Functional Molecular Junctions Derived from Double Self‐Assembled Monolayers

Information processing using molecular junctions is becoming more important as devices are miniaturized to the nanoscale. Herein, we report functional molecular junctions derived from double self‐assembled monolayers (SAMs) intercalated between soft graphene electrodes. Newly assembled molecular junctions are fabricated by placing a molecular SAM/(top) electrode on another molecular SAM/(bottom) electrode by using a contact‐assembly technique. Double SAMs can provide tunneling conjugation across the van der Waals gap between the terminals of each monolayer and exhibit new electrical functions. Robust contact‐assembled molecular junctions can act as platforms for the development of equivalent contact molecular junctions between top and bottom electrodes, which can be applied independently to different kinds of molecules to enhance either the structural complexity or the assembly properties of molecules.     

Miller–Urey Spark‐Discharge Experiments in the Deuterium World

We designed and conducted a series of primordial‐soup Miller‐Urey style experiments with deuterated gases and reagents to compare the spark‐discharge products of a “deuterated world” with the standard reaction in the “hydrogenated world”. While the deuteration of the system has little effect on the distribution of amino acid products, significant differences are seen in other regions of the product‐space. Not only do we observe about 120 new species, we also see significant differences in their distribution if the two hydrogen isotope worlds are compared. Several isotopologue matches can be identified in both, but a large proportion of products have no equivalent in the corresponding isotope world with ca. 43 new species in the D world and ca. 39 new species in the H world. This shows that isotopic exchange (the addition of only one neutron) may lead to significant additional complexity in chemical space under otherwise identical reaction conditions.     

Dependency of the Tunneling Decay Coefficient in Molecular Tunneling Junctions on the Topography of the Bottom Electrodes

A controversy in molecular electronics is the unexplained large spread in values of the tunneling decay coefficient β in tunneling junctions with self‐assembled monolayers of n‐alkanethiolates (SC_n). We show control of the β value over the range 0.4–1.0 n_C⁻¹ in junctions by changing the topography of the bottom electrodes that support the SAMs. Very low β values (0.4–0.5 n_C⁻¹) are obtained for rough surfaces with large areas of exposed grain boundaries, while β=1.0 n_C⁻¹ for smooth surfaces with small areas of exposed grain boundaries.     

Proto‐Urea‐RNA (Wöhler RNA) Containing Unusually Stable Urea Nucleosides

The RNA world hypothesis assumes that life on Earth began with nucleotides that formed information‐carrying RNA oligomers able to self‐replicate. Prebiotic reactions leading to the contemporary nucleosides are now known, but their execution often requires specific starting materials and lengthy reaction sequences. It was therefore proposed that the RNA world was likely proceeded by a proto‐RNA world constructed from molecules that were likely present on the early Earth in greater abundance. Herein, we show that the prebiotic starting molecules bis‐urea (biuret) and tris‐urea (triuret) are able to directly react with ribose. The urea‐ribosides are remarkably stable because they are held together by a network of intramolecular, bifurcated hydrogen bonds. This even allowed the synthesis of phosphoramidite building blocks and incorporation of the units into RNA. Investigations of the nucleotides’ base‐pairing potential showed that triuret:G RNA base pairs closely resemble U:G wobble base pairs. Based on the probable abundance of urea on the early Earth, we postulate that urea‐containing RNA bases are good candidates for a proto‐RNA world.     

Steep pH Gradients and Directed Colloid Transport in a Microfluidic Alkaline Hydrothermal Pore

All life on earth depends on the generation and exploitation of ionic and pH gradients across membranes. One theory for the origin of life proposes that geological pH gradients were the prebiotic ancestors of these cellular disequilibria. With an alkaline interior and acidic exterior, alkaline vents match the topology of modern cells, but it remains unknown whether the steep pH gradients persist at the microscopic scale. Herein, we demonstrate the existence of 6 pH‐unit gradients across micrometer scales in a microfluidic vent replicate. Precipitation of metal sulfides at the interface strengthens the gradients, but even in the absence of precipitates laminar flow sustains the disequilibria. The gradients drive directed transport at the fluid interface, leading to colloid accumulation or depletion. Our results confirm that alkaline vents can provide an exploitable pH gradient, supporting their potential role at the emergence of chemiosmosis and the origin of life.     

Non-Enzymatic RNA Backbone Proofreading through Energy-Dissipative Recycling

Non-enzymatic oligomerization of activated ribonucleotides leads to ribonucleic acids that contain a mixture of 2′,5′- and 3′,5′-linkages, and overcoming this backbone heterogeneity has long been considered a major limitation to the prebiotic emergence of RNA. Herein, we demonstrate non-enzymatic chemistry that progressively converts 2′,5′-linkages into 3′,5′-linkages through iterative degradation and repair. The energetic costs of this proofreading are met by the hydrolytic turnover of a phosphate activating agent and an acylating agent. With multiple rounds of this energy-dissipative recycling, we show that all-3′,5′-linked duplex RNA can emerge from a backbone heterogeneous mixture, thereby delineating a route that could have driven RNA evolution on the early earth.     

Photodriven Charge Separation and Transport in Self‐Assembled Zinc Tetrabenzotetraphenylporphyrin and Perylenediimide Charge Conduits

Zinc tetrabenzotetraphenyl porphyrin (ZnTBTPP) covalently attached to four perylenediimide (PDI) acceptors self‐assembles into a π‐stacked, segregated columnar structure, as indicated by small‐ and wide‐angle X‐ray scattering. Photoexcitation of ZnTBTPP rapidly produces a long‐lived electron–hole pair having a 26 Å average separation distance, which is much longer than if the pair is confined within the covalent monomer. This implies that the charges are mobile within their respective segregated ZnTBTPP and PDI charge conduits.     

A Stark Contrast to Modern Earth: Phosphate Mineral Transformation and Nucleoside Phosphorylation in an Iron‐ and Cyanide‐Rich Early Earth Scenario

Organophosphates were likely an important class of prebiotic molecules. However, their presence on the early Earth is strongly debated because the low availability of phosphate, which is generally assumed to have been sequestered in insoluble calcium and iron minerals, is widely viewed as a major barrier to organophosphate generation. Herein, we demonstrate that cyanide (an essential prebiotic precursor) and urea‐based solvents could promote nucleoside phosphorylation by transforming insoluble phosphate minerals in a “warm little pond” scenario into more soluble and reactive species. Our results suggest that cyanide and its derivatives (metal cyanide complexes, urea, ammonium formate, and formamide) were key reagents for the participation of phosphorus in chemical evolution. These results allow us to propose a holistic scenario in which an evaporitic environment could concentrate abiotically formed organics and transform the underlying minerals, allowing significant organic phosphorylation under plausible prebiotic conditions.     

Intermolecular Interactions in Mixed Self‐Assembled Monolayers of Ferrocene

Electrochemical characterization of mixed self‐assembled monolayers (SAMs) of 6‐ferrocenyl‐1‐hexanethiol (FcH) and mercaptoundecanoic acid tyrosinamide (MUATyr) on gold is reported. Single‐component SAMs of FcH presented repulsive intermolecular interactions (vGθ_T=?1.12), while mixed SAMs of FcH/MUATyr (1 : 1) exhibited attractive interactions (vGθ_T=+0.20), with a homogeneous distribution of both components. Electrochemical kinetic determinations on mixed SAMs of FcH/MUATyr, indicated a secondary electron transfer pathway between the redox centers of both components. Higher amounts of FcH in the mixed SAMs lowered the observed rate of electron transfer of MUATyr. The oxidation of FcH caused an anodic shift of 160 mV in the voltammetric wave of MUATyr.