Cover Picture

The cover picture shows two new catalytic asymmetric reactions in front of an enantiomeric pair of lurs—one of the national symbols of Denmark. Chiral bisoxazoline copper complexes catalyze the reactions. The reaction on the left is the direct enantioselective Mannich reaction of carbonyl compounds with imines to give highly functionalized 4‐oxo‐glutamic esters, while the reaction on the right is the enantioselective nitro‐Mannich reaction of nitro alkanes with imines to give optically active β‐nitro‐α‐amino esters. Why the lur in relation to the present chemistry? Lurs exist as pairs of enantiomers and they probably belong to some of the first man‐made pair of enantiomers, as they are from the Bronze Age (1000–500 BC). The lurs are the oldest musical instruments that can still be played, and are used as enantiomers. Side by side stood two lur‐players, symmetric in every detail, the soft curves of the instruments swaying upwards and outwards at each side. The sonorous notes emphasized the solemn nature of the rituals. It is conceivable that the sound of the lur also accompanied the crackle of the funeral pyre when one of the tribe was cremated and laid to rest in the burial mound of his forefathers. The lurs are made of bronze (copper) and were discovered in lakes; less than 50 are known. The most famous pair of lurs was found in Brudevælte and is the pair shown on the cover. Further information about lurs can be obtained from kaj@chem.au.dk. The picture of the lurs and the accompanying music (click here to listen to the music: www.angewandte.com) are used with permission from The National Museum. For more details about the two new catalytic asymmetric reactions, see Jørgensen et al. on p. 2992 ff. and p. 2995 ff.     

Femtomolar electrochemical detection of DNA targets using metal sulfide nanoparticles

A new electrochemical DNA sensor providing detection capabilities down to 100 attomol of target DNA has been developed. The method applies CdS, ZnS, and PbS nanoparticles conjugated with short DNA sequences which are immobilized via hybridization with complementary sequences on a gold surface. When the DNA target is added, it can be identified by ousting the existing hybridization between one of the DNA-nanoparticle conjugates and the surface DNA. The nanoparticles remaining at the surface are detected by stripping voltammetry. The setup is constructed to give a signal-off response with a build-in control signal as only one of two different metal sulfide signaling probes on the surface is removed by hybridization with the DNA target. The competition assay is, in principle, label-free since no labels are required for detection after addition of DNA target. The dissociation of PbS nanoparticles from the surface after addition of the DNA target has been imaged by fluid phase AFM.     

Efficient N-arylation and N-alkenylation of the five DNA/RNA nucleobases

A general approach to N-arylation and N-alkenylation of all five DNA/RNA nucleobases at the nitrogen atom normally attached to the sugar moiety in DNA or RNA has been developed. Various protected or masked nucleobases engaged readily in the copper-mediated Chan-Lam-Evans-modified Ullmann condensation with a range of different boronic acids at room temperature and were subsequently converted to the corresponding deprotected or unmasked adducts. Different N(3)-protecting groups were examined in the case of thymine, where the benzoyl group afforded the highest yields. A 4-alkylthio-substituted pyrimidin-2(1H)-one served as both a cytosine and a uracil precursor and was N-arylated and N-alkenylated in high yields. Adenine was efficiently and selectively N-arylated and N-alkenylated at the N(9) position by employing a bis-Boc-protected adenine derivative, while a bis-Boc-protected 2-amino-6-chloropurine served as guanine precursor and could also be selectively N(9)-arylated and N(9)-alkenylated.     

Exploring Effects of Protease Choice and Protease Combinations in Enzymatic Protein Hydrolysis of Poultry By-Products

