A thermostable azo-linker for reversible photoregulation of DNA replication

Rapid and reversible optical switching of cell membrane area by an amphiphilic azobenzene

Cellular membrane area is a key parameter for any living cell that is tightly regulated to avoid membrane damage. Changes in area-to-volume ratio are known to be critical for cell shape, but are mostly investigated by changing the cell volume via osmotic shocks. In turn, many important questions relating to cellular shape, membrane tension homeostasis and local membrane area cannot be easily addressed because experimental tools for controlled modulation of cell membrane area are lacking. Here we show that photoswitching an amphiphilic azobenzene can trigger its intercalation into the plasma membrane of various mammalian cells ranging from erythrocytes to myoblasts and cancer cells. The photoisomerization leads to a rapid (250-500 ms) and highly reversible membrane area change (ca 2 % for erythrocytes) that triggers a dramatic shape modulation of living cells.

Reversible On-Off Photoswitching of DNA Replication Using a Dumbbell Oligodeoxynucleotide

In most organisms, DNA extension is highly regulated; however, most studies have focused on controlling the initiation of replication, and few have been done to control the regulation of DNA extension. In this study, we adopted a new strategy for azODNs to regulate DNA extension, which is based on azobenzene oligonucleotide chimeras regulated by substrate binding affinity, and the conformation of the chimera can be regulated by a light source with a light wavelength of 365 nm. The results showed that the primer was extended with Taq DNA polymerase after visible light treatment, and DNA extension could be effectively hindered with UV light treatment. We also verify the reversibility of the photoregulation of primer extension through photoswitching of dumbbell asODNs by alternate irradiation with UV and visible light. Our method has the advantages of fast and simple, green response and reversible operations, providing a new strategy for regulating gene replication.

Organocatalytic Reduction of Aromatic Nitro Compounds: The Use of Solid-Supported Phenyl(2-quinolyl)methanol

The reduction of aromatic nitro compounds has been performed employing a catalytic amount of Wang resin-supported phenyl(2-quinolyl)methanol (Wang-PQM) in the presence of an excess of NaBH₄ to regenerate the reactive reducing species at the end of the process. The reduction products are easily isolated through a simple filtration/extraction protocol, and the catalyst can be efficiently recovered and recycled. The condensation route is generally preferred, and azo- and/or hydrazo-arenes can be easily prepared in high yields.

Conformational changes of DNA induced by a trans-azobenzene derivative via non-covalent interactions

In biological environments and in aqueous solution, DNA generally adopts the canonical B conformation. Recently, an azobenzene photoswitch containing a polyamine chain with three positive charges was shown to induce a reversible conformational transition between the A and B forms of DNA, the transition being triggered by trans-cis isomerization of the photoswitch upon non-covalent intercalation. It was proposed that, in its trans conformation, azobenzene stabilizes the A form of DNA. The structural details and the mechanism upon which trans-azobenzene induces the B-to-A DNA transition remain, however, unclear. In the present work, two possible intercalating modes of trans-azobenzene, from the minor groove and from the major groove, were investigated with all-atom molecular-dynamics simulations. Intercalation from the major groove was found to be the most probable binding mode due to favorable electrostatic and π-π stacking interactions. The free-energy profile associated with the B-to-A conformational transition reveals that intercalation from the major groove leads to a conformational change of DNA, showing a slight tendency to interconvert from B- to A-DNA, in agreement with the CD spectrum obtained from the experiment. However, the presence of only one interacting azobenzene is not sufficient to lead to a global conformational change to A-DNA. The present results are expected to serve in the design of DNA switches, which can induce reversible DNA conformational changes.

Photochromism into nanosystems: towards lighting up the future nanoworld

The ability to manipulate the structure and function of promising nanosystems via energy input and external stimuli is emerging as an attractive paradigm for developing reconfigurable and programmable nanomaterials and multifunctional devices. Light stimulus manifestly represents a preferred external physical and chemical tool for in situ remote command of the functional attributes of nanomaterials and nanosystems due to its unique advantages of high spatial and temporal resolution and digital controllability. Photochromic moieties are known to undergo reversible photochemical transformations between different states with distinct properties, which have been extensively introduced into various functional nanosystems such as nanomachines, nanoparticles, nanoelectronics, supramolecular nanoassemblies, and biological nanosystems. The integration of photochromism into these nanosystems has endowed the resultant nanostructures or advanced materials with intriguing photoresponsive behaviors and more sophisticated functions. In this Review, we provide an account of the recent advancements in reversible photocontrol of the structures and functions of photochromic nanosystems and their applications. The important design concepts of such truly advanced materials are discussed, their fabrication methods are emphasized, and their applications are highlighted. The Review is concluded by briefly outlining the challenges that need to be addressed and the opportunities that can be tapped into. We hope that the review of the flourishing and vibrant topic with myriad possibilities would shine light on exploring the future nanoworld by encouraging and opening the windows to meaningful multidisciplinary cooperation of engineers from different backgrounds and scientists from the fields such as chemistry, physics, engineering, biology, nanotechnology and materials science.

