Solvation free energy of the proton in acetonitrile

Molecularly imprinted solid-phase extraction combined with non-ionic hydrophobic deep eutectic solvents dispersed liquid-liquid microextraction for efficient enrichment and determination of the estrogens in serum samples

Hormonal drugs in biological samples are usually in low concentration and highly intrusive. It is of great significance to enhance the sensitivity and specificity of the detection process of hormone drugs in biological samples by utilizing appropriate sample pretreatment methods for the detection of hormone drugs. In this study, a sample pretreatment method was developed to effectively enrich estrogens in serum samples by combining molecularly imprinted solid-phase extraction, which has high specificity, and non-ionic hydrophobic deep eutectic solvent-dispersive liquid-liquid microextraction, which has a high enrichment ability. The theoretical basis for the effective enrichment of estrogens by non-ionic hydrophobic deep eutectic solvent was also computed by simulation. The results showed that the combination of molecularly imprinted solid-phase extraction and deep eutectic solvent-dispersive liquid-liquid microextraction could improve the sensitivity of HPLC by 33∼125 folds, and at the same time effectively reduce the interference. In addition, the non-ionic hydrophobic deep eutectic solvent has a relatively low solvation energy for estrogen and possesses a surface charge similar to that of estrogen, and thus can effectively enrich estrogen. The study provides ideas and methods for the extraction and determination of low-concentration drugs in biological samples and also provides a theoretical basis for the application of non-ionic hydrophobic deep eutectic solvent extraction.

Hydration of [Formula: see text]aminobenzoic acid: structures and non-covalent bondings of aminobenzoic acid-water clusters

CONTEXT

Micro-hydration of the aminobenzoic acid is essential to understand its interaction with surrounding water molecules. Understanding the micro-hydration of the aminobenzoic acid is also essential to study its remediation from wastewater. Therefore, we explored the potential energy surfaces (PESs) of the para-aminobenzoic acid-water clusters, ABW[Formula: see text], [Formula: see text], to study the microsolvation of the aminobenzoic acid in water. In addition, we performed a quantum theory of atoms in molecules (QTAIM) analysis to identify the nature of non-covalent bondings in the aminobenzoic acid-water clusters. Furthermore, temperature effects on the stability of the located isomers have been examined. The located structures have been used to calculate the hydration free energy and the hydration enthalpy of the aminobenzoic acid using the cluster continuum solvation model. The hydration free energy and the hydration enthalpy of the aminobenzoic acid at room temperature are evaluated to be -7.0 kcal/mol and -18.1 kcal/mol, respectively. The hydration enthalpy is in perfect agreement with a previous experimental estimate. Besides, temperature effects on the calculated hydration enthalpy and free energy are reported. Finally, we calculated the gas phase binding energies of the most stable structures of the ABW[Formula: see text] clusters using twelve functionals of density functional theory (DFT), including empirical dispersion. The DFT functionals are benchmarked against the DLPNO-CCSD(T)/CBS. We have found that the three most suitable DFT functionals are classified in the following order: PW6B95D3 > MN15 > [Formula: see text]B97XD. Therefore, the PW6B95D3 functional is recommended for further study of the aminobenzoic acid-water clusters and similar systems.

METHODS

The exploration started with classical molecular dynamics simulations followed by complete optimization at the PW6B95D3/def2-TZVP level of theory. Optimizations are performed using Gaussian 16 suite of codes. QTAIM analysis is performed using the AIMAll program.

Structures of DMSO clusters and quantum cluster equilibrium (QCE)

