COVID-19 is currently spreading all over the world, and causing enormous damage to health, economies, and daily lives. In order to overcome this pandemic, huge amounts of work have been accomplished, and many papers published. However, most of these works are from medical institutes and/or hospitals, and the attempts to solve this tragedy by chemical approaches have been rather scarce. This account surveys chemical information on COVID-19 with special emphasis on molecular-level understanding. In the first part, the fundamentals of causative pathogen SARS-CoV-2 (structures of genome and proteins of this virus) are briefly described. Next, the molecular structure of the spike on the viral surface, the key component for the infection of human beings, is shown. Then, the binding mode of these spikes to the receptors on human cells (ACE2) is presented in detail, based on the structural data. The conformational change of spike proteins is critically important for the virus to enter human cells. Furthermore, the roles of mutation of SARS-CoV-2 in the promotion of pathogenicity are discussed primarily in terms of the spike/ACE2 interactions. Finally, the origins of unprecedentedly high pathogenicity of this virus are proposed. This account should help the readers to understand the current status of our chemical knowledge on COVID-19, promoting the research to attack the worst pandemic of the last 100 years.
Different mechanisms of H-bond formation between sulfate anion and water are presented using molecular dynamics simulations. Multi-centered hydrogen bonds were observed. Always the hydrogen bridge making/breaking goes according to the large angular jump mechanism. Moreover, classical, bifurcated and trifurcated hydrogen bonds between water and sulfate have transitional character. This is supported by free energies of binding of water to sulfate ion determined for particular types of hydrogen bridges. This phenomenon is similar to the one observed in the hydration shell of perchlorate anion. Nevertheless the amplitudes of angular jump as well as hydrogen bond lifetimes are different in both cases.
In-situ powder X-ray diffraction study of AlMepO-α under varied nitrogen equilibrium pressures identifies two phases np and lp with the same space group and slightly different lattice constants and reveals their structures with different nitrogen contents. A crystallographically estimated adsorption isotherm fairly well simulates the measured two-step isotherm.
Self-assembled macaroni fullerene C60 crystals (MFCs) of uniform shape and narrow size distribution are produced using the dynamic liquid-liquid interfacial precipitation method under ambient conditions. High temperature heat treatment (900 °C) of MFCs yields mesoporous carbons tubes (MCTs) retaining the initial morphology. This novel mesoporous carbon material exhibits excellent electrochemical supercapacitive performance due to high surface areas (1544 m2 g−1), large pore volume (2.936 cm3 g−1) and interconnected porous structures. In a three-electrode aqueous electrolyte system, the electrode achieved high specific capacitance ca. 422 F g−1 at a current density of 1 A g−1 followed by excellent cycling stability (>95%) after 10,000 charging-discharging cycles at 20 A g−1. We believe that the novel mesoporous carbon material derived from a π-electron carbon source can be used as an alternative electrode material in advanced supercapacitor devices.
Hydrogenation of carboxylic acids (CAs) to alcohols represents one of the most ideal reduction methods for utilizing abundant CAs as alternative carbon and energy sources. However, systematic studies on the effects of metal-to-ligand relationships on the catalytic activity of metal complex catalysts are scarce. We previously demonstrated a rational methodology for CA hydrogenation, in which CA-derived cationic metal carboxylate [(PP)M(OCOR)]+ (M = Ru and Re; P = one P coordination) served as the catalyst prototype for CA self-induced CA hydrogenation. Herein, we report systematic trial-and-error studies on how we could achieve higher catalytic activity by modifying the structure of bidentate diphosphine (PP) ligands of molecular Ru catalysts. Carbon chains connecting two P atoms as well as Ar groups substituted on the P atoms of PP ligands were intensively varied, and the induction of active Ru catalysts from precatalyst Ru(acac)3 was surveyed extensively. As a result, the activity and durability of the (PP)Ru catalyst substantially increased compared to those of other molecular Ru catalyst systems, including our original Ru catalysts. The results validate our approach for improving the catalyst performance, which would benefit further advancement of CA self-induced CA hydrogenation.
