Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

First principle studies of oxygen reduction reaction on N doped graphene: Impact of N concentration, position and co-adsorbate effect

Density Functional Theory calculations were performed on N doped graphene sheet to investigate the trends for adsorption energy variation of oxygen reduction reaction intermediates (HOO*, O*, HO*) when the N concentration increases from 0N (0%) to 1N (33%), to 2N (67%) and to 3N (100%) around the C active site. The impact of the distance between the doping N atoms and the C active site is also studied. Last, the impact of additionally co-adsorbed HO*/O* intermediates was probed. For all the studied systems the magnitudes with which varies the adsorption energies are shaped by the HO*/HOO* capability of accommodating less charge than O* (i.e according to octet rule 1e− vs. 2e−). When N concentration increases, adsorption energy of O* increases with a much higher magnitude than that of HO*/HOO* (i.e with 5 eV vs. 2.7 eV, when going from 0N to 3N). In the presence of the O* co-adsorbate, adsorption energy of intermediates on the investigated active site decrease with a much higher magnitude than when 1HO* is present as co-adsorbate (≈2 eV vs. 1 eV). The theoretical overpotential trends are evaluated using ΔGHO*-ΔGO* descriptor and are found to be significantly influenced by all these environmental changes around the active site. By applying the water stabilization effects, the activity trends remain the same as when it is not taken into account. These results reveal aspects of ORR activity variations that take place when N is clustering on graphene sheets, structures that can be possible as a function of synthesis procedures that could lead to unevenly distribution of dopants in the matrix

Correlations between Density-Based Bond Orders and Orbital-Based Bond Energies for Chemical Bonding Analysis

Quantum chemistry-based codes and methods provide valuable computational tools to estimate reaction energetics and elucidate reaction mechanisms. Electronic structure methods allow directly studying the chemical transformations in molecular systems involving breaking and making of chemical bonds and the associated changes in the electronic structure. The link between the electronic structure and chemical bonding can be provided through the crystal orbital Hamilton population (COHP) analysis that allows quantifying the bond strength by computing Hamilton-weighted populations of localized atomic orbitals. Another important parameter reflecting the nature and strength of a chemical bond is the bond order that can be assessed by the density derived electrostatic and chemical (DDEC6) method which relies on an electron and spin density-partitioning scheme. Herein, we describe a linear correlation that can be established between the DDEC6-derived bond orders and the bond strengths computed with the COHP formalism. We demonstrate that within defined boundaries, the COHP-derived bond strengths can be consistently compared among each other and linked to the DDEC6-derived bond orders independent of the used model. The validity of these correlations and the effective model independence of the electronic descriptors are demonstrated for a variety of gas-phase chemical systems, featuring different types of chemical bonds. Furthermore, the applicability of the derived correlations to the description of complex reaction paths in periodic systems is demonstrated by considering the zeolite-catalyzed Diels-Alder cycloaddition reaction between 2,5-dimethylfuran and ethylene.

Exploring the Electronic Structure of New Doped Salt Hydrates, Mg1–xCaxCl2·nH2O, for Thermochemical Energy Storage

Chloride-based salt hydrates, MgCl2·nH2O and CaCl2·nH2O (n = 0,1,2,4,6), are promising materials for thermochemical heat storage systems due to their high sorption energy capacity. However, both salts have their own shortcoming characteristics within the operational temperature of the thermochemical heat storage applications. While the higher hydrates of CaCl2·nH2O (n = 4,6) have a low melting point, the lower hydrates of MgCl2·nH2O (n = 0,1,2) can form the highly toxic and corrosive HCl gas. Both shortcomings cap the individual use of these salts to a restricted range of the available hydrates. A combination of these two salts showed to have the potential to overcome these shortcomings. The present study focuses on finding stable configurations of potential superior salt hydrate combinations using the evolutionary algorithm USPEX as well as manual mutations of known pristine structures. The newly found structures are less stable than the pure salts, but stable enough to be combined. Extensive electronic density-derived tools, like the Density Derived Electronic and Chemical (DDEC6) bond orders and net atomic charges, as well as Bader topological analysis, are used to predict the HCl gas formation based on the chemical environment in the new metastable structures. We find that doping MgCl2·nH2O with calcium considerably reduces HCl formation compared to its pure form, caused by a combination of the stronger Ca-Cl interaction than Mg-Cl and a less polar H2O molecule in a calcium environment than in a magnesium environment. This provides the possibility to shift the p, T-equilibrium curve of HCl outside the thermal storage operational window

