Computational Study of Cesium Cation Interactions with Neutral and Anionic Compounds Related to Soil Organic Matter

Assessment of the Accuracy of DFT-Predicted Li+-Nucleic Acid Binding Energies

Understanding how lithium interacts with complex biosystems is crucial for uncovering the roles of this alkali metal in biology and designing extraction techniques for battery production and environmental remediation. In this light, fundamental information about Li⁺ binding to nucleic acids is required. Herein, a new database of Li⁺-nucleic acid interactions is presented that contains CCSD(T)/CBS benchmark energies for all nucleobase and phosphate binding locations. Furthermore, the performance of 54 DFT functionals in combination with three triple-zeta (TZ) basis sets (6-311+G(3df,2p), aug-cc-pVTZ, and def2-TZVPP) is tested. The results identify a range of functionals across different families (B2-PLYP, PBE-QIDH, ωB97, ωB97X-D, MN15, B3PW91, B97-2, TPSS, BP86-D3(BJ), and PBE) that can accurately describe coordinated Li⁺-nucleic acid interactions, with the average mean percent error (AMPE) across binding positions and basis sets being below 2%. Nevertheless, only three functionals tested (B2-PLYP, PBE-QIDH, and ωB97X-D) preserve this accuracy for metal cation-π interactions, suggesting that caution is warranted when choosing a functional to describe a diverse range of Li⁺-nucleic acid complexes. Removal of counterpoise corrections has very little impact on the reliability of most functionals, while the effect of empirical dispersion corrections varies depending on the functional choice and interaction type. While increasing the basis set to quadruple-zeta quality had little impact on the AMPE, the accuracy of double-zeta basis sets varies with family. Importantly, DFT methods reproduce the CCSD(T)/CBS trend in the preferred binding position for a given nucleic acid component and the global trend across components (phosphate ≫ G > C ≫ A ∼ T = U), as well as the geometries of the metal-nucleic acid complexes. The overall top performing functional is PBE-QIDH, which results in deviations from CCSD(T)/CBS values as small as ∼0.1 kcal/mol for nucleobase contacts and ∼1 kcal/mol for phosphate interactions. The most accurate DFT methods identified in the present work are recommended for future investigations of lithium interactions in larger nucleic acid systems to provide insights into the biological roles of this metal and the design of novel biosensing strategies.

Alkali Metal Cations Bonding to Carboxylate Anions: Studies using Mass Spectrometry and Quantum Chemical Calculations

Data on the gas-phase energetics of anion/cation interactions are relatively scarce. In this work, gas-phase alkali metal cation basicity (AMCB) scales were established for a series of 15 benzoate ions XC₆H₄COO^- with Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺ on the basis of mass spectrometry experiments and high-level calculations. A wide range of electron-donating and electron-withdrawing substituents were included in the study. The thermochemical values were calculated by ab initio methodologies and extrapolated to the complete basis set limit. For each metal cation, the experimental relative cation basicity values of the anions were established quantitatively by applying the Cooks' kinetic method to the cation-bound heterodimers [(XC₆H₄COO^-)M⁺(YC₆H₄COO^-)]^-, generated by electrospray ionization. The self-consistency of these AMCB scales was ascertained by multiple overlap of the individual relative basicities. In parallel, the proton gas-phase basicities (GBs) of the benzoate anions (gas-phase acidities of the respective benzoic acids) were calculated in order to compare the results of the theoretical method with known experimental GB values. The experimental and calculated GB values agree quite accurately (average absolute deviation = 3.2 kJ mol^-1). The relative experimental AMCB scales and the absolute calculated AMCB scales are highly correlated, and the two sets agree by better than 4 kJ mol^-1. It is also demonstrated that the five series of calculated AMCBs are highly correlated with the calculated GB.

Alkali Metal Cation Affinities of Neutral Maingroup-Element Hydrides across the Periodic Table

We have carried out an extensive quantum chemical exploration of gas-phase alkali metal cation affinities (AMCAs) of archetypal neutral bases across the periodic system using relativistic density functional theory. One objective of this work is to provide an intrinsically consistent set of values of the 298 K AMCAs of all neutral maingroup-element hydrides XH_n of groups 15–18 along the periods 1–6. Our main purpose is to understand these trends in terms of the underlying bonding mechanism using Kohn–Sham molecular orbital theory together with a canonical energy decomposition analysis (EDA). We compare the trends in XH_n AMCAs with the trends in XH_n proton affinities (PAs). We also examine the differences between the trends in AMCAs of the neutral XH_n bases with those in the corresponding anionic XH_n–1^– bases. Furthermore, we analyze how the cation affinity of our neutral Lewis bases changes along the group-1 cations H⁺, Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺.

