenge remains on how to gently release and recover viable ctDNA captured on DNA probe-based devices. Here, a reusable detector was successfully manufactured for the capture and release of ctDNA by means of an UCNPs@SiO2-Azo/CD-probe. Biocompatible NIR light is used to excite UCNPs and convert into local UV light. Continuous irradiation induces a rapid release of the entire ctDNA-probe–CD complex from the functionalized surface via the trans−cis isomerization of azo units without disrupting the ctDNA-structure receptor. Specifically, these composite chips allow reloading DNA probes for reusable ctDNA detection with no obvious influence on their efficiency. The results of our study demonstrated the potential application of this platform for the quantitative detection of ctDNA and the individualized analysis of cancer patients.

Structure-Performance Relationships for Tail Substituted Zwitterionic Betaine-Azobenzene Surfactants

Azobenzene-containing surfactants (azo-surfactants) have garnered significant attention for their use in generating photoresponsive foams, interfaces, and colloidal systems. The photoresponsive behavior of azo-surfactants is driven by the conformational and electronic changes that occur when the azobenzene chromophore undergoes light-induced trans ⇌ cis isomerization. Effective design of surfactants and targeting of their properties requires a robust understanding of how the azobenzene functionality interacts with surfactant structure and influences overall surfactant behavior. Herein, a library of tail substituted azo-surfactants were synthesized and studied to better understand how surfactant structure can be tailored to exploit the azobenzene photoswitch. This work shows that tail group structure (length and branching) has a profound influence on the critical micelle concentration of azo-surfactants and their properties once adsorbed to an air-water interface. Neutron scattering studies revealed the unique role that intermolecular π-π azobenzene interactions have on the self-assembly of azo-surfactants, and how the influence of these interactions can be tuned using tail group structure to target specific aqueous aggregate morphologies.

Photoswitching Affinity and Mechanism of Multivalent Lectin Ligands

Multivalent receptor–ligand binding is a key principle in a plethora of biological recognition processes. Immense binding affinities can be achieved with the correct spatial orientation of the ligands. Accordingly, the incorporation of photoswitches, which can be used to reversibly change the spatial orientation of molecules, into multivalent ligands is a means to alter the binding affinity and possibly also the binding mode of such ligands. We report a divalent ligand for the model lectin wheat germ agglutinin (WGA) containing an arylazopyrazole photoswitch. This switch, which has recently been introduced as an alternative to the more commonly used azobenzene moiety, is characterized by almost quantitative E/Z photoswitching in both directions, high quantum yields, and high thermal stability of the Z isomer. The ligand was designed in a way that only one of the isomers is able to bridge adjacent binding sites of WGA leading to a chelating binding mode. Photoswitching induces an unprecedentedly high change in lectin binding affinity as determined by isothermal titration calorimetry (ITC). Furthermore, additional dynamic light scattering (DLS) data suggest that the binding mode of the ligand changes from chelating binding of the E isomer to crosslinking binding of the Z isomer.

A compatibility study on the glycosylation of 4,4′-dihydroxyazobenzene

Photoresponsive glycoconjugates based on the azobenzene photoswitch are valuable molecules which can be used as tools for the investigation of carbohydrate–protein interactions or as precursors of shape-switchable molecular architectures, for example. To access such compounds, glycosylation of 4,4′-dihydroxyazobenzene (DHAB) is a critical step, frequently giving heterogeneous results because DHAB is a challenging glycosyl acceptor. Therefore, DHAB glucosylation was studied using nine different glycosyl donors, and reaction conditions were systematically varied in order to find a reliable procedure, especially towards the preparation of azobenzene bis-glucosides. Particular emphasis was put on glucosyl donors which were differentiated at the primary 6-position (N₃, OAc) for further functionalisation. The present study allowed us to identify suitable glycosyl donors and reaction conditions matching with DHAB, affording the bis-glycosylated products in fair yields and good stereocontrol.

The glycosylation of 4,4′-dihydroxyazobenzene was investigated to identify suitable conditions providing access to valuable photoswitchable glycoconjugates.

