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The superconducting properties of atomic layers are strongly affected by the presence of surfaces and interfaces. In this study, we aim to elucidate the mechanism by which the superconducting transition temperature Tc is modulated by the adsorption of organic molecules. We have performed a comprehensive study on the atomic layer superconductor Si(111)-(√7 × √3)-In with adsorption of ZnPc molecules using electron transport measurements, angle-resolved photoemission spectroscopy, and ab initio calculations. Through comparison with previous studies, the results show that the observed Tc increase cannot be attributed to the charge transfer from molecules as previously thought. We propose a new mechanism based on the push-back effect caused by molecule adsorption. [ABSTRACT FROM AUTHOR]

Single-molecule junctions (SMJs) have attracted wide attention due to their unique electronic property originating from their structure, i.e. single molecule connected to the electrodes at both ends. Although the junction structure has significant effects on the electronic property of the SMJs, the experimental method to define the geometry of the bridged molecule is limited. Recently, we have succeeded in the observation of surface-enhanced Raman scattering (SERS) spectroscopy in combination with the current-voltage (IV) response measurement, revealing the junction structure of SMJs. The IV response obtained by the combination measurement provides the electronic structure of the molecule fluctuated by the connection to the metal electrodes, allowing the analysis of the effect of the charge transfer on the SERS spectra. The strong electronic coupling between metal and molecule enhances the charge transfer resonance and it triggered the excitation of the "Raman silent mode" in the bulk state. Therefore, we have detected the unique SERS spectra in SMJs and revealed the contribution of the charge transfer effects on the SERS spectra at the single-molecule level. [ABSTRACT FROM AUTHOR]

Ionic liquids have been recognized as ideal electrolytes for electrochemical systems owing to their unique properties such as non-volatility, non-flammability, high ionic conductivity, and gel-forming property with polymers. The examples include lithium batteries, fuel cells, double-layer capacitors, actuators, and dye-sensitized solar cells (DSSCs). Here, we revealed the details of charge transport in conventional ionic liquids, proton-conducting protic ionic liquids, and electron-transporting ionic liquids. The latter two examples were task-specific ionic liquids, potentially applicable as fuel cell electrolytes under non-humidifying conditions and also as non-volatile electrolytes in DSSCs, where charge transport occurs via the so-called Grotthuss-like mechanism. To realize polymer electrolytes with high ionic conductivity, we exploited the high ionic conductivity of ionic liquids. In situ free radical polymerization of compatible vinyl monomers in an ionic liquid afforded a novel series of polymer electrolytes, which we named ‘ion gels’. The ionic conductivity at ambient temperature reached a value close to 10-2 S cm-1. The number of carrier ions, calculated from the Nernst-Einstein equation, was found to increase in the ion gels from the corresponding value for the ionic liquid itself, which seems to be caused by the interaction between the polymer matrix and the ionic liquid. [ABSTRACT FROM AUTHOR]

This review summarizes the results of the author's basic research on organic electrochemistry conducted at Gifu Pharmaceutical University over about 40 years. After completing graduate school, the author became a research associate in Prof. Tanekazu Kubota's laboratory and started research on molecular spectroscopy in 1983. After Prof. Kubota retired in 1989, the author continued investigations in the field of organic electrochemistry as an independent researcher. At that time, a research environment in which ab initio molecular orbital calculations can be used as an analytical tool for experimental research was developed, and the author commenced research on organic electrochemistry combined with quantum chemical calculations as a lifework. The author's research topics were basic research on the molecular theory of redox potentials of organic molecules, molecular design of functional molecules, intermolecular interactions of organic molecules involving electron transfers and electron transfer systems composed of bioactive quinones, and analytical application research based on the basic electrochemistry. In this review article, the essence of the research results is introduced while reflecting on the existing situation at the time of the research. The author concludes the review by expressing gratitude to all colleagues for supporting the research in the author's laboratory.

The chemical labeling of proteins with synthetic small compounds is a key technique in chemical biology, protein-based therapy, and material science. Much of the chemical labeling of native proteins, however, depends on the labeling of lysine and cysteine residues. While those methods have contributed significantly to native protein labeling, alternative methods that can modify different amino acid residues are still required. Here we report the development of a novel methodology of oxidative tyrosine labeling, which was inspired by the single-electron transfer reaction in biological systems. The tyrosine labeling methods were developed using small compounds such as N-methyl luminol derivative, N'-acyl-N,N-phenylenediamine, and 1-methyl-4-aryl-urazole under labeling conditions using a hemin, peroxidase, or ruthenium photocatalyst. These methods were applied to target- and site-selective protein modification.

