Photo-Controlled Macroscopic Self-Assembly Based on Photo-Switchable Hetero-Complementary Quadruple Hydrogen Bonds

A photo-switchable hetero-complementary quadruple H-bonding array, which consists of an azobenzene-derived ureidopyrimidinone (UPy) module ( Azo-UPy ) and a nonphotoactive diamidonaphthyridine (DAN) derivative ( Napy-1 ), is constructed based on a reversible photo-locking approach. Upon UV (390 nm)/Vis (460 nm) light irradiations, photo-switchable quadruple H-bonded dimerization between Azo-UPy and Napy-1 can be achieved with exhibiting 4.8×10⁴-fold differences in binding strength (ON/OFF ratios). Furthermore, smart polymeric gels with unique photo-controlled macroscopic self-assembly behavior can be fabricated by introducing such quadruple H-bonding array as photo-regulable noncovalent interfacial connections.     

Carbene adduct of cyclopalladated ferrocenylimine as an efficient catalyst for the amination of aryl chlorides

A novel air- and moisture-stable carbene adduct of cyclopalladated ferrocenylimine has been synthesized and characterized. The structure of this compound was determined by X-ray crystal structure analysis. This adduct has been applied as an efficient catalyst for the amination of aryl chlorides.     

Cyclopalladated ferrocenylimine: a highly effective catalyst for the borylation/suzuki coupling reaction

The cyclopalladated ferrocenylimine was an efficient catalyst for the borylation/Suzuki coupling reaction. The catalytic loading for the reaction containing bromoarenes was 1 mol %. When iodobenzene was used, the catalytic loading was as low as 0.1 mol %. Furthermore, the cyclopalladated ferrocenylimine also exhibited excellent catalytic power in the case of substrates containing electron-donating substituents, with yields reaching 93% or higher.     

Substituent effects in trans‐p,p′‐disubstituted azobenzenes: X‐ray structures at 100 K and DFT‐calculated structures

The crystal and molecular structures of two para‐substituted azobenzenes with π‐electron‐donating –NEt₂ and π‐electron‐withdrawing –COOEt groups are reported, along with the effects of the substituents on the aromaticity of the benzene ring. The deformation of the aromatic ring around the –NEt₂ group in N,N,N′,N′‐tetraethyl‐4,4′‐(diazenediyl)dianiline, C₂₀H₂₈N₄, (I), may be caused by steric hindrance and the π‐electron‐donating effects of the amine group. In this structure, one of the amine N atoms demonstrates clear sp²‐hybridization and the other is slightly shifted from the plane of the surrounding atoms. The molecule of the second azobenzene, diethyl 4,4′‐(diazenediyl)dibenzoate, C₁₈H₁₈N₂O₄, (II), lies on a crystallographic inversion centre. Its geometry is normal and comparable with homologous compounds. Density functional theory (DFT) calculations were performed to analyse the changes in the geometry of the studied compounds in the crystalline state and for the isolated molecules. The most significant changes are observed in the values of the N=N—C—C torsion angles, which for the isolated molecules are close to 0.0°. The HOMA (harmonic oscillator model of aromaticity) index, calculated for the benzene ring, demonstrates a slight decrease of the aromaticity in (I) and no substantial changes in (II).     

Improving the Switching Capacity of Glyco-Self-Assembled Monolayers on Au(111)

Self-assembled monolayers (SAMs) decorated with photoisomerizable azobenzene glycosides are useful tools for investigating the effect of ligand orientation on carbohydrate recognition. However, photoswitching of SAMs between two specific states is characterized by a limited capacity. The goal of this study is the improvement of photoswitchable azobenzene glyco-SAMs. Different concepts, in particular self-dilution and rigid biaryl backbones, have been investigated. The required SH-functionalized azobenzene glycoconjugates were synthesized through a modular approach, and the respective glyco-SAMs were fabricated on Au(111). Their photoswitching properties have been extensively investigated by applying a powerful set of methods (IRRAS, XPS, and NEXAFS). Indeed, the combination of tailor-made biaryl-azobenzene glycosides and suitable diluent molecules led to photoswitchable glyco-SAMs with a significantly enhanced and unprecedented switching capacity.     

