ABSTRACT
Objective The epidemic of COVID-19 and its variants is endangering human health. Wearing protective masks can effectively reduce the infection risk by resisting the inhalation of the polluted air containing the coronavirus. Electrospun polyamide nanofibers can be used as the core layer of protective masks and have lately received growing attention because of their high filtration performance and robust mechanical properties. However, existing electrospun polyamide nanofiber filters are usually prepared from toxic solvents which could cause severe environmental pollution and endanger workers' health, hence, their practical application should be restricted. Therefore, it is imperative to seek and develop green-solvent-based polyamide nanofiber filters. Method Innovative polyamide nanofiber filters were developed by direct electrospinning technique based on green solvents (Fig. 1). Ethanol as the solvent and water as the nonsolvent were adopted to prepare the green-solvent-based polyamide (GSPA) nanofibers by designing spinning solutions with different ethanol/water mass ratios (i.e., 10: 0, 9: 1, 8: 2, 7: 3, and 6: 4) . During electrospinning process, the working voltage, tip-to-collector distance, and solution extrusion speed were set as 30 kV, 15 cm and 1 mL/h, respectively. The nanofibers prepared with the different ethanol/water ratios were denoted as GSPA - 0, GSPA - 1, GSPA - 2, GSPA-3, and GSPA-4, respectively. Results It was found that water content had a great influence on the morphological structures of polyamide nanofibers (Fig. 2) - After introducing a small amount of water, the obtained GSPA - 1 nanofibers featuring thinner diameter of 332 nm were compared to the GSPA-0 nanofibers (499 nm). The enhanced conductivity (10. 5 μS/cm) of waterborne spinning solutions (Fig. 3) stimulated more charges on spinning jets and led to larger electrostatic force, thus greatly elongating the jets and thinning the fiber diameter. However, with the further increment of water concentrations from 20% to 40%, the obtained fibers exhibited an increased average diameter ranging from 443 to 1 553 nm, which was mainly attributed to the larger viscosity of spinning solutions. Although water cannot dissolve polyamide, homogenous waterborne polyamide/ethanol solutions can still be obtained with different ethanol/water mass ratios within a broad area in the stable region (Fig. 3) - The average pore size of GSPA -1 membranes decreased by 55% compared with that of GSPA-0 membranes, contributing to high filtration efficiency. Moreover, with different concentrations (10%, 20%, 30%) of water, the fluffy structure of GSPA nanofibers were achieved with a high porosity (> 80%), which would offer more passageways to transmit air rapidly. As the water concentration increased, the breaking strength of membranes increased at first and then decreased (Fig. 5), and the GSPA- 1 membranes exhibited the highest breaking strength of 5. 6 MPa, which was believed to be related to the enhanced entanglements and contacts among the adjacent fibers because of the small fiber diameter. The GSPA -1 membranes displayed the highest filtration efficiency (99. 02%) for the most penetration particles (PM0.3) by virtue of the small fiber diameter but suffered from poor permeability with a pressure drop of 158 Pa. Moreover, the GSPA- 1 membranes possessed the highest quality factor of 0. 029 3 Pa, suggesting the optimal filtration performance among different GSPA membranes. A high PM0.3 removal efficiency (>95%) was achieved for GSPA-1 filters under various airflow velocities ranging from 10 to 90 L/min (Fig. 7). Compared with conventional melt-blown fibers, the GSPA nanofibers featured a smaller diameter and higher Knudsen number (Fig. 8), and PM0.3 were captured mainly on the surfaces of green polyamide nanofibers (Fig. 9), demonstrating the higher adsorption ability benefiting from the larger specific surface area. Conclusion A cleaner production of polyamide nanofibers for air filtration was proposed by direct electrospinning based on green and sustaina le binary solvents of water and ethanol. For the first time, the structure including fiber diameter, porosity, and pore size of electrospun polyamide nanofibers were precisely tailored by manipulating water concentration in spinning solutions. The prepared environmentally friendly polyamide nanofiber filters feature the interconnected porous structure with the nanoscale ID building blocks (332 nm), mean pore size (0.7 μm), and porosity (84%), thus achieving efficient PM0.3 capture performance with the filtration efficiency of 99. 02% and pressure drop of 158 Pa, which could be comparable to previous toxic-solvent-processed nanofibers. Moreover, the GSPA nanofibers exhibit robust mechanical properties with an impressive breaking strength (5 . 6 MPa) and elongation (163. 9%), contributing to withstanding the external forces and deformation in the practical assembly and usage of resultant filters. It is envisaged that the green-solvent-based polyamide nanofibers could be used as promising candidates for next-generation air filters, and the proposed waterborne spinning strategy can provide valuable insights for cleaner production of advanced polyamide textiles. © 2023 China Textile Engineering Society. All rights reserved.
