Tag: Tokyo University of Science

For the first time ever, a research group consisting of Dr. Toshiki Furuya, Associate Professor at the Department of Applied Biological Science, Tokyo University of Science, Japan, has succeeded in isolating bacteria from the seeds of passion fruit (Passiflora edulis). Their research, which also unearths the surviving mechanisms of these bacteria inside the seeds, has been published in the journal MicrobiologyOpen.

In their study, the scientists focused on the seeds of P. edulis. The seeds of this fruit are full of secondary metabolites with strong antimicrobial properties, such as resveratrol and piceatannol—the latter present at high levels of up to 2.2 mg/g.

As Dr. Furuya reveals the rationale behind choosing passion fruit seeds for the study, “The extraordinarily high concentration of piceatannol protects P. edulis seeds from microorganisms. We thought it would be interesting to know if any endophytic microorganism could survive this extreme environment and if yes, how.”

Earlier reports showed that endophytes capable of surviving in an environment rich in biologically active compounds possessed biocatalytic activities related to the metabolism of these compounds. The fact that their biocatalytic potential could be exploited for therapeutic purposes made the scientists even more eager to explore the presence of endophytic bacteria.

The scientists collected and surface-sterilized the seeds of naturally grown P. edulis before either cutting or crushing them and placing them on solid agar-based growth media to check for microbial growth. While no microbial colony appeared from the cut or homogenized seeds, interestingly, the seedlings sprouting from the cut seeds, when exposed to growth media, gave rise to microbial colonies. The scientists then performed sequencing to identify the bacteria that appeared on the agar plate.

The findings were remarkable. From the seedlings, the scientists isolated 19 strains, including three previously unreported strains of bacteria from various genera. They hypothesized that inside the seeds, piceatannol exerted bacteriostatic (or “bacterial growth-stalling”) rather than bactericidal (or “bacteria-killing”) effects on the residing bacteria.

Ms. Aoi Ishida, the co-author of the study explains: “Due to the presence of a high concentration of piceatannol, the growth of the bacteria was stagnated inside the seed, but when transmitted to the next-generation seedlings during germination, the bacteria were relieved from the effect of piceatannol and able to grow again.”

The scientists also found one of the bacteria, Brevibacterium sp. PE28-2, to possess the ability to convert resveratrol and piceatannol to their respective derivatives. This is the first endophyte shown to exhibit such activity.

Dr. Furuya and Ms. Ishida are very hopeful that the method established in this study is expected to be effective in isolating several useful endophytic bacteria from a variety of plants. Moreover, considering the current focus on engineering new biomolecules with diverse applications, the results of this study would accelerate research on seed endophytic bacteria.

In a pioneering study, scientists from Japan established that psychological stress can negatively affect neurogenesis and cause depression in a mouse model.

Recent research has explained how vicarious social defeat can cause psychological stress in mice. This involves the mouse being made to experience the defeat of another mouse in an experimental social setting. Using this model, a group of scientists from Japan attempted to establish a link between depressive symptoms and hippocampal neurogenesis.

Professor Akiyoshi Saitoh from Tokyo University of Science, one of the lead authors of the study, further explains the motivation behind this research, “The number of individuals suffering from depression has been on the rise the world over. However, the detailed pathophysiology of depression still remains to be elucidated. So, we decided to focus on the possible mechanism of psychological stress in adult hippocampal neurogenesis, to understand its role in depressive disorders.” The study was published in the journal Behavioural Brain Research.

After exposing the mice to chronic vicarious social defeat stress, Prof. Saitoh and the team, including Mr Toshinori Yoshioka and Dr Daisuke Yamada from Tokyo University of Science, analyzed their behaviour and brains in close detail.

Aside from behavioural deficits like social withdrawal, the stressed mice also showed a significant decrease in the survival rate of newborn neurons in the dentate gyrus, a region in the hippocampus responsible for sensory perception and memory, compared to the non-stressed controls. This condition persisted for up to four weeks, after “stressing” the mice. However, cell growth, differentiation, and maturation did not differ between the groups of mice during the period of observation. Notably, the cell survival rate was restored in the stressed mice after treatment with a chronic antidepressant called fluoxetine.