Molecular machines leverage sub-nanometer level intermolecular forces and host–guest interactions to perform useful work observable at the macroscopic level. The development of molecular machines for the past three decades has resulted in successful applications from molecular switches, chemical sensing, to actuators. However, the application of molecular machines and supramolecular chemistry in energy production is rare and has been highly anticipated. This review introduces the advancement of supramolecular thermocells, initially proposed by our research group, which use thermo-responsive host–guest interaction to regenerate electrochemical energy from low-grade heat sources. The selective transport of a redox species carried by the host molecule from the cooled to the heated electrode creates a concentration gradient of the guest redox species and provides an additional voltage to the thermocell. The key properties of useful host molecules for the supramolecular thermocells are: (1) high selectivity of the host molecule to capture either the oxidized or reduced species as the guest, (2) inhibition of the redox activity after the encapsulation, (3) large entropy change at the release of the guest molecule in response to the temperature changes. Design principles and promising candidates of molecular machines for the future development of supramolecular thermocells are presented here.
Novel C,O-chelated bora-heterocycles were synthesized. Reaction of potassium acyltrifluoroborates with tetrahydroquinolin-8-ol furnished C,N-swapped boranils in a single step. All five obtained borates showed photoluminescence in solid state. One of them showed yellow-to-orange reversible mechanochromic luminescence. Further derivatization afforded a B-chiral borate with an O,C,O-tridentate ligand that showed significant thermochromism.
Calibration curves are essential constructs in analytical chemistry to determine parameters of sensing performance. In the classification of sensing data of complex samples without a clear dependence on a given analyte, however, establishing a calibration curve is not possible. In this paper we introduce the concept of a multidimensional calibration space, which could serve as reference to classify any unknown sample as in determining an analyte concentration from a calibration curve. This calibration space is defined from a set of rules generated using a machine learning method based on trees applied to the dataset. The number of attributes employed in the rules defines the dimension of the calibration space and is established to warrant full coverage of the dataset. We demonstrate the calibration space concept with impedance spectroscopy data from sensors, biosensors and an e-tongue, but the concept can be extended to any type of sensing data and classification task. Using the calibration space should allow for the correct classification of unknown samples, provided that the data used to generate rules via machine learning can cover the whole range of sensing measurements. Furthermore, an inspection in the rules can assist in the design of sensing systems for optimized performance.
Molecular dynamics simulations are used to study the fracture mechanism of the joining interface of a polymer and metal oxide. A polyphenylene sulfide (PPS) layer is sandwiched between two plates of aluminum oxide and one of the plates is pulled to simulate fracture under tensile force. The stress-strain curve for the polymer-metal interface is similar in shape to the stress-strain curve for constant cross-sectional strain in bulk PPS. In the simulations, fracture of the polymer-metal joint is initiated by the formation of small voids inside the polymer layer, which occurs at the yield point of the polymer-metal interface. Annealing prior to tensile loading is determined to enhance the joint strength.
In this study, we report the synthesis and crystal structures of coordination polymers employing tetrabromobenzenedicarboxylate (Br4bdc2−) and pyrazine (pyz). Uncoordinated pyz molecules are stabilized between the layers by both hydrogen H-bonding and π–π stacking interactions in [M(Br4bdc)(pyz)(H2O)2](pyz), where M = Co(II) and Zn(II). In addition, water molecules are incorporated between the layers in [Cu(Br4bdc)(pyz)(H2O)2](H2O) owing to Jahn–Teller distortion of the Cu(II) ions, which prevents π–π stacking interactions between the pyz and Br4bdc2−. Depending on the metal(II) centers, structural changes that occur during the heating and hydration processes exhibit different behavior. Co(II) compound slowly changes structure by heating and rapidly recovers the crystalline state in air. Conversely, Zn(II) compound assumes the amorphous phase by heating and slowly yields the crystalline phase in ambient conditions. Although the Cu(II) compound also shows structural changes by heating, the dehydrated phase exhibits hydrophobic characteristics. Ion conductivity measurements of the as-synthesized forms show conductivities of 1.9 × 10−6 Scm−1, 4.6 × 10−7 Scm−1, and 1.3 × 10−6 Scm−1, for the Co(II), Zn(II), and Cu(II) complexes at 90 °C and 95% relative humidity (RH), respectively. The relatively low values of the as-synthesized Co(II) and Zn(II) compounds are attributed to the H-bonding interaction and π–π stacking of pyz molecules, which prevent the dynamics of the pyz molecules needed for proton conduction.
A personal history of sumanene chemistry: from the encounter with Prof. Mehta’s first report to the synthesis of pristine triazasumanene is described.
