Indirect Photodegradation of Sulfamethoxazole and Trimethoprim by Hydroxyl Radicals in Aquatic Environment: Mechanisms, Transformation Products and Eco-Toxicity Evaluation

The bacteriostatic antibiotics, sulfamethoxazole (SMX) and trimethoprim (TMP), have frequently been found in wastewater and surface water, which raises the concerns about their ecotoxicological effects. The indirect photochemical transformation has been proven to be an efficient way to degrade SMX and TMP. In this study, the reaction mechanisms of the degradation by SMX and TMF by OH radicals were investigated by theoretical calculations. Corresponding rate constants were determined and the eco-toxicity of SMX and TMP and its degradations products were predicted using theoretical models. The results indicate that the most favorable pathways for the transformation of SMX and TMP are both •OH-addition reaction of benzene ring site with lowest Gibbs free energy barriers (6.86 and 6.21 kcal mol−1). It was found that the overall reaction rate constants of •OH-initial reaction of SMX and TMP are 1.28 × 108 M−1 s−1 and 6.21 × 108 M−1 s−1 at 298 K, respectively. When comparing the eco-toxicity of transformation products with parent SMX and TMP, it can be concluded that the acute and chronic toxicities of the degraded products are reduced, but some products remain harmful for organisms, especially for daphnid (toxic or very toxic level). This study can give greater insight into the degradation of SMX and TMP by •OH through theoretical calculations in aquatic environment

Evaluation of faciocutaneous clues to systemic diseases: A learning module for Chinese undergraduate medical students

Background: Medical students will encounter cutaneous lesions associated with systemic disorders during their training and career. However, there are no chapters in Chinese undergraduate medical textbooks regarding these lesions. Objective: The objective of the present study was to evaluate the impact of an additional learning module about cutaneous lesions associated with systemic disorders for Chinese undergraduates. Methods: In this medical course, we introduced a case-based clinical learning module. This module was evaluated with a pre-/postcourse questionnaire and a final multichoice examination. Results: After learning, more students agreed that some skin lesions could serve as “windows” to hidden systemic diseases, and it was more important to learn how to distinguish lesions associated with systemic diseases from simplex ones. We found that the group that was provided conventional teaching plus this module scored significantly better (52.75 ± 23.96) than the conventional teaching group (40.53 ± 21.43; t = 2.370, p = 0.020) in the final multichoice examination. Conclusion: Introducing this additional learning module may offer an early opportunity to explore systemic diseases from a dermatological view and is likely to lay the foundations for interdisciplinary collaboration in the future practice for medical students

Synergistic Reaction of SO2 with NO2 in Presence of H2O and NH3: A Potential Source of Sulfate Aerosol

Effect of H2O and NH3 on the synergistic oxidation reaction of SO2 and NO2 is investigated by theoretical calculation using the molecule system SO2-2NO2-nH2O (n = 0, 1, 2, 3) and SO2-2NO2-nH2O-mNH3 (n = 0, 1, 2; m = 1, 2). Calculated results show that SO2 is oxidized to SO3 by N2O4 intermediate. The additional H2O in the systems can reduce the energy barrier of oxidation step. The increasing number of H2O molecules in the systems enhances the effect and promotes the production of HONO. When the proportion of H2O to NH3 is 1:1, with NH3 included in the system, the energy barrier is lower than two pure H2O molecules in the oxidation step. The present study indicates that the H2O and NH3 have thermodynamic effects on promoting the oxidation reaction of SO2 and NO2, and NH3 has a more significant role in stabilizing product complexes. In these hydrolysis reactions, nethermost barrier energy (0.29 kcal/mol) can be found in the system SO2-2NO2-H2O. It is obvious that the production of HONO is energetically favorable. A new reaction mechanism about SO2 oxidation in the atmosphere is proposed, which can provide guidance for the further study of aerosol surface reactions

A hypervalent and cubically coordinated molecular phase of IF8 predicted at high pressure

Up to now, the maximum coordination number of iodine is seven in neutral iodine heptafluoride (IF 7 ) and eight in anionic octafluoride (IF 8− ). Here, we explore pressure as a method for realizing new hypercoordinated iodine compounds. First-principles swarm structure calculations have been used to predict the high-pressure and T → 0 K phase diagram of binary iodine fluorides. The investigated compounds are predicted to undergo complex structural phase transitions under high pressure, accompanied by various semiconductor to metal transitions. The pressure induced formation of a neutral octafluoride compound, IF 8 , consisting of eight-coordinated iodine is one of several unprecedented predicted structures. In sharp contrast to the square antiprismatic structure in IF 8− , IF 8 , which is dynamically unstable under atmospheric conditions, is stable and adopts a quasi-cube molecular configuration with R3& symmetry at 300 GPa. The metallicity of IF 8 originates from a hole in the fluorine 2p-bands that dominate the Fermi surface. The highly unusual coordination sphere in IF 8 at 300 GPa is a consequence of the 5d levels of iodine coming down and becoming part of the valence, where they mix with iodine\u27s 5s and 5p levels and engage in chemical bonding. The valence expansion of iodine under pressure effectively makes IF 8 not only hypercoordinated, but also hypervalent

Hard and superconducting cubic boron phase via swarm-intelligence structural prediction driven by a machine-learning potential

Boron is an intriguing element due to its electron deficiency and the ability to form multicenter bonds in allotropes and borides, exhibiting diversified structures, unique chemical bonds, and interesting properties. Using swarm-intelligence structural prediction driven by a machine learning potential, we identified a boron phase with a 24-atom cubic unit cell, called c−B24, consisting of a B6 octahedron in addition to well-known B2 pairs and B12 icosahedra at ambient pressure. There appear unusual four-center-two-electron (4c-2e) bonds in the B12 icosahedron, originating from the peculiar bonding pattern between the B2 pair and B12 icosahedron, which is in sharp contrast with the 3c-2e and 2c-2e bonds in α−B12. More interestingly, c−B24 is a metal with a superconducting critical temperature of 13.8 K at ambient pressure. The predicted Vickers hardness (23.1 GPa) indicates that c−B24 is a potential hard material. Notably, it also has a good shear/tensile resistance (48.9/29.3 GPa). Our work not only enriches the understanding of the chemical properties of boron, but also sparks efforts on trying to synthesize this particular compound, c−B24.The authors acknowledge the funding support from the Natural Science Foundation of China under Grants No. 21873017, No. 21573037, No. 11704062, and No. 51732003, the Postdoctoral Science Foundation of China under Grant No. 2013M541283, the Natural Science Foundation of Jilin Province (20190201231JC), the “111” Project (No. B13013). The work was carried out at National Supercomputer Center in Tianjin, and the calculations were performed on TianHe-1 (A). A.B. acknowledges financial support from the Spanish Ministry of Science and Innovation (PID2019-105488GBI00) and from Jilin Province Out-standing Young Talents project (Grant No. 20190103040JH).Peer reviewe