Regarding the results, Mr. Toshinori Yoshioka adds, “We have found out that chronic mental stress affects the neurogenesis of the hippocampal dentate gyrus. Also, we believe that this animal model will play an important role in elucidating the pathophysiology of depression, and in the development of the corresponding novel drug.”

Overall, this study has provided important insights into the pathophysiology of depression. Also, it goes without saying how this study paves the way for future research into the role of psychological stress in depression.

Precise metal nanoclusters (NCs) are ideal for developing practical catalysts for chemical reactions. However, their catalytic activity is reduced either due to protective molecules called “ligands” surrounding them or aggregation resulting from ligand removal. In a new study, scientists from Japan elucidate the ligand removal mechanism for gold NCs and irradiate them with UV light to prevent aggregation, creating a high-functioning photocatalyst.

“When the ligands are removed without special treatment, the metal NCs easily aggregate on the support and lose their size-specific properties. It is essential understand the mechanism of ligand calcination to create highly functional heterogeneous catalysts under appropriate conditions,” says Prof. Yuichi Negishi of Tokyo University of Science, Japan, who researches on the synthesis of
nanoclusters.

In a new study published in Angewandte Chemie, Prof. Negishi led a team of researchers, including Assistant Professor Tokuhisa Kawawaki, Mr Yuki Kataoka, Ms Momoko Hirata, and Mr Yuki Akinaga, to dig deep into the mechanism of the ligand removal process in NCs. For their experiments, the researchers synthesized gold NCs protected by two ligands, 2-phenylethanethiolate and mercaptobenzoic acid and then supported them on a photocatalytic metal oxide.

Next, the team heated the prepared material at different temperatures ranging from 195°C to 500°C. After every step, they analyzed the products using techniques such as infrared spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy to identify the changes in their chemical composition.

After the ligands were completely released, the team embedded the gold NCs within a thin film of chromium oxide by irradiating the sample with UV light in order to prevent aggregation of the NCs. This process generated a photocatalyst with useful properties like high water-splitting activity and stability.

These findings guide the design for metal NC-based catalysts in the future, with applications in hydrogen generation for hydrogen fuel cells. “With our research, we hope to build a clean, sustainable, society, one brick at a time,” concludes Prof. Negishi.

Wearable technology seems all poised to take over next-generation electronics, yet most wireless communication techniques are not up to the task. To tackle this issue, scientists from the Tokyo University of Science, Japan, delved deep into human-body communications (HBC), in which human tissue is used as the transmission medium for electromagnetic signals. Their findings pave the way to more efficient and safer head-worn devices, such as binaural hearing aids and earphones.

To explore the full potential of HBC, researchers from Japan, including Dr. Dairoku Muramatsu from Tokyo University of Science and Professor Ken Sasaki from The University of Tokyo focused on using HBC for a yet unexplored use: binaural hearing aids.

Such hearing aid devices come in pairs—one for each ear—and greatly improve intelligibility and sound localization for the wearer by communicating with each other to adapt to the sound field. Because these hearing aids are in direct contact with the skin, they made for a perfect candidate application for HBC.

In a recent study, which was published in the journal Electronics, the researchers investigated, through detailed numerical simulations, how electric fields emitted from an electrode in one ear distribute themselves in the human head and reach a receiving electrode on the opposite ear, and whether it could be leveraged in a digital communication system. In fact, the researchers had previously conducted an experimental study on HBC with real human subjects, the results of which were also published in Electronics.

Using human-body models of different degrees of complexity, the researchers first determined the best representation to ensure accurate results in their simulations and then once this was settled, they proceeded to explore the effects of various system parameters and characteristics.

