Masahiko Hara

Controlling the interfacial properties of organic materials using external stimuli is crucial for applications in adhesion, tribology, and electrochemistry. In particular, light irradiation provides a precise, non-contact method for dynamically manipulating molecular structures and surface morphology. Azobenzene-based photoresponsive self-assembled monolayers (SAMs) undergo reversible trans–cis isomerization, inducing conformational changes. However, conventional SAMs form densely packed structures that restrict the free volume required for efficient isomerization. To address this limitation, reducing molecular packing density is essential to achieving functional surface responses to light irradiation. This study addressed the challenge of constructing azobenzene-based photoresponsive low-density SAMs by controlling their formation kinetics. We demonstrate that combining bulky substituents in azobenzenethiol with kinetic control of SAM formation enables the creation of low-density SAMs capable of dynamic surface morphological changes upon photoisomerization. Unlike conventional densely packed SAMs, where the azobenzene moieties remain static, the proposed approach facilitates the reversible emergence and disappearance of nanoscale "nanobumps.” X-ray photoelectron spectroscopy and atomic force microscopy analyses confirm this behavior results from a combination of molecular packing density and thiolate binding states, which are absent in conventional high-density SAMs. This study offers new insights into the design of functional photoresponsive surfaces and presents a strategy for developing light-controllable interfacial systems with potential applications in molecular switches and adaptive coatings.

Gold nanoparticles (Au NPs) are unique catalysts due to their increased coordination unsaturation via nanoparticulation. Effective functioning requires an appropriate support to maintain particle dispersion without compromising nanoscale properties. Cross‐linked hydrophilic polymer‐derived hydrogels are ideal supports, particularly for biological and biomedical reactions, due to their aqueous affinity and biocompatibility. However, applications in confined spaces, such as in vivo environments, necessitate hydrogel micronization. This study introduces microsized DNA hydrogels as support for Au catalysts. DNA motif‐composed hydrogel particles exhibit high crosslinking density and produce small Au NPs owing to short DNA strands. This system significantly enhances catalytic efficiency compared to similar‐sized Au NP gel‐supported catalysts and requires minimal gold catalyst. Modulating DNA hydrogel crosslinking density allows easy control of Au NP size and catalytic activity, further improved by increased hydrogel surface area through microparticulation. These findings demonstrate DNA nanotechnology's versatility in tailoring DNA hydrogel properties and Au NP catalytic behavior. Computer‐aided design enables precise particle property and motif arrangement manipulation, offering promising customizable catalytic systems.

Gold nanoparticles (Au NPs) are unique catalysts because the nanoparticulation increases the number high coordination unsaturation sites. For Au NPs to act as catalysts, the choice of a suitable support for the desired reaction is essential to ensure homogeneous dispersion of the particles while maintaining their nanosize. As a support material, hydrogels obtained by three-dimensional crosslinking of hydrophilic polymers are suitable dispersants for Au NPs. In addition, their high affinity for water-rich environments and high biocompatibility have attracted attention for biological and biomedical reactions. However, application in small, confined spaces such as in vivo requires micronization of the hydrogel. Here, we have developed a gold catalyst supported on micro-sized DNA hydrogels with variable internal crosslinking densities composed of simple DNA nanostructures called motifs. The short strand length of the DNA motif resulted in DNA hydrogel particles with high crosslinking density and Au NPs with small particle size. Furthermore, our micro-sized DNA hydrogel particle-supported gold catalyst system sufficiently advanced the model reaction with a very small amount of gold catalyst compared to a gel-supported gold catalyst system with a comparable Au NP size. The crosslinking density of the DNA hydrogel particles, and thus the size of the resulting Au NPs, can be easily varied and the catalytic activity can be enhanced by increasing the surface area of the hydrogel catalyst support through microparticulation. Our findings based on DNA nanotechnology suggest that the physical properties of the DNA hydrogel particles, such as particle size and crosslinking density, and the catalytic activity of the Au NPs, can be easily designed using computer software, as can the arrangement and length of the motifs that form the constituent units.

