Poly(ionic liquid) complex with spontaneous micro-/mesoporosity: template-free synthesis and application as catalyst support

A facile, template-free synthetic route is reported toward poly(ionic liquid) complexes (PILCs) which for the first time exhibit stable micro-/mesoporous structure. This is accomplished via in situ ionic complexation between imidazolium-based PILs and poly(acrylic acid) in various alkaline organic solvents. The PILC can be highly loaded with copper salts and can be used as a catalytic support for effective aerobic oxidation of activated hydrocarbons under mild conditions.     

Quadracyclic Adenine: A Non‐Perturbing Fluorescent Adenine Analogue

Fluorescent‐base analogues (FBAs) comprise a group of increasingly important molecules for the investigation of nucleic acid structure and dynamics as well as of interactions between nucleic acids and other molecules. Here, we report on the synthesis, detailed spectroscopic characterisation and base‐pairing properties of a new environment‐sensitive fluorescent adenine analogue, quadracyclic adenine (qA). After developing an efficient route of synthesis for the phosphoramidite of qA it was incorporated into DNA in high yield by using standard solid‐phase synthesis procedures. In DNA qA serves as an adenine analogue that preserves the B‐form and, in contrast to most currently available FBAs, maintains or even increases the stability of the duplex. We demonstrate that, unlike fluorescent adenine analogues, such as the most commonly used one, 2‐aminopurine, and the recently developed triazole adenine, qA shows highly specific base‐pairing with thymine. Moreover, qA has an absorption band outside the absorption of the natural nucleobases (>300 nm) and can thus be selectively excited. Upon excitation the qA monomer displays a fluorescence quantum yield of 6.8 % with an emission maximum at 456 nm. More importantly, upon incorporation into DNA the fluorescence of qA is significantly less quenched than most FBAs. This results in quantum yields that in some sequences reach values that are up to fourfold higher than maximum values reported for 2‐aminopurine. To facilitate future utilisation of qA in biochemical and biophysical studies we investigated its fluorescence properties in greater detail and resolved its absorption band outside the DNA absorption region into distinct transition dipole moments. In conclusion, the unique combination of properties of qA make it a promising alternative to current fluorescent adenine analogues for future detailed studies of nucleic acid‐containing systems.     

Synthesis and Optical Properties of Diaza‐ and Tetraazatetracenes

A series of functionalized diaza‐ and tetraazatetracenes was synthesized, either by condensation of an aromatic diamine with an ortho‐quinone/diethyloxalate followed by chlorination with POCl₃ to give diazatetracenes or by palladium‐catalyzed coupling of a phenylenediamine with various 2,3‐dichloroquinoxalines to give tetraazatetracenes (after oxidation with MnO₂). Representative examples included halogenated and nitrated derivatives. The optical properties of these azatetracenes were discussed with respect to their molecular structures and substitution patterns. The diazatetracenes and tetraazatetracenes formed two different groups that had significantly different electronic structures and properties. Furthermore, 1,2,3,4‐tetrafluoro‐6,11‐bis((triisopropylsilyl)ethynyl)benzo[b]phenazine was synthesized, which is the first reported fluorinated diazatetracene. Single‐crystal X‐ray analysis of this compound is reported.     

Application and Mechanistic Studies of a Water‐Oxidation Catalyst in Alcohol Oxidation by Employing Oxygen‐Transfer Reagents

By using a dimeric ruthenium complex in combination with tert‐butyl hydrogen peroxide (TBHP) as stoichiometric oxidant, a mild and efficient protocol for the oxidation of secondary benzylic alcohols was obtained, thereby giving the corresponding ketones in high yields within 4 h. However, in the oxidation of aliphatic alcohols, the TBHP protocol suffered from low conversions owing to a competing Ru‐catalyzed disproportionation of the oxidant. Gratifyingly, by switching to Oxone (2 KHSO₅ ? KHSO₄ ? K₂SO₄ triple salt) as stoichiometric oxidant, a more efficient and robust system was obtained that allowed for the oxidation of a wide range of aliphatic and benzylic secondary alcohols, giving the corresponding ketones in excellent yields. The mechanism for these reactions is believed to involve a high‐valent Ru^V–oxo species. We provide support for such an intermediate by means of mechanistic studies.     

Synthesis of (S)-(+)-cericlamine through lipase-catalyzed aminolysis of azo acetates

The kinetic enzymatic resolution of azo acetates via aminolysis with Candida antarctica lipase B has been investigated using benzylamine as amine component. The products obtained from this biotransformation in high enantiomeric purity can serve as valuable precursors for various amino alcohols, as exemplified by the synthesis of the serotonin reuptake inhibitor (S)-(+)-cericlamine.     

