Synthesis of Zwitterionic Phospholipid-Connected Silane Coupling Agents and Their Hybridization with Graphene Oxide.

The hybridization of lipids with graphene is expected to produce a promising, novel biomaterial. However, there are limited examples of the covalent introduction of lipid molecules, especially the immobilization of lipid molecules, onto graphene on a substrate. Therefore, we investigated the hybridization of a silane coupling agent having phospholipid moieties with graphene oxide on substrates prepared by photo-oxidation using chlorine dioxide. Three silane coupling agents with different carbon chain lengths (C4, C6, C8) were synthesized and phospholipid molecules were introduced onto graphene on a substrate. Phospholipid-immobilized graphene on a grid for TEM (transmission electron microscope) was used for EM analysis of proteins (glyceraldehyde 3-phosphate dehydrogenase and ß-galactosidase), enabling the observation of sufficient particles compared to the conventional graphene grid.

Polyethylene, whose surface has been modified by UV irradiation, induces cytotoxicity: A comparison with microplastics found in beaches.

Microplastics, plastic particles 5 mm or less in size, are abundant in the environment; hence, the exposure of humans to microplastics is a great concern. Usually, the surface of microplastics found in the environment has undergone degradation by external factors such as ultraviolet rays and water waves. One of the characteristics of changes caused by surface degradation of microplastics is the introduction of oxygen-containing functional groups. Surface degradation alters the physicochemical properties of plastics, suggesting that the biological effects of environmentally degraded plastics may differ from those of pure plastics. However, the biological effects of plastics introduced with oxygen-containing functional groups through degradation are poorly elucidated owing to the lack of a plastic sample that imitates the degradation state of plastics found in the environment. In this study, we investigated the degradation state of microplastics collected from a beach. Next, we degraded a commercially available polyethylene (PE) particles via vacuum ultraviolet (VUV) irradiation and showed that chemical surface state of PE imitates that of microplastics in the environment. We evaluated the cytotoxic effects of degraded PE samples on immune and epithelial cell lines. We found that VUV irradiation was effective in degrading PE within a short period, and concentration-dependent cytotoxicity was induced by degraded PE in all cell lines. Our results indicate that the cytotoxic effect of PE on different cell types depends on the degree of microplastic degradation, which contributes to our understanding of the effects of PE microplastics on humans.

[Preparation of Degraded Microplastics That Imitate Surface Properties in the Environment].

Microplastics are small pieces of plastic that are less than 5 mm in length. These plastics have been detected in various environments, including the ocean, soil, and air. Their abundance have raised concerns regarding their potential effects on living organisms, including humans. The surface of microplastics degrades due to external factors such as ultraviolet rays and water waves in the environment. Therefore, assessing the biological impact of microplastics and considering their state of degradation is important. Among the physical properties of microplastics, we focused on the chemical degradation of microplastics. Specifically, we used vacuum ultraviolet (VUV) light to accelerate the degradation of polyethylene (PE) and prepared PE samples representing the degradation of PE to varying degrees. The surface properties of PE samples prepared using VUV were similar to those obtained from the environment. Cytotoxicity tests were then used to evaluate the effects of undegraded and degraded PE on cells. We found that the severity of cytotoxicity increased with the extent to which the PE would have been degraded, suggesting that the degree of degradation is strongly linked to the severity of the observed deleterious effects on living organisms. In conclusion, this finding contributes to our understanding of the effects of polyethylene microplastics on the human body.

[Mechanisms of Cell Toxicity Caused by Degraded Microplastics].

Microplastics (MPs), defined as plastic particles less than 5 mm in size, are ubiquitous in the environment. The accumulation of MPs in various environmental compartments, such as the ocean, soil, and air, has raised considerable concerns regarding their impact on ecological systems, including marine life and human health. Notably, MPs have been detected in marine organisms such as shellfish and fish, and have even been found in the human body, including in the blood and placenta. Moreover, considering that MPs have been detected in drinking water, human exposure to these particles in daily life is inevitable. To assess the risk posed by MPs to human health, it is essential to consider their physiological and chemical properties, including size, shape, surface modification, and material composition. However, current risk analyses focus primarily on spherical MPs with smooth surfaces, which differ substantially from most of the MPs detected in the environment. Environmental factors, such as ocean waves and ultraviolet radiation, alter the properties of MPs, including size, shape, and surface characteristics. In this review, we summarize current research on MPs, with a particular emphasis on the effects of MP degradation on human health. Furthermore, we generated MPs with surface degradation and evaluated their impact on cell toxicity, along with the underlying biological mechanisms.