Topology and Electronic Density Driven Generation of Alkali Cation Complexes

The formation and characterization of K⁺ and Cs⁺ complexes originating from the cooperativity of three non-covalent interactions is explored. The tridimensional preorganization of the naphthothiophene platform displays a favorable well-defined bay region combining a π fragment and a carbonyl moiety flanking a central sulfur atom. A joint theoretical and experimental infrared multiple photon dissociation (IRMPD) study allowed deciphering the key contribution of the orthogonal phenyl fragment to the elaboration of alkali metal complexes. In combination with S and CO interactions, the π-cation interaction significantly enhances the binding energies of naphthothiophene derivatives.

Cation-π interactions in competition with cation microhydration: a theoretical study of alkali metal cation-pyrene complexes

Cation–π interactions were systematically investigated for the adsorption of H⁺ and alkali metal cations M⁺ to pyrene by means of Møller–Plesset perturbation theory (MP2) and density functional theory (DFT). The main aims were to determine the preferred adsorption sites and how the microhydration shell influences the adsorption process. The preferred adsorption sites were characterized in terms of structural parameters and energetic stability. Stability analysis of the M⁺–pyrene complexes revealed that the binding strength and the barrier to transitions between neighboring sites generally decreased with increasing cation size from Li⁺ to Cs⁺. Such transitions were practically barrierless (<<1 kcal/mol) for the large Rb⁺ and Cs⁺ ions. Further, the influence of the first hydration shell on the adsorption behavior was investigated for Li⁺ and K⁺ as representatives of small and large (alkali metal) cations, respectively. While the isolated complexes possessed only one minimum, two minima—corresponding to an inner and an outer complex—were observed for microhydrated complexes. The small Li⁺ ion formed a stable hydration shell and preferentially interacted with water rather than pyrene. In contrast, K⁺ favored cation–π over cation–water interactions. It was found that the mechanism for complex formation depends on the balance between cation–π interactions, cation–water complexation, and the hydrogen bonding of water to the π-system.

Variation in available cesium concentration with parameters during temperature induced extraction of cesium from soil

Cesium extraction behavior of brown forest type soil collected from paddy fields in Fukushima nuclear accident affected areas was studied. In nitric acid or sulfuric acid solutions at elevated temperature, the concentration of Cs in soil available for extraction, m0, has been estimated on the basis of modified canonical equation and the equations derived from assumed equilibria. With the variation in temperature, mixing time, and soil to solvent ratio, the observed m0 values in 0.5 M acid solution ranged between 1.5 and 2.9 mg cesium per kilogram of soil. By increasing the acid concentration to 3 M, the value of m0 could be sharply increased to 5.1 mg/kg even at 95 °C. This variation in the extractable concentration of cesium with the parameters signifies the existence of different binding sites in the soil matrix. The results observed for uncontaminated sample could be reproduced with the radioactive cesium contaminated sample belonging to the same soil group.

Dealing with the aftermath of Fukushima Daiichi nuclear accident: decontamination of radioactive cesium enriched ash

Environmental radioactivity, mainly in the Tohoku and Kanto areas, due to the long living radioisotopes of cesium is an obstacle to speedy recovery from the impacts of the Fukushima Daiichi Nuclear Power Plant accident. Although incineration of the contaminated wastes is encouraged, safe disposal of the Cs enriched ash is the big challenge. To address this issue, safe incineration of contaminated wastes while restricting the release of volatile Cs to the atmosphere was studied. Detailed study on effective removal of Cs from ash samples generated from wood bark, household garbage, and municipal sewage sludge was performed. For wood ash and garbage ash, washing only with water at ambient conditions removed radioactivity due to (134)Cs and (137)Cs, retaining most of the components other than the alkali metals with the residue. However, removing Cs from sludge ash needed acid treatment at high temperature. This difference in Cs solubility is due to the presence of soil particle originated clay minerals in the sludge ash. Because only removing the contaminated vegetation is found to sharply decrease the environmental radioactivity, volume reduction of contaminated biomass by incineration makes great sense. In addition, need for a long-term leachate monitoring system in the landfill can be avoided by washing the ash with water. Once the Cs in solids is extracted to the solution, it can be loaded to Cs selective adsorbents such as Prussian blue and safely stored in a small volume.

A study of the cesium cation bonding to carboxylate anions by the kinetic method and quantum chemical calculations

Collision-induced dissociation (CID) of the Cs(+) heterodimer adducts of the nitrate anion (NO(3)(-)) and a variety of substituted benzoates (XBenz(-)) [(XBenz(-))(Cs(+))(NO(3)(-))](-) produces essentially nitrate and benzoate ions. A plot of the natural logarithm of their intensity ratio, ln[I (NO(3)(-))/I(XBenz(-))], versus the calculated cesium cation affinity (DFT B3LYP) of the substituted benzoate ions (equivalent to the enthalpy of heterolytic dissociation of the salt) is reasonably linear. This suggests that the kinetic method can be used as a source of data on the intrinsic interaction between the anionic and the cationic moieties in a salt.