Thermotropic liquid crystals having tripeptide moieties are reported. A series of peptide chains including arginine-glycine-aspartic acid (RGD), glycine-glycine-aspartic acid (GGD), and triglycine (GGG) moieties is connected to a rigid-rod core through a flexible tetraoxyethylene spacer. These bioconjugated mesogens form intermolecular hydrogen bonds through amide groups in the tripeptide moieties. It is found that side chains in the tripeptide-conjugated mesogens constrain intermolecular hydrogen bonding in the bulk states, which affects the formation of the liquid-crystalline phases. The rigid-rod mesogens bearing RGD and GGD peptide sequence exhibit smectic phases with high thermal stability of the mesophases. The liquid-crystalline assemblies of the mesogen-containing peptides are macroscopically oriented by mechanical shearing. The present design of bioconjugated liquid crystals could lead to the development of new self-assembled materials for biological applications.
Lithium-excess layered positive electrodes containing Fe and Ni are promising materials for the next generation of high voltage lithium ion batteries (LIB) because they are more chemically stable than those using Co and use more widely available metals. However, a positive electrode driven with a high voltage generates an electrochemical decomposition reaction of the electrolyte at the electrode interface and a significant deterioration in performance occurs. In order to suppress electrolysis of the electrolyte solution, a promising solution is to form a solid electrolyte interphase (SEI) on the electrode to mediate contact between the electrolyte solution and the electrode. In this study, we discovered that a pyridinium series salt, an ionic liquid, used as an additive, forms a good SEI on the positive electrode surface to improve the overall performance of the LIBs, such as improved cycle capacity and inhibited gas generation. Furthermore, from XPS, TOF-SIMS, 1H NMR and SEM measurements, we discuss the chemical makeup of the SEI and its formation mechanism, and propose a powerful method to achieve the next generation of high energy-density lithium ion batteries.
Hollow siloxane-based nanoparticles (HSNs) have attracted significant attention because of many potential applications. The interior and exterior properties of HSNs can be varied by forming double shells with different compositions, which leads to new functionalities. In this study, we prepared colloidal monodisperse HSNs (smaller than 50 nm in diameter) with a double mesoporous shell by the stepwise addition of two different bridged organoalkoxysilanes [(EtO)3Si-C2H4-Si(OEt)3 (BTEE1) and (EtO)3Si-C2H2-Si(OEt)3 (BTEE2)] to a dispersion of colloidal silica nanoparticles (ca. 20 nm in diameter) in the presence of surfactants. The hollow structure was formed by dissolution-redeposition of the silica core during the formation of an organosiloxane shell. Upon addition of BTEE1 in the first step, core-shell structure was formed. Subsequent addition of BTEE2 led to the formation of mesoporous HSNs composed of an inner shell containing ethylene (-CH2-CH2-) groups and an outer shell containing ethenylene (-CH=CH-) groups. Suppression of the diffusion of the second organosilane species into the inner region of HSNs was critical for the formation of the double shell. The ethenylene groups in the outer shell allowed for chemical modification by thiol-ene reaction while maintaining the hollow inner space of the HSNs, which will lead to the application of HSNs in various fields.
Benzene, toluene, and m-xylenes are among the pollutants in the environment that may harm human health. These fugitive volatile organic compound (VOC) emissions from refineries and petrochemical industries are perennial, although at low concentrations in ppm levels. On similar grounds, the separation of benzene, toluene, and m-xylene compounds (BTX) from the feed gas of the sulfur recovery unit in natural gas processing industries is critical, as it is known to severely poison the catalyst in the Claus process. In this connection, a new hybrid material was synthesized using a precursor (metal-organic framework (MOF)) and silica aerogels (SA). The precursor (ZIF-8) proportion was varied to understand its effect on the structural and adsorption characteristics. Various advanced analytical characterizations were performed to understand the physicochemical characteristics of the synthesized material. Additionally, the synthesized materials were subjected to gas-phase adsorption of BTX to generate the adsorption isotherm at 25 °C. The hybrid material SA-ZIF-8 (20%) having a ZIF-8 proportion of 20% were found to have better adsorption capacity than the virgin ZIF-8 and silica aerogel adsorbents. The maximum adsorption capacity near the 90% saturation vapor pressure corresponds to 337 mg/g, 227 mg/g, and 263 mg/g at 25 °C for BTX, respectively.