2,2':6',2'-terpyridine substituted in the 4'-position by the solubilizing and sterically demanding tert-butyl group: a surprisingly new ligand

We describe the synthesis and characterization of 4'-tert-butyl-2,2':6',2'-terpyridine (4'-(t)Butpy, 1), a convergent tpy ligand that exhibits both a sterically demanding and solubilizing 4'-substituent. In the solid state, molecules of 1 pack with alternating tpy and tert-butyl domains, and the bulky alkyl substituents prevent the molecules from engaging in the face-to-face π-interactions which are typical of simple tpy ligands. Instead, the predominant packing forces involve CH···N hydrogen bonds and weak CH···π contacts. The syntheses of the homoleptic complexes [M(1)(2)][PF(6)](2) (M = Fe, Co, Zn and Ru) and the heteroleptic [Ru(tpy)(1)][PF(6)](2) are described. The complexes have been fully characterized in solution, including the (1)H NMR spectroscopic characterization of the paramagnetic [Co(1)(2)][PF(6)](2). Cyclic voltammetric data are consistent with the tert-butyl substituent being slightly electron releasing. The single crystal structures of [Zn(1)(2)][PF(6)](2) and [Ru(1)(2)][PF(6)](2) have been determined; the compounds are essentially isomorphous. The packing of the cations is such that the tert-butyl substituents are accommodated in pockets between the tpy domains of adjacent cations, and as a consequence, the {M(tpy)(2)}-embrace that is a ubiquitous feature of many related structures is not observed.     

Non-singular dislocation loops in gradient elasticity

Using gradient elasticity, we give in this Letter the non-singular fields produced by arbitrary dislocation loops in isotropic media. We present the ‘modified’ Mura, Peach–Koehler and Burgers formulae in the framework of gradient elasticity theory.     

Triphenylene silanes for direct surface anchoring in binary mixed self-assembled monolayers

New triphenylene-based silanes 2-(ω-(chlorodimethylsilyl)-n-alkyl)-3,6,7,10,11-penta-m-alkoxytriphenylene 4 (Tm-Cn) with n = 8 or 9 and m = 7, 8, 9, 10, or 11 were synthesized, and their self-assembly behavior in the liquid state and at glass and silicon oxide surfaces was investigated. The mesomorphic properties of triphenylene silanes 4 (Tm-Cn) and their precursors 3 (Tm-Cn) were determined by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. From the small-angle X-ray scattering (SAXS) regime, a preferential discotic lamellar mesophase can be deduced, and wide-angle X-ray scattering (WAXS) highlights the liquid-like characteristics of the alkyl side chains. To transfer these bulk structural properties to thin films, self-assembled monolayers (SAMs) were obtained by adsorption from solution and characterized by water contact angle measurements, null ellipsometry, and atomic force microscopy (AFM). Employing the concentration as an additional degree of freedom, binary SAMs of 2-(ω-(chlorodimethylsilyl)-undecyl)-3,6,7,10,11-penta-decyloxytriphenylene 4 (T10-C11) were coassembled with chlorodecyldimethylsilane or chlorodimethyloctadecylsilane, and their capability as model systems for organic templating was evaluated. The structure of the resulting binary mixed SAMs was analyzed by water contact angle measurements, null ellipsometry, and X-ray reflectivity (XRR) in combination with theoretical modeling by a multidimensional Parratt algorithm and AFM. The composition dependence of film thickness and roughness can be explained by a microscopic model including the steric hindrance of the respective molecular constituents.     

Self-assembly of class II hydrophobins on polar surfaces

Hydrophobins are structural proteins produced by filamentous fungi that are amphiphilic and function through self-assembling into structures such as membranes. They have diverse roles in the growth and development of fungi, for example in adhesion to substrates, for reducing surface tension to allow aerial growth, in forming protective coatings on spores and other structures. Hydrophobin membranes at the air-water interface and on hydrophobic solids are well studied, but understanding how hydrophobins can bind to a polar surface to make it more hydrophobic has remained unresolved. Here we have studied different class II hydrophobins for their ability to bind to polar surfaces that were immersed in buffer solution. We show here that the binding under some conditions results in a significant increase of water contact angle (WCA) on some surfaces. The highest contact angles were obtained on cationic surfaces where the hydrophobin HFBI has an average WCA of 62.6° at pH 9.0, HFBII an average of 69.0° at pH 8.0, and HFBIII had an average WCA of 61.9° at pH 8.0. The binding of the hydrophobins to the positively charged surface was shown to depend on both pH and ionic strength. The results are significant for understanding the mechanism for formation of structures such as the surface of mycelia or fungal spore coatings as well as for possible technical applications.     

Supported lipopolysaccharide bilayers

In this report, the formation of supported lipopolysaccharide bilayers (LPS-SLBs) is studied with extracted native and glycoengineered LPS from Escherichia coli ( E. coli ) and Salmonella enterica sv typhimurium ( S. typhimurium ) to assemble a platform that allows measurement of LPS membrane structure and the detection of membrane tethered saccharide-protein interactions. We present quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence recovery after photobleaching (FRAP) characterization of LPS-SLBs with different LPS species, having, for example, different molecular weights, that show successful formation of SLBs through vesicle fusion on SiO(2) surfaces with LPS fractions up to 50 wt %. The thickness of the LPS bilayers were investigated with AFM force-distance measurements which showed only a slight thickness increase compared to pure POPC SLBs. The E. coli LPS were chosen to study the saccharide-protein interaction between the Htype II glycan epitope and the Ralstonia solanacearum lectin (RSL). RSL specifically recognizes fucose sugars, which are present in the used Htype II glycan epitope and absent in the epitopes LPS1 and EY2. We show via fluorescence microscopy that the specific, but weak and multivalent interaction can be detected and discriminated on the LPS-SLB platform.