First synthesis of acylated nitrocyclopropanes.

Although nitrocyclopropanedicarboxylic acid esters are widely used in organic syntheses, nitrocyclopropanes with an acyl group have not yet been synthesized. When adducts of ß-nitrostyrene and 1,3-dicarbonyl compounds are treated with (diacetoxyiodo)benzene and tetrabutylammonium iodide, iodination occurs at the α-position of the nitro group, and the subsequent O-attack of the enol moiety leads to 2,3-dihydrofuran. Cyclopropane was successfully synthesized through C-attack as the acyl group became bulkier. The obtained nitrocyclopropane was transformed into furan upon treatment with tin(II) chloride via a ring-opening/ring-closure process.

Chlorine-radical-mediated C-H oxygenation reaction under light irradiation.

The oxygenation of C(sp3)-H bonds is a key chemical reaction in the production of fine chemicals and pharmaceuticals. Hydrogen atom transfer has recently gained significant attention for its ability to functionalise C-H bonds. The C-H bond can be activated by transferring the H radical to a hydrogen acceptor such as the chlorine radical (Cl˙). Thus, the Cl˙ generated by light irradiation can be used to initiate C-H oxygenation reactions, in which molecular oxygen is used as the oxidant. In this review article, we have summarised the recent advances in the field of Cl˙-mediated C-H oxygenation reactions. Reactions with catalysts such as metal chlorides, organophotoredox catalysts (acridinium ions), and chlorine dioxide radicals under light irradiation have been discussed. We conclude the review by providing suggestions for future research studies in the field. We expect that this review article will provide valuable information for the development of Cl˙-mediated C-H oxygenation reactions, contribute to the understanding of the reactivity of Cl˙, and inspire other useful synthetic chemical applications for C-H oxygenation reactions.

One-step antibacterial modification of polypropylene non-woven fabrics via oxidation using photo-activated chlorine dioxide radicals.

In this study, we examined the modification of polypropylene non-woven fabrics (PP NWFs) via a one-step oxidation treatment using photo-activated chlorine dioxide radicals (ClO2˙). The oxidised PP NWFs exhibited excellent antibacterial activity against both Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). The mound structure and antibacterial activity in the modified PP NWFs disappeared upon washing with a polar organic solvent. After washing, nanoparticles of around 80 nm in diameter were observed in the solution. The results of several mechanistic studies suggest that nanoparticles can contribute to the antimicrobial activity of oxidised PP NWFs.

Epoxidized graphene grid for highly efficient high-resolution cryoEM structural analysis.

Functionalization of graphene is one of the most important fundamental technologies in a wide variety of fields including industry and biochemistry. We have successfully achieved a novel oxidative modification of graphene using photoactivated ClO2· as a mild oxidant and confirmed the oxidized graphene grid is storable with its functionality for at least three months under N2 atmosphere. Subsequent chemical functionalization enabled us to develop an epoxidized graphene grid (EG-grid™), which effectively adsorbs protein particles for electron cryomicroscopy (cryoEM) image analysis. The EG-grid dramatically improved the particle density and orientation distribution. The density maps of GroEL and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) were reconstructed at 1.99 and 2.16 Å resolution from only 504 and 241 micrographs, respectively. A sample solution of 0.1 mg ml-1 was sufficient to reconstruct a 3.10 Å resolution map of SARS-CoV-2 spike protein from 1163 micrographs. The map resolutions of ß-galactosidase and apoferritin easily reached 1.81 Å and 1.29 Å resolution, respectively, indicating its atomic-resolution imaging capability. Thus, the EG-grid will be an extremely powerful tool for highly efficient high-resolution cryoEM structural analysis of biological macromolecules.

One-pot chlorocarboxylation of toluenes with chlorine dioxide under photoirradiation.

Chlorocarboxylation of toluene was achieved by photoirradiation of a chlorine dioxide radical (ClO2˙) under ambient conditions (298 K and 1 atm). 2- and 4-Chlorobenzoic acids were obtained in a 1 : 1 yield ratio. This is a single step synthesis under metal-free and mild conditions.

A new approach to 10-arylated 5H-dibenzo[b,f]azepines using syn-selective hydrohalogenation of ethynylaniline.