ABSTRACT
Several synthetic routes of nirmatrelvir (the ingredient of a new drug to treat COVID-19 made by Pfizer) have been reported. We focused on a second route to improve the synthetic method of nirmatrelvir with a methodology that included different steps. The first step was an analysis of reaction byproducts using acetonitrile as a solvent of the condensation reaction to improve the inversion rate. Then, we used isobutyl acetate as a crystalline solvent to obtain the key intermediate as a solvate, which was a stable crystal product with high purity. Complementarily, we also used trifluoroacetic anhydride as the primary-amide dehydrating agent, and 2-methyl tetrahydrofuran as the solvent to prepare nirmatrelvir, which led to an overall yield of 48% via four steps and a purity of 99.5% according to high-performance liquid chromatography. We also investigated the crystal form of nirmatrelvir: the single-crystal features and transformation from a crystal form to nirmatrelvir were dependent upon temperature. Our data have great value for study of the synthetic method and crystal stability of nirmatrelvir. © 2023 The Royal Society of Chemistry.
ABSTRACT
Hydrocortisone (termed as D1) and dexamethasone (termed as D2) are corticosteroids currently used to treat COVID-19. COVID-19 is a disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Exploring additional chemical properties of drugs used in the treatment protocols for COVID-19 could help scientists alike improve these treatment protocols and potentially even the vaccines (i.e., Janssen, Moderna, AstraZeneca, Pfizer-BioNTech). In this work, the charge-transfer (CT) properties of these two corticosteroids (D1 and D2) with two universal acceptors: 7,8,8-tetracyanoquinodimethane (termed as TCNQ) and fluoranil (termed as TFQ) in five different solvents were investigated. The examined solvents were MeOH, EtOH, MeCN, CH2Cl2, and CHCl3. The CT interactions formed stable corticosteroid CT complexes in all examined solvents. Several spectroscopic parameters were derived, and the oscillator strength (f) and transition dipole moment (µe.g. ) values revealed that the interaction between the investigated corticosteroids with TCNQ acceptor is much stronger than their interaction with TFQ acceptor. The CT interactions were proposed to process via n â π* transition.
ABSTRACT
COVID-19 is the disease caused by a novel coronavirus (CoV) named the severe acute respiratory syndrome coronavirus 2 (termed SARS coronavirus 2 or SARS-CoV-2). Since the first case reported in December 2019, infections caused by this novel virus have led to a continuous global pandemic that has placed an unprecedented burden on health, economic, and social systems worldwide. In response, multiple therapeutic options have been developed to stop this pandemic. One of these options is based on traditional corticosteroids, however, chemical modifications to enhance their efficacy remain largely unexplored. Obtaining additional insight into the chemical and physical properties of pharmacologically effective drugs used to combat COVID-19 will help physicians and researchers alike to improve current treatments and vaccines (i.e., Pfizer-BioNTech, AstraZeneca, Moderna, Janssen). Herein, we examined the charge-transfer properties of two corticosteroids used as adjunctive therapies in the treatment of COVID-19, hydrocortisone and dexamethasone, as donors with 2,3-dichloro-5,6-dicyano-p-benzoquinone as an acceptor in various solvents. We found that the examined donors reacted strongly with the acceptor in CH2Cl2 and CHCl3 solvents to create stable compounds with novel clinical potential.
ABSTRACT
Population growth has led to an increased demand for raw minerals and energy resources;however, their supply cannot easily be provided in the same proportions. Modern technologies contain materials that are becoming more finely intermixed because of the broadening palette of elements used, and this outcome creates certain limitations for recycling. The recovery and separation of individual elements, critical materials and valuable metals from complex systems requires complex energy-consuming solutions with many hazardous chemicals used. Significant pressure is brought to bear on the improvement of separation and recycling approaches by the need to balance sustainability, efficiency, and environmental impacts. Due to the increase in environmental consciousness in chemical research and industry, the challenge for a sustainable environment calls for clean procedures that avoid the use of harmful organic solvents. Ionic liquids, also known as molten salts and future solvents, are endowed with unique features that have already had a promising impact on cutting-edge science and technologies. This review aims to address the current challenges associated with the energy-efficient design, recovery, recycling, and separation of valuable metals employing ionic liquids.