Mechanistic insight into the [4 + 2] Diels-Alder cycloaddition over first row d-block cation-exchanged faujasites

The Diels-Alder cycloaddition (DAC) is a powerful tool to construct C-C bonds. The DAC reaction can be accelerated in several ways, one of which is reactant confinement as observed in supramolecular complexes and Diels-Alderases. Another method is altering the frontier molecular orbitals (FMOs) of the reactants by using homogeneous transition-metal complexes whose active sites exhibit d-orbitals suitable for net-bonding orbital interactions with the substrates. Both features can be combined in first row d-block (TM) exchanged faujasite catalysts where the zeolite framework acts as a stabilizing ligand for the active site while confining the reactants. Herein, we report on a mechanistic and periodic DFT study on TM-(Cu(I), Cu(II), Zn(II), Ni(II), Cr(III), Sc(III), V(V))exchanged faujasites to elucidate the effect of d-shell filling on the DAC reaction between 2,5-dimethylfuran and ethylene. Two pathways were found: one being the concerted one-step and the other being the stepwise two-step pathway. A decrease in d-shell filling results in a concomitant increase in reactant activation as evidenced by increasingly narrow energy gaps and lower activation barriers. For models holding relatively small d-block cations, the zeolite framework was found to bias the DAC reaction toward an asynchronous one-step pathway instead of the two-step pathway. This work is an example of how the active site properties and the surrounding chemical environment influence the reaction mechanism of chemical transformations.

Mechanistic Insight into the [4 + 2] DielsAlder Cycloaddition over First Row dBlock Cation-Exchanged Faujasites

The Diels-Alder cycloaddition (DAC) is a powerful tool to construct C-C bonds. The DAC reaction can be accelerated in several ways, one of which is reactant confinement as observed in supramolecular complexes and Diels-Alderases. Another method is altering the frontier molecular orbitals (FMOs) of the reactants by using homogeneous transition-metal complexes whose active sites exhibit d-orbitals suitable for net-bonding orbital interactions with the substrates. Both features can be combined in first row d-block (TM) exchanged faujasite catalysts where the zeolite framework acts as a stabilizing ligand for the active site while confining the reactants. Herein, we report on a mechanistic and periodic DFT study on TM-(Cu(I), Cu(II), Zn(II), Ni(II), Cr(III), Sc(III), V(V))exchanged faujasites to elucidate the effect of d-shell filling on the DAC reaction between 2,5-dimethylfuran and ethylene. Two pathways were found: one being the concerted one-step and the other being the stepwise two-step pathway. A decrease in d-shell filling results in a concomitant increase in reactant activation as evidenced by increasingly narrow energy gaps and lower activation barriers. For models holding relatively small d-block cations, the zeolite framework was found to bias the DAC reaction toward an asynchronous one-step pathway instead of the two-step pathway. This work is an example of how the active site properties and the surrounding chemical environment influence the reaction mechanism of chemical transformations.

Electronic Structure Analysis of the Diels-Alder Cycloaddition Catalyzed by Alkali-Exchanged Faujasites

The Diels-Alder cycloaddition (DAC) reaction is a commonly employed reaction for the formation of C-C bonds. DAC catalysis can be achieved by using Lewis acids and via reactant confinement in aqueous nanocages. Low-silica alkali-exchanged faujasite catalysts combine these two factors in one material. They can be used in the tandem DAC/dehydration reaction of biomass-derived 2,5-dimethylfuran (DMF) with ethylene toward p-xylene, in which the DAC reaction step initiates the overall reaction cycle. In this work, we performed periodic density functional theory (DFT) calculations on the DAC reaction between DMF and C2H4 in low-silica alkali(M)-exchanged faujasites (MY; Si/Al = 2.4; M = Li+, Na+, K+, Rb+, Cs+). The aim was to investigate how confinement of reactants in MY catalysts changed their electronic structure and the DAC-reactivity trend among the evaluated MY zeolites. The conventional high-silica alkali-exchanged isolated site model (MFAU; Si/Al = 47) served as a reference. The results show that confinement leads to initial-state (IS) destabilization and transition-state (TS) stabilization. Among the tested MY, most significant IS destabilization is found in RbY. Only antibonding orbital interactions between the reactants/reactive complex and cations were found, indicating that TS stabilization arises from ionic interactions. Additionally, in RbY the geometry of the transition state is geometrically most similar to that of the initial and final state. RbY also exhibits an optimal combination of the confinement-effects, resulting in having the lowest computed DAC-activation energy. The overall effect is a DAC-reactivity trend inversion in MY as compared to the trend found in MFAU where the activation energy correlates with the Lewis acidity of the exchangeable cations.ChemE/Algemee