Cascade One‐Pot Synthesis of Orange‐Red‐Fluorescent Polycyclic Cinnolino[2,3‐f]phenanthridin‐9‐ium Salts by Palladium(II)‐Catalyzed C−H Bond Activation of 2‐Azobiaryl Compounds and Alkenes

Quaternary ammonium salts were synthesized in moderate to good yields through double oxidative C?H bond activation on azobenzenes. The mechanism of the highly regioselective reaction of 2‐azobiaryls with alkenes to give orange‐red‐fluorescent cinnolino[2,3‐f]phenanthridin‐9‐ium salts and 15H‐cinnolino[2,3‐f]phenanthridin‐9‐ium‐10‐ide is proposed to involve ortho C?H olefination of the 2‐azobiaryl compound with the alkene, intramolecular aza‐Michael addition, concerted metalation–deprotonation (CMD), reductive elimination, and oxidation.     

An efficient and recyclable water-soluble cyclopalladated complex for aqueous Suzuki reactions under aerial conditions

Several water-soluble cyclopalladated complexes with five- or six-membered rings have been prepared as air-stable solids from Schiff base ligands bearing an N-phenyl sulfonate groups. Cyclopalladated complexes with six-membered rings show high catalytic efficiency for the Suzuki reactions of aryl bromides with phenylboronic acid in aqueous solvents under mild conditions. Palladium complex 1 can be used for five reaction cycles in high conversions for the Suzuki reactions in neat water without additives. The catalytic process for the Suzuki couplings is proved by TEM analysis to proceed on Pd(0) nanoparticles. Surfactant-protected palladium nanoparticles present lower activities and poorer recyclability for the coupling reactions than those generated in situ without additives.     

Visible-Light Switching of Metallosupramolecular Assemblies**

A photoswitchable ligand and palladium(II) ions form a dynamic mixture of self-assembled metallosupramolecular structures. The photoswitching ligand is an ortho-fluoroazobenzene with appended pyridyl groups. Combining the E-isomer with palladium(II) salts affords a double-walled triangle with composition [Pd₃L₆]⁶⁺ and a distorted tetrahedron [Pd₄L₈]⁸⁺ (1 : 2 ratio at 298 K). Irradiation with 410 nm light generates a photostationary state with approximately 80 % of the E-isomer of the ligand and results in the selective disassembly of the tetrahedron, the more thermodynamically stable structure, and the formation of the triangle, the more kinetically inert product. The triangle is then slowly transformed back into the tetrahedron over 2 days at 333 K. The Z-isomer of the ligand does not form any well-defined structures and has a thermal half-life of 25 days at 298 K. This approach shows how a thermodynamically preferred self-assembled structure can be reversibly pumped to a kinetic trap by small perturbations of the isomer distribution using non-destructive visible light.     

Nick sealing by T4 DNA ligase on a modified DNA template: tethering a functional molecule on D-threoninol

Efficient DNA nick sealing catalyzed by T4 DNA ligase was carried out on a modified DNA template in which an intercalator such as azobenzene had been introduced. The intercalator was attached to a D-threoninol linker inserted into the DNA backbone. Although the structure of the template at the point of ligation was completely different from that of native DNA, two ODNs could be connected with yields higher than 90% in most cases. A systematic study of sequence dependence demonstrated that the ligation efficiency varied greatly with the base pairs adjacent to the azobenzene moiety. Interestingly, when the introduced azobenzene was photoisomerized to the cis form on subjection to UV light (320-380 nm), the rates of ligation were greatly accelerated for all sequences investigated. These unexpected ligations might provide a new approach for the introduction of functional molecules into long DNA strands in cases in which direct PCR cannot be used because of blockage of DNA synthesis by the introduced functional molecule. The biological significance of this unexpected enzymatic action is also discussed on the basis of kinetic analysis.