We examined the surface structure, binding conditions, electrochemical behavior, and thermal stability of self-assembled monolayers (SAMs) on Au(111) formed by N-(2-mercaptoethyl)heptanamide (MEHA) containing an amide group in an inner alkyl chain using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) to understand the effects of an internal amide group as a function of deposition time. The STM study clearly showed that the structural transitions of MEHA SAMs on Au(111) occurred from the liquid phase to the formation of a closely packed and well-ordered β-phase via a loosely packed α-phase as an intermediate phase, depending on the deposition time. XPS measurements showed that the relative peak intensities of chemisorbed sulfur against Au 4f for MEHA SAMs formed after deposition for 1 min, 10 min, and 1 h were calculated to be 0.0022, 0.0068, and 0.0070, respectively. Based on the STM and XPS results, it is expected that the formation of a well-ordered β-phase is due to an increased adsorption of chemisorbed sulfur and the structural rearrangement of molecular backbones to maximize lateral interactions resulting from a longer deposition period of 1 h. CV measurements showed a significant difference in the electrochemical behavior of MEHA and decanethiol (DT) SAMs as a result of the presence of an internal amide group in the MEHA SAMs. Herein, we report the first high-resolution STM image of well-ordered MEHA SAMs on Au(111) with a (3 × 2√3) superlattice (β-phase). We also found that amide-containing MEHA SAMs were thermally much more stable than DT SAMs due to the formation of internal hydrogen networks in MEHA SAMs. Our molecular-scale STM results provide new insight into the growth process, surface structure, and thermal stability of amide-containing alkanethiols on Au(111).

Previously proposed hypotheses on the origin of life are reviewed and it is demonstrated that none of them can provide the energy flux of ionizing radiation (UV/X/γ photons, and high-energy charged particles and neutrons) required to synthesize organic materials as demonstrated by the experiments by Miller and Urey in 1953. In order to overcome this difficulty, Ebisuzaki and Maruyama, in 2017, proposed a new hypothesis called the “Nuclear Geyser Model” of the origin of life, in which high-energy flux from a natural nuclear reactor drives chemical reactions to produce major biological molecules, such as amino acids, nucleotides, sugars, and fatty acids from raw molecules (H₂O, N₂, and CO₂). Natural nuclear reactors were common on the surface of Hadean Earth, because the ²³⁵U/²³⁸U ratio was as high as 20%, which is much higher than the present value (0.7%), due to the shorter half-life of ²³⁵U than ²³⁸U. Ebisuzaki and Maruyama further posited that aqueous electrons and glyceraldehyde play key roles in the networks of chemical reactions in a nuclear geyser and suggested that primordial life depended on glyceraldehyde phosphate (GAP) from the nuclear geyser system as energy, carbon, and phosphate sources, pointing to a possible parallelism with the anaerobic glycolysis pathway; in particular, the lower stem path starting from GAP through Acetyl Coenzyme A to produce ATP and reduction power. It is shown that microbes (members of candidate division OD1) inhabiting high alkali hot springs, a modern analogue of the Hadean Earth environment, do not possess genes associated with conventional metabolisms, such as those of the TCA cycle, but only have genes in the lower stem path of the glycolysis. This is named the “Hadean Primordial Pathway”, because it is believed that this striking result points to a plausible origin of metabolic pathways of extant organisms. Also proposed is a step-by-step scenario of the evolution of the metabolism: 1) Chemical degradation of GAP supplied from the nuclear geyser to lactate; 2) Catalytic reactions to produce reductive power and acetyl coenzyme A (or its primitive form) and self-reproductive reactions by ribozymes on the surface of minerals (pyrite and struvite), which precipitate in a nuclear geyser (RNA world); 3) Enzymatic reactions by proteins with pyrites and the struvite in their reaction centers (RNP world); and, 4) Metabolism of extant organisms with the full assembly of enzymes produced by translating molecular machines with information stored in DNA sequences (DNA world). It is further inferred that relics of primordial metabolic evolution in the Hadean nuclear geyser can be seen at the reaction centers of enzymes of both pyrite and struvite types, nucleotide-like molecules as a cofactor of the enzymes, Calvin Cycle of photosynthesis, and chemical abundance of cytoplasm.

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The interaction strength of progressively longer oligomers of glycine, (Gly), di-Gly, tri-Gly, and penta-Gly, with a natural pyrite surface was directly measured using the force mode of an atomic force microscope (AFM). In recent years, selective activation of abiotically formed amino acids on mineral surfaces, especially that of pyrite, has been proposed as an important step in many origins of life scenarios. To investigate such notions, we used AFM-based force measurements to probe possible non-covalent interactions between pyrite and amino acids, starting from the simplest amino acid, Gly. Although Gly itself interacted with the pyrite surface only weakly, progressively larger unbinding forces and binding frequencies were obtained using oligomers from di-Gly to penta-Gly. In addition to an expected increase of the configurational entropy and size-dependent van der Waals force, the increasing number of polar peptide bonds, among others, may be responsible for this observation. The effect of chain length was also investigated by performing similar experiments using l-lysine vs. poly-l-lysine (PLL), and l-glutamic acid vs. poly-l-glutamic acid. The results suggest that longer oligomers/polymers of amino acids can be preferentially adsorbed on pyrite surfaces.