ChemistryOpen

The cover picture illustrates the concept of using metal-conjugated affinity labels (m-ALs) to convert proteases into well-defined and catalytically active artificial metalloenzymes. The X-ray structure of the papain-bound inhibitor E64c (orange) served as the basis to predict the orientation of the half-sandwich rhodium(III) moiety (yellow sphere) within the binding pocket of the protease. The well-defined position of the affinity label on the protein surface leads to a distinct environment of the metal center, which translates into enantiomeric ratios of up to 82:18 in the aqueous hydrogenation of ketones. For more details, see the Communication by Jörg Eppinger et al., on p. 50 ff.

“We reasoned that covalent approaches so far suffered from an ill-defined orientation of the metal center on the protein surface. Using specifically designed metal-conjugated affinity labels to introduce metal centers into the binding pocket of cysteine proteases, we generate a structurally distinct binding mode of the cofactor.” This and more about the story behind the cover research can be found on p. 50.

How to train a protein: Metal-conjugated affinity labels were used to selectively position catalytically active metal centers in the binding pocket of proteases. The resulting artificial metalloenzymes achieve up to 82 % e.r. in the hydrogenation of ketones. The modular setup enables a rapid generation of artificial metalloenzyme libraries, which can be adapted to a broad range of catalytic conditions.

Like beads on a string: A synthetic method for the directional construction of strings of spherical fullerenes along stacks of planar oligothiophenes is described. The key to success was the preparation of fullerenes with two solubilizing tri(ethylene glycol) tails (bold) and an aromatic aldehyde for covalent capture by hydrazides along the oligothiophene stacks (red).

The fast and the fluoride: A pyridine derivative functionalized with tert-butyldimethylsilyl ether has been synthesized and used as a selective chromofluorogenic fluoride sensor in water/cetyltrimethylammonium bromide solutions. The chromofluorogenic response arises from the fluoride-induced hydrolysis of the silyl ether moiety, which generates a coloured and highly emissive phenolate anion.

Back to generation one! Catalyzed by the first-generation Grubbs ruthenium complex, intramolecular [2+2+2] cycloaddition of triynes to their benzene derivatives 2 and tandem cross-metathesis reactions of enediynes to their conjugated triene derivatives 4 perform smoothly in moderate to good yields under mild conditions. A possible reaction mechanism is presented on the basis of deuterium-labeling results.

The impact of Ag nanoparticles: A new approach to both sizing nanoparticles in solution and determining their agglomeration and aggregation state solely by electrochemical methods is presented. The data obtained by this method is critically compared to results of nanoparticle tracking analysis.