A study of the effects of single and combined protease hydrolysis on myofibrillar versus collagenous proteins of poultry by-products has been conducted. The aim was to contribute with knowledge for increased value creation of all constituents of these complex by-products. A rational approach was implemented for selecting proteases exhibiting the most different activity towards the major protein-rich constituents of mechanically deboned chicken residue (MDCR). An initial activity screening of 18 proteases on chicken meat, turkey tendons and MDCR was conducted. Based on weight yield, size exclusion chromatography (SEC) and SDS-PAGE, stem Bromelain and Endocut-02 were selected. Studies on hydrolysis of four different poultry by-products at 40 °C, evaluated by protein yield, SEC, and SDS-PAGE, indicate that the proteases’ selectivity difference can be utilized in tailor-making hydrolysates, enriched in either meat- and collagen-derived peptides or gelatin. Three modes of stem Bromelain and Endocut-02 combinations during hydrolysis of MDCR were performed and compared with single protease hydrolysis. All modes of the protease combinations resulted in a similar approximately 15% increase in product yield, with products exhibiting similar SEC and SDS-PAGE profiles. This shows that irrespective of the modes of combination, the use of more than one enzyme in hydrolysis of collagen-rich material can provide means to increase the total protein yield and ultimately contribute to increased value creation of poultry by-products.     

Multilayer DNA origami packed on hexagonal and hybrid lattices

"Scaffolded DNA origami" has been proven to be a powerful and efficient approach to construct two-dimensional or three-dimensional objects with great complexity. Multilayer DNA origami has been demonstrated with helices packing along either honeycomb-lattice geometry or square-lattice geometry. Here we report successful folding of multilayer DNA origami with helices arranged on a close-packed hexagonal lattice. This arrangement yields a higher density of helical packing and therefore higher resolution of spatial addressing than has been shown previously. We also demonstrate hybrid multilayer DNA origami with honeycomb-lattice, square-lattice, and hexagonal-lattice packing of helices all in one design. The availability of hexagonal close-packing of helices extends our ability to build complex structures using DNA nanotechnology.     

Spectroelectrochemical cell for in situ studies of solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are able to produce electricity and heat from hydrogen‐ or carbon‐containing fuels with high efficiencies and are considered important cornerstones for future sustainable energy systems. Performance, activation and degradation processes are crucial parameters to control before the technology can achieve breakthrough. They have been widely studied, predominately by electrochemical testing with subsequent micro‐structural analysis. In order to be able to develop better SOFCs, it is important to understand how the measured electrochemical performance depends on materials and structural properties, preferably at the atomic level. A characterization of these properties under operation is desired. As SOFCs operate at temperatures around 1073 K, this is a challenge. A spectroelectrochemical cell was designed that is able to study SOFCs at operating temperatures and in the presence of relevant gases. Simultaneous spectroscopic and electrochemical evaluation by using X‐ray absorption spectroscopy and electrochemical impedance spectroscopy is possible.     

Synthesis of linear and tripoidal oligo(phenylene ethynylene)-based building blocks for application in modular DNA-programmed assembly

Rigid linear and tripoidal organic modules based on the oligo(phenylene ethynylene) backbone having salicylaldehyde-derived termini are synthesized. A highly functionalized 5-iodosalicyl aldehyde was prepared and coupled to each ethynyl group of 1,4-diethynylbenzene or 1,3,5-triethynylbenzene in Sonogashira couplings. The two or three termini of the compounds are functionalized for incorporation in linear and branched oligonucleotide strands. For the linear module (LM), the two termini are equipped with amide spacers, and one of these was functionalized with a DMTr (dimethoxytrityl)-protected hydroxy group and the other with a phosphoramidite. One of the tripoidal modules is prepared with DMTr groups in two of its three termini. A tripoidal module is also synthesized with three different groups on its hydroxy termini: a phosphoramidite, a DMTr group, and an Fmoc group. Extended studies have shown that these rigid linear and tripoidal organic modules can be incorporated into short oligonucleotides. Several of these modules can be applied for DNA-directed assembly and covalent coupling into structures of predetermined connectivity. Such structures have potential application for molecular electronics and nanotechnology.     

Catalytic asymmetric Henry reactions of silyl nitronates with aldehydes

A catalytic enantioselective Henry reaction of silyl nitronates with aldehydes has been developed. Different chiral Lewis acids have been tested for the reaction and it has been found that a variety of chiral copper-ligand complexes can catalyze the Henry reaction. The best yield, diastereo- and enantioselectivity of the nitroalcohols formed are obtained by the application of a copper(II)-diphenyl-bisoxazoline complex as the catalyst in the presence of tetrabutylammonium triphenylsilyldifluorosilicate (TBAT). In order to minimize the epimerization of the nitroaldol products they were converted into the corresponding Mosher esters. The reaction proceeds well for different aromatic aldehydes reacting with alkyl nitronates.