Highly Efficient Cyclic Dinucleotide Based Artificial Metalloribozymes for Enantioselective Friedel–Crafts Reactions in Water

The diverse secondary structures of nucleic acids are emerging as attractive chiral scaffolds to construct artificial metalloenzymes (ArMs) for enantioselective catalysis. DNA-based ArMs containing duplex and G-quadruplex scaffolds have been widely investigated, yet RNA-based ArMs are scarce. Here we report that a cyclic dinucleotide of c-di-AMP and Cu²⁺ ions assemble into an artificial metalloribozyme (c-di-AMP⋅Cu²⁺) that enables catalysis of enantioselective Friedel–Crafts reactions in aqueous media with high reactivity and excellent enantioselectivity of up to 97 % ee. The assembly of c-di-AMP⋅Cu²⁺ gives rise to a 20-fold rate acceleration compared to Cu²⁺ ions. Based on various biophysical techniques and density function theory (DFT) calculations, a fine coordination structure of c-di-AMP⋅Cu²⁺ metalloribozyme is suggested in which two c-di-AMP form a dimer scaffold and the Cu²⁺ ion is located in the center of an adenine-adenine plane through binding to two N7 nitrogen atoms and one phosphate oxygen atom.     

Redox-Active Ligand Assisted Catalytic Water Oxidation by a RuIV=O Intermediate

Water splitting is one of the most promising solutions for storing solar energy in a chemical bond. Water oxidation is still the bottleneck step because of its inherent difficulty and the limited understanding of the O−O bond formation mechanism. Molecular catalysts provide a platform for understanding this process in depth and have received wide attention since the first Ru-based catalyst was reported in 1982. Ru^V=O is considered a key intermediate to initiate the O−O bond formation through either a water nucleophilic attack (WNA) pathway or a bimolecular coupling (I2M) pathway. Herein, we report a Ru-based catalyst that displays water oxidation reactivity with Ru^IV=(O) with the help of a redox-active ligand at pH 7.0. The results of electrochemical studies and DFT calculations disclose that ligand oxidation could significantly improve the reactivity of Ru^IV=O toward water oxidation. Under these conditions, sustained water oxidation catalysis occurs at reasonable rates with low overpotential (ca. 183 mV).     

A Supramolecular Artificial Light-Harvesting System with Two-Step Sequential Energy Transfer for Photochemical Catalysis

An artificial light-harvesting system with sequential energy-transfer process was fabricated based on a supramolecular strategy. Self-assembled from the host–guest complex formed by water-soluble pillar[5]arene (WP5), a bola-type tetraphenylethylene-functionalized dialkyl ammonium derivative (TPEDA), and two fluorescent dyes, Eosin Y (ESY) and Nile Red (NiR), the supramolecular vesicles achieve efficient energy transfer from the AIE guest TPEDA to ESY. ESY can function as a relay to further transfer the energy to the second acceptor NiR and realize a two-step sequential energy-transfer process with good efficiency. By tuning the donor/acceptor ratio, bright white light emission can be successfully achieved with a CIE coordinate of (0.33, 0.33). To better mimic natural photosynthesis and make full use of the harvested energy, the WP5⊃TPEDA-ESY-NiR system can be utilized as a nanoreactor: photocatalyzed dehalogenation of α-bromoacetophenone was realized with 96 % yield in aqueous medium.     

Semiconductor/Covalent-Organic-Framework Z-Scheme Heterojunctions for Artificial Photosynthesis

A strategy to covalently connect crystalline covalent organic frameworks (COFs) with semiconductors to create stable organic–inorganic Z-scheme heterojunctions for artificial photosynthesis is presented. A series of COF–semiconductor Z-scheme photocatalysts combining water-oxidation semiconductors (TiO₂, Bi₂WO₆, and α-Fe₂O₃) with CO₂ reduction COFs (COF-316/318) was synthesized and exhibited high photocatalytic CO₂-to-CO conversion efficiencies (up to 69.67 μmol g⁻¹ h⁻¹), with H₂O as the electron donor in the gas–solid CO₂ reduction, without additional photosensitizers and sacrificial agents. This is the first report of covalently bonded COF/inorganic-semiconductor systems utilizing the Z-scheme applied for artificial photosynthesis. Experiments and calculations confirmed efficient semiconductor-to-COF electron transfer by covalent coupling, resulting in electron accumulation in the cyano/pyridine moieties of the COF for CO₂ reduction and holes in the semiconductor for H₂O oxidation, thus mimicking natural photosynthesis.     

Between Autonomy and Accommodation:The German Physical Society during the Third Reich

I first sketch the history of the German Physical Society (Deutsche Physikalische Gesellschaft,DPG) from its founding by six young Berlin scientists as the Physical Society of Berlin (Physikalische Gesellschaft zu Berlin) in 1845, through its renaming as the DPG in 1899 and its rise to prominence by the beginning of the 1930s. I then turn to the history of the DPG during the Third Reich, which can be divided into two periods, from the transfer of power in Germany to the Nazis in 1933 to 1940, and from 1941 to 1945. During the first period, Johannes Stark (1874–1957), one of the leaders of the “German Physics” (Deutsche Physik) movement, attempted to gain election as the Chairman of the DPG in September 1933 but was repulsed. A period of relative autonomy of the DPG from Nazi ideology and policies ensued, which gradually was transformed into one of accommodation, until at the end of the 1938, Peter Debye (1884–1966), then Chairman of the DPG, bowed to governmental demands and Nazi activists in the DPG, introduced Nazi principles, and strongly advised the Jewish members of the DPG to withdraw from it. Debye left Germany in early 1940, and after a transitional period in which Jonathan Zenneck (1871–1959) served as Acting Chairman, Carl Ramsauer (1879–1955) was elected Chairman of the DPG in December 1940, thus opening the second period, the Ramsauer era, which lasted from 1941 until the end of the war in 1945. Ramsauer oversaw the self-coordination (Selbstgleichschaltung) of the DPG to the Nazi regime, and as an industrial physicist he led the DPG to establish ever more alliances with powerful figures in the military-industrial complex of Nazi Germany, which worked to the advantage both of Ramsauer and the DPG and to that of the Nazi regime during the course of the war. Finally, as the military defeat of Germany loomed, Ramsauer took steps aimed at insuring the survival of German physics in the postwar period. After the war, he masked the wartime activities of himself and the DPG, thereby contributing to the postwar conspiracy of silence or minimization of the Nazi past in Germany. Dieter Hoffmann is a research scholar at the Max Planck Institute for the History of Science and a professor at Humboldt University in Berlin.