Molecular Gears: From Solution to Surfaces

This review highlights the major efforts devoted to the development of molecular gears over the past 40 years, from pioneering covalent bis-triptycyl systems undergoing intramolecular correlated rotation in solution, to the most recent examples of gearing systems anchored on a surface, which allow intermolecular transmission of mechanical power. Emphasis is laid on the different strategies devised progressively to control the architectures of molecular bevel and spur gears, as intramolecular systems in solution or intermolecular systems on surfaces, while aiming at increased efficiency, complexity and functionality.     

A pseudo-ligand approach to virtual screening

A virtual screening method is presented that is grounded on a receptor-derived pharmacophore model termed "virtual ligand" or "pseudo-ligand". The model represents an idealized constellation of potential ligand sites that interact with residues of the binding pocket. For rapid virtual screening of compound libraries the potential pharmacophore points of the virtual ligand are encoded as an alignment-free correlation vector, avoiding spatial alignment of pharmacophore features between the pharmacophore query (i.e., the virtual ligand) and the candidate molecule. The method was successfully applied to retrieving factor Xa inhibitors from a Ugi three-component combinatorial library, and yielded high enrichment of actives in a retrospective search for cyclooxygenase-2 (COX-2) inhibitors. The approach provides a concept for "de-orphanizing" potential drug targets and identifying ligands for hitherto unexplored or allosteric binding pockets.     

Pharmacophore alignment search tool: influence of scoring systems on text-based similarity searching

The text-based similarity searching method Pharmacophore Alignment Search Tool is grounded on pairwise comparisons of potential pharmacophoric points between a query and screening compounds. The underlying scoring matrix is of critical importance for successful virtual screening and hit retrieval from large compound libraries. Here, we compare three conceptually different computational methods for systematic deduction of scoring matrices: assignment-based, alignment-based, and stochastic optimization. All three methods resulted in optimized pharmacophore scoring matrices with significantly superior retrospective performance in comparison with simplistic scoring schemes. Computer-generated similarity matrices of pharmacophoric features turned out to agree well with a manually constructed matrix. We introduce the concept of position-specific scoring to text-based similarity searching so that knowledge about specific ligand-receptor binding patterns can be included and demonstrate its benefit for hit retrieval. The approach was also used for automated pharmacophore elucidation in agonists of peroxisome proliferator activated receptor gamma, successfully identifying key interactions for receptor activation.     

From Solid‐Solution Electrodes and the Rocking‐Chair Concept to Today's Batteries

Lithium‐ion batteries (LIBs) have become ubiquitous power sources for small electronic devices, electric vehicles, and stationary energy storage systems. Despite the success of LIBs which is acknowledged by their increasing commodity market, the historical evolution of the chemistry behind the LIB technologies is laden with obstacles and yet to be unambiguously documented. This Viewpoint outlines chronologically the most essential findings related to today's LIBs, including commercial electrode and electrolyte materials, but furthermore also depicts how the today popular and widely emerging solid‐state batteries were instrumental at very early stages in the development of LIBs.     

2-Methoxyhydroquinone from Vanillin for Aqueous Redox-Flow Batteries

We show the synthesis of a redox-active quinone, 2-methoxy-1,4-hydroquinone (MHQ), from a bio-based feedstock and its suitability as electrolyte in aqueous redox flow batteries. We identified semiquinone intermediates at insufficiently low pH and quinoid radicals as responsible for decomposition of MHQ under electrochemical conditions. Both can be avoided and/or stabilized, respectively, using H₃PO₄ electrolyte, allowing for reversible cycling in a redox flow battery for hundreds of cycles.     

Ground state spectrum of methylcyanide

The rotational spectrum of methylcyanide (acetonitrile) in the ground vibrational state was measured in the spectral region from 91 to 810 GHz using the Cologne and Tsukuba spectrometers operated in the Doppler-limited and sub-Doppler saturation layouts. The resolution of the saturation Lamb-dip measurements is estimated to be about 1 kHz at the best of circumstances and the measuring accuracy of 10-60 kHz depending very sensitively on the quality of the spectrum. In the cases of rotational transitions with the low quantum number J (J<18) and with a low difference of the rotational quantum numbers J−K, the resolved or partly resolved hyperfine structures of the rotational transitions were observed. Together with the most accurate data from the literature, the newly measured experimental data were analyzed using the traditional polynomial energy formula as well as the Padè approximant for the effective rotational Hamiltonian. The resulting rotational, centrifugal distortion, and hyperfine structure spectroscopic constants were obtained with a significantly higher accuracy than the ones listed in the literature. In addition, an anomalous accidental resonance was detected between the K=14 ground state levels and the K=12, +l levels in the excited v₈=1 vibrational state.