Dimethylsulfoxide (DMSO) clusters are crucial for understanding processes in liquid DMSO. Despite its importance, DMSO clusters have received negligible attention due to the complexity of their potential energy surfaces (PESs). In this work, we explored the PESs of the DMSO clusters from dimer to decamer, starting with classical molecular dynamics, followed by full optimizations at the PW6B95-D3/def2-TZVP level of theory. In addition, the binding energies, the binding enthalpy per DMSO, and the quantum theory of atoms in molecules (QTAIM) analysis of the most stable isomers are reported. Temperature effects on the stability of the isomers have also been assessed. After thoroughly exploring the PESs of the DMSO clusters, 159 configurations have been used to apply the quantum cluster equilibrium (QCE) theory to liquid DMSO. The quantum cluster equilibrium theory has been applied to determine the liquid properties of DMSO from DMSO clusters. Thus, using the QCE, the population of the liquid DMSO, its infrared spectrum, and some thermodynamic properties of the liquid DMSO are predicted. The QCE results show that the population of the liquid DMSO is mainly dominated by the DMSO dimer and decamer, with the contribution in trace of the DMSO monomer, trimer, tetramer, pentamer, and octamer. More interestingly, the predicted infrared spectrum of liquid DMSO is in qualitative agreement with the experiment.

Solvation of Manganese(III) Ion in Water and in Ammonia

In this work, we have studied the solvation of manganese(III) ion in water and in ammonia using three levels of theory: MP2, MN15, and ωB97XD associated with the aug-cc-pVDZ basis set. The studied systems are constituted of Mn³⁺(H₂O)₆ and Mn³⁺(NH₃)₆ in gas and solvent phases as well as Mn³⁺(H₂O)₁₈ and Mn³⁺(NH₃)₁₈ in the gas phase. Four aspects of the solvation of manganese(III) ion have been examined for the aforementioned systems at the three levels of theory. First, we started by locating the Jahn-Teller elongated and compressed configuration in Mn³⁺(H₂O)₆ and Mn³⁺(NH₃)₆. Second, we calculated the spin state energies and the spin state free energies for temperatures ranging from 50 to 400 K to look at possible spin crossover in the studied systems. Third, we carried out a quantum theory of atoms in molecules (QTAIM) analysis, and we determined the ionic radii of manganese(III) ion in water and in ammonia. Fourth, we calculated the solvation free energies and the solvation enthalpies of manganese(III) ion in water and in ammonia using the cluster continuum solvation model. For these four aspects of the solvation of manganese(III) ion, most of the reported properties are provided in this work for the first time. We particularly found that the calculated solvation enthalpy of the manganese(III) ion in water is in good agreement with an experimental estimate.

Universal Trends between Acid Dissociation Constants in Protic and Aprotic Solvents

pKa values in non-aqueous solvents are of critical importance in many areas of chemistry. Our knowledge is, despite their relevance, still limited to the most fundamental properties and few pKa values in the most common solvents. Taking advantage of a recently introduced computationally efficient procedure we computed the pKa values of 182 compounds in 21 solvents. This data set is used to establish for the first time universal trends between all solvents. Our computations indicate, that the total charge of the molecule and the charge of the acidic group combined with the Kamlet-Taft solvatochromic parameters are sufficient to predict pKa values with at least semi- quantitative accuracy. We find, that neutral acids such as alcohols are strongly affected by the solvent properties. This is contrasted by cationic acids like ammonium ions whose pKa is often almost completely independent from the choice of solvent.

Conformational energies of microsolvated Na+ clusters with protic and aprotic solvents from GFNn-xTB methods

Performance of contemporary tight-binding semiempirical GFNn-xTB methods for the conformational energies of singly charged sodium clusters Na⁺ (S)_n (n = 4-8) with 3 protic and 8 aprotic solvents is examined against the reference RI-MP2/CBS method. The median Pearson correlation coefficients of ρ = 0.84 (GFN2-xTB) and ρ = 0.82 (GFN1-xTB) do not give the clear preference to any tested approach. GFN1-xTB method demonstrates more stable performance than its GFN2-xTB successor with the average mean absolute errors (MAEs)/mean signed errors (MSEs) of 1.2/0.2 and 2.3/1.6 kcal mol^-1 , respectively. Conformational energies produced by the computationally efficient DFT functional PBE and double-ζ basis set complemented with -D3(BJ) dispersion correction are suitable for the preliminary sampling (median ρ = 0.93), but should be used with a caution for the calculations of the average ensemble properties (MAE/MSE = 1.7/1.1 kcal mol^-1 ). Higher-ranking PBE0-D3(BJ) and ωB97M-V with triple-ζ basis sets yield significantly lower MAEs/MSEs of 0.55/0.20 and 0.51/0.23 kcal mol^-1 , respectively.

