Photoswitchable Carbohydrate-Based Macrocyclic Azobenzene: Synthesis, Chiroptical Switching, and Multistimuli-Responsive Self-Assembly.

A one-pot O-alkylation mediated macrocyclization approach has been used for the synthesis of carbohydrate-based macrocyclic azobenzene. The synthesized macrocycle can be reversibly isomerized between E and Z isomers upon UV or visible irradiation with excellent photostability and thermal stability (t1/2 =51 days at 20 °C for the Z isomer). A chirality transfer from the chiral sugar unit to azobenzene was observed by circular dichroism (CD). DFT and TD-DFT calculations were performed to calculate the optimal geometry and the theoretical absorption and CD spectra. Comparison of the experimental CD spectra with the theoretical ones suggests that both E- and Z-macrocycles adopt preferentially P-helicity for the azobenzene moiety. Furthermore, the macrocycle showed gelation ability in cyclohexane and ethanol with multistimuli-responsive behavior upon exposure to environmental stimuli including thermal-, photo-, and mechanical responses. Moreover, these organogels display temperature-dependent helical inversion, which can be tuned by a repeated heating-cooling procedure.

Identification of acylation products in SHAPE chemistry.

SHAPE chemistry (selective 2'-hydroxyl acylation analyzed by primer extension) has been developed to specifically target flexible nucleotides (often unpaired nucleotides) independently to their purine or pyrimidine nature for RNA secondary structure determination. However, to the best of our knowledge, the structure of 2'-O-acylation products has never been confirmed by NMR or X-ray data. We have realized the acylation reactions between cNMP and NMIA under SHAPE chemistry conditions and identified the acylation products using standard NMR spectroscopy and LC-MS/MS experiments. For cAMP and cGMP, the major acylation product is the 2'-O-acylated compound (>99%). A trace amount of N-acylated cAMP has also been identified by LC-UV-MS2. While for cCMP, the isolated acylation products are composed of 96% of 2'-O-acylated, 4% of N,O-diacylated, and trace amount of N-acylated compounds. In addition, the characterization of the major 2'-O-acylated compound by NMR showed slight differences in the conformation of the acylated sugar between the three cyclic nucleotides. This interesting result should be useful to explain some unexpected reactivity of the SHAPE chemistry.

Stereoselective synthesis and properties of glycoazobenzene macrocycles through intramolecular glycosylation.

An intramolecular glycosylation strategy was used to synthesize a series of new glycoazobenzene macrocycles with high α-selectivity and interesting chiroptical properties. The photoisomerization of an azobenzene template influences mainly the efficiency of the glycosylation.

Glycomacrocycle-Based Azobenzene Derivatives as Chiral Dopants for Photoresponsive Cholesteric Liquid Crystals.

We demonstrate photoresponsive cholesteric liquid crystals (CLCs) doped with glycomacrocyclic azobenzene derivatives, which exhibit large conformational changes, providing dynamic control of helical superstructures in response to a light stimulus. An unprecedented shortening of the helical pitch length and the empowerment of helical twisting power up to 500% are observed upon trans (E) to cis (Z) photoisomerization. Light-driven dynamic helix twisting and untwisting behavior affords the first example of glycomacrocyclic azobenzene-based CLCs, which can drive the mechanical movement of micro-objects. Two modes of rotation-two-directional or one-directional rotational motion (crankshaft mode)-are realized. In particular, the latter mode based on the reversible cholesteric texture transition between homogeneous stripes and focal conics leads to the accumulation of the rotation angles achieving the amplified mechanical movements.