Dr. Muramatsu SAYS, “We calculated the input impedance characteristics of the transceiver electrodes, the transmission characteristics between transceivers, and the electric field distributions in and around the head. In this way, we clarified the transmission mechanisms of the proposed HBC system.”

Finally, with these results, they determined the best electrode structure out of the ones they tested. They also calculated the levels of electromagnetic exposure caused by their system and found that it would be completely safe for humans, according to modern safety standards.

Overall, this study showcases the potential of HBC and extends the applicability of this promising technology. After all, hearing aids are but one of all modern head-worn wireless devices. For example, HBC could be implemented in wireless earphones to enable them to communicate with each other using far less power.

Moreover, because the radio waves used in HBC attenuate quickly outside of the body, HBC-based devices on separate people could operate at similar frequencies in the same space without causing noise or interference.

“With our results, we have made great progress towards reliable, low-power communication systems that are not limited to hearing aids but also applicable to other head-mounted wearable devices. Not just this, accessories such as earrings and piercings could also be used to create new communication systems,” concludes Dr. Muramatsu.

Assistant Professor Yuji Ogihara from the Tokyo University of Science analyzed approximately 8,000 names of infants born between 2004 and 2018 obtained from the database of a life insurance company. He first chose four recent common names for boys and girls each (Boys: “大翔,” “陽翔,” “翔,” “颯,” Girls: “結愛,” “陽菜,” “愛,” “杏”) on the basis of popularity rankings for each year.

He then comprehensively surveyed all their readings and calculated the ratio and number of ways to read each name. These results were published on June 21, 2021 in the international journal Humanities and Social Sciences Communications.

Assistant Professor Ogihara discovered that there are at least 18 ways to read “大翔” (Figure 2), and at least 14 ways to read “結愛” (Figure 3). Even single-character names like “颯,” and “杏,” had seven and five readings, respectively. The readings each differed greatly in pronunciation, length, and meaning. Assistant Professor Ogihara showed that the
other names have many readings, too.

He further found that parents were not only using the common readings of each character, but also using readings that do not exist for a character or using a character for its meaning and imagery. For example, “大翔” was also read as “Tsubasa”(meaning “wing”). Neither “大” nor “翔” formally have “Tsubasa” as a reading. “翔” is read as “Tsubasa” because it has the meanings “flap” and “fly,” and a reading associated with the imagery of the character is observed. The character “大” is given, but not pronounced, and the meaning “to flap broadly” is obtained. Hence, the character is only added for its imagery or meaning.

Assistant Professor Ogihara also saw a pattern of abbreviating common readings. For example, “大翔” was read as “Taishi.” “大” has the reading “tai,” and “翔” has the reading “shou.” “Shou” was abbreviated to “shi” and combined with “tai.” He also found instances where the meanings of characters are read in foreign languages. Take “結愛 Yura,” for example. While “結” comes from the common reading “yu(u),” “愛” is generally not read as “ra,” but because “愛” means “love” (rabu) in English, it is possible to omit the “bu” and use it as “ra.”

In this study, Assistant Professor Ogihara systematically analyzed actual name data and empirically investigated the difficulty of correctly reading Japanese names. The investigation of these difficulties contributes to deepening our understanding of naming practices and the characteristics of names, not only in Japan but in the Sinosphere, which includes East and Southeast Asia.

A vital piece of gas engines, combustors—the chambers in which the combustion powering the engine occurs—have the problem of breaking down due to fatal high-frequency oscillations during the combustion process. Now, through advanced time-series analyses based on complex systems, researchers from Tokyo University of Science and Japan Aerospace Exploration Agency have found what causes them, opening up novel paths to solving the problem.

In a breakthrough, published in Physics of Fluids, a team including Prof. Hiroshi Gotoda, Ms. Satomi Shima, and Mr. Kosuke Nakamura from Tokyo University of Science (TUS), in collaboration with Dr. Shingo Matsuyama and Dr. Yuya Ohmichi from the Japan Aerospace Exploration Agency (JAXA), have used advanced time-series analyses based on complex systems to find out.