Metal nanoparticle pastes are useful for nanoinks to form fine conductive patterns in printed electronics. This study reports a novel method for room-temperature coalescence of Cu-Ag core-shell nanoparticles (Cu@Ag NPs), which are expected to have the properties of both migration and oxidation resistance originating from Cu and Ag, respectively. First, oleylamine/oleic-acid capped Cu@Ag NPs were synthesized by the galvanic replacement method. Second, the ligand exchange reaction to tri-n-octylphosphine oxide (TOPO) was carried out on the surface of Cu@Ag NPs. Finally, TOPO-capped Cu@Ag NPs were dipped into methanol containing a sintering agent and/or a reducing agent. When HCl was added as a sintering agent to methanol, the crystallite size of Cu@Ag NPs significantly increased. Furthermore, the almost complete removal of organic compounds and suppression of significant oxidation of Ag and Cu were observed. In consideration of these results, a Cu/Ag conductive thin film was prepared from TOPO-capped Cu@Ag NPs by dipping into methanol containing HCl at room temperature under air atmosphere. Electrical resistivity of the obtained Cu/Ag thin film was (5.1 ± 1.7) × 10−5 Ω m. Microstructural observations and X-ray diffractions of the Cu/Ag thin film revealed that Cu@Ag NPs effectively coalesced at room temperature with slight oxidation.
Mesoporous silica nanoparticles (MSNs) with closed pores have significant potential for applications such as low-dielectric-constant materials and bio-imaging owing to their controlled accessibility. In this study, we successfully prepared MSNs with closed pores by a simple hydrothermal treatment in ethanol. The mesostructure changed from open to closed mesopores through hydrothermal treatment. This simple method enabled the preparation of closed pores with encapsulated guest species.
The adopted ligand type of a palladium precursor has a great influence on the microstructure, morphology and catalytic performance of obtained Pd-based monolith catalysts by a one-step method with redox reactions of two galvanic cells. In the sequence of ligand type NH3, en, Gly and EDTA, the obtained Pd-AlOOH/Al-x (x = NH3, en, Gly, EDTA) monolith catalysts showed gradually increasing specific surface areas, micro/mesopore volumes and catalytic activities in toluene total oxidation reaction, because more AlOOH nanosheets and Pd nanoparticles were generated to form a more uniform and well-dispersed three-dimensional-network structure film on the Al substrate surface.
To obtain further insight into the mechanism of carbon-induced signal enhancement of arsenic (As) at m/z = 75 in inductively coupled plasma mass spectrometry (ICP-MS), the formation process of arsenic oxide ion (AsO+) and the influence of carbon matrix on the process were investigated. The formation process of AsO+ was investigated using arsenous acid isotopically labeled with a highly enriched stable oxygen isotope 18O (H3As18O3). H3As18O3 sample solutions with or without carbon matrix [i.e., 5% (v/v) isopropanol] were analyzed via ICP-MS, and axial intensity profiles of 75As18O+ and 75As16O+ in the ICP were obtained by measuring the signals at axial sampling positions from 3 to 28 mm away from the load coil. Results suggested that AsO+ was formed via two different processes in the ICP: process 1, which involved the decomposition of As-containing molecules (i.e., H3AsO3) to AsO+, and process 2, which involved the recombination between As+ and oxygen originating from liquids introduced into the ICP (e.g., solvents) or gases (e.g., entrained atmospheric gases). In addition, results suggested that carbon matrix has the potential to enhance process 1.
Nitrogenization of porous carbon provides an effective methodology to promote capacitive deionization (CDI) performance. Exploring a new class of nitrogen-doped porous carbons from waste biomass over commercially available activated carbons is of significant interest in CDI. In this contribution, we present the preparation of nitrogen-doped porous carbon microtubes (N-CMTs) by pyrolyzing willow catkins, a naturally abundant biomass with urea as the nitrogen source. Due to the naturally occurring hollow microtube structure and the high nitrogen content, the as-prepared N-CMTs show an enhanced desalination performance compared to undoped samples. A high deionization capacity of 16.78 mg g−1 predicted by Langmuir isotherm and a stable cycling performance over ten cycles are observed. The result advocates the importance and significance of naturally developed architectures and chemistry for practical CDI application.