Reactive oxygen species (ROS) are known to play a variety of roles in many important events in vivo. However, the overproduction of ROS causes serious adverse effects to living beings. Numerous drugs have been developed and applied to reduce overproduced ROS, but these have failed to be clinically approved. Since most of these antioxidants are low molecular weight (LMW) compounds, they not only eliminate ROS related to diseases, but also destroy the essential redox reactions necessary for basic energy production in living bodies. In the mitochondria of normal cells, ATP production by electron transport chain is carried out, and a large amount of ROS is thus generated; however, LMW antioxidants also nonspecifically enter normal cells and affect essential oxidation. To improve selective antioxidant properties without damage to these normal redox reactions, we designed new polymer antioxidants. These polymers have self-assembling properties and form nanoparticles (RNPs) in which nitroxide radicals covalently attach as a side chain of the hydrophobic segment in the amphiphilic block copolymers, which are then compartmentalized into the solid core of the nanoparticles. Unlike LMW antioxidants, RNPs have extremely poor in vivo toxicity, as they are less likely to be taken up by healthy cells. Since one of RNPs, RNP N has pH-sensitive disintegration properties, it disintegrates at pH lower than 7.0 such as solid tumors and inflammation. It can therefore be used in pH responsive bioimaging and therapy. We have used RNPs experimentally in the treatment of several diseases and confirmed their effectiveness.

Redox metabolism plays a central role in maintaining homeostasis in living organisms. The electron transfer system in mitochondria produces ATP via endogenous redox molecules such as flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), and coenzyme Q10 (CoQ10), which have flavin or quinone moieties. One-electron transfer reactions convert FMN, FAD, and CoQ10 to the free radical intermediates FMNH and FADH, and CoQ10H, respectively. Dynamic nuclear polarization-magnetic resonance imaging (DNP-MRI) allows us to visualize free radicals in vitro and in vivo. We present a spectroscopic imaging technology with DNP-MRI, which enables the imaging of multiple free radical intermediates such as FADH and CoQH. DNP-MRI can also identify various endogenous free radical intermediates derived from redox transformations.

To elucidate molecular bases of multiple system atrophy (MSA), we first focused on recently identified MSA multiplex families. Though linkage analyses followed by whole genome resequencing, we have identified a causative gene, COQ2, for MSA. We then conducted comprehensive nucleotide sequence analysis of COQ2 of sporadic MSA cases and controls, and found that functionally deleterious COQ2 variants confer a strong risk for developing MSA. COQ2 encodes an enzyme in the biosynthetic pathway of coenzyme Q10. Decreased synthesis of coenzyme Q10 is considered to be involved in the pathogenesis of MSA through decreased electron transport in mitochondria and increased vulnerability to oxidative stress.

Several versatile and rational design strategies for novel fluorescence probes including those based on photoinduced electron transfer have been successfully established. Indeed, based on these design strategies, various novel fluorescence probes were successfully developed including those for reactive oxygen species and reporter enzymes. Furthermore, we have succeeded to visualize tiny tumors in living mice by using cancer-specific antibodies tagged with acidic-pH activatable fluorescence probes. Here, I will describe the details of probe design as well as some imaging results with living cells and animals by applying our novel fluorescence probes.

Fluorescence imaging is the most powerful technique currently available for continuous observation of dynamic intracellular processes in living cells. However, only a very limited range of biomolecules can be visualized because of the lack of flexible design strategies for fluorescence probes. In our laboratory, it was elucidated that fluorescein which has been widely employed as a core of fluorescence probes could be understood as a directly linked electron donor/fluorophore acceptor system. Fluorescence properties of fluorescein derivatives could be easily anticipated and modulated by controlling the rate of photoinduced electron transfer (PeT) from the donor moiety to the xanthene fluorophore. Further, we found that the opposite direction of PeT from the singlet excited fluorophore to the electron acceptor moiety could be occurred. More than twenty probes for imaging of nitric oxide, beta-galactosidase, highly reactive oxygen species, zinc ion et al. have been developed according to precise and rational design strategies based on PeT mechanism.