Explaining their work, Prof. Gotoda says, “Our main purpose was to reveal the physical mechanism behind the formation and sustenance of high-frequency combustion oscillations in a cylindrical combustor using sophisticated analytical methods inspired by symbolic dynamics and complex networks.” These findings have also been covered by the American Society of Physics in their news section, and by the Institute of Physics on their news platform Physics World.

The combustor the scientists picked to simulate is one of model rocket engines. They were able to pinpoint the moment of transition from the stable combustion state to combustion oscillations and visualize it. They found that significant periodic flow velocity fluctuations in fuel injector affect the ignition process, resulting in changes to the heat release rate. The heat release rate fluctuations synchronize with the pressure fluctuations inside the combustor, and the whole cycle continues in a series of feedback loops that sustain combustion oscillations.

Additionally, by considering a spatial network of pressure and heat release rate fluctuations, the researchers found that clusters of acoustic power sources periodically form and collapse in the shear layer of the combustor near the injection pipe’s rim, further helping drive the combustion oscillations.

These findings provide reasonable answers for why combustion oscillations occur, albeit specific to liquid rocket engines. Prof. Gotoda explains, “Combustion oscillations can cause fatal damage to combustors in rocket engines, aero engines, and gas turbines for power generation. Therefore, understanding the formation mechanism of combustion oscillations is an important research subject. Our results will greatly contribute to our understanding of the mechanism of combustion oscillations generated in liquid rocket engines.”

Indeed, these findings are significant and can be expected to open doors to novel routes of
exploration to prevent combustion oscillations in critical engines.

Two-dimensional “nanosheets” made of bonds between metal atoms and organic molecules are attractive candidates for photoelectric conversion, but get corroded easily. In a new study, scientists from Japan and Taiwan present a new nanosheet design using iron and benzene hexathiol that exhibits record stability to air exposure for 60 days, signalling the commercial optoelectronic applications of these 2D materials in the future.

Converting light to electricity effectively has been one of the persistent goals of scientists in the field of optoelectronics. While improving the conversion efficiency is a challenge, several other requirements also need to be met. For instance, the material must conduct electricity well, have a short response time to changes in input (light intensity), and, most importantly, be stable under long-term exposure.

Lately, scientists have been fascinated with “coordination nanosheets” (CONASHs), that
are organic-inorganic hybrid nanomaterials in which organic molecules are bonded to metal atoms in a 2D network. The interest in CONASHs stems mainly from their ability to absorb light at multiple wavelength ranges and convert them into electrons with greater efficiency than other types of nanosheets. This feat was observed in a CONASH comprising a zinc atom bonded with a porphyrin-dipyrrin molecule. Unfortunately, the CONASH quickly became corroded due to the low stability of organic molecules in liquid electrolytes (a medium commonly used for current conduction).

“The durability issue needs to be solved to realize the practical applications of CONASH-based photoelectric conversion systems,” says Professor Hiroshi Nishihara from Tokyo University of Science (TUS), Japan, who conducts research on CONASH and has been trying to solve the CONASH stability problem.

Now, in a recent study published in Advanced Science as a result of a collaborative research between National Institute for Materials Science (NIMS), Japan and TUS, Prof. Nishihara and his colleagues, Dr. Hiroaki Maeda and Dr. Naoya Fukui from TUS, Dr. Ying-Chiao Wang and Dr. Kazuhito Tsukagoshi from NIMS, Mr. Chun-Hao Chiang and Prof. Chun-Wei Chen from National Taiwan University, Taiwan, and Dr. Chi-Ming Chang and Prof. Wen-Bin Jian from National Chiao-Tung University, Taiwan, have designed a CONASH comprising an iron (Fe) ion bonded to a benzene hexathiol (BHT) molecule that has demonstrated the highest stability under air exposure reported so far. The new FeBHT CONASH-based photodetector can retain over 94% of its photocurrent after 60 days of exposure! Moreover, the device requires no external power source.

