A Molecular Circuit Regenerator to Implement Iterative Strand Displacement Operations

The predictable chemistry of Watson–Crick base-pairing imparts a unique structural programmability to DNA, enabling the facile design of molecular reactions that perform computations. However, many of the current architectures limit devices to a single operational cycle. Herein, we introduce the design of the “regenerator”, a device based on coupled enthalpic and entropic reactions that permits the regeneration of molecular circuit components.     

Rational Fabrication of Anti‐Freezing,Non‐Drying Tough Organohydrogels by One‐Pot Solvent Displacement

Tough hydrogels, polymeric network structures with excellent mechanical properties (such as high stretchability and toughness), are emerging soft materials. Despite their remarkably mechanical features, tough hydrogels exhibit two flaws (freezing around the icing temperatures of water and drying under arid conditions). Inspired by cryoprotectants (CPAs) used in the inhibition of the icing of water in biological samples, a versatile and straightforward method is reported to fabricate extreme anti‐freezing, non‐drying CPA‐based organohydrogels with long‐term stability by partially displacing water molecules within the pre‐fabricated hydrogels. CPA‐based Ca‐alginate/polyacrylamide (PAAm) tough hydrogels were successfully fabricated with glycerol, glycol, and sorbitol. The CPA‐based organohydrogels remain unfrozen and mechanically flexible even up to −70 °C and are stable under ambient conditions or even vacuum.     

Target‐Induced Catalytic Assembly of Y‐Shaped DNA and Its Application for In Situ Imaging of MicroRNAs

DNA is a highly programmable material that can be configured into unique high‐order structures, such as DNA branched junctions containing multiple helical arms converging at a center. Herein we show that DNA programmability can deliver in situ growth of a 3‐way junction‐based DNA structure (denoted Y‐shaped DNA) with the use of three hairpin‐shaped DNA molecules as precursors, a specific microRNA target as a recyclable trigger, and a DNA polymerase as a driver. We demonstrate that the Y‐shaped configuration comes with the benefit of restricted freedom of movement in confined cellular environment, which makes the approach ideally suited for in situ imaging of small RNA targets, such as microRNAs. Comparative analysis illustrates that the proposed imaging technique is superior to both the classic fluorescence in situ hybridization (FISH) method and an analogous amplified imaging method via programmed growth of a double‐stranded DNA (rather than Y‐shaped DNA) product.     

A Double‐Passivation Water‐Based Galvanic Displacement Method for Reproducible Gram‐Scale Production of High‐Performance Platinum‐Alloy Electrocatalysts

Preparation of large quantities of high‐performance supported Pt‐alloy electrocatalysts is crucial for the faster development and implementation of low‐temperature proton exchange membrane fuel cells (PEMFCs). One of the prospective nanofabrication synthesis methods is based on the galvanic displacement (GD) reaction. A facile, highly reproducible, gram scale, water‐based double passivation GD method is now presented for the synthesis of carbon‐supported Pt‐M nanoparticles (M=Cu, Ni, Co). It offers great flexibility over the catalyst design, such as the choice of the sacrificial metal (M), variation of the chemical composition of alloy, variation of total metal loading (Pt+M) on carbon support, or even variation of the carbon support itself. The obtained Pt‐alloy catalysts are several times more active compared to a Pt reference and exhibits better stability during accelerated degradation tests performed at 60 °C.     

Bestimmung von Enzym-Coenzym-Dissoziationskonstanten durch Verdr?ngung von Tetrajodfluorescein aus den Enzym-Farbstoff-Komplexen

Zusammenfassung Die Bindung des Farbstoffs Tetrajodfluorescein an verschiedene Dehydrogenasen wird herangezogen, um die Dissoziationskonstanten von Enzym-Coenzym-Komplexen zu bestimmen, da der Farbstoff und pyridinhaltige Coenzyme um die gleiche Bindungsstelle konkurrieren. Durch Zugabe der interessierenden Coenzyme läßt sich somit der Farbstoff aus seiner Bindungsstelle am Enzym verdrängen.Die Bindung und die Verdrängung des Farbstoffs läßt sich durch Differenzspektrophotometrie untersuchen, wobei die Eigenschaften der Enzym-Farbstoff- und der Enzym-Coenzym-Komplexe aus den Differenzspektren entnehmbar sind. Dabei ergibt sich folgender Zusammenhang:K _D,EL =K · K _D,EF , d.h. die gesuchte Dissoziationskonstante des Enzym-Coenzym-Komplexes ist das Produkt aus der Dissoziationskonstanten des Enzym-Farbstoff-Komplexes und der KopplungskonstantenK zwischen Farbstoff und Coenzym bei der Verdrängungsreaktion.Um Anwendbarkeit und Genauigkeit dieser Methodik zu zeigen, werden die Dissoziationskonstanten von NAD⁺ bzw. NADH an Alkoholdehydrogenase aus Hefe und Pferdeleber und an Lactatdehydrogenase aus Rinder- und Kaninchenmuskel bestimmt und mit den bekannten Werten verglichen.Fräulein I. Günther danken wir für ihre Hilfe bei den Messungen und Auswertungen.