The neutral and charged yttrium metal-ammonia complexes, Y(NH3)80,±, are investigated using state-of-the-art quantum chemical calculations. The electronic structure of these complexes is described as ...an Y(NH3)83+ core with two, three, and four electrons orbiting in its periphery. Unlike the so far reported solvated electron precursors containing alkali, alkaline earth or first-row transition metals, yttrium complexes are the only ones which can accommodate eight ammonia ligands and up to four peripheral electrons. For the neutral species, two electrons occupy the diffuse s-type orbital (1s) and one diffuse p-type orbital (1p). For the cationic counterpart one electron is removed from the 1p orbital, while for the anion another electron is added to the 1p shell. The calculated low-lying electronic states with excitation energies up to 2.0 eV populate the 1s, 1p, and 1d outer orbitals. The first ionization energy of Y(NH3)8 is 2.74 eV and its electron affinity is 0.64 eV. The present results suggest that saturated yttrium ammonia solutions will turn into solids (liquid or expanded metals), where a grid of Y(NH3)83+ centers will be surrounded by "free" electrons.
Neutral and positively charged calcium ammonia complexes are investigated by means of high-level quantum chemical calculations. We report optimal structures, binding energies, and vibrational spectra ...for Ca(NH3)1–8 0,+. The bigger Ca(NH3)6–8 0,+ complexes can be classified as solvated electron precursors (SEPs) and are best described as a Ca(NH3)6–8 2+ core with two or one peripheral electrons. In their ground state, only ∼10% of the outer electron density is estimated to be within the calcium van der Waals radius. For these systems, we calculated several low-lying electronic states, where electrons populate diffuse outer orbitals. The Aufbau principle for the outer electrons is found to be identical to previously studied SEPs: 1s, 1p, 1d, 1f, 2s, and 2p. We show that going from Ca(NH3)5, which has an incomplete first coordination shell and the two valence electrons that are mainly in the valence sphere of calcium, to Ca(NH3)6, both the vibrational and electronic features change abruptly. Infrared, visible, and ultraviolet spectroscopy can be used to identify and characterize calcium SEPs.
Advances in superconductor technology have been pursued for decades, moving towards room temperature models, such as a postulated nitrogen-doped lutetium hydride network. While experimental ...observations have been contradictory, insight into the building blocks of potential new superconductor materials can be gained theoretically, unravelling the fascinating electronic structure of these compounds at a molecular level. Here, the fundamental building blocks of lutetium materials (LuH, LuN, and LuNH) have been examined. The structures, spectroscopic constants for the ground and excited states, and the potential energy curves have been obtained for these species using complete active self-consistent field (CASSCF) and multireference configuration interaction with Davidson's correction (MRCI+Q) methods. For LuNH, the energetic properties of its isomers are determined. The bond dissociation energies of the three building blocks are calculated with the state-of-the-art
f
-block
ab initio
correlation consistent composite approach (
f
-ccCA) and the high accuracy extrapolated
ab initio
thermochemistry (HEAT) scheme. As well, an analysis of different formation pathways of LuNH has been provided.
The discrepancy in single reference
versus
multireference guess orbitals in the strongly correlated LuN.
Statistical Assessment of Modeling of Proteins and Ligands (SAMPL) challenges provide routes to compare chemical quantities determined using computational chemistry approaches to experimental ...measurements that are shared after the competition. For this effort, several computational methods have been used to calculate the binding energies of Octa Acid (OA) and exo-Octa Acid (exoOA) host–guest systems for SAMPL7. The initial poses for molecular dynamics (MD) were generated by molecular docking. Binding free energy calculations were performed using molecular mechanics combined with Poisson–Boltzmann or generalized Born surface area solvation (MMPBSA/MMGBSA) approaches. The factors that affect the utility of the MMPBSA/MMGBSA approaches including solvation, partial charge, and solute entropy models were also analyzed. In addition to MD calculations, quantum mechanics (QM) calculations were performed using several different density functional theory (DFT) approaches. From SAMPL6 results, B3PW91-D3 was found to overestimate binding energies though it was effective for geometry optimizations, so it was considered for the DFT geometry optimizations in the current study, with single-point energy calculations carried out with B2PLYP-D3 with double-, triple-, and quadruple-ζ level basis sets. Accounting for dispersion effects, and solvation models was deemed essential for the predictions. MMGBSA and MMPBSA correlated better to experiment when used in conjunction with an empirical/linear correction.
