A predictive model for salt nanoparticle formation using heterodimer stability calculations

Acid–base clusters and stable salt formation are critical drivers of new particle formation events in the atmosphere. In this study, we explore salt heterodimer (a cluster of one acid and one base) stability as a function of gas-phase acidity, aqueous-phase acidity, heterodimer proton transference, vapor pressure, dipole moment and polarizability for salts comprised of sulfuric acid, methanesulfonic acid and nitric acid with nine bases. The best predictor of heterodimer stability was found to be gas-phase acidity. We then analyzed the relationship between heterodimer stability and J4×4, the theoretically predicted formation rate of a four-acid, four-base cluster, for sulfuric acid salts over a range of monomer concentrations from 105 to 109 molec cm−3 and temperatures from 248 to 348 K and found that heterodimer stability forms a lognormal relationship with J4×4. However, temperature and concentration effects made it difficult to form a predictive expression of J4×4. In order to reduce those effects, heterodimer concentration was calculated from heterodimer stability and yielded an expression for predicting J4×4 for any salt, given approximately equal acid and base monomer concentrations and knowledge of monomer concentration and temperature. This parameterization was tested for the sulfuric acid–ammonia system by comparing the predicted values to experimental data and was found to be accurate within 2 orders of magnitude. We show that one can create a simple parameterization that incorporates the dependence on temperature and monomer concentration on J4×4 by defining a new term that we call the normalized heterodimer concentration, Φ. A plot of J4×4 vs. Φ collapses to a single monotonic curve for weak sulfate salts (difference in gas-phase acidity >95 kcal mol−1) and can be used to accurately estimate J4×4 within 2 orders of magnitude in atmospheric models.

Influence of Multiple & Cooperative Hydrogen Bonding on the Acidity of Polyhydroxylated Piperidines: Electron Density Topological Analysis

Hydrogen bonds are the presiding concepts for arranging the three-dimensional forms of biological molecules like proteins, carbohydrates and nucleic acids, and acts as guides for proton transfer reactions. Gas-phase acidity and pKa calculations in dimethyl sulfoxide on a line of polyhydroxylated piperidines specify that multiple hydrogen bonds lead to enhance acidities.The gas-phase acidity (GPA) of polyhydroxylated piperidines was investigated by MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p) method. For each structure, varied primary and secondary hydroxyl groups were deprotonated. The natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) analyses have also been used to realize the character of the hydrogen bonding interactions in these compounds. The results show by adding each hydroxyl group, ΔHacid in the gas phase (it becomes less endothermic) and pKa value in the solution phase was decreased. Therefore, intramolecular hydrogen bonds lead to enhance the acid strength. In both the gas phase and solution phase, the β-Nojrimycin-OH2 (β-1-OH2) was found to be the most acidic compound with calculated gas-phase acidity (GPA) of 349.4 kcal.mol-1 and the pKa value of 22.0 (8.0 pKa units more acidic than 1-propanol).It was also shown, applying the polarized continuum model (PCM), there is a superior linear correlation with the gas phase acidities (GPAs) of polyhydroxylated piperidines and their calculated pKa (DMSO) values.

A Predictive Model for Salt Nanoparticle Formation UsingHeterodimer Stability Calculations

Acid–base clusters and stable salt formation are critical drivers of new particle formation events in the atmosphere. In this study, we explore the relationship between J1.5, the theoretically predicted formation rate of clusters larger than 4 acid and 4 base molecules, and acid–base heterodimer stability, a property that is relatively easy to calculate using computational methods. Heterodimer stability as a function of gas-phase acidity, aqueous-phase acidity, heterodimer proton transference, vapor pressure, dipole moment, and polarizability were explored for the salts comprised of sulfuric acid, methanesulfonic acid, and nitric acid with nine bases. The best predictor of heterodimer stability was found to be gas-phase acidity. The relationship between heterodimer stability and J1.5 was analyzed for sulfuric acid salts over a range of monomer concentrations from 105 to 109 molec cm−3 and temperatures from 248 to 348 K. Heterodimer concentration was calculated from heterodimer stability and yielded an expression for predicting J1.5 for any salt, given approximately equal acid and base monomer concentrations and knowledge of monomer concentration and temperature. This parameterization was tested for the sulfuric acid–ammonia system by comparing the predicted values to experimental data and was found to be accurate within 2 orders of magnitude. We show that one can create a simple parameterization that incorporates the dependence on temperature and monomer concentration on J1.5 by defining a new term that we call the normalized heterodimer concentration, Φ. A plot of J1.5 vs. Φ collapses to a single monotonic curve for all weak salts of sulfuric acid, and can be used to accurately estimate J1.5 in atmospheric models.

Analysis of the Gas Phase Acidity of Substituted Benzoic Acids Using Density Functional Concepts

A theoretical study of the effect of the substituent Z on the gas phase acidity of substituted benzoic acids ZC6H4COOH in terms of density functional theory descriptors (chemical potential, softness and Fukui function) is presented. The calculated gas phase ΔacidG° values obtained were close to the experimental ones reported in the literature. The good relationship between the ΔacidG° values and the electronegativity of ZC6H4COOH and its fragments, suggested a better importance of the inductive than polarizability contributions. The balance of inductive and resonance contributions of the substituent in the acidity of substituted benzoic acids showed that the highest inductive and resonance effects were for the -SO2CF3 and -NH2 substituents in the para- and ortho-position, respectively. The Fukui function confirmed that the electron-releasing substituent attached to the phenyl ring of benzoic acid decreased the acidity in the trend ortho > meta > para, and the electron-withdrawing substituent increased the acidity in the trend ortho < meta < para.