A new synthetic method for 10-arylated dibenzo[b,f]azepines was developed. The pseudo-intramolecular hydrohalogenation of 2-(2'-bromophenyl)ethynylaniline, which proceeded in a syn-selective manner without forming any detectable over-addition product, was a crucial step. All attempts of subsequent arylation via Suzuki-Miyaura cross coupling and construction of a seven membered ring via Ullmann-type intramolecular coupling were unsuccessful because of dehydrohalogenation or other side reactions. This problem was overcome by the N-acetylation of the amino group, which facilitated the abovementioned coupling reactions to afford the desired 10-arylated dibenzoazepines.

A Mechanistic Study for Aziridination of Nitroalkenes Mediated by N-Chlorosuccinimide.

Direct aziridination of a nitrostyrene is achieved upon treatment with an alkylamine and N-chlorosuccinimide. The reaction is initiated by the Michael addition of amine to nitroalkene. Subsequent N-chlorination and nucleophilic substitution at the nitrogen atom afford 1-alkyl-2-nitroaziridine diastereoselectively. This reaction mechanism was clarified by NMR studies.

Visible-light-induced phosgenation of amines by chloroform oxygenation using chlorine dioxide.

We report the visible-light-induced in situ preparation of COCl2 through the oxygenation of chloroform in the presence of chlorine dioxide, which leads to the safe constructions of carbamoyl chlorides with good-to-high yields and wide substrate scopes. In addition, this method can also be applied to the synthesis of various carbonates.

Development of a synthetic equivalent of α,α-dicationic acetic acid leading to unnatural amino acid derivatives via tetrafunctionalized methanes.

Diethyl mesoxalate (DEMO) exhibits high electrophilicity and accepts the nucleophilic addition of a less nucleophilic acid amide to afford N,O-hemiacetal. However, our research showed that elimination of the amide moiety proceeded more easily than dehydration upon treatment with a base. This problem was overcome by reacting DEMO with an acid amide in the presence of acetic anhydride to efficiently obtain N,O-acetal. Acetic acid was eliminated leading to the formation of N-acylimine in situ upon treatment with the base. N-Acylimine is also electrophilic, accepting the second nucleophilic addition by pyrrole or indole to form α,α-disubstituted malonates. Subsequent hydrolysis followed by decarboxylation resulted in (α-indolyl-α-acylamino)acetic acid formation; homologs of tryptophan. Through this process, DEMO serves as a synthetic equivalent of α,α-dicationic acetic acid to facilitate nucleophilic introduction of the two substituents.

Synthesis of Nitroaromatic Compounds via Three-Component Ring Transformations.

1-Methyl-3,5-dinitro-2-pyridone serves as an excellent substrate for nucleophilic-type ring transformation because of the electron deficiency and presence of a good leaving group. In this review, we focus on the three-component ring transformation (TCRT) of dinitropyridone involving a ketone and a nitrogen source. When dinitropyridone is allowed to react with a ketone in the presence of ammonia, TCRT proceeds to afford nitropyridines that are not easily produced by alternative procedures. Ammonium acetate can be used as a nitrogen source instead of ammonia to undergo the TCRT, leading to nitroanilines in addition to nitropyridines. In these reactions, dinitropyridone serves as a safe synthetic equivalent of unstable nitromalonaldehyde.

One-pot and metal-free synthesis of 3-arylated-4-nitrophenols via polyfunctionalized cyclohexanones from ß-nitrostyrenes.

ß-Nitrostyrenes underwent a Diels-Alder reaction with Danishefsky's diene to afford cyclohexenes together with the corresponding hydrolyzed products, 3-arylated-5-methoxy-4-nitrocyclohexanones. When the reaction was conducted in the presence of water, the cyclohexenes were efficiently hydrolyzed into cyclohexanones. Subsequent aromatization by heating the cyclohexanone with a catalytic amount of iodine in dimethyl sulfoxide gave 3-arylated-4-nitrophenols. The reaction of nitrostyrenes with Danishefsky's diene could be conducted in one pot to directly afford the corresponding nitrophenols. Moreover, a heteroaryl group, e.g., a thienyl group could be introduced into the nitrophenol framework.

Photochemical C-H oxygenation of side-chain methyl groups in polypropylene with chlorine dioxide.