Ionic Liquid Promoted Diazenylation of N-Heterocyclic Compounds with Aryltriazenes under Mild Conditions

An efficient, mild, and metal-free approach to direct diazenylation of N-heterocyclic compounds with aryltriazenes using Brønsted ionic liquid as a promoter has been developed for the first time. Many N-heterocyclic azo compounds were synthesized in good to excellent yields at room temperature under an open atmosphere. Notably, the promoter 1,3-bis(4-sulfobutyl)-1H-imidazol-3-ium hydrogen sulfate could be conveniently recycled and reused with the same efficacies for at least four cycles.

Photoregulating RNA digestion using azobenzene linked dumbbell antisense oligodeoxynucleotides

Introduction of 4,4'-bis(hydroxymethyl)-azobenzene (azo) to dumbbell hairpin oligonucleotides at the loop position was able to reversibly control the stability of the whole hairpin structure via UV or visible light irradiation. Here, we designed and synthesized a series of azobenzene linked dumbbell antisense oligodeoxynucleotides (asODNs) containing two terminal hairpins that are composed of an asODN and a short inhibitory sense strand. Thermal melting studies of these azobenzene linked dumbbell asODNs indicated that efficient trans to cis photoisomerization of azobenzene moieties induced large difference in thermal stability (ΔTm = 12.1-21.3 °C). In addition, photomodulation of their RNA binding abilities and RNA digestion by RNase H was investigated. The trans-azobenzene linked asODNs with the optimized base pairs between asODN strands and inhibitory sense strands could only bind few percentage of the target RNA, while it was able to recover their binding to the target RNA and degrade it by RNase H after light irradiation. Upon optimization, it is promising to use these azobenzene linked asODNs for reversible spatial and temporal regulation of antisense activities based on both steric binding and RNA digestion by RNase H.

Photoswitching properties of hairpin ODNs with azobenzene derivatives at the loop position

Photoisomerization of an azobenzene moiety modulates the thermodynamic stability of hairpin ODNs by interfering with stacking interation between azobenzene and neighbouring base pair and dihedral angle of the neighbouring base pair.

Protein tetrazinylation via diazonium coupling for covalent and catalyst-free bioconjugation

This work reports an efficient reagent 1 for direct and covalent introduction of tetrazines onto the surface of proteins and viruses under mild conditions.

Phenylazoindole dyes--part I: the syntheses, characterizations, crystal structures, quantum chemical calculations and antimicrobial properties

In this study, the synthesis of four new phenylazo indole dyes (dye 1-4) were carried out by diazotization of 4-aminoacetophenone and coupling with various 2- and 1,2-disubstituted indole derivatives. The dyes were characterized by UV-vis, FT-IR, (1)H NMR, HRMS and X-ray single crystal diffraction methods. Azo-hydrazone tautomeric bahavior of the dyes in different solvents (DMSO, methanol, acetic acid and chloroform) was investigated by using (1)H NMR and UV-vis results. The experimental results were compared with the corresponding calculated values. The results of experimental data and theoretical calculations showed that the azo tautomer is more stable than hydrazone tautomer. In addition to this, the antimicrobial activity of the dyes was also evaluated.

Effect of the ortho modification of azobenzene on the photoregulatory efficiency of DNA hybridization and the thermal stability of its cis form

We synthesized various azobenzenes methylated at their ortho positions with respect to the azo bond for more effective photoregulation of DNA hybridization. Photoregulatory efficiency, evaluated from the change of T(m) (DeltaT(m)) induced by trans-cis isomerization, was significantly improved for all ortho-modified azobenzenes compared with non-modified azobenzene due to the more stabilized trans form and the more destabilized cis form. Among the synthesized azobenzenes, 4-carboxy-2',6'-dimethylazobenzene (2',6'-Me-Azo), in which two ortho positions of the distal benzene ring with respect to carboxyl group were methylated, exhibited the largest DeltaT(m), whereas the newly synthesized 2,6-Me-Azo (4-carboxy-2,6-dimethylazobenzene), which possesses two methyl groups on the two ortho positions of the other benzene ring, showed moderate improvement of DeltaT(m). Both NMR spectroscopic analysis and computer modeling revealed that the two methyl groups on 2',6'-Me-Azo were located near the imino protons of adjacent base pairs; these stabilized the DNA duplex by stacking interactions in the trans form and destabilized the DNA duplex by steric hindrance in the cis form. In addition, the thermal stability of cis-2',6'-Me-Azo was also greatly improved, but not that of cis-2,6-Me-Azo. Solvent effects on the half-life of the cis form demonstrated that cis-to-trans isomerization of all the modified azobenzenes proceeded through an inversion route. Improved thermal stability of 2',6'-Me-Azo but not 2,6-Me-Azo in the cis form was attributed to the retardation of the inversion process due to steric hindrance between lone pair electrons of the pi orbital of the nitrogen atom and the methyl group on the distal benzene ring.