What made such a feat possible? Put simply, the scientists made some smart choices. Firstly, they went for an all-solid architecture by replacing the liquid electrolyte with a solid-state layer of Spiro-OMeTAD, a material known to be an efficient transporter of “holes” (vacancies left behind by electrons). Secondly, they synthesized the FeBHT network from a reaction between iron ammonium sulfate and BHT, which accomplished two things: one, the reaction was slow enough to keep the sulfur group protected from being oxidized, and two, it helped the resultant FeBHT network become resilient to oxidation, as the scientists confirmed using density functional theory calculations.

In addition, the FeBHT CONASH favoured high electrical conductivity, showed an enhanced
photoresponse with a conversion efficiency of 6% (the highest efficiency previously reported was 2%), and a response time < 40 milliseconds for UV light illumination.

With these results, the scientists are thrilled about the prospects of CONASH in commercialized optoelectronic applications. “The high performance of the CONASH-based photodetectors coupled with the fact that they are self-powered can pave the way for their practical applications such as in light-receiving sensors that can be used for mobile applications and recording the light exposure history of objects,” says Prof. Nishihara excitedly.

Scientists at Tokyo University of Science, Japan, engineered a long polymer with copper-containing side units that create regions with locally high copper density, boosting the antibacterial activity of hydrogen peroxide and paving the way to a new drug design concept.

Scientists are exploring a novel approach to boost the in vivo antibacterial activity of hydrogen peroxide (H₂O₂), a commonly used disinfectant. In a recent study published in Macromolecular Rapid Communications, a team led by Assistant Professor Shigehito Osawa and Professor Hidenori Otsuka reported their success in enhancing H₂O₂ activity using
carefully tailored copper-containing polymers.

To understand their approach, it helps to know how H2O2 acts against bacteria in the first place, and the role that copper plays. H2O2 can be decomposed into a hydroxyl radical (•OH) and a hydroxide anion (OH−), the former of which is highly toxic to bacteria as it readily destroys certain biomolecules. Copper in its first oxidation state, Cu(I), can catalyze the splitting of H2O2 into a hydroxyl radical and a hydroxide anion, turning into Cu(II) in the process through oxidation (Figure 1). Curiously, H2O2 can also catalyze the reduction of Cu(II) to Cu(I), but only if this reaction is somehow facilitated. One way to achieve this is to have Cu(II)-containing complexes get close enough together.

However, when using Cu(II)-containing complexes dissolved in a solution, the only way for them to come close together is by accidentally bumping into each other, which requires an excessively high concentration of copper.

The team found a workaround to this issue by drawing inspiration from cellular chemistry, as Dr. Osawa explains: “In living organisms, copper forms complexes with proteins to efficiently catalyze redox reactions. For example, tyrosinase has two copper complex sites in close proximity to each other, which facilitates the formation of reaction intermediates between oxygen species and copper complexes. We thought we could leverage this type of mechanism in artificially produced polymers with copper complexes, even if dispersed in a solution.”

With this idea, the researchers developed a long polymer chain with dipicolylamine (DPA) as copper-containing complexes. These DPA–copper complexes were attached to the long polymer backbone as “pendant groups.” When these polymers are dispersed in a solution, the Cu(II) atoms in the pendant groups are kept in close proximity and locally high densities, vastly increasing the chances that two of them will be close enough to be reduced to Cu(I) by H2O2. Through various experiments, the scientists demonstrated that the use of these tailored polymers resulted in higher catalytic activity for the splitting of H2O2 resulting in more OH• even for lower concentrations of copper. Further tests using Escherichia coli cultures showed that these polymers greatly enhanced the antibacterial potential of H2O2.

While the results of this study open up a new design avenue for antimicrobial drugs, there may also be useful applications in the food industry as well. “Because copper is an essential
nutrient for living organisms, the antibacterial agent developed in this study holds promise as an efficient food preservative, which could contribute to increasing the variety of foods that can be preserved over long shelf times,” highlights Dr Osawa.