Scaling relations for acidity and reactivity of zeolites

Zeolites are widely applied as solid acid catalysts in various technological processes. In this work we have computationally investigated how catalytic reactivity scales with acidity for a range of zeolites with different topology and chemical composition. We found that straightforward correlations are limited to zeolites with same topology. The adsorption energies of bases such as carbon monoxide (CO), acetonitrile (CH3CN), ammonia (NH3), trimethylamine (N(CH3)3), and pyridine (C5H5N) give same acidity trend for FAU zeolites with varying composition. Crystal orbital Hamilton populations (COHP) analysis provides a detailed molecular orbital picture of adsorbed base molecules on the Brønsted acid sites (BAS). Bonding is dominated by strong σ donation from guest molecules to the BAS for the adsorbed CO and CH3CN complexes. The bond order parameters derived for the CH3CN adsorption complex is a useful acidity descriptor for the intrinsic acid strength of FAU zeolites. For FAU zeolites the activation energy for the conversion of π-adsorbed isobutene into alkoxy species correlates well with the acidity determined by the NH3 adsorption energies. Other zeolites such as MFI and CHA do not follow the scaling relations obtained for FAU, which we ascribe due to the different dispersion and steric effects induced by zeolite framework topology

Gibbs Ensemble Monte Carlo for Reactive Force Fields to Determine the Vapor-Liquid Equilibrium of CO₂and H₂O

Absorption and reactive properties of fluids in porous media are key to the design and improvement of numerous energy related applications. Molecular simulations of these systems require accurate force fields that capture the involved chemical reactions and have the ability to describe the vapor-liquid equilibrium (VLE). Two new reactive force fields (ReaxFF) for CO2 and H2O are developed, which are capable of not only modeling bond breaking and formation in reactive environments but also predicting their VLEs at saturation conditions. These new force fields include extra terms (ReaxFF-lg) to improve the long-range interactions between the molecules. For validation, we have developed a new Gibbs ensemble Monte Carlo (GEMC-ReaxFF) approach to predict the VLE. Computed VLE data show good agreement with National Institute of Standards and Technology reference data as well as existing nonreactive force fields. This validation proves the applicability of the GEMC-ReaxFF method to test new reactive force fields, and simultaneously it proves the applicability to extend newly developed ReaxFF force fields to other more complex reactive systems.Engineering Thermodynamic

Reactive Grand-Canonical Monte Carlo Simulations for Modeling Hydration of MgCl₂

Thermochemical heat-storage applications, based on the reversible endo-/exothermic hydration reaction of salts, are intensively investigated to search for compact heat-storage devices. To achieve a truly valuable storage system, progressively complex salts are investigated. For these salts, the equilibrium temperature and pressure conditions are not always easy to predict. However, these conditions are crucial for the design of thermochemical heat-storage systems. A biased grand-canonical Monte Carlo (GCMC) tool is developed, enabling the study of equilibrium conditions at the molecular level. The GCMC algorithm is combined with reactive force field molecular dynamics (ReaxFF), which allows bond formation within the simulation. The Weeks-Chandler-Andersen (WCA) potential is used to scan multiple trial positions for the GCMC algorithm at a small cost. The most promising trial positions can be selected for recomputation with the more expensive ReaxFF. The developed WCA-ReaxFF-GCMC tool was used to study the hydration of MgCl2·nH2O. The simulation results show a good agreement with experimental and thermodynamic equilibriums for multiple hydration levels. The hydration shows that water, present at the surface of crystalline salt, deforms the surface layers and promotes further hydration of these deformed layers. Additionally, the WCA-ReaxFF-GCMC algorithm can be used to study other, non-TCM-related, reactive sorption processes. Engineering ThermodynamicsProcess and Energ