E–Z isomerization of the –CN– bond in anthracene-based acylhydrazone derivatives under visible light

The E–Z isomerizations of the –CN– group upon visible light irradiation induced the photoresponsive behaviour of AHP-mB8.

Light-Triggered Specific Cancer Cell Release from Cyclodextrin/Azobenzene and Aptamer-Modified Substrate

Cell adhesion behaviors of stimuli-responsive surfaces have attracted significant attention for their potential biomedical applications. Distinct from temperature and pH stimuli, photoswitching avoids the extra input of thermal energy or chemicals. Herein, we designed a novel reusable cyclodextrin (CD)-modified surface to realize photoswitched specific cell release utilizing host-guest interactions between CD and azobenzene. The azobenzene-grafted specific cell capture agent was assembled onto the CD-modified surface to form a smart surface controlling cell adhesion by light radiation. After UV light irradiation, the azobenzene switched from trans- to cis-isomers, and the cis-azobenzene was not recognized by CD due to the unmatched host-guest pairs; thus, the captured MCF-7 cells could be released. Light-triggered specific cancer cell release with high efficiency may afford a smart surface with significant potential applications for the isolation and analysis of circulating tumor cells.

Selective photoregulation of the activity of glycogen synthase and glycogen phosphorylase, two key enzymes in glycogen metabolism

Glycogen is a polymer of α-1,4- and α-1,6-linked glucose units that provides a readily available source of energy in living organisms. Glycogen synthase (GS) and glycogen phosphorylase (GP) are the two enzymes that control, respectively, the synthesis and degradation of this polysaccharide and constitute adequate pharmacological targets to modulate cellular glycogen levels, by means of inhibition of their catalytic activity. Here we report on the synthesis and biological evaluation of a selective inhibitor that consists of an azobenzene moiety glycosidically linked to the anomeric carbon of a glucose molecule. In the ground state, the more stable (E)-isomer of the azobenzene glucoside had a slight inhibitory effect on rat muscle GP (RMGP, IC50 = 4.9 mM) and Escherichia coli GS (EcGS, IC50 = 1.6 mM). After irradiation and subsequent conversion to the (Z)-form, the inhibitory potency of the azobenzene glucoside did not significantly change for RMGP (IC50 = 2.4 mM), while its effect on EcGS increased 50-fold (IC50 = 32 μM). Sucrose synthase 4 from potatoes, a glycosyltransferase that does not operate on glycogen, was only slightly inhibited by the (E)-isomer (IC50 = 0.73 mM). These findings could be rationalized on the basis of kinetic and computer-aided docking analysis, which indicated that both isomers of the azobenzene glucoside mimic the EcGS acceptor substrate and exert their inhibitory effect by binding to the glycogen subsite in the active center of the enzyme. The ability to selectively photoregulate the catalytic activity of key enzymes of glycogen metabolism may represent a new approach for the treatment of glycogen metabolism disorders.

Synthesis and Properties of Photoswitchable Carbohydrate Fluorosurfactants

We describe the parallel synthesis, photocontrollable surface tension, and antibacterial performance of a new class of carbohydrate fluorosurfactant. Novel fluorosurfactants comprised a mono- or disaccharide head group linked to an azobenzene unit that was variably substituted with a trifluoromethyl group. Fluorosurfactants were rapidly assembled using the venerable CuI-catalysed azide–alkyne cycloaddition reaction and exhibited light-addressable surface activity, excellent water solubility, and selective antibacterial activity against Gram-positive Staphylococcus aureus. Notably, the physicochemical and biological activity of these novel materials was heavily dependent on the nature of the head group and the position of the trifluoromethyl substituent on the azobenzene ring. The UV-adapted cis-isomer of fluorosurfactants displayed good thermal stability at ambient temperature, with little reversion to the stable trans isomer after 16 h. These novel, light-responsive materials should find broad interest in a range of biomedical and technological fields, including drug and gene delivery, self-cleaning oleophobic surfaces, and antibacterial coatings for medical devices.