Structure of Charged Cyclohexyldiamines in Aqueous Solution: A Theoretical and Experimental Study

Abstract

The structure of mono- and diprotonated cyclohexyldiamine isomers in aqueous solution is investigated theoretically by the application of the CPCM continuum solvation model combined with the MP2/aug-cc-pVDZ model chemistry. The calculated Gibbs energy of hydration (ΔGhyd) is expressed in different terms with physical meaning: cavity formation, solute conformational variation, and solute-solvent interaction. Significant differences of the ΔGhyd values are found among isomers, which are interpreted based on the analysis of the factors accounting for the stability of the conformers/isomers in the gas and solution phases. Particular attention is given to the role played by the formation of an intramolecular hydrogen bond in the monoprotonated forms and by the Coulombic repulsion between the NH3(+) groups in the diprotonated ones. From the Gibbs energies of the acid/base pairs in the gas phase and respective hydration Gibbs energies, the acidity constants (pKa) are calculated and interpreted. For some isomers, the constants are also determined experimentally by potentiometric titration. A good agreement was found between the calculated and experimental values.

Conformational Preference and Chiroptical Response of Carbohydratesd-Ribose and 2-Deoxy-d-ribose in Aqueous and Solid Phases

“…The resulting geometries were optimized in a second step with two different functionals: on the one hand, the M06-2X, and on the other hand, the B3LYP , hybrid functionals, and in both cases with the Pople’s basis set 6-311++G­(d,p) which includes diffuse and polarization functions for heavy and light atoms. The solvent effect has been simulated with the PCM-water method, − including, in this case, the solute–solvent dispersion interaction energy, the solute–solvent repulsion interaction energy and the solute cavitation energy. All these structures were again compared to remove the repeated ones.…”

Importance of Co‐operative Hydrogen Bonding in the Apramycin‐Ribosomal Decoding A‐Site Interaction

“…Gas phase computational work on the relative strengths of the intramolecular hydrogen in protonated cis ‐ and trans ‐2‐aminocyclohexanol concur with this conclusion. [32] …”

A density functional theory study on the structure formation of Al(III) carboxylate complexes in aqueous aluminum sols

“…The CPCM has been found to be a reliable continuum solvation model for bringing theoretical calculations closer to experimental results. [30][31][32][33] The zero-point energies (ZPEs) utilized for energy correction were obtained by calculating the vibrational frequencies of all species at the same basis set level. The free energies (G) discussed in this work were the sum of the entropy correction (-TS 298 ), the ZPE correction (E ZPE , 0 K), the electron energy (E elect , 0 K), and the thermal correction (E corr , 298 K).…”

“…The CPCM has been found to be a reliable continuum solvation model for bringing theoretical calculations closer to experimental results. [ 30–33 ]…”