Applications of redox processes range over a number of scientific fields. This review article summarizes the theory behind the calculation of redox potentials in solution for species such as organic compounds, inorganic complexes, actinides, battery materials, and mineral surface-bound-species. Different computational approaches to predict and determine redox potentials of electron transitions are discussed along with their respective pros and cons for the prediction of redox potentials. Subsequently, recommendations are made for certain necessary computational settings required for accurate calculation of redox potentials. This article reviews the importance of computational parameters, such as basis sets, density functional theory (DFT) functionals, and relativistic approaches and the role that physicochemical processes play on the shift of redox potentials, such as hydration or spin orbit coupling, and will aid in finding suitable combinations of approaches for different chemical and geochemical applications. Identifying cost-effective and credible computational approaches is essential to benchmark redox potential calculations against experiments. Once a good theoretical approach is found to model the chemistry and thermodynamics of the redox and electron transfer process, this knowledge can be incorporated into models of more complex reaction mechanisms that include diffusion in the solute, surface diffusion, and dehydration, to name a few. This knowledge is important to fully understand the nature of redox processes be it a geochemical process that dictates natural redox reactions or one that is being used for the optimization of a chemical process in industry. In addition, it will help identify materials that will be useful to design catalytic redox agents, to come up with materials to be used for batteries and photovoltaic processes, and to identify new and improved remediation strategies in environmental engineering, for example the reduction of actinides and their subsequent immobilization. Highly under-investigated is the role of redox-active semiconducting mineral surfaces as catalysts for promoting natural redox processes. Such knowledge is crucial to derive process-oriented mechanisms, kinetics, and rate laws for inorganic and organic redox processes in nature. In addition, molecular-level details still need to be explored and understood to plan for safer disposal of hazardous materials. In light of this, we include new research on the effect of iron-sulfide mineral surfaces, such as pyrite and mackinawite, on the redox chemistry of actinyl aqua complexes in aqueous solution.

Carbonate anion exchange reactions with water in the uranyl-carbonate and calcium-uranyl-carbonate aqueous systems have been investigated using computational methods. Classical molecular dynamics (MD) simulations with the umbrella sampling technique were employed to determine potentials of mean force for the exchange reactions of water and carbonate. The presence of calcium counter-ions is predicted to increase the stability of the uranyl-carbonate species in accordance with previous experimental observations. However, the free energy barrier to carbonate exchange with water is found to be comparable both in the presence and absence of calcium cations. Possible implications of these results for uranyl adsorption on mineral surfaces are discussed. Density functional theory (DFT) calculations were also used to confirm the trends observed in classical molecular dynamics simulations and to corroborate the validity of the potential parameters employed in the MD scheme.

Pyrite, one of the most important minerals to catalyze redox reactions in nature and a bulk low-spin Fe mineral, needs to provide high-spin Fe on surfaces to moderate spin-forbidden transitions. Here, the spin state of pyrite is investigated using density functional theory (DFT) calculations on cluster and periodic models. The energies of clusters Fe_xS_2x (where x = 4, 8, 16, and 32) were calculated as a function of total spin and different up/down spin configurations. The undercoordinated Fe on surfaces, edges, and corners were found to provide intermediate and high-spin Fe necessary for catalysis. Generally, the lower the crystal field splitting energy (CFSE), Δ, for a particular Fe atom, the higher is the spin density. Pyrite bulk (3D) and surfaces (2D) (+ water to mimic aqueous systems) were examined. The calculated bulk band gap (0.95 eV) is in excellent agreement with previous reports. For the surface, a conducting state is predicted. The calculated CFSE for bulk Fe(II) in pyrite (∼2.2 eV) agrees with previous CFT results; due to surface states, this CFSE decreases to ∼1 eV on terraces. This study highlights the importance of accurately describing the spin state of pyrite.

An efficient synthesis of 3-aminochromones and 3-alkylchromones by a N-heterocyclic carbene (NHC) catalyzed intramolecular hydroacylation reaction of corresponding salicylaldehyde derived nitriles and activated alkynes respectively in ionic liquids under microwave conditions is reported. This protocol has the advantages of environmental friendliness, higher yields, shorter reaction times, and convenient operation using the commercially available thiazolium catalyst. The origin of the chemical reactivity of the NHC-catalyzed intramolecular hydroacylation reaction of nitriles is studied using Density Functional Theory (DFT). The results suggest that 3-aminochromone formation occurs via an acyl anion intermediate called a Breslow intermediate (INT2) through TS2. The Breslow intermediate (INT2) forms a carbon–carbon bond with the nitrile carbon to produce an imine intermediate INT3viaTS3, which further undergoes imine to amine tautomerism to give the end product. Some of the derivatives of 3-aminochromone are subjected to amine functionalization in one pot to obtain a library of compounds for anticancer activity. Among the investigated compounds, 2c (SVM-2), 4c (SVM-4) and 2d (SVM-9) show IC₅₀ values of 5.18, 4.89 and 27.3 μM respectively in HeLa S3 cancer cells. Compound 5c (SVM-5) shows IC₅₀ values of 13.3 and 14.2 μM in A549 and HeLa S3 cancer cells, respectively. Compounds 2c (SVM-2) and 4c (SVM-4) produce morphological changes and control the colony formation in HeLa S3 cells, which indicates that these small molecules are potential candidates for anticancer drugs.

Of particular interest within the +6 uranium complexes is the linear uranyl( vi ) cation and it forms numerous coordination complexes in solution and exhibits incongruent redox behavior depending on coordinating ligands. This DFT study predicts VI/V reduction potentials of a range of uranyl( vi ) complexes in non-aqueous solutions within ∼0.10−0.20 eV of experiment.