Three ionization states of carboxyphosphate, a proposed key intermediate in the ATP-grasp carboxylase superfamily of enzymes, were investigated using density functional theory (DFT), Moller-Plesset second-order perturbation theory (MP2), and coupled-cluster theory with single and double perturbative triple excitations (CCSD(T)). Five DFT methods were combined with Dunning's augmented correlation consistent polarized valence n zeta basis sets (aug-cc-pVnZ, n = D, T, Q, 5) and compared to the MP2/CBS and CCSD(T) computational standards to evaluate the different ionization state conformations and energies in vacuum, as well as implicit solvent. Energetic and structural convergence was evaluated as a function of the number of basis functions by systematically incrementing Dunning's basis sets. The majority of structural and energetic convergence across all chemical theories was captured by Dunning's aug-cc-pVTZ basis set. All functionals were found to be within 1.3 kcal/mol of CCSD(T) standards; However, B3LYP fails to locate stationary points for three of the di-anionic conformations.  Truhlar's M06-2X and BB1K functionals were most consistent CCSD(T) calculations (=1.0 kcal) across all ionization states and conformations. Truhlar's M06-2X functional gave the most consistent agreement with accepted MP2 calculations for bond lengths (=0.02 �), angles (=1.4�), and dihedrals (=1.4�). All computed DFT bond lengths were =0.07 �, angles =1.8�, and dihedrals =3.1� relative to MP2. We find that M062X/aug-cc-pVTZ most consistently gave the best agreement with both CCSD(T) and MP2 calculations over all ionization state conformations among the methods tested; However, all DFT functionals were found to be in good agreement with the MP2/CBS and CCSD(T) computational standards.

Structural and energetic analysis of carboxyphosphate

247th National Meeting (2014)

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