Mayuri Gupta

Modeling temperature dependency of amine basicity using PCM and SM8T implicit solvation models.

PCM and SM8T continuum solvation models are used to study the temperature dependency of a set of amines in the temperature range 273-393 K using density functional theoretical calculations. Gaseous phase calculations are done using B3LYP and M06 functionals at the 6-311++G(d,p) basis set level. pK(a) values calculated computationally are compared with experimental values in the given temperature region using both continuum solvation models. The continuum solvation models predict the temperature trends of pK(a) compared to experimental trends very nicely. Accurate pK(a) values at 298 K are however required as input to the model. The absolute values of pK(a) values are not reproduced well by these continuum solvation models, and a correction term is therefore introduced. A set of 10 amines, which have potential for CO(2) capture, and where also a large experimental data set of temperature dependent pK(a) values is available, were studied in this work. The temperature dependency of pK(a) values of amines provides a basis for selection for optimum solvents for postcombustion CO(2) capture processes.

Theoretical study of differential enthalpy of absorption of CO2 with MEA and MDEA as a function of temperature.

Temperature dependent correlations for enthalpy of deprotonation, carbamate formation, and heat of absorption of the overall reaction between aqueous MEA and MDEA and gaseous CO2 are calculated on the basis of computational chemistry based ln K values input to the Gibbs-Helmholtz equation. Temperature dependency of reaction equilibrium constants for deprotonation and carbamate formation reactions is calculated with the SM8T continuum solvation model coupled with density functional theoretical calculations at the B3LYP/6-311++G(d,p) level of theory. Calculated reaction equilibrium constants and enthalpies of individual reactions and overall heat of absorption are compared against experimental data in the temperature range 273.15-373 K. Temperature dependent correlations for different reaction equilibrium constants and enthalpies of reactions are given. These correlated results can be used in thermodynamic models such as UNIQUAC and NRTL for better understanding of post-combustion CO2 capture solvent chemistry.

Explicit Solvation Shell Model and Continuum Solvation Models for Solvation Energy and pKa Determination of Amino Acids.

The study of the Explicit Solvation Shell Model (ESS) presented recently [da Silva, E. F.; Svendsen, H. F.; Merz, K. M. J. Phys. Chem. A 2009, 113, 6404.] for calculation of solvation free energy of ions is extended for the study for amino acids. Solvation free energies and pKa of a data set of 10 amino acids is calculated using ESS. The data set of amino acids is selected based on their potential to be regarded as solvents for postcombustion CO2 capture processes. Calculated results are compared against experimental pKa and pKa calculated from PCM, SM8T, and DivCon continuum solvation models. Error estimates of pKa from different models vs experimental pKa data are also given to evaluate the results calculated by different solvation models. This study also involves a comprehensive study of gas phase basicity, proton affinity,ΔGacid0, ΔHacid0, protonation entropy with density functional methods (B3LYP/6-311++G(d,p)) and composite methods (G3MP2B3, G3MP2, CBS-QB3, G4MP2) and their comparison with experimen...

Modeling temperature dependency of ionization constants of amino acids and carboxylic acids.

The temperature sensitivity of pK(a) values for a data set of 10 amino acids and 5 carboxylic acids is studied using PCM and SM8T continuum solvation models coupled with density functional theoretical calculations at the B3LYP/6-311++G(d,p) level of theory. The data set of amino acids was chosen on the basis of their potential to be solvents for postcombustion CO2 capture processes and available literature data. Calculated results are compared with experimental data in a temperature range of 273-393 K. Both solvation models predict temperature sensitivity of pK(a) of the amino group of amino acids very nicely. It is observed that the temperature dependencies of pK(a) of the carboxyl group of amino acids and carboxylic acids predicted by these models do not agree well with experimental temperature dependencies of carboxylic acids. This issue is discussed in the context of the basic parametrization of these continuum solvation models.

Temperature sensitivity of piperazine and its derivatives using polarizable continuum solvation model

Temperature dependency of piperazine and related amines in the temperature range 298–393 K is studied using density functional theoretical calculations. B3LYP functional and 6-311++G (d, p) basis set was used in all the calculations. From the pKa and carbamate formation reaction energy values it can be seen that the structural changes of amines have a critical effect on their behavior and that it varies significantly with temperature.