The chlorine dioxide radical (ClO2˙) was found to act as an efficient oxidizing agent for the aerobic C-H oxygenation of the side-chain methyl groups in polypropylene under photoirradiation and ambient conditions (298 K and 1 atm). The oxygenated side-chain methyl groups were selectively converted to carboxylic acid and hydroxy groups.

Alkynylation and Cyanation of Alkenes Using Diverse Properties of a Nitro Group.

In the work being reported here, ß-nitrostyrenes bearing an ethoxycarbonyl group at the ß-position serve as scaffolds for the synthesis of α,ß-difunctionalized alkenes. Nitrocinnamates undergo Michael addition reactions with versatile sp3- and sp2-nucleophiles such as alcohols, Grignard reagents, alkylcopper, and dialkylzinc to afford ß-substituted nitroethane derivatives. However, various attempts to obtain a double bond via nitrous acid elimination failed because steric repulsion between the newly introduced sp3/sp2 substituent and the nitro group hampered the required anti-coplanar conformation. This problem was successfully overcome using a smaller sp-nucleophile such as lithium acetylide, potassium cyanide, or trimethylsilyl cyanide. While treatment of the adduct with a strong base did not lead to the elimination of nitrous acid, the weaker triethylamine efficiently afforded functionalized enynes and acrylonitriles in high yields.

Phosphine Induced Dimerization of Propargyl Alcohols Leading to Allyl Propargyl Ethers.

A facile method for synthesizing allyl propargyl ethers (APEs) was developed based on the dimerization of propargyl alcohols. The reaction proceeded via an oxaphosphetane intermediate, which was generated without the use of a strong base, thus making this process a pseudo-Wittig reaction under mild reaction conditions. A wide variety of functional groups, including formyl and pyridyl groups were tolerated, thus yielding the corresponding functionalized APEs, which are otherwise not readily prepared via conventional methods. Moreover, a cross-reaction was found to occur when the reaction was conducted in the presence of alcohols that were more acidic than propargyl alcohol, which suggests that the proton transfer from the intermediately formed betaine to the second alcohol is crucial for undergoing the dimerization.

Direct Aziridination of Nitroalkenes Affording N-Alkyl-C-nitroaziridines and the Subsequent Lewis Acid Mediated Isomerization to ß-Nitroenamines.

A mild and highly diastereoselective one-pot synthesis of trans-N-alkyl-C-nitroaziridines was achieved by treatment of nitroalkenes with aliphatic amines and N-chlorosuccinimide. Treatment of the obtained aziridines with a Lewis acid resulted in a facile ring opening reaction, accompanied by rearrangement and isomerization into functionalized (Z)-ß-nitroenamines.

Quantification and Theoretical Analysis of the Electrophilicities of Michael Acceptors.

In order to quantify the electrophilic reactivities of common Michael acceptors, we measured the kinetics of the reactions of monoacceptor-substituted ethylenes (H2C═CH-Acc, 1) and styrenes (PhCH═CH-Acc, 2) with pyridinium ylides 3, sulfonium ylide 4, and sulfonyl-substituted chloromethyl anion 5. Substitution of the 57 measured second-order rate constants (log k) and the previously reported nucleophile-specific parameters N and sN for 3-5 into the correlation log k = sN(E + N) allowed us to calculate 15 new empirical electrophilicity parameters E for Michael acceptors 1 and 2. The use of the same parameters sN, N, and E for these different types of reactions shows that all reactions proceed via a common rate-determining step, the nucleophilic attack of 3-5 at the Michael acceptors with formation of acyclic intermediates, which subsequently cyclize to give tetrahydroindolizines (stepwise 1,3-dipolar cycloadditions with 3) and cyclopropanes (with 4 and 5), respectively. The electrophilicity parameters E thus determined can be used to calculate the rates of the reactions of Michael acceptors 1 and 2 with any nucleophile of known N and sN. DFT calculations were performed to confirm the suggested reaction mechanisms and to elucidate the origin of the electrophilic reactivities. While electrophilicities E correlate poorly with the LUMO energies and with Parr's electrophilicity index ω, good correlations were found between the experimentally observed electrophilic reactivities of 44 Michael acceptors and their calculated methyl anion affinities, particularly when solvation by dimethyl sulfoxide was taken into account by applying the SMD continuum solvation model. Because of the large structural variety of Michael acceptors considered for these correlations, which cover a reactivity range of 17 orders of magnitude, we consider the calculation of methyl anion affinities to be the method of choice for a rapid estimate of electrophilic reactivities.