How to Predict the pK a of Any Compound in Any Solvent

Acid-base properties of molecules in nonaqueous solvents are of critical importance for almost all areas of chemistry. Despite this very high relevance, our knowledge is still mostly limited to the pK _a of rather few compounds in the most common solvents, and a simple yet truly general computational procedure to predict pK _a's of any compound in any solvent is still missing. In this contribution, we describe such a procedure. Our method requires only the experimental pK _a of a reference compound in water and a few standard quantum-chemical calculations. This method is tested through computing the proton solvation energy in 39 solvents and by comparing the pK _a of 142 simple compounds in 12 solvents. Our computations indicate that the method to compute the proton solvation energy is robust with respect to the detailed computational setup and the construction of the solvation model. The unscaled pK _a's computed using an implicit solvation model on the other hand differ significantly from the experimental data. These differences are partly associated with the poor quality of the experimental data and the well-known shortcomings of implicit solvation models. General linear scaling relationships to correct this error are suggested for protic and aprotic media. Using these relationships, the deviations between experiment and computations drop to a level comparable to that observed in water, which highlights the efficiency of our method.

Structures, binding energies and non-covalent interactions of furan clusters

Understanding of the furan solvent is subjected to the knowledge of the structures of the furan clusters and interactions taking place therein. Although, furan clusters can be very important to determine the dynamics and the properties of the furan solvent, there has been only a few investigations reported on furan dimer. In this work, we have explored the potential energy surfaces (PESs) of the furan clusters using two incremental levels of theory. Structures have been initially generated using classical molecular dynamics followed by full optimization at the MP2/aug-cc-pVDZ level of theory. The results show that the most stable structure of the furan dimer has a stacking configuration while that of the trimer has a cyclic configuration. We have noted that the structures of the furan tetramer have no definite configurations. In addition, we have performed a quantum theory of atoms in molecule (QTAIM) analysis to identify all possible non-covalent interactions of the furan clusters. The results show that six different types of non-covalent interactions can be identified in furan clusters. We have noted that the CH⋯C and CH⋯O hydrogen bondings are the strongest non-covalent interactions while the H⋯H bonding interaction is found to be the weakest. Furthermore, we have assessed the performance of ten DFT functionals in calculating the binding energies of the furan clusters. The ten DFT functionals (M05, M05-2X, M06, M06-2X, M08HX, PBE0, ωB97XD, PW6B95D3, APFD and MN15) have been benchmarked to DLPNO-CCSD(T)/CBS. The functionals M05-2X and M06 are recommended for further affordable investigations of the furan clusters.

Free energy and enthalpy data of neutral and protonated clusters in the solvent phase

Structures of neutral and protonated acetonitrile in the solvent phase are important to describe proton behavior and to calculate thermodynamic quantities related to the solvation of ions or molecules in acetonitrile. In this work, we provide data related to the calculation of the solvation free energy and enthalpy of the proton in acetonitrile. We have thoroughly explored the potential energy surfaces (PESs) of neutral and protonated acetonitrile clusters from dimer to heptamer in the solvent phase at both MN15/6-31++G(d,p) and MP2/aug-cc-pVDZ levels of theory. We report the structures and relative stability of neutral and protonated acetonitrile clusters in the solvent phase at the MN15/6-31++G(d,p) level of theory. In addition, enthalpies and free energies of neutral and protonated acetonitrile are also reported at the MP2/aug-cc-pVDZ and MP2/CBS levels of theory. Furthermore, Cartesian coordinates of the clusters in the solvent phase as optimized at the MP2/aug-cc-pVDZ level of theory are provided as supplementary file. The data provided in this work will be useful for further investigations that would involve neutral and protonated acetonitrile clusters. The free energies and enthalpies of the investigated clusters in the solvent phase have been used to compute the solvation free energy and enthalpy of the proton in acetonitrile. For more insights on the solvation free energy and enthalpy of the proton in acetonitrile, see the related main research paper [1].