•Accident causation models.•Accident assessment studies.•Occupational safety and health risk management.•Literature review.
During the last decades, there has been a growing awareness about ...occupational safety and health risks by the various interested parties in the construction industry. However, despite the substantial improvements achieved, the rate of accidents is still significantly higher than in most of the other industries. Two major reasons have been used to explain this high rate of accidents in the construction industry: (i) the intrinsic riskiness due to the nature of the activities and the particular characteristics of constructions projects and organizations and (ii) the financial and economic issues regarding the implementation of additional safety measures in a growing competitive market.
This companion paper is presented in two parts. The present document refers to Part 1 and reviews the major lines of research and main contributions in the field of occupational safety and health in the construction industry. The review covers occupational safety and health research, organized in accident understanding studies, accident analysis studies and accident modeling studies, and occupational safety and health risk management, in particular risk criteria and limits. The review reveals the need for a methodology to quantify occupational safety and health risk in construction projects following the guidelines set by the international standard ISO 31000:2009. Part 2 proposes and details the Occupational Safety and Health Potential Risk Model (OSH-PRM) that was designed to allow estimating the statistical cost of occupational safety and health risk.
The frequency and severity of natural or human-induced disaster events, such as floods, earthquakes, hurricanes, fires, pandemics, hazardous material spills, groundwater contamination, structural ...failures, explosions, etc., as well as their impacts, have greatly increased in recent decades due to population growth and extensive urbanization, among other factors. The World Bank estimates that the total cost of cities’ and communities’ vulnerability to these types of disasters could reach more than USD 300 billion per year by 2030. However, it has been argued that investment to improve the quality and resilience of engineered physical assets that are the backbone of modern societies, such as critical infrastructure, industrial facilities, and buildings, could significantly contribute to more sustainable and prosperous societies. Engineered assets are key to the delivery of essential services, such as transport, food, water, electricity supply, health and safety, etc. Some of these physical assets are integrated into asset systems and national or regional networks, with life cycles of several decades or even centuries. It is, therefore, of great importance that strategies and life cycle decisions, such as those related to short- and long-term capital investment planning, maintenance strategies, operational plans, and asset disposal, lead to the maximization of the value derived from these assets. Moreover, it is essential that the achievement of these goals is sustainable over time. Organizations dealing with engineering assets, both public and private, must, therefore, integrate sustainability and resilience concerns into everyday operations, using budgets that are often restricted, while also meeting demanding performance requirements in risky and uncertain environments. This Special Issue collates a selection of papers reporting the latest research and case studies regarding the trends and emerging strategies used to address these challenges, with contributions discussing how asset management principles and techniques can help to push the boundaries of sophistication and innovation to improve the life cycle management of engineered assets to ensure more sustainable and resilient cities and societies.
Nuclear receptors are the fundamental building blocks of gene expression regulation and the focus of many drug targets. While binding to DNA, nuclear receptors act as transcription factors, governing ...a multitude of functions in the human body. Peroxisome proliferator-activator receptor γ (PPARγ) and the retinoid X receptor α (RXRα) form heterodimers with unique properties and have a primordial role in insulin sensitization. This PPARγ/RXRα heterodimer has been shown to be impacted by per- and polyfluoroalkyl substances (PFAS) and linked to a variety of significant health conditions in humans. Herein, a selection of the most common PFAS (legacy and emerging) was studied utilizing molecular dynamics simulations for PPARγ/RXRα. The local and global structural effects of PFAS binding on the known ligand binding pockets of PPARγ and RXRα as well as the DNA binding domain (DBD) of RXRα were inspected. The binding free energies were predicted computationally and were compared between the different binding pockets. In addition, two electronic structure approaches were utilized to model the interaction of PFAS within the DNA binding domain, density functional theory (DFT) and domain-based pair natural orbital coupled cluster with perturbative triples (DLPNO–CCSD(T)) approaches, with implicit solvation. Residue decomposition and hydrogen-bonding analysis were also performed, detailing the role of prominent residues in molecular recognition. The role of l-carnitine is explored as a potential in vivo remediation strategy for PFAS interaction with the PPARγ/RXRα heterodimer. In this work, it was found that PFAS can bind and act as agonists for all of the investigated pockets. For the first time in the literature, PFAS are postulated to bind to the DNA binding domain in a nonspecific manner. In addition, for the PPARγ ligand binding domain, l-carnitine shows promise in replacing smaller PFAS from the pocket.
Investigation of the ground and excited states of RuO2+ is carried out using multireference quantum chemical methodologies. The electronic structure is explored in detail, and accurate spectroscopic ...constants for 12 states are reported. Although ruthenium belongs to the same group as iron, the ground state of RuO2+ is 1Σ+ with a strong oxo character as opposed to the 3Δ of FeO2+ with primarily oxyl character. To see the effect of the different electronic structure of RuO2+ on the O–H and C–H bond activation processes, we studied its reaction with one water or methane molecule. Reaction energies and activation barriers are given for six low-lying electronic states of singlet, triplet, and quintet spin multiplicities. It is found that the higher-energy quintet state (5Σ+) provides the lowest activation energies and is the same state responsible for the C–H activation for FeO2+ complexes. The reason is attributed to its weaker metal–oxygen bond (longer bond length), which is “prepared” to be activated at the same time with the O–H and C–H bonds. The effect of an ammonia ligand in the chemical activity is also discussed.
Computational chemistry provides a powerful route to determine thermochemical properties. For transition metal thermochemistry, typically, high-level quantum methodologies are required. Ab initio ...composite methods - which aim to replicate the predictions possible from a high-level method/advanced basis set with predictions from a series of lower-level methods/basis sets to reduce computational cost - have proven to be effective for transition metal species, with better than chemical accuracy for transition metal energetics (<12 kJ mol
−1
), on average. While useful, to provide a more robust computational approach, Super ccCA (s-ccCA) is introduced herein and varies from its predecessor, ccCA, by utilising higher-level coupled-cluster corrections along with a spin-orbit contribution from a Breit-Pauli Hamiltonian. In this work, s-ccCA has been utilised for the prediction of dissociation energies of 3d and 4d molecules. A set of borides, sulphides and carbides in conjunction with three early first-row transition metals (Sc, Ti, V) and three second-row transition metals (Y, Zr, Nb) were studied with this new composite method. The energies calculated herein were compared with the experiment and shown to be in excellent agreement. The energetic predictions show that for cases where a balance of static and dynamic correlation is of paramount importance, s-ccCA offers an effective approach.
Peroxisome proliferator receptor gamma (PPARγ), a type II nuclear receptor, fundamental in the regulation of genes, glucose metabolism, and insulin sensitization has been shown to be impacted by per- ...and poly-fluoroalkyl substances (PFASs). To consider the influence of PFASs upon PPARγ, the molecular interactions of 27 PFASs have been investigated. Two binding sites have been identified on the PPARγ homodimer structure: the dimer pocket and the ligand binding pocket, the former has never been studied prior. Molecular dynamics calculations were performed to gain insights about PFASs-PPARγ binding and the role of acidic and basic residues. The electrostatic interactions for acidic and basic residues far from the binding site were probed, together with their effect on PPARγ recognition. Short-range electrostatic and van der Waals interactions with nearby residues and their influence on binding energies were investigated. As the negative effects of perfluorooctane sulfonate acid were previously shown to be alleviated by one of its natural ligands, l-carnitine, here, the utility of l-carnitine as a possible inhibitor for other PFASs has been considered. A comparison of the binding patterns of l-carnitine and PFASs provides insights toward mitigation strategies for PFASs.
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