Comparisons of computational and experimental thermochemical properties of α-amino acids.

This study provides comprehensive benchmark calculations for the thermochemical properties of the common α-amino acids. Calculated properties include the proton affinity, gas-phase basicity, protonation entropy, ΔH°(acid), ΔG°(acid), and enthalpies of formation for the protonated and deprotonated α-amino acids. In order to determine the performance at various levels of theory, including density functional methods and composite methods, the calculated thermochemical properties are compared to experimental results. For all the common α-amino acids investigated, the thermochemical properties computed with the Gaussian-n theories were found to be quite consistent with each other in terms of mean absolute deviation from experiment. While all Gaussian-n theory values can serve as benchmarks, we focus on the G3MP2 values as it is the least resource-